Evaluating screening for autism spectrum disorder using cluster randomization

We evaluated the rate of autism spectrum disorder (ASD) in a group invited to a screening program compared to the rates in two groups who received usual care. The population eligible for screening was all children in Iceland registered for their 30-month well-child visits at primary healthcare centers (PHCs) from March 1, 2016, to October 31, 2017 (N = 7173). The PHCs in the capital area of Reykjavik were the units of cluster randomization. Nine PHCs were selected for intervention (invited group), while eight PHCs received usual care (control group 1). PHCs outside the capital area were without randomization (control group 2). An interdisciplinary team, including a pediatrician contributing with physical and neurological examination, a psychologist evaluating autism symptoms using a diagnostic instrument, and a social worker interviewing the parents, reached a consensus on the clinical diagnosis of ASD according to the ICD-10 diagnostic system. Children in the population were followed up for at least two years and 119 cases were identified. The overall cumulative incidence of ASD was 1.66 (95% confidence interval (CI): 1.37, 1.99). In the invited group the incidence rate was 2.13 (95% CI: 1.60, 2.78); in control group 1, the rate was 1.83 (95% CI: 1.31, 2.50); and in control group 2, the rate was 1.02 (95% CI: 0.66, 1.50). Although the rate of ASD was higher in the invited group than in the control groups, the wide confidence intervals prevented us from concluding definitively that the screening detected ASD more readily than usual care.

Comprehensive evaluation of the incidence and prevalence of surgically diagnosed pelvic endometriosis in a complete population

INTRODUCTION

The incidence and prevalence of pelvic endometriosis is still being debated. Population-based studies have shown annual incidences between 0.1% and 0.3%, which translates to a prevalence of symptom-giving disease of between 2% and 6% over a 20-year span in the reproductive years. However, a prevalence of 10% or higher is often assumed. We used Iceland's extensive record linkage possibilities, secure access to patient data and personal identification numbers to search for all cases with a surgical and/or histological first diagnosis over a 15-year study period.

MATERIAL AND METHODS

Information was obtained from all healthcare facilities where an operative and/or histological diagnosis of pelvic endometriosis might have been made during 2001-2015. Hospital discharge diagnostic data and private clinic data sources were scrutinized and double-checked through a central register. Individual medical records, operation notes and pathology records were inspected. Visually and pathologically diagnosed cases were included. The data covered women aged 15-69 years, but the age range 15-49 (reproductive years) was specifically considered. Annual incidence was estimated per 10 000 person-years and prevalence possibilities calculated for varying disease durations. Disease severity was staged (revised American Society for Reproductive Medicine classification) and main lesion sites determined.

RESULTS

A total of 1634 women 15-69 years old were diagnosed; 1487 of them between 15 and 49 years old. Histological verification was obtained for 57.1%. The age-standardized annual incidence for all confirmed endometriosis diagnoses was 12.5/10 000 person-years among women in their reproductive years. The overall estimate of prevalence was 0.6%-3.6%, dependent on duration of symptoms from 5 up to 30 years. The most common sites by order of frequency were ovaries, deep pelvis, central pelvis, vesicouterine pouch and uterine appendages. Of the women, 1080 (66.1%) had minimal/mild and 553 (33.8%) moderate/severe disease.

CONCLUSIONS

We have in a comprehensive study covering a recent 15-year period confirmed an annual incidence of pelvic endometriosis of between 0.1% and 0.15% in the female population of reproductive age. Endometriosis is variably severe but, depending on the duration of symptomatic disease, the approximated prevalence during women's reproductive years could range from 1% to 4%.

Ambient air pollution and emergency department visits and hospitalisation for cardiac arrest: a population-based case-crossover study in Reykjavik, Iceland

OBJECTIVES

To assess the association between traffic-related ambient air pollution and emergency hospital visits for cardiac arrest.

DESIGN

Case-crossover design was used with a lag time to 4 days.

