Intensive care admissions and outcomes associated with short-term exposure to ambient air pollution: a time series analysis

PURPOSE

Short-term exposure to outdoor air pollution has been positively associated with numerous measures of acute morbidity and mortality, most consistently as excess cardiorespiratory disease associated with fine particulate matter (PM_2.5), particularly in vulnerable populations. It is unknown if the critically ill, a vulnerable population with high levels of cardiorespiratory disease, is affected by air pollution.

METHODS

We performed a time series analysis of emergency cardiorespiratory, stroke and sepsis intensive care (ICU) admissions for the years 2008-2016, using data from the Australian and New Zealand Intensive Care Society Adult Patient Database (ANZICS-APD). Case-crossover analysis was conducted to assess the relationship between air pollution and the frequency and severity of ICU admissions having adjusted for temperature, humidity, public holidays and influenza activity.

RESULTS

46,965 episodes in 87 separate ICUs were analysed. We found no statistically significant associations with admission counts. However, ICU admissions ending in death within 30 days were significantly positively associated with short-term exposure to PM_2.5 [RR 1.18, 95% confidence interval (CI) 1.02-1.37, per 10 µg/m³ increase]. This association was more pronounced in those aged 65 and over (RR 1.33, 95% CI 1.11-1.58, per 10 µg/m³).

CONCLUSIONS

Increased ICU mortality was associated with higher levels of PM_2.5. Larger studies are required to determine if the frequency of ICU admissions is positively associated with short-term exposure to air pollution.

Measurement error in a multi-level analysis of air pollution and health: a simulation study

BACKGROUND

Spatio-temporal models are increasingly being used to predict exposure to ambient outdoor air pollution at high spatial resolution for inclusion in epidemiological analyses of air pollution and health. Measurement error in these predictions can nevertheless have impacts on health effect estimation. Using statistical simulation we aim to investigate the effects of such error within a multi-level model analysis of long and short-term pollutant exposure and health.

METHODS

Our study was based on a theoretical sample of 1000 geographical sites within Greater London. Simulations of "true" site-specific daily mean and 5-year mean NO₂ and PM₁₀ concentrations, incorporating both temporal variation and spatial covariance, were informed by an analysis of daily measurements over the period 2009-2013 from fixed location urban background monitors in the London area. In the context of a multi-level single-pollutant Poisson regression analysis of mortality, we investigated scenarios in which we specified: the Pearson correlation between modelled and "true" data and the ratio of their variances (model versus "true") and assumed these parameters were the same spatially and temporally.

RESULTS

In general, health effect estimates associated with both long and short-term exposure were biased towards the null with the level of bias increasing to over 60% as the correlation coefficient decreased from 0.9 to 0.5 and the variance ratio increased from 0.5 to 2. However, for a combination of high correlation (0.9) and small variance ratio (0.5) non-trivial bias (> 25%) away from the null was observed. Standard errors of health effect estimates, though unaffected by changes in the correlation coefficient, appeared to be attenuated for variance ratios > 1 but inflated for variance ratios < 1.

CONCLUSION

While our findings suggest that in most cases modelling errors result in attenuation of the effect estimate towards the null, in some situations a non-trivial bias away from the null may occur. The magnitude and direction of bias appears to depend on the relationship between modelled and "true" data in terms of their correlation and the ratio of their variances. These factors should be taken into account when assessing the validity of modelled air pollution predictions for use in complex epidemiological models.

Ambient air pollution and the prevalence of rhinoconjunctivitis in adolescents: a worldwide ecological analysis

Whether exposure to outdoor air pollution increases the prevalence of rhinoconjunctivitis in children is unclear. Using data from Phase Three of the International Study of Asthma and Allergies in childhood (ISAAC), we investigated associations of rhinoconjunctivitis prevalence in adolescents with model-based estimates of ozone, and satellite-based estimates of fine (diameter < 2.5 μm) particulate matter (PM_2.5) and nitrogen dioxide (NO₂). Information on rhinoconjunctivitis (defined as self-reported nose symptoms without a cold or flu accompanied by itchy watery eyes in the past 12 months) was available on 505,400 children aged 13-14 years, in 183 centres in 83 countries. Centre-level prevalence estimates were calculated and linked geographically with estimates of long-term average concentrations of NO₂, ozone and PM_2.5. Multi-level models were fitted adjusting for population density, climate, sex and gross national income. Information on parental smoking, truck traffic and cooking fuel was available for a restricted set of centres (77 in 36 countries). Between centres within countries, the estimated change in rhinoconjunctivitis prevalence per 100 children was 0.171 (95% confidence interval: - 0.013, 0.354) per 10% increase in PM_2.5, 0.096 (- 0.003, 0.195) per 10% increase in NO₂ and - 0.186 (- 0.390, 0.018) per 1 ppbV increase in ozone. Between countries, rhinoconjunctivitis prevalence was significantly negatively associated with both ozone and PM_2.5. In the restricted dataset, the latter association became less negative following adjustment for parental smoking and open fires for cooking. In conclusion, there were no significant within-country associations of rhinoconjunctivitis prevalence with study pollutants. Negative between-country associations with PM_2.5 and ozone require further investigation.

Incorporating Measurement Error from Modeled Air Pollution Exposures into Epidemiological Analyses

PURPOSE OF REVIEW

Outdoor air pollution exposures used in epidemiological studies are commonly predicted from spatiotemporal models incorporating limited measurements, temporal factors, geographic information system variables, and/or satellite data. Measurement error in these exposure estimates leads to imprecise estimation of health effects and their standard errors. We reviewed methods for measurement error correction that have been applied in epidemiological studies that use model-derived air pollution data.

RECENT FINDINGS

We identified seven cohort studies and one panel study that have employed measurement error correction methods. These methods included regression calibration, risk set regression calibration, regression calibration with instrumental variables, the simulation extrapolation approach (SIMEX), and methods under the non-parametric or parameter bootstrap. Corrections resulted in small increases in the absolute magnitude of the health effect estimate and its standard error under most scenarios. Limited application of measurement error correction methods in air pollution studies may be attributed to the absence of exposure validation data and the methodological complexity of the proposed methods. Future epidemiological studies should consider in their design phase the requirements for the measurement error correction method to be later applied, while methodological advances are needed under the multi-pollutants setting.

Air pollution and the incidence of ischaemic and haemorrhagic stroke in the South London Stroke Register: a case-cross-over analysis

Background

Few European studies investigating associations between short-term exposure to air pollution and incident stroke have considered stroke subtypes. Using information from the South London Stroke Register for 2005–2012, we investigated associations between daily concentrations of gaseous and particulate air pollutants and incident stroke subtypes in an ethnically diverse area of London, UK.

Methods

Modelled daily pollutant concentrations based on a combination of measurements and dispersion modelling were linked at postcode level to incident stroke events stratified by haemorrhagic and ischaemic subtypes. The data were analysed using a time-stratified case–cross-over approach. Conditional logistic regression models included natural cubic splines for daily mean temperature and daily mean relative humidity, a binary term for public holidays and a sine–cosine annual cycle. Of primary interest were same day mean concentrations of particulate matter <2.5 and <10 µm in diameter (PM_2.5, PM₁₀), ozone (O₃), nitrogen dioxide (NO₂) and NO₂+nitrogen oxide (NO_X).

Results

Our analysis was based on 1758 incident strokes (1311 were ischaemic and 256 were haemorrhagic). We found no evidence of an association between all stroke or ischaemic stroke and same day exposure to PM_2.5, PM₁₀, O₃, NO₂ or NO_X. For haemorrhagic stroke, we found a negative association with PM₁₀ suggestive of a 14.6% (95% CI 0.7% to 26.5%) fall in risk per 10 µg/m³ increase in pollutant.

Conclusions

Using data from the South London Stroke Register, we found no evidence of a positive association between outdoor air pollution and incident stroke or its subtypes. These results, though in contrast to recent meta-analyses, are not inconsistent with the mixed findings of other UK studies.

Myocardial infarction, ST-elevation and non-ST-elevation myocardial infarction and modelled daily pollution concentrations: a case-crossover analysis of MINAP data

Objectives

To investigate associations between daily concentrations of air pollution and myocardial infarction (MI), ST-elevation MI (STEMI) and non-ST-elevation MI (NSTEMI).