SETTING

The Reykjavik capital area and the study population was the inhabitants 18 years and older identified by encrypted personal identification numbers and zip codes.

PARTICIPANTS AND EXPOSURE

Cases were those with emergency visits to Landspitali University Hospital during the period 2006-2017 and who were given the primary discharge diagnosis of cardiac arrest according to the International Classification of Diseases 10th edition (ICD-10) code I46. The pollutants were nitrogen dioxide (NO₂), particulate matter with aerodynamic diameter less than 10 µm (PM₁₀), particulate matter with aerodynamic diameter less than 2.5 µm (PM_2.5) and sulfur dioxide (SO₂) with adjustment for hydrogen sulfide (H₂S), temperature and relative humidity.

MAIN OUTCOME MEASURE

OR and 95% CIs per 10 µg/m³ increase in concentration of pollutants.

RESULTS

The 24-hour mean NO₂ was 20.7 µg/m³, mean PM₁₀ was 20.5 µg/m³, mean PM_2.5 was 12.5 µg/m³ and mean SO₂ was 2.5 µg/m³. PM₁₀ level was positively associated with the number of emergency hospital visits (n=453) for cardiac arrest. Each 10 µg/m³ increase in PM₁₀ was associated with increased risk of cardiac arrest (ICD-10: I46), OR 1.096 (95% CI 1.033 to 1.162) on lag 2, OR 1.118 (95% CI 1.031 to 1.212) on lag 0-2, OR 1.150 (95% CI 1.050 to 1.261) on lag 0-3 and OR 1.168 (95% CI 1.054 to 1.295) on lag 0-4. Significant associations were shown between exposure to PM₁₀ on lag 2 and lag 0-2 and increased risk of cardiac arrest in the age, gender and season strata.

CONCLUSIONS

A new endpoint was used for the first time in this study: cardiac arrest (ICD-10 code: I46) according to hospital discharge registry. Short-term increase in PM₁₀ concentrations was associated with cardiac arrest. Future ecological studies of this type and their related discussions should perhaps concentrate more on precisely defined endpoints.

Ambient nitrogen dioxide is associated with emergency hospital visits for atrial fibrillation: a population-based case-crossover study in Reykjavik, Iceland

BACKGROUND

In Iceland air quality is generally good; however, previous studies indicate that there is an association between air pollution in Reykjavik and adverse health effects as measured by dispensing of medications, mortality, and increase in health care utilisation. The aim was to study the association between traffic-related ambient air pollution in the Reykjavik capital area and emergency hospital visits for heart diseases and particularly atrial fibrillation and flutter (AF).

METHODS

A multivariate time-stratified case-crossover design was used to study the association. Cases were those patients aged 18 years or older living in the Reykjavik capital area during the study period, 2006-2017, who made emergency visits to Landspitali University Hospital for heart diseases. In this population-based study, the primary discharge diagnoses were registered according to International Classification of Diseases, 10th edition (ICD-10). The pollutants studied were NO₂, PM₁₀, PM_2.5, and SO_2, with adjustment for H₂S, temperature, and relative humidity. The 24-h mean of pollutants was used with lag 0 to lag 4.

RESULTS

During the study period 9536 cases of AF were identified. The 24-h mean NO₂ was 20.7 μg/m³. Each 10 μg/m³ increase in NO₂ was associated with increased risk of heart diseases (ICD-10: I20-I25, I44-I50), odds ratio (OR) 1.023 (95% CI 1.012-1.034) at lag 0. Each 10 μg/m³ increase in NO₂ was associated with an increased risk of AF (ICD-10: I48) on the same day, OR 1.030 (95% CI: 1.011-1.049). Females were at higher risk for AF, OR 1.051 (95% CI 1.019-1.083) at lag 0, and OR 1.050 (95% CI 1.019-1.083) at lag 1. Females aged younger than 71 years had even higher risk for AF, OR 1.077 (95% CI: 1.025-1.131) at lag 0. Significant associations were found for other pollutants and emergency hospital visits, but they were weaker and did not show a discernable pattern.

CONCLUSIONS

Short-term increase in NO₂ concentrations was associated with heart diseases, more precisely with AF. The associations were stronger among females, and among females at younger age. This is the first study in Iceland that finds an association between air pollution and cardiac arrhythmias, so the results should be interpreted with caution.

Validation of the Modified Checklist for Autism in Toddlers, Revised with Follow-up in a Population Sample of 30-Month-Old Children in Iceland: A Prospective Approach

The Modified Checklist for Autism in Toddlers, Revised with Follow-up was validated on a population sample in Reykjavik, Iceland. The participants (N = 1585) were screened in well-child care at age 30 months and followed up for at least 2 years to identify autism cases. The sensitivity, specificity, positive and negative predictive values were 0.62, 0.99, 0.72, and 0.99, respectively. True-positive children were diagnosed 10 months earlier than false-negative children. Autism symptom severity and the proportions of children with verbal and performance IQs/DQs < 70 were similar between groups. Although the sensitivity was suboptimal, the screening contributed to lowering the age at diagnosis for many children. Adding autism-specific screening to the well-child care program should be considered.

Incidence of cancer among licenced commercial pilots flying North Atlantic routes

BACKGROUND

To evaluate cancer incidence among licenced commercial pilots in association with cosmic radiation.

METHODS

Cohort study where ionizing radiation dose of cosmic radiation was estimated from airline data and software program and cancer incidence was obtained by record linkage with nation-wide cancer registry. All licenced commercial male airline pilots were followed from 1955 to 2015, ever or never employed at airline with international routes. Standardized incidence ratios were calculated and relative risk by Poisson regression, to examine exposure-response relation.

RESULTS

Eighty three cancers were registered compared with 92 expected; standardized incidence ratios were 0.90 (95% CI 0.71 to 1.11) for all cancers, 3.31 (95% CI 1.33 to 6.81) for malignant melanoma, and 2.49 (95% CI 1.69 to 3.54), for basal cell carcinoma of skin. The risk for all cancers, malignant melanoma, prostate cancer, basal cell carcinoma of skin, and basal cell carcinoma of trunk increased with an increase in number of employment years, cumulative air hours, total cumulative radiation dose, and cumulative radiation dose sustained up to age of 40 years. The relative risk for the highest exposure categories of cumulative radiation dose were 2.42 (95% CI 1.50 to 3.92) for all cancers, 2.57 (95% CI 1.18 to 5.56) for prostate cancer, 9.88 (95% CI 1.57 to 190.78) for malignant melanoma, 3.61 (95% CI 1.64 to 8.48) for all basal cell carcinoma, and 6.65 (95% CI 1.61 to 44.64) for basal cell carcinoma of trunk.

CONCLUSIONS

This study was underpowered to study brain cancer and leukaemia risk. Basal cell carcinoma of skin is radiation-related cancer, and may be attributed to cosmic radiation. Further studies are needed to clarify the risk of cancers in association with cosmic radiation, other workplace exposure, host factors, and leisure sun-exposure, as clothes, and glass in cockpit windows shield pilots from the most potent ultraviolet-radiation.

Malignant mesothelioma incidence by nation-wide cancer registry: a population-based study

BACKGROUND

Malignant mesothelioma caused by asbestos exposure has a long latency period. A ban on asbestos use may not be apparent in decreased incidence in the population until after several decades. The aim was to evaluate changes in the incidence of malignant mesothelioma, and the possible impact of the asbestos ban implemented in Iceland in 1983.

METHODS

This is a population study on aggregate level; the source of data was the Icelandic Cancer Registry, the National Cause-of-Death Registry, and the National Register. Volume of asbestos import was obtained from Customs Tariff. The import figures reflect fairly accurately the amount used, as there are no mines in the country.