Methods

Modelled daily ground-level gaseous, total and speciated particulate pollutant concentrations and ground-level daily mean temperature, all at 5 km×5 km horizontal resolution, were linked to 202 550 STEMI and 322 198 NSTEMI events recorded on the England and Wales Myocardial Ischaemia National Audit Project (MINAP) database. The study period was 2003–2010. A case-crossover design was used, stratified by year, month and day of the week. Data were analysed using conditional logistic regression, with pollutants modelled as unconstrained distributed lags 0–2 days. Results are presented as percentage change in risk per 10 µg/m³ increase in the pollutant relevant metric, having adjusted for daily mean temperature, public holidays, weekly influenza consultation rates and a sine-cosine annual cycle.

Results

There was no evidence of an association between MI or STEMI and any of O₃, NO₂, PM_2.5, PM₁₀ or selected PM_2.5 components (sulfate and elemental carbon). For NSTEMI, there was a positive association with daily maximum 1-hour NO₂ (0.27% (95% CI 0.01% to 0.54%)), which persisted following adjustment for O₃ and adjustment for PM_2.5. The association appeared to be confined to the midland and southern regions of England and Wales.

Conclusions

The study found no evidence of an association between the modelled pollutants (including components) investigated and STEMI but did find some evidence of a positive association between NO₂ and NSTEMI. Confirmation of this association in other studies is required.

Long-term exposure to ambient ozone and mortality: a quantitative systematic review and meta-analysis of evidence from cohort studies

OBJECTIVES

While there is good evidence for associations between short-term exposure to ozone and a range of adverse health outcomes, the evidence from narrative reviews for long-term exposure is suggestive of associations with respiratory mortality only. We conducted a systematic, quantitative evaluation of the evidence from cohort studies, reporting associations between long-term exposure to ozone and mortality.

METHODS

Cohort studies published in peer-reviewed journals indexed in EMBASE and MEDLINE to September 2015 and PubMed to October 2015 and cited in reviews/key publications were identified via search strings using terms relating to study design, pollutant and health outcome. Study details and estimate information were extracted and used to calculate standardised effect estimates expressed as HRs per 10 ppb increment in long-term ozone concentrations.

RESULTS

14 publications from 8 cohorts presented results for ozone and all-cause and cause-specific mortality. We found no evidence of associations between long-term annual O3 concentrations and the risk of death from all causes, cardiovascular or respiratory diseases, or lung cancer. 4 cohorts assessed ozone concentrations measured during the warm season. Summary HRs for cardiovascular and respiratory causes of death derived from 3 cohorts were 1.01 (95% CI 1.00 to 1.02) and 1.03 (95% CI 1.01 to 1.05) per 10 ppb, respectively.

CONCLUSIONS

Our quantitative review revealed a paucity of independent studies regarding the associations between long-term exposure to ozone and mortality. The potential impact of climate change and increasing anthropogenic emissions of ozone precursors on ozone levels worldwide suggests further studies of the long-term effects of exposure to high ozone levels are warranted.

Childhood intermittent and persistent rhinitis prevalence and climate and vegetation: a global ecologic analysis

BACKGROUND

The effect of climate change and its effects on vegetation growth, and consequently on rhinitis, are uncertain.

OBJECTIVE

To examine between- and within-country associations of climate measures and the normalized difference vegetation index with intermittent and persistent rhinitis symptoms in a global context.

METHODS

Questionnaire data from 6- to 7-year-olds and 13- to 14-year-olds were collected in phase 3 of the International Study of Asthma and Allergies in Childhood. Associations of intermittent (>1 symptom report but not for 2 consecutive months) and persistent (symptoms for ≥2 consecutive months) rhinitis symptom prevalences with temperature, precipitation, vapor pressure, and the normalized difference vegetation index were assessed in linear mixed-effects regression models adjusted for gross national income and population density. The mean difference in prevalence per 100 children (with 95% confidence intervals [CIs]) per interquartile range increase of exposure is reported.

RESULTS

The country-level intermittent symptom prevalence was associated with several country-level climatic measures, including the country-level mean monthly temperature (6.09 °C; 95% CI, 2.06-10.11°C per 10.4 °C), precipitation (3.10 mm; 95% CI, 0.46-5.73 mm; per 67.0 mm), and vapor pressure (6.21 hPa; 95% CI, 2.17-10.24 hPa; per 10.4 hPa) among 13- to 14-year-olds (222 center in 94 countries). The center-level persistent symptom prevalence was positively associated with several center-level climatic measures. Associations with climate were also found for the 6- to 7-year-olds (132 center in 57 countries).

CONCLUSION

Several between- and within-country spatial associations between climatic factors and intermittent and persistent rhinitis symptom prevalences were observed. These results provide suggestive evidence that climate (and future changes in climate) may influence rhinitis symptom prevalence.

Measurement error in time-series analysis: a simulation study comparing modelled and monitored data

Background

Assessing health effects from background exposure to air pollution is often hampered by the sparseness of pollution monitoring networks. However, regional atmospheric chemistry-transport models (CTMs) can provide pollution data with national coverage at fine geographical and temporal resolution. We used statistical simulation to compare the impact on epidemiological time-series analysis of additive measurement error in sparse monitor data as opposed to geographically and temporally complete model data.

Methods

Statistical simulations were based on a theoretical area of 4 regions each consisting of twenty-five 5 km × 5 km grid-squares. In the context of a 3-year Poisson regression time-series analysis of the association between mortality and a single pollutant, we compared the error impact of using daily grid-specific model data as opposed to daily regional average monitor data. We investigated how this comparison was affected if we changed the number of grids per region containing a monitor. To inform simulations, estimates (e.g. of pollutant means) were obtained from observed monitor data for 2003–2006 for national network sites across the UK and corresponding model data that were generated by the EMEP-WRF CTM. Average within-site correlations between observed monitor and model data were 0.73 and 0.76 for rural and urban daily maximum 8-hour ozone respectively, and 0.67 and 0.61 for rural and urban log_e(daily 1-hour maximum NO₂).

Results

When regional averages were based on 5 or 10 monitors per region, health effect estimates exhibited little bias. However, with only 1 monitor per region, the regression coefficient in our time-series analysis was attenuated by an estimated 6% for urban background ozone, 13% for rural ozone, 29% for urban background log_e(NO₂) and 38% for rural log_e(NO₂). For grid-specific model data the corresponding figures were 19%, 22%, 54% and 44% respectively, i.e. similar for rural log_e(NO₂) but more marked for urban log_e(NO₂).

Conclusion

Even if correlations between model and monitor data appear reasonably strong, additive classical measurement error in model data may lead to appreciable bias in health effect estimates. As process-based air pollution models become more widely used in epidemiological time-series analysis, assessments of error impact that include statistical simulation may be useful.

Twenty-five years of volatile substance abuse mortality: a national mortality surveillance programme

AIMS

To investigate trends in volatile substance abuse (VSA) deaths over 25 years.

DESIGN

A national mortality surveillance programme with standardised data collection procedures.

SETTING

The UK and islands. PARTICIPANTS/MEASUREMENTS: All VSA deaths, 1983-2007.

FINDINGS

In the five quinquennia from 1983 to 2007 the numbers of VSA deaths were 499, 609, 378, 349 and 258 respectively. There were gradual increases in the mean age at death in males and females and in the number of VSA deaths in women. Coincident with the 1992 Department of Health Advertising Campaign, VSA deaths in boys and girls (<18 years of age) fell by an estimated 56% (95% CI: 36%-70%) and 64% (20%-84%), respectively, from the underlying trend, but there was no evidence of any similar step change in either group following the 1999 Legislation prohibiting sales of cigarette lighter refills containing butane to those under the age of 18 years. Between 1983-1987 and 2003-2007, the ratio of aerosol to gas fuel deaths fell by an estimated 80% (57% to 91%) in adults, while the ratio of glue to gas fuel deaths fell by an estimated 95% (89% to 97%) in adults and an estimated 87% (-1% to 98%) in children.

CONCLUSIONS

Between 1983 and 2007, in the United Kingdom, the numbers of deaths associated with volatile substance abuse peaked in the early 1990s and fell to their lowest level in the mid-2000s. The age at death increased in both males and females. There was a fall in the proportion of volatile substance abuse deaths involving glues and a rise, particularly in adults, in the proportion involving gas fuels.