RESULTS

Asbestos import peaked in 1980 at 15.0 kg/capita/year, diminishing to 0.3 kg/capita/year ten years after the ban in 1983, and to zero in the most recent years. Seventy-nine per cent of the cases of malignant mesothelioma were men, and 72 % were of pleural origin. Mesothelioma incidence increased steadily from 1965 to 2014, when it reached 21.4 per million among men, and 5.6 among women. Mortality in 2014 was 22.2 per million among men, and 4.8 among women.

CONCLUSION

Malignant mesothelioma incidence and mortality increased in the population during the period, despite the ban on asbestos use from 1983. This is in agreement with the long latency time for malignant mesothelioma. In line with the previously high per capita volume of asbestos import, many buildings, equipment, and structures contain asbestos, so there is an on-going risk of asbestos exposure during maintenance, renovations and replacements. It is thus difficult to predict when the incidence of malignant mesothelioma will decrease in the future. During the last ten-year period, the incidence in Iceland was higher than the recently reported incidence in neighbouring countries.

Association between Daily Hydrogen Sulfide Exposure and Incidence of Emergency Hospital Visits: A Population-Based Study

BACKGROUND

The adverse health effects of high concentrations of hydrogen sulfide (H2S) exposure are well known, though the possible effects of low concentrations have not been thoroughly studied. The aim was to study short-term associations between modelled ambient low-level concentrations of intermittent hydrogen sulfide (H2S) and emergency hospital visits with heart diseases (HD), respiratory diseases, and stroke as primary diagnosis.

METHODS

The study is population-based, using data from patient-, and population-registers from the only acute care institution in the Reykjavik capital area, between 1 January, 2007 and 30 June, 2014. The study population was individuals (≥18yr) living in the Reykjavik capital area. The H2S emission originates from a geothermal power plant in the vicinity. A model was used to estimate H2S exposure in different sections of the area. A generalized linear model assuming Poisson distribution was used to investigate the association between emergency hospital visits and H2S exposure. Distributed lag models were adjusted for seasonality, gender, age, traffic zones, and other relevant factors. Lag days from 0 to 4 were considered.

RESULTS

The total number of emergency hospital visits was 32961 with a mean age of 70 years. In fully adjusted un-stratified models, H2S concentrations exceeding 7.00μg/m3 were associated with increases in emergency hospital visits with HD as primary diagnosis at lag 0 risk ratio (RR): 1.067; 95% confidence interval (CI): 1.024-1.111, lag 2 RR: 1.049; 95%CI: 1.005-1.095, and lag 4 RR: 1.046; 95%CI: 1.004-1.089. Among males an association was found between H2S concentrations exceeding 7.00μg/m3, and HD at lag 0 RR: 1.087; 95%CI: 1.032-1.146 and lag 4 RR: 1080; 95%CI: 1.025-1.138; and among those 73 years and older at lag 0 RR: 1.075; 95%CI: 1.014-1.140 and lag 3 RR: 1.072; 95%CI: 1.009-1.139. No associations were found with other diseases.

CONCLUSIONS

The study showed an association between emergency hospital visits with HD as primary diagnosis and same day H2S concentrations exceeding 7.00μg/m3, more pronounced among males and those 73 years and older than among females and younger individuals.

Association of Cancer Incidence and Duration of Residence in Geothermal Heating Area in Iceland: An Extended Follow-Up

BACKGROUND

Residents of geothermal areas have higher incidence of non-Hodgkin's lymphoma, breast cancer, prostate cancer, and kidney cancers than others. These populations are exposed to chronic low-level ground gas emissions and various pollutants from geothermal water. The aim was to assess whether habitation in geothermal areas and utilisation of geothermal water is associated with risk of cancer according to duration of residence.