Asthma and occupation in the 1958 birth cohort

OBJECTIVE

To examine the association of adult onset asthma with lifetime exposure to occupations and occupational exposures.

METHODS

We generated lifetime occupational histories for 9488 members of the British 1958 birth cohort up to age 42 years. Blind to asthma status, jobs were coded to the International Standard Classification of Occupations 1988 and an Asthma Specific Job Exposure Matrix (ASJEM) with an expert re-evaluation step. Associations of jobs and ASJEM exposures with adult onset asthma were assessed in logistic regression models adjusting for sex, smoking, social class at birth and childhood hay fever.

RESULTS

Of the 7406 cohort members with no asthma or wheezy bronchitis in childhood, 639 (9%) reported asthma by age 42 years. Adult onset asthma was associated with 18 occupations, many previously identified as risks for asthma (eg, farmers: OR 4.26, 95% CI 2.06 to 8.80; hairdressers: OR 1.88, 95% CI 1.24 to 2.85; printing workers: OR 3.04, 95% CI 1.49 to 6.18). Four were cleaning occupations and a further three occupations were likely to use cleaning agents. Adult onset asthma was associated with five of the 18 high-risk specific ASJEM exposures (flour exposure: OR 2.12, 95% CI 1.17 to 3.85; enzyme exposure: OR 2.32, 95% CI 1.22 to 4.42; cleaning/disinfecting products: OR 1.67, 95% CI 1.26 to 2.22; metal and metal fumes: OR 1.45, 95% CI 1.02 to 2.07; textile production: OR 1.71, 95% CI 1.12 to 2.61). Approximately 16% (95% CI 3.8% to 27.1%) of adult onset asthma was associated with known asthmagenic occupational exposures.

CONCLUSIONS

This study suggests that about 16% of adult onset asthma in British adults born in the late 1950s could be due to occupational exposures, mainly recognised high-risk exposures.

Satellite-based estimates of ambient air pollution and global variations in childhood asthma prevalence

BACKGROUND

The effect of ambient air pollution on global variations and trends in asthma prevalence is unclear.

OBJECTIVES

Our goal was to investigate community-level associations between asthma prevalence data from the International Study of Asthma and Allergies in Childhood (ISAAC) and satellite-based estimates of particulate matter with aerodynamic diameter < 2.5 µm (PM₂.₅) and nitrogen dioxide (NO₂), and modelled estimates of ozone.

METHODS

We assigned satellite-based estimates of PM₂.₅ and NO₂ at a spatial resolution of 0.1° × 0.1° and modeled estimates of ozone at a resolution of 1° × 1° to 183 ISAAC centers. We used center-level prevalence of severe asthma as the outcome and multilevel models to adjust for gross national income (GNI) and center- and country-level sex, climate, and population density. We examined associations (adjusting for GNI) between air pollution and asthma prevalence over time in centers with data from ISAAC Phase One (mid-1900s) and Phase Three (2001-2003).

RESULTS

For the 13- to 14-year age group (128 centers in 28 countries), the estimated average within-country change in center-level asthma prevalence per 100 children per 10% increase in center-level PM₂.₅ and NO₂ was -0.043 [95% confidence interval (CI): -0.139, 0.053] and 0.017 (95% CI: -0.030, 0.064) respectively. For ozone the estimated change in prevalence per parts per billion by volume was -0.116 (95% CI: -0.234, 0.001). Equivalent results for the 6- to 7-year age group (83 centers in 20 countries), though slightly different, were not significantly positive. For the 13- to 14-year age group, change in center-level asthma prevalence over time per 100 children per 10% increase in PM₂.₅ from Phase One to Phase Three was -0.139 (95% CI: -0.347, 0.068). The corresponding association with ozone (per ppbV) was -0.171 (95% CI: -0.275, -0.067).

CONCLUSION

In contrast to reports from within-community studies of individuals exposed to traffic pollution, we did not find evidence of a positive association between ambient air pollution and asthma prevalence as measured at the community level.

Job choice and the influence of prior asthma and hay fever

OBJECTIVES

To investigate whether prior symptoms of allergic disease influence first job undertaken on leaving school.

METHODS

The study included 5020 members of the 1958 British birth cohort who provided a job history (including start dates) at age 33 and for whom information on allergic disease in childhood and adolescence was reported by parents at ages 7, 11 and 16. Occupational group (high risk, low risk, reference) was based on first job and its probable asthma risk.

RESULTS

With occupational group defined using only job title, the RR of taking a high risk over a reference level job was an estimated 30% (RR ratio (RRR) 0.70; 95% CI 0.56 to 0.88) lower among those with than without prior reported symptoms of hay fever/allergic rhinitis but an estimated 60% (RRR 1.60; 1.17 to 2.19) higher among those with symptoms of asthma/wheezy bronchitis in adolescence compared to those with no history of asthma/wheezy bronchitis. With occupational group defined using an asthma specific job exposure matrix, a similar association was observed for prior hay fever/allergic rhinitis (RRR 0.77; 0.62 to 0.96) but not for asthma/wheezy bronchitis (RRR 1.18; 0.85 to 1.64). There was no evidence of an association between prior eczema and occupational group of first job.

CONCLUSION

Whether our findings indicate avoidance or residual confounding, it would be prudent for future studies of occupation and the incidence or recurrence of asthma in adult life to adjust for any previous history of hay fever/allergic rhinitis.

Bronchodilator treatment and asthma death: a new analysis of a British case-control study

We investigated the relationship between asthma mortality and long-acting beta(2)-agonists (LABA), including interactions with age, inhaled corticosteroids (ICS) and social deprivation. We used a new, expanded dataset of recorded medication extracted blind from the anonymised primary care records of an earlier British case-control study. The cases were 532 asthma deaths aged < 65 occurring between 1994 and 1998 and the controls were 532 asthma admissions, matched for age, hospital, and index date (date of death/asthma admission). The exposure periods prior to the index date were current (≤ 2 months) or recent ( > 2-6 months). We found no evidence of an overall association with current (OR = 0.89 [95% confidence interval 0.61-1.30]) or recent (1.08 [0.76-1.53]) mention of LABA, but there was some evidence of a positive interaction with age. Among controls with mention of LABA, a concurrent mention of ICS (within 1 month) was common (85% and 93% for the two respective periods) which limited our power to investigate any interaction between LABA and ICS. There was no coherent evidence of effect modification by social deprivation. In a population based case-control study where prescription of LABA without concomitant ICS was uncommon there was no evidence of an overall association between LABA and asthma death.

Prenatal Irradiation and Spatial Memory in Mice: Investigation of Critical Period

Pregnant CD1 mice were exposed on various gestational or postnatal days to 1 Gy of 250 kV X-rays. Ten adult, male offspring from each exposure condition were tested in a radial arm maze. Compared to sham-exposed control mice, acquisition of spatial information was unimpaired in animals exposed on gestational days 13 or 15, or on postnatal day 10, but animals exposed on gestational day 18 or postnatal day 1 showed sustained deficits in acquisition. These results appear consistent with the known time-course for the proliferation and migration of the dentate granule cells of the hippocampus in the mouse, and are discussed in relation to the dependence on hippocampal integrity of the acquisition and use of spatial information. The results suggest that comparable deficits in mental function might be expected in humans similarly exposed to ionizing radiation during periods of proliferation and migration of the dentate granule cells.

C-reactive protein, obesity, atopy and asthma symptoms in middle-aged adults

Recent research has suggested an association between circulating C-reactive protein (CRP) and adult asthma, confined to those without evidence of allergic predisposition. The current authors investigated the role of smoking and obesity as possible explanations for this relationship. At 44-45 yrs of age, members of the British 1958 birth cohort participated in a biomedical survey involving the measurement of the following: CRP; the specific immunoglobulin E to grass, cat and dust mite; standing height; and weight. Information on asthma and related symptoms was collected by computer-aided interview when the subjects were 42 yrs of age. Complete data were available for a total of 6,490 subjects. CRP levels were positively correlated with the body mass index (BMI) and were found to be higher among females when compared with males, and higher among heavy smokers (> or = 20 cigarettes x day(-1)) when compared with never-smokers. After adjustment for sex and region, the odds ratios, comparing asthma prevalence in subjects above the fourth CRP quartile with subjects below the first quartile, were 1.85 (95% confidence interval 1.15-2.99) for nonatopics and 0.94 (0.62-1.41) for atopics, changing to 1.36 (0.80-2.32) and 1.07 (0.67-1.69), respectively, when additionally adjusted for smoking and BMI. Any association between C-reactive protein and asthma prevalence confined to nonatopics may be due to confounding factors. Alternatively, it may reflect a more general association of C-reactive protein with smoking-related obstructive airways disease.

Childhood asthma in South London: trends in prevalence and use of medical services 1991-2002

BACKGROUND

Hospital admission rates for asthma in Britain rose during the 1980s and fell during the 1990s, but less is known about recent trends in the prevalence of asthma.

METHODS

In 1991 and 2002 the same questionnaire was distributed to parents of all school pupils in year 3 (aged 7-8 years) in the London borough of Croydon. Parents of currently wheezy children were then invited for home interview (100% targeted in 1991, 66% in 2002).

RESULTS

The prevalence of wheeze during the previous year increased from 12.9% in 1991 to 17.8% in 2002 (prevalence ratio 1.39 (95% CI 1.23 to 1.56)). Increases were observed in frequent (1.54 (95% CI 1.16 to 2.03)) and infrequent attacks, severe speech limiting episodes (2.25 (95% CI 1.34 to 3.77)), and night waking (1.36 (95% CI 1.07 to 1.72)), and in the reported use of steroids (19.9% v 64.1% of currently wheezy children). Nevertheless, the proportions reporting a visit to the GP at his/her surgery for wheeze in the previous year (prevalence ratio 1.15 (95% CI 0.91 to 1.45)) or an outpatient visit (0.98 (95% CI 0.49 to 1.94)) changed little and an increase in reported casualty attendance (1.66 (95% CI 0.89 to 3.07)) was non-significant.

CONCLUSIONS

There is evidence of an increase in the prevalence of asthma among British primary school children between 1991 and 2002. The absence of a corresponding increase in health service utilisation data may reflect more widespread prophylactic treatment and/or changes in the use and provision of medical services.

Deaths certified as asthma and use of medical services: a national case-control study

BACKGROUND

Studies have linked asthma death to either increased or decreased use of medical services.

METHODS

A population based case-control study of asthma deaths in 1994-8 was performed in 22 English, six Scottish, and five Welsh health authorities/boards. All 681 subjects who died were under the age of 65 years with asthma in Part I on the death certificates. After exclusions, 532 hospital controls were matched to 532 cases for age, district, and date of asthma admission/death. Data were extracted blind from primary care records.

RESULTS

The median age of the subjects who died was 53 years; 60% of cases and 64% of controls were female. There was little difference in outpatient attendance (55% and 55%), hospital admission for asthma (51% and 54%), and median inpatient days (20 days and 15 days) in the previous 5 years. After mutual adjustment and adjustment for sex, using conditional logistic regression, three variables were independently associated with asthma death: fewer general practice contacts (odds ratio 0.82 (95% confidence interval (CI) 0.74 to 0.91) per 5 contacts) in the previous year, more home visits (1.14 (95% CI 1.08 to 1.21) per visit) in the previous year, and fewer peak expiratory flow recordings (0.83 (95% CI 0.74 to 0.92) per occasion) in the previous 3 months. These associations were similar after adjustment for markers of severity, psychosocial factors, systemic steroids, short acting bronchodilators and antibiotics, although the association with peak flow was weakened and just lost significance.

CONCLUSION

Asthma death is associated with less use of primary care services. Both practice and patient factors may be involved and a better understanding of these may offer possibilities for reducing asthma death.

Bronchodilator treatment and deaths from asthma: case-control study

OBJECTIVE

To investigate the association between bronchodilator treatment and death from asthma.

DESIGN

Case-control study.

SETTING

33 health authorities or health boards in Great Britain.

PARTICIPANTS

532 patients under age 65 who died from asthma and 532 controls with a hospital admission for asthma matched for period, age, and area.

MAIN OUTCOME MEASURES

Odds ratios for deaths from asthma associated with prescription of bronchodilators and other treatment, with sensitivity analyses adjusting for age at onset, previous hospital admissions, associated chronic obstructive lung disease, and number of other drug categories.

RESULTS

After full adjustment, there were no significant associations with drugs prescribed in the 4-12 months before the index date. For prescriptions in the 1-5 years before, mortality was positively associated with inhaled short acting beta2 agonists (odds ratio 2.05, 95% confidence interval 1.26 to 3.33) and inversely associated with antibiotics (0.59, 0.39 to 0.89). The former association seemed to be confined to those aged 45-64, and the association with antibiotics was more pronounced in those under 45. Significant age interactions across all periods suggested inverse associations with oral steroids confined to the under 45 age group. An inverse association with long acting beta2 agonists and a positive association with methylxanthines in the 1-5 year period were non-significant.

CONCLUSION

There was no evidence of adverse effects on mortality with medium to long term use of inhaled long acting beta2 agonist drugs. The association with short acting beta(2) agonists has several explanations, only one of which may be a direct adverse effect.

Psychological, social and health behaviour risk factors for deaths certified as asthma: a national case-control study

BACKGROUND

Uncontrolled studies suggest that psychosocial factors and health behaviour may be important in asthma death.

METHODS

A community based case-control study of 533 cases, comprising 78% of all asthma deaths under age 65 years and 533 hospital controls individually matched for age, district and asthma admission date corresponding to date of death was undertaken in seven regions of Britain (1994-98). Data were extracted blind from anonymised copies of primary care records for the previous 5 years and non-blind for the earlier period.

RESULTS

60% of cases and 63% of controls were female. The median age in both groups was 53. Cases had an earlier age of asthma onset, more chronic obstructive lung disease, and were more obese. 48% of cases and 42% of controls had a health behaviour problem; repeated non-attendance/poor inhaler technique was related to increased risk of death. Overall, 85% and 86%, respectively, had a psychosocial problem. Four psychosocial factors were associated with increased risk of death (psychosis, alcohol/drug abuse, financial/employment problems, learning difficulties) and two with reduced risk (anxiety/prescription of antidepressant drugs and sexual problems). While alcohol/drug abuse lost significance after adjustment for psychosis, other associations appeared independent of each other and of indicators of severity and co-morbidity. None of the remaining 13 factors including family problems, domestic abuse, bereavement, and social isolation were significantly related to risk of asthma death.

CONCLUSION

There was an apparently high burden of psychosocial problems in both cases and controls. The associations between health behaviour, psychosocial factors, and asthma death are varied and complex with a limited number of factors showing positive relationships.

Ischaemic heart disease and Cag A strains of Helicobacter pylori in the Caerphilly heart disease study

OBJECTIVE

To look for the presence of the more virulent strains of Helicobacter pylori (H pylori) in men who developed ischaemic heart disease over a 10 year period and in controls.

DESIGN

The Caerphilly prospective heart disease study recruited 2512 men aged 45-59 years during 1979-83. Western blot analysis or enzyme linked immunosorbent assay (ELISA) was performed on serum taken from those who subsequently died of ischaemic heart disease, or developed non-fatal myocardial infarction, to determine H pylori and Cag A status. Similar information was available on age matched controls.

RESULTS

During the first decade of the study, 312 men died of ischaemic heart disease or developed non-fatal myocardial infarction. Serum was available from 172 of these (55%). There was no evidence of an association between Cag A seropositivity and incident ischaemic heart disease or ischaemic heart disease mortality, either before or after adjustment for potential confounders (adjusted odds ratios 1.18 (95% confidence interval (CI) 0.76 to 1.85) and 1.13 (95% CI 0.61 to 2.07), respectively). Further, the odds ratios for ischaemic heart disease incidence and ischaemic heart disease mortality by H pylori seropositivity did not appear to depend on the presence or absence of Cag A strains (p = 0.76 and 0.77, respectively).

CONCLUSIONS

In this cohort of middle aged men, followed over a 10 year period, there is little evidence of an association between Cag A seropositivity and either incident ischaemic heart disease or ischaemic heart disease mortality.