METHODS

The cohort obtained from the census 1981 was followed to the end of 2013. Personal identifier was used in record linkage with nation-wide emigration, death, and cancer registries. The exposed population, defined by community codes, was located on young bedrock and had utilised geothermal water supply systems since 1972. Two reference populations were located by community codes on older bedrock or had not utilised geothermal water supply systems for as long a period as had the exposed population. Adjusted hazard ratio (HR), 95% confidence intervals (CI) non-stratified and stratified on cumulative years of residence were estimated in Cox-model.

RESULTS

The HR for all cancer was 1.21 (95% CI 1.12-1.30) as compared with the first reference area. The HR for pancreatic cancer was 1.93 (1.22-3.06), breast cancer, 1.48 (1.23-1.80), prostate cancer 1.47 (1.22-1.77), kidney cancer 1.46 (1.03-2.05), lymphoid and haematopoietic tissue 1.54 (1.21-1.97), non-Hodgkin´s lymphoma 2.08 (1.38-3.15) and basal cell carcinoma of the skin 1.62 (1.35-1.94). Positive dose-response relationship was observed between incidence of cancers and duration of residence, and between incidence of cancer and degree of geothermal/volcanic activity in the comparison areas.

CONCLUSIONS

The higher cancer incidence in geothermal areas than in reference areas is consistent with previous findings. As the dose-response relationships were positive between incidence of cancers and duration of residence, it is now more urgent than before to investigate the chemical and physical content of the geothermal water and of the ambient air of the areas to detect recognized or new carcinogens.

Hydrogen sulfide and traffic-related air pollutants in association with increased mortality: a case-crossover study in Reykjavik, Iceland

OBJECTIVES

To study the association between daily mortality and short-term increases in air pollutants, both traffic-related and the geothermal source-specific hydrogen sulfide (H₂S).

DESIGN

Population-based, time stratified case-crossover. A lag time to 4 days was considered. Seasonal, gender and age stratification were calculated. Also, the best-fit lag when introducing H₂S >7 µg/m(3) was selected by the Akaike Information Criterion (AIC).

SETTING

The population of the greater Reykjavik area (n=181,558) during 2003-2009.

PARTICIPANTS

Cases were defined as individuals living in the Reykjavik capital area, 18 years or older (N=138,657), who died due to all natural causes (ICD-10 codes A00-R99) other than injury, poisoning and certain other consequences of external causes, or cardiovascular disease (ICD-10 codes I00-I99) during the study period.

MAIN OUTCOME MEASURE

Percentage increases in risk of death (IR%) following an interquartile range increase in pollutants.

RESULTS

The total number of deaths due to all natural causes was 7679 and due to cardiovascular diseases was 3033. The interquartile range increased concentrations of H₂S (2.6 µg/m(3)) were associated with daily all natural cause mortality in the Reykjavik capital area. The IR% was statistically significant during the summer season (lag 1: IR%=5.05, 95% CI 0.61 to 9.68; lag 2: IR%=5.09, 95% CI 0.44 to 9.97), among males (lag 0: IR%=2.26, 95% CI 0.23 to 4.44), and among the elderly (lag 0: IR%=1.94, 95% CI 0.12 to 1.04; lag 1: IR%=1.99, 95% CI 0.21 to 1.04), when adjusted for traffic-related pollutants and meteorological variables. The traffic-related pollutants were generally not associated with statistical significant IR%s.

CONCLUSIONS

The results suggest that ambient H₂S air pollution may increase mortality in Reykjavik, Iceland. To the best of our knowledge, ambient H₂S exposure has not previously been associated with increased mortality in population-based studies and therefore the results should be interpreted with caution. Further studies are warranted to confirm or refute whether H₂S exposure induces premature deaths.

Number of visits to the emergency department and risk of suicide: a population-based case-control study

BACKGROUND

The aim was to study whether number of visits to emergency department (ED) is associated with suicide, taking into consideration known risk factors.

METHODS

This is a population-based case-control study nested in a cohort. Computerized database on attendees to ED (during 2002-2008) was record linked to nation-wide death registry to identify 152 cases, and randomly selected 1520 controls. The study was confined to patients attending the ED, who were subsequently discharged, and not admitted to hospital ward. Odds ratio (OR) and 95% confidence intervals (CI) of suicide risk according to number of visits (logistic regression) adjusted for age, gender, mental and behavioral disorders, non-causative diagnosis, and drug poisonings.

RESULTS

Suicide cases had on average attended the ED four times, while controls attended twice. The OR for attendance due to mental and behavioral disorders was 3.08 (95% CI 1.61-5.88), 1.60 (95% CI 1.06-2.43) for non-causative diagnosis, and 5.08 (95% CI 1.69-15.25) for poisoning. The ORs increased gradually with increasing number of visits. Adjusted for age, gender, and the above mentioned diagnoses, the OR for three attendances was 2.17, for five attendances 2.60, for seven attendances 5.97, and for nine attendances 12.18 compared with those who had one visit.

CONCLUSIONS

Number of visits to the ED is an independent risk factor for suicide adjusted for other known and important risk factors. The prevalence of four or more visits was 40% among cases compared with 10% among controls. This new risk factor may open new venues for suicide prevention.

Cancer mortality and other causes of death in users of geothermal hot water

BACKGROUND

Residents of geothermal areas have increased incidence of non-Hodgkin's lymphoma, breast, prostate, and kidney cancers. The aim was to study whether this is also reflected in cancer mortality among the population using geothermal hot water for space heating, washing, and showering.

METHODS

The follow-up was from 1981 to 2009. Personal identifier of those 5-64 years of age was used in record linkage with nationwide death registry. Thus, vital and emigration status was ascertained. The exposed population was defined as inhabitants of communities with district heating generated from geothermal wells since 1972. Reference populations were inhabitants of other areas with different degrees of volcanic/geothermal activity. Hazard ratio (HR) and 95% confidence intervals (CI) were adjusted for age, gender, education, housing, reproductive factors and smoking habits.

RESULTS

Among those using geothermal water, the HR for all causes of death was 0.98 (95% CI 0.91-1.05) as compared with cold reference area. The HR for breast cancer was 1.53 (1.04-2.24), prostate cancer 1.74 (1.21-2.52), kidney cancer 1.78 (1.03-3.07), and for non-Hodgkin's lymphoma 2.01 (1.05-3.38). HR for influenza was 3.36 (1.32-8.58) and for suicide 1.49 (1.03-2.17).

CONCLUSION

The significant excess mortality risk of breast and prostate cancers, and non-Hodgkin's lymphoma confirmed the results of similarly designed studies in Iceland on cancer incidence among populations from high-temperature geothermal areas and users of geothermal hot water. The risk is not confined to cancers with good prognosis, but also concerns fatal cancers. Further studies are needed on the chemical and physical content of the water and the environment emissions in geothermal areas.

Survival of patients with alcohol use disorders discharged from an emergency department: a population-based cohort study

OBJECTIVES

The aim was to study the cause-specific mortality of users of the emergency department (ED) who received a diagnosis of alcohol use disorder (AUD) in comparison with mortality of other users of the department.

DESIGN

A population-based prospective cohort study.

PARTICIPANTS

All patients aged 18 years and above who were subsequently discharged home from the ED during the years 2002-2008. A total of 107,237 patients were followed by record linkage to a nationwide cause-of-death registry: 1210 patients with AUD as the main discharge diagnosis and 106,027 patients in the comparison group. HR and 95% CIs were calculated.

SETTING

ED at Landspitali-the National University Hospital of Iceland, Reykjavik, Iceland. The hospital offers tertiary care and is the number one trauma centre and community hospital for the greater Reykjavik area. According to the population registry, 78% of the inhabitants of the area attended the ED during the study period.