C-reactive protein: relation to total mortality, cardiovascular mortality and cardiovascular risk factors in men

BACKGROUND

There is much interest in reported associations between serum C-reactive protein and incident ischaemic heart disease. It is uncertain what this association represents. We aimed to assess the effect of confounding from a number of different sources in the Caerphilly Prospective Heart Disease Study and in particular whether the low grade inflammation indicated by C-reactive protein may be the mechanism whereby non-circulating risk factors may influence pathogenesis of ischaemic heart disease.

METHODS

Plasma specimens collected during 1979-83 from 1395 men with sufficient sample remaining were assayed for serum C-reactive protein by ELISA. Subsequent mortality and incident ischaemic heart disease events were ascertained from death certificates, hospital records and electrocardiographic changes at 5-yearly follow-up examinations.

RESULTS

There was a positive association between C-reactive protein and incident ischaemic heart disease (P<0.005) mainly with fatal disease (P<0.002). There was also a positive association with all-cause mortality (P<0.0001). C-reactive protein was significantly associated with a number of non-circulating risk factors including body mass index (P<0.0001), smoking (P<0.0001), low forced expiratory volume in 1 s (P<0.0001), height (P=0.025), low childhood social class (P=0.014) and age (P=0.036). C-reactive protein was also associated positively with circulating risk factors including viscosity, leukocyte count, fibrinogen (all P<0.0001) and insulin (P=0.0058). After adjustment for non-circulating risk factors the association with all-incident ischaemic heart disease and ischaemic heart disease death became non-significant, but the association with all-cause mortality remained (P=0.033). Further adjustment for fibrinogen however removed any hint of an increasing trend in odds for all three outcomes.

CONCLUSION

C-reactive protein levels are raised in association with a variety of established cardiovascular risk factors. Neither C-reactive protein nor the systemic inflammation it represents appears to play a direct role in the development of ischaemic heart disease.

Diet, lung function, and lung function decline in a cohort of 2512 middle aged men

BACKGROUND

A prospective cohort study of 2512 Welshmen aged 45-59 living in Caerphilly in 1979-1983 was used to investigate associations between diet and lung function.

METHODS

At baseline (phase I) and at five year follow up (phase II), forced expiratory volume in one second (FEV(1)) was measured using a McDermott spirometer and dietary data were obtained using a semi-quantitative food frequency questionnaire.

RESULTS

Good lung function, indicated by high maximum FEV(1) given age and height, was associated with high intakes of vitamin C, vitamin E, beta-carotene, citrus fruit, apples, and the frequent consumption of fruit juices/squashes. Lung function was inversely associated with magnesium intake but there was no evidence of an association with fatty fish. Following adjustment for confounders including body mass index, smoking history, social class, exercise, and total energy intake, only the associations with vitamin E and apples persisted, with lung function estimated to be 39 ml (95% confidence interval (CI) 9 to 69) higher for vitamin E intakes one standard deviation (SD) apart and 138 ml higher (95% CI 58 to 218) for those eating five or more apples per week compared with non-consumers. Decline in lung function between phases was not significantly associated with the changing intakes of apples or vitamin E. An association between high average apple consumption and slow decline in lung function lost significance after adjustment for confounders.

CONCLUSIONS

A strong positive association is seen between lung function and the number of apples eaten per week cross sectionally, consistent with a protective effect of hard fruit rather than soft/citrus fruit. The recent suggestion that such effects are reversible was not supported by our longitudinal analysis.

Chlamydia pneumoniae serology, lung function decline, and treatment for respiratory disease

Associations have been reported between Chlamydia pneumoniae seropositivity and both acute and chronic obstructive airway diseases. Plasma specimens collected between 1979 and 1983 from 1, 773 men 45 to 59 yr of age in Caerphilly, South Wales, were tested for IgG and IgA antibodies to C. pneumoniae (TW183) by microimmunofluorescence. Subsequent mortality and medication for obstructive airway disease were ascertained at 5-yr follow-up examinations. Spirometry was performed at the first and second examinations and analyzed both cross-sectionally and longitudinally; 642 men (36%) had IgG antibodies at a titer of 1:16 or above, of whom 362 also had detectable IgA antibodies. No statistically significant associations were found between either IgG titer or IgA titer and any of the outcome measures: inhaler therapy at entry; commencement of inhalers during follow-up; death from respiratory causes; baseline FEV(1), FVC, and FEV(1)/FVC ratio; and decline in FEV(1) (p > 0.1 throughout). Men with high IgG titers (>/= 1:64) had a slower rate of decline of FEV(1) than did seronegative subjects (adjusted mean difference in 5-yr change in FEV(1): +22 ml, 95% confidence interval: -31 ml to +76 ml). Men with high IgA titers (>/= 1:16) had a slightly faster rate of decline (-12 ml, - 96 ml to +71 ml). This first prospective assessment suggests that chronic C. pneumoniae infection is not a major risk factor for progressive airflow obstruction.

Relation of Chlamydia pneumoniae serology to mortality and incidence of ischaemic heart disease over 13 years in the caerphilly prospective heart disease study

OBJECTIVES

To investigate the effect of Chlamydia pneumoniae infection on future development of ischaemic heart disease and mortality.

DESIGN

Prospective longitudinal study.

SETTING

Caerphilly, South Wales.

SUBJECTS

Plasma specimens were collected during 1979-83 from 1773 men aged 45-59 years. These were tested for IgG and IgA antibodies to C pneumoniae (TW183) by microimmunofluorescence.

OUTCOME MEASURES

13 year mortality and incident ischaemic heart disease events were ascertained from death certificates, hospital records, and electrocardiographic changes at follow up every 4 to 5 years.

RESULTS

642 men (36.2%) had IgG antibodies at a titre of >/=1 in 16, of whom 362 (20.4% of all men) also had detectable IgA antibodies. The prevalence of ischaemic heart disease (a history of past or current disease) at entry was similar at all IgG antibody titres but was positively related to IgA antibody titre. IgA antibody titre was positively correlated with plasma viscosity but not with other cardiovascular risk factors. Incidence of ischaemic heart disease was not associated with either IgG antibody titre or IgA antibody titre, but there were stronger and significant relations of IgA antibodies with all cause mortality and fatal ischaemic heart disease, which persisted after adjustment for conventional cardiovascular risk factors. The odds ratios associated with detectable IgA antibodies were 1.07 (95% confidence interval 0.75 to 1.53) for all incident ischaemic heart disease, 1. 83 (1.17 to 2.85) for fatal ischaemic heart disease, and 1.50 (1.10 to 2.04) for all cause mortality.

CONCLUSION

This is the first prospective demonstration of an association between IgA antibodies to C pneumoniae, a putative marker of chronic infection, and subsequent risk of death from ischaemic heart disease. In contrast to earlier case-control studies, IgG antibodies were not associated with either prevalent or incident ischaemic heart disease.

Fresh fruit intake and asthma symptoms in young British adults: confounding or effect modification by smoking?

Antioxidant vitamins have been postulated as a protective factor in asthma. The associations between the frequency of fresh fruit consumption in summer, and the prevalence of self-reported asthma symptoms were investigated. The analysis was based on 5,582 males and 5,770 females, born in England, Wales and Scotland between March 3-9, 1958 and aged 33 yrs at the time of survey. The 12-month period prevalence of wheeze and frequent wheeze were inversely associated with frequent intakes of fresh fruit and salad/raw vegetables and positively associated with smoking and lower social class. After adjustment for mutual confounding and sex, associations with smoking persisted, but those with social class and salad/raw vegetable consumption lost significance. The frequency of fresh fruit intake was no longer associated with wheeze after adjustment, but was inversely associated with frequent wheeze and speech-limiting attacks. The association with frequent wheeze differed significantly between smoking groups (never, former, current) and appeared to be confined to exsmokers and current smokers. These findings support postulated associations between infrequent fresh fruit consumption and the prevalence of frequent or severe asthma symptoms in adults. Associations appeared to be restricted to smokers, with effect modification as a more likely explanation of this pattern than residual confounding by smoking.

Cytomegalovirus seropositivity and incident ischaemic heart disease in the Caerphilly prospective heart disease study

OBJECTIVE

To assess the role of cytomegalovirus (CMV) infection in primary ischaemic heart disease.

METHODS

Plasma specimens collected during 1979-83 from men in Caerphilly, south Wales, were analysed for IgG antibodies to CMV by enzyme linked immunosorbent assay and latex tests. Incident ischaemic heart disease events were ascertained after five and 10 years from death certificates, hospital records, and ECG changes; 195 incident ischaemic heart disease cases were compared with 216 controls of a similar age drawn from the rest of the cohort.