RESULTS

72 patients died in the AUD group and 4807 in the comparison group. The adjusted HR for all causes of death was 1.91 (95% CI 1.51 to 2.42). The HR for AUDs was 47.68 (95% CI 11.56 to 196.59) while for alcohol liver disease the HR was 19.06 (95% CI 6.07 to 59.87). The HR was also elevated for diseases of the circulatory system: HR 2.52 (95% CI 1.73 to 3.68); accidental poisoning: HR=13.64, (95% CI 3.98 to 46.73); suicide: HR=2.72 (95% CI 1.08 to 6.83); and event of undetermined intent: HR=10.89 (95% CI 4.53 to 26.16).

CONCLUSIONS

AUD as the discharge diagnosis at the ED, among patients who were not admitted to a hospital ward but discharged home, predicts increased mortality. As the results conclusively show the vulnerability of these patients, one can question whether their needs are adequately met at the ED.

Increased cardiovascular mortality and suicide after methyl chloride exposure

OBJECTIVES

Methyl chloride leakage from a refrigerator occurred on board an Icelandic fishing vessel in 1963. Many of the crew members were hospitalized due to various neurological symptoms and signs. The aim was to study long-term mortality.

METHODS

This is a cohort study. Five referents were selected from registries of deckhands and officers matched to each crew member according to age and occupation. Follow-up was through record linkage of personal identifiers with the nation-wide mortality registry. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated in Cox proportional hazards model.

RESULTS

The intoxicated crew was composed of 20 deckhands and 7 officers; the reference group counted 100 deckhands and 35 officers. Follow-up to the end of 2010; 14 of the exposed deckhands and 6 of the officers had died, versus 49 deckhands and 26 officers among the reference group. For all cardiovascular events, the HR was 2.06 (95% CI 1.02-4.15), for acute coronary heart disease, the HR was 3.12 (95% CI 1.11-8.78), for cerebrovascular diseases, the HR was 5.35 (1.18-24.35), and for suicide, the HR was 13.76 (1.18-160.07).

CONCLUSIONS

Follow-up showed increased mortality due to cardiovascular diseases after 47 years. The suicide cases had developed severe depression after the methyl chloride intoxication that was related to the exposure. The use of the personal identifiers and the population registries strengthen the study. Detailed information on risk factors for chronic diseases is lacking in this study; however, the matching by occupation renders some similarity to the groups compared in the study.

All-cause mortality and suicide within 8 days after emergency department discharge

AIM

The aim of the study was to evaluate the association of death within 8-30 days after discharge home from the emergency department with a non-causative diagnosis in a prospective cohort study.

METHODS

The 227,097 visits to the emergency department were filed by personal identification number and included information on gender, age, admission, discharge, and diagnosis. The visits were classified by main diagnosis at discharge into those with non-causative diagnosis and those with other diagnoses. Mortality per 100,000 within 8, 15 and 30 days and the corresponding hazard ratio (HR) and 95% confidence intervals (CI) were calculated for all causes of death and for selected causes of death in a time-dependent analysis.

RESULTS

The HRs of all causes of death for patients with a non-causative diagnosis were 0.64 (95% CI 0.41-1.01) within 8 days, 0.70 (95% CI 0.50-0.99) within 15 days, and 0.82 (95% CI 0.65-1.04) within 30 days as compared to those with a causative diagnosis. The HRs within 30 days among those with a non-causative diagnosis at discharge were 1.48 (95% CI 1.03-2.13) for malignant neoplasm, 3.72 (95% CI 1.44-9.60) for suicide, and 0.50 (95% CI 0.32-0.79) for diseases of the circulatory system.

CONCLUSION

Death within 8 days after discharge home from the ED is a rare event. Death of patients that occur shortly after discharge who had received a non-causative diagnosis as the main diagnosis may indicate a misjudgement of the patients' condition at that time.