RESULTS

164 cases (84%) and 180 controls (83%) were seropositive for CMV. Optical density, an indicator of CMV antibody titre, was similar for cases and controls. Among controls, seropositivity was not associated with age, socioeconomic status currently or in childhood, smoking, height, body mass index, blood pressure, total cholesterol, fibrinogen, plasma viscosity, or leucocyte count. The unadjusted odds ratio relating CMV seropositivity to incident ischaemic heart disease was 1.06 (95% confidence interval 0.63 to 1.79) and was little changed (1.11, 0.63 to 1.97) after adjustment for age, smoking, body mass index, systolic blood pressure, total cholesterol, and socioeconomic status currently and in childhood.

CONCLUSIONS

CMV infection is unlikely to be a strong risk factor for development of myocardial infarction in middle aged men.

Relation of Helicobacter pylori infection to 13-year mortality and incident ischemic heart disease in the caerphilly prospective heart disease study

BACKGROUND

Associations have been suggested between Helicobacter pylori seropositivity, cardiovascular risk factors, and ischemic heart disease (IHD). The effect of this common infection on mortality is uncertain.

METHODS AND RESULTS

Plasma specimens collected during 1979 to 1983 from 1796 men in Caerphilly, South Wales, were analyzed for IgG antibodies to H pylori. Cause of death and occurrence of incident IHD events were ascertained over an average of 13.7 years from death certificates, hospital records, and ECG changes at 5-yearly follow-up examinations. Seventy percent of men were seropositive. The prevalence of IHD at entry was similar in men with and without H pylori antibodies (odds ratio [OR], 1.10; 95% CI, 0.87 to 1.40). Seropositivity was significantly (P<0.05) associated with poorer socioeconomic status currently and in childhood, shorter stature, and poorer ventilatory function at entry but not with age, smoking, body mass index, blood pressure, total cholesterol, HDL cholesterol, LDL cholesterol, fibrinogen, plasma viscosity, or heat shock protein antibodies. Thirteen-year incidence of IHD was not significantly associated with H pylori (OR, 1.05; 95% CI, 0.80 to 1.39), but there was a stronger relationship with all-cause mortality (OR, 1.46; 95% CI, 1.12 to 1.92) and fatal IHD (OR, 1.54; 95% CI, 1.03 to 2.30). After adjustment for cardiovascular risk factors and both adult and childhood socioeconomic status, ORs were slightly reduced and lost statistical significance (OR=1.32 [95% CI, 0.99 to 1.78] for all-cause mortality and OR=1.52 [95% CI, 0.99 to 2.34] for fatal IHD).

CONCLUSIONS

H pylori infection is unlikely to be as strong a risk factor for IHD as some previous studies have suggested, but its relationship to mortality, including fatal IHD, deserves further investigation. The mechanism underlying these associations is unlikely to involve hypertension, circulating lipid profile, fibrinogen, or cross-reacting antibodies to bacterial heat shock proteins.

Investigation into the increase in hay fever and eczema at age 16 observed between the 1958 and 1970 British birth cohorts

OBJECTIVE

To investigate whether changes in certain perinatal and social factors explain the increased prevalence of hay fever and eczema among British adolescents between 1974 and 1986.

DESIGN

Two prospective birth cohort studies.

SETTING

England, Wales, and Scotland.

SUBJECTS

11,195 children born 3-9 March 1958 and 9387 born 5-11 April 1970.

MAIN OUTCOME MEASURES

Parental reports of eczematous rashes and of hay fever or allergic rhinitis in the previous 12 months at age 16.

RESULTS

The prevalence of the conditions over the 12 month period increased between 1974 and 1986 from 3.1% to 6.4% (prevalence ratio 2.04 (95% confidence interval 1.79 to 2.32)) for eczema and from 12.0% to 23.3% (prevalence ratio 1.93 (1.82 to 2.06)) for hay fever. Both conditions were more commonly reported among children of higher birth order and those who were breast fed for longer than 1 month. Eczema was more commonly reported among girls and hay fever among boys. The prevalence of hay fever decreased sharply between social classes I and V, increased with maternal age up to the early 30s, and was lower in children whose mothers smoked during pregnancy. Neither condition varied significantly with birth weight. When adjusted for these factors, the relative odds of hay fever (1986 v 1974) increased from 2.23 (2.05 to 2.43) to 2.40 (2.19 to 2.63). Similarly, the relative odds of eczema rose from 2.02 (1.73 to 2.36) to 2.14 (1.81 to 2.52).

CONCLUSIONS

Taken together, changes between cohorts in sex, birth weight, birth order, maternal age, breast feeding, maternal smoking during pregnancy, and father's social class at birth did not seem to explain any of the observed rise in the prevalence of hay fever and eczema. However, correlates of these factors which have changed over time may still underlie recent increases in allergic disease.

The home environment and asthma symptoms in childhood: two population based case-control studies 13 years apart

BACKGROUND

Prevalence surveys of asthma and/or wheezing among all children aged between 7 1/2 and 8 1/2 attending state and private schools in the London Borough of Croydon were conducted in February 1978 and February 1991. Two population based case-control studies drawn from the survey responders were used to investigate the association between childhood wheeze and characteristics of the home environment and to assess whether changes in these characteristics between 1978 and 1991 may have contributed to an increase in the population prevalence of wheeze among school children.

METHODS

Information on exposure to potential indoor environmental risk factors was obtained from parents by home interview and compared between cases-that is, children with frequent (> or = 5) or in-frequent (1-4) attacks of asthma or wheezing in the past 12 months- and controls, with adjustment for study. Changes in exposure over time were assessed by comparing control groups.

RESULTS

Between 1978 and 1991 the population prevalence odds of wheeze increased by 20% (OR 1.20; 95% CI 1.04 to 1.39). Change in parental smoking, gas cooking, pet ownership, and central heating did not appear to explain the rise. Use of non-feather pillows was positively associated with childhood wheeze even after adjusting for other risk factors and after re-coding from non-feather to feather cases thought to have changed pillow in response to symptoms (OR 1.54; 95% CI 1.13 to 2.10). The proportion of control children reportedly using non-feather pillows was 44% in 1978 and 67% in 1991.

CONCLUSIONS

Increased use of non-feather pillows was the only domestic indoor exposure studied which appeared to explain a modest rise in prevalence of wheeze from 1978 to 1991. Our analysis attempts to address behavioural change in response to the child's symptoms but an artifact arising from lifelong avoidance of feather bedding in atopic families cannot be entirely discounted.

Incidence and prognosis of asthma and wheezing illness from early childhood to age 33 in a national British cohort

OBJECTIVE

To describe the incidence and prognosis of wheezing illness from birth to age 33 and the relation of incidence to perinatal, medical, social, environmental, and lifestyle factors.

DESIGN

Prospective longitudinal study.

SETTING

England, Scotland and Wales.

SUBJECTS

18,559 people born on 3-9 March 1958. 5801 (31%) contributed information at ages 7, 11, 16, 23, and 33 years. Attrition bias was evaluated using information on 14, 571 (79%) subjects.

MAIN OUTCOME MEASURE

History of asthma, wheezy bronchitis, or wheezing obtained from interview with subjects' parents at ages 7, 11, and 16 and reported at interview by subjects at ages 23 and 33.

RESULTS

The cumulative incidence of wheezing illness was 18% by age 7, 24% by age 16, and 43% by age 33. Incidence during childhood was strongly and independently associated with pneumonia, hay fever, and eczema. There were weaker independent associations with male sex, third trimester antepartum haemorrhage, whooping cough, recurrent abdominal pain, and migraine. Incidence from age 17 to 33 was associated strongly with active cigarette smoking and a history of hay fever. There were weaker independent associations with female sex, maternal albuminuria during pregnancy, and histories of eczema and migraine. Maternal smoking during pregnancy was weakly and inconsistently related to childhood wheezing but was a stronger and significant independent predictor of incidence after age 16. Among 880 subjects who developed asthma or wheezy bronchitis from birth to age 7, 50% had attacks in the previous year at age 7; 18% at 11, 10% at 16, 10% at 23, and 27% at 33. Relapse at 33 after prolonged remission of childhood wheezing was more common among current smokers and atopic subjects.

CONCLUSION

Atopy and active cigarette smoking are major influences on the incidence and recurrence of wheezing during adulthood.

Trends in prevalence and severity of childhood asthma

OBJECTIVE

To test the null hypothesis that there has been no change in the prevalence or severity of childhood asthma over recent years.

DESIGN

Repeated population prevalence survey with questionnaires completed by parents followed by home interviews with parents.

SETTING

London borough of Croydon, 1978 and 1991.

SUBJECTS

All children in one year of state and private primary schools aged 7 1/2 to 8 1/2 years at screening survey.

MAIN OUTCOME MEASURES

Trends in symptoms, acute severe attacks, and chronic disability.

RESULTS

For 1978 and 1991 respectively, the response rates were 4147/4763 and 3070/3786, and home interviews were obtained from 273/288 and 319/395 parents of currently wheezy children. Between 1978 and 1991 there were significant relative increases in prevalence ratios in the 12 month prevalence of attacks of wheezing or asthma (1.16; 95% confidence interval 1.02 to 1.31), the one month prevalence of wheezing episodes (1.78; 1.15 to 2.74), and the one month prevalence of night waking (1.81; 1.01 to 3.23) but not in frequent (> or = 5) attacks over the past year (1.05; 0.79 to 1.40). There were substantial and significant decreases in the 12 month prevalence of absence from school of more than 10 days due to wheezing (0.52; 0.30 to 0.90), any days in bed (0.67; 0.44 to 1.01), and restriction of activities at home (0.51; 0.31 to 0.83) and an equivalent but not significant fall in speech limiting attacks (0.51; 0.24 to 1.11).

CONCLUSION

The small increase in the prevalence of wheezy children and relatively greater increase in persistent wheezing suggests a change in the environmental determinants of asthma. In contrast and paradoxically the frequency of wheezing attacks remains unchanged and there are indications that severe attacks and chronic disability have fallen by about half; this may be due to an improvement in treatment received by wheezy children.

Effects of prenatal exposure to 50 Hz magnetic fields on development in mice: I. Implantation rate and fetal development

Pregnant CD1 mice were exposed or sham-exposed from day 0 to day 17 of gestation to a 50 Hz sinusoidal magnetic field at 20 mT (rms). Preimplantation and postimplantation survival were assessed and fetuses examined for the presence of gross external, internal, and skeletal abnormalities. There were no statistically significant field-dependent effects on preimplantation or postimplantation survival, sex ratio, or the incidence of fetuses with internal or skeletal abnormalities. Magnetic field exposure was, however, associated with longer and heavier fetuses at term, with fewer external abnormalities. The results lend no support to suggestions of increased rates of spontaneous abortion or congenital malformation following prenatal exposure to power frequency magnetic fields.

Mortality and occupational exposure to radiation: first analysis of the National Registry for Radiation Workers

OBJECTIVE

To study cause specific mortality of radiation workers with particular reference to associations between fatal neoplasms and level of exposure to radiation.

DESIGN

Cohort study.

SETTING

United Kingdom.

SUBJECTS

95,217 radiation workers at major sites of the nuclear industry.

MAIN OUTCOME MEASURE

Cause of death.

RESULTS

Most standardised mortality ratios were below 100: 83 unlagged, 85 with a 10 year lag for all causes; 84 unlagged, 86 lagged for all cancers; and 80 for all known other causes, indicating a "healthy worker effect." The deficit of lung cancer (75 unlagged, 76 lagged) was significant at the 0.1% level. Standardised mortality ratios were significantly raised (214 unlagged, 303 lagged) for thyroid cancer, but there was no evidence for any trend with external recorded radiation dose. Dose of external radiation and mortality from all cancers were weakly correlated (p = 0.10), and multiple myeloma was more strongly correlated (p = 0.06); for leukaemia, excluding chronic lymphatic, the trend was significant (p = 0.03; all tests one tailed). The central estimates of lifetime risk derived from these data were 10.0% per Sv (90% confidence interval less than 0 to 24%) for all cancers and 0.76% per Sv (0.07 to 2.4%) for leukaemia (excluding chronic lymphatic leukaemia). These are, respectively, 2.5 times and 1.9 times the risk estimates recommended by the International Commission on Radiological Protection, but 90% confidence intervals are large and the commission's risk factors fall well within the range. The positive trend with dose for all cancers, from which the risk estimate was derived, was not significant. The positive association between leukaemia (except chronic lymphatic leukaemia) was significant and robust in subsidiary analyses. This study showed no association between radiation exposure and prostatic cancer.

CONCLUSION

There is evidence for an association between radiation exposure and mortality from cancer, in particular leukaemia (excluding chronic lymphatic leukaemia) and multiple myeloma, although mortality from these diseases in the study population overall was below that in the general population. The central estimates of risk from this study lie above the most recent estimates of the International Commission on Radiological Protection for leukaemia (excluding chronic lymphatic leukaemia) and for all malignancies. However, the commission's risk estimates are well within the 90% confidence intervals from this study. Analysis of combined cohorts of radiation workers in the United States indicated lower risk estimates than the commission recommends, and when the American data are combined with our analysis the overall risks are close to those estimated by the commission. This first analysis of the National Registry for Radiation Workers does not provide sufficient evidence to justify a revision in risk estimates for radiological protection purposes.

The influence of pregnancy and reproductive span on the occurrence of autoimmune thyroiditis

A study comparing the reproductive histories of 89 women affected by Hashimoto's thyroiditis (HT) with 89 matched controls has been carried out to determine whether endogenous hormones contribute to the development of the disease. There was no evidence of an association between HT and parity and no trend to an increasing disease risk with increasing parity. However, patients with HT had a longer reproductive span. There was a significant trend to a lower risk with later age at menarche (relative risk (RR) of menarche at 13-14 years compared with less than or equal to 12 years = 0.71, and greater than or equal to 15 years compared with less than or equal to 12 years = 0.45), and an increased risk with a later menopause (greater than or equal to 51 years compared with less than or equal to 50 years, RR = 3.00, P less than 0.025). An additional finding was an increased hysterectomy rate among the cases. These observations may be explained if the hyperoestrogenic state associated with a longer reproductive span acted to modulate the immune process in autoimmune thyroid disease.

Body fatness and frame size: the Caerphilly study

The effect of adjusting height-weight indices for frame size on the prediction of body fatness was investigated in a community sample of 2512 men aged 45-59 years. Body fatness was assessed from skinfold thickness measurements at four sites: triceps, biceps, subscapular and supra-iliac. Body diameters (biacromial, bi-iliocristal, wrist or knee) were used as estimates of frame size. Body diameters were not independent of body fatness, wrist diameter showing the lowest association with skinfold thickness measurements. Adjustment of weight/height2 (W/H2) for frame size had little effect on the prediction of body fatness, the correlation coefficient for body fatness with W/H2 (r = 0.76) being almost identical to that for W/H2 adjusted for wrist diameter (r = 0.74).

Changes in asthma prevalence: two surveys 15 years apart

In 1973 a survey was conducted among 12 year old children living in a defined area of South Wales. In 1988 the survey was repeated in the same area, again among 12 year old children. Questionnaires were completed for all 965 children in the population sample; peak expiratory flow rates were performed on them all, and repeated (except for five children) after an exercise provocation test. The prevalence of a history of wheeze at any time had increased from 17% to 22%, while that of a history of asthma at any time had increased from 6% to 12%. Current asthma had increased from 4% to 9%, but wheezing in the past year not attributed to asthma had remained at 6%. The exercise provocation tests suggested that both mild and severe asthma had become more common. Increases had also occurred in the frequencies of a history of eczema (from 5% to 16%) and of hay fever (from 9% to 15%). It seems that the prevalence of asthma has risen, and that this cannot be wholly explained by a greater readiness to diagnose the disease.

Coffee, blood pressure and plasma lipids: a randomized controlled trial

A randomized controlled trial was conducted to examine the effects of coffee (as commonly drunk in Britain) on blood pressure and plasma lipids in healthy subjects. Fifty-four subjects followed three regimens successively, the order being randomized according to a Latin square design: five or more cups of coffee daily for 4 weeks; five or more cups of decaffeinated coffee daily for 4 weeks but no ordinary coffee; no coffee for 4 weeks. Coffee appeared to cause a small rise (of 3 mm Hg) in recumbent systolic blood pressure; this effect was less than, and obscured by, changes induced by posture and mild stress. No consistent changes attributable to coffee were found in diastolic blood pressure or pulse rate. Small changes in the expected directions occurred in plasma high density lipoprotein (HDL) cholesterol and apolipoprotein AI (decrease), and in total cholesterol, non-HDL cholesterol and apolipoprotein B (increase), but none of these were statistically significant. The effect of coffee on risk of heart disease in Britain is probably small.

Environmental factors and symptoms in infants at high risk of allergy

STUDY OBJECTIVE

To identify environmental determinants of six symptoms associated with allergic disease in infancy.

DESIGN

Infants were participants in a prospective randomised controlled trial of feeding practices in families with a history of atopy.

SETTING

Infants were recruited in two maternity hospitals in S Wales and followed up in the community for 1 year.

PARTICIPANTS

Mothers of 519 infants agreed to participate, but 36 were excluded (mainly for moving home or failing to attend for follow-up), leaving 483 in the study (253 male, 230 female). Infants were followed up and examined for evidence of allergic disease at 3, 6, and 12 months.

MEASUREMENTS AND MAIN RESULTS

At each examination, mothers were questioned about episodes of illness in the infant, and the data presented relate to (reported and observed) eczema and nasal discharge, and (reported) wheeze, prolonged colds, diarrhoea and vomiting. Mothers kept a diary with details of feeding for the first 6 months. All homes were visited by a nurse who took samples of dust for dust mite antigen analysis. Extensive socio-demographic data were collected. None of the factors studied showed a convincing relationship with eczema. In a multiple logistic regression analysis breast feeding appeared to protect against wheeze, nasal discharge, colds, vomiting and diarrhoea. Having more siblings increased the likelihood of prolonged colds, and (together with overcrowding) of wheeze and nasal discharge. Maternal smoking and low social class were associated with wheeze, and house dust antigen with prolonged colds. Respiratory symptoms were associated with some aspects of housing but these could not be distinguished clearly from other social factors. Babies born in Autumn were at increased risk of wheeze, vomiting and diarrhoea.

CONCLUSIONS

Environmental factors play an important part in determining risk of symptoms in potentially atopic babies. These factors are in principle open to manipulation.

Infant feeding and allergy: 12-month prospective study of 500 babies born into allergic families

This investigation studied 487 babies for symptoms of allergic disease during their first year of life. Because of their positive family histories all the babies are at high risk of becoming allergic. The babies were randomly divided such that cows' milk was deliberately withheld from one group; infants in this group were fed with a soya substitute where required. No benefit resulted from withholding cows' milk, indeed symptoms were more usually associated with this group. Breast feeding, even for a short period, was clearly associated with a lower incidence of wheeze, prolonged colds, diarrhoea, and vomiting. It seemed that the duration of breast feeding was less important than whether or not the child had been breast-fed at all. Wheezing was both more common among boys than girls (P less than .05) and if the mother was a smoker. Other environmental features related to wheezing were social class, month of birth, lack of breast feeding, exposure to dampness, mould and coal fires, but not to domestic pets nor to the numbers of mites found in bedding and carpets. Mite exposure was, however, associated with prolonged colds. Eczema was the only allergic symptom not positively associated with any environmental factor; moreover, it was neither associated with a lack of breast feeding nor with inclusion of cows' milk in the diet. Eczema was associated with the incidence of positive skin prick tests and IgE antibodies to egg white. IgE and IgG4 antibodies were estimated at birth (mothers' and cord bloods) and 3 and 12 months later.(ABSTRACT TRUNCATED AT 250 WORDS)

Type A behaviour, eating pattern and nutrient intake: the Caerphilly Study

Relationships between type A behaviour and eating pattern and nutrient intake were investigated in a representative sample of 532 employed men aged 45-59 years drawn from the Caerphilly study. Eating pattern and nutrient intake were assessed by 7-day weighed dietary records. A change in Framingham type A scores from the lower third to the upper third was associated with a 9% reduction in meal size and a 6% increase in meal frequency. No trends with type A were found for nutrient intake in absolute terms. For means of nutrient intake as a percentage of energy, however, higher values for sugar and lower values for starch and polyunsaturated fat were observed with higher type A scores. In multiple regression analysis, after control for the effects of age, height, social class and smoking, significant associations with type A were found only for meal size, dietary fibre per MJ and sugar as a percentage of energy. It is concluded that diet is unlikely to be an explanation of the relationship between type A and ischaemic heart disease.

Heart disease in British vegetarians

A prospective study was conducted among customers of health food shops and members of societies interested in health foods. A total of 10,896 persons were followed for 10-12 y, including 4671 vegetarians and 6225 nonvegetarians. Mortality from ischemic heart disease (IHD) was significantly lower in the vegetarians than in the nonvegetarians; the difference was especially marked among the men. In a subset of 300 subjects, serum cholesterol and body mass index were lower in the vegetarians than in the nonvegetarians but there were no consistent differences in blood pressure between the two groups. Vegetarianism seems to confer some protection against IHD but it is not clear whether this is due to abstinence from meat or to a high consumption of vegetables.

Type A behaviour and prevalent heart disease in the Caerphilly study: increase in risk or symptom reporting?

Type A behaviour was assessed by modified Framingham scale in a total sample of 1956 employed men in the Caerphilly study. Prevalent heart disease was measured by cardiovascular questionnaire to obtain evidence of myocardial infarction and angina, and by electrocardiogram (ECG) for evidence of ischaemia. Type A was inversely related to age and systolic blood pressure and was positively related to social class and height. It was not related to serum cholesterol or alcohol consumption. After control for age, systolic blood pressure, height, smoking and social class, type A was found to be independent of angina but positively associated with an increased risk of possible myocardial infarction (MI). Type A was also associated with increased risk of confirmed MI. An inverse association was found between type A and asymptomatic ischaemic heart disease (IHD). The association between type A and symptomatic IHD could be due to symptom reporting.

Dietary determinants of plasma lipids and lipoproteins: the Caerphilly Study

Associations between nutrient intakes and plasma lipids were examined in a representative sample of 653 middle-aged men in Caerphilly, South Wales. Nutrient intakes were calculated from 7-d weighed intake records and were expressed both as g/d and as a percentage of total energy intake. In multivariate analyses, after taking the effects of potential confounding factors (age, body mass index and smoking habit) into account, the percentage of variance in the plasma lipid concentrations which could be explained solely by the dietary variables was very small, ranging from 1 to 7 per cent. Associations which were statistically significant included a positive association between saturated fat intake and both total cholesterol and low density lipoprotein cholesterol; a negative association between carbohydrate intake and both total cholesterol and high density lipoprotein cholesterol (HDL-C); a positive association between magnesium intake and an HDL-C subfraction (HDL2-C); a positive association between alcohol intake and each of the following: HDL-C, its subfractions and triglyceride.

Prevention of mite infestation of bedding by means of an impregnated sheet. A randomized controlled trial

A randomized controlled trial was conducted to test the effect of a sheet impregnated with benzyl benzoate in preventing mite infestation of new bedding. Impregnated sheets were placed on the mattresses of 17 subjects, while 19 subjects received placebo sheets. Over the following 2 years infestation occurred more commonly, and tended to be heavier, in the beds with inactive sheets than in those with impregnated sheets; among the 27 beds with three items of new bedding sampled on four occasions, a mite count of five or more occurred significantly more often where the sheet was inactive than where it was active (11 of 13 and 5 of 14 respectively). The application of a sheet impregnated with benzyl benzoate appears to prevent mite infestation and may be useful for patients with mite allergy who obtain new bedding as part of a mite-avoidance regimen.

Infant feeding and allergy

The effect of withholding cows' milk was examined in 487 infants at high risk of allergic disease. Before birth they were randomly allocated either to a control group, most of whom received cows' milk preparations, or to an intervention group, who were offered a soya based substitute. Eczema and wheezing occurred to a similar extent in the two groups during the first year of life, although napkin rash, diarrhoea, and oral thrush were commoner in the intervention group, especially during the first three months. Breast feeding for any length of time was associated with a reduced incidence of wheezing and diarrhoea.