Cancer incidence among population utilizing geothermal hot water: a census-based cohort study

The aim of the study was to assess whether utilization of geothermal hot-water is associated with risk of cancer. The cohort from census was followed from 1981 to 2010 in nation-wide death and cancer registries. The moving apart of American-Eurasian tectonic plates, observed in Iceland, results in high volcanic activity. The definition of the study populations was based on geological information. The target population was inhabitants of communities located on bedrock younger than 3.3 million years, utilizing hot-water supply generated from geothermal wells since 1972. The two reference populations were inhabitants of communities without this hot-water supply located on areas with less volcanic/geothermal activity, and bedrock older than 3.3 million years. Hazard ratio (HR), and 95% confidence intervals (CI) were adjusted for age, gender, education, housing, reproductive factors and smoking. HR in the geothermal hot-water supply areas for all cancer was 1.15 (95% CI 1.05-1.25) as compared with nongeothermal areas. The HR for breast cancer was 1.40 (1.12-1.75), prostate cancer 1.61 (1.29-2.00), kidney cancer 1.64 (1.11-2.41), lymphatic and haematopoietic tissue cancers 1.45 (1.08-1.95), and for basal cell carcinoma (BCC) of the skin 1.46 (1.16-1.82). Positive exposure-response relations were observed between the risk of these cancers and the degree of volcanic/geothermal activity in the reference areas. Increased incidence of all cancers, breast, prostate, kidney cancer and BCC of the skin was found among the population utilizing geothermal hot-water for decades. More precise information on exposure is needed in future studies.

Association of air pollution and use of glyceryl trinitrate against angina pectoris: a population-based case-crossover study

BACKGROUND

Ambient air pollution has been associated with increased cardiovascular morbidity and mortality. In Reykjavik, Iceland, air pollutant concentrations exceed official health limits several times every year. The aim was to study the association of concentrations of NO2, O3, PM10, and H2S in the Reykjavik capital area with the dispensing of anti-angina pectoris medication, glyceryl trinitrate to the inhabitants.

METHODS

Data on daily dispensing of glyceryl trinitrate, were retrieved from the Icelandic Medicines Registry. Data on hourly concentrations of NO2, O3, PM10, and H2S were obtained from the Environment Agency of Iceland. A case-crossover design was used, based on the dispensing of glyceryl trinitrate to 5,246 individuals (≥18 years) between 2005 and 2009.

RESULTS

For every 10 μg/m3 increase of NO2 and O3 3-day mean concentrations, the odds ratio (OR) for daily dispensing of glyceryl trinitrates was 1.136 (95% confidence intervals (CI) 1.069-1.207) and 1.094 (95% CI 1.029-1.163) at lag 0, and OR was 1.096 (95% CI 1.029-1.168) and 1.094 (95% CI 1.028-1.166) at lag 1, respectively.

CONCLUSIONS

These findings suggest that NO2 and O3 ambient air concentrations may adversely affect cardiovascular health, as measured by the dispensing of glyceryl trinitrates for angina pectoris. Further, the findings suggest that data on the dispensing of medication may be a valuable health indicator when studying the effect of air pollution on cardiovascular morbidity.

Incidence of cancer among residents of high temperature geothermal areas in Iceland: a census based study 1981 to 2010

BACKGROUND

Residents of geothermal areas are exposed to geothermal emissions and water containing hydrogen sulphide and radon. We aim to study the association of the residence in high temperature geothermal area with the risk of cancer.

METHODS

This is an observational cohort study where the population of a high-temperature geothermal area (35,707 person years) was compared with the population of a cold, non-geothermal area (571,509 person years). The cohort originates from the 1981 National Census. The follow up from 1981 to 2010 was based on record linkage by personal identifier with nation-wide death and cancer registries. Through the registries it was possible to ascertain emigration and vital status and to identify the cancer cases, 95% of which had histological verification. The hazard ratio (HR) and 95% confidence intervals (CI) were estimated in Cox-model, adjusted for age, gender, education and housing.

RESULTS

Adjusted HR in the high-temperature geothermal area for all cancers was 1.22 (95% CI 1.05 to 1.42) as compared with the cold area. The HR for pancreatic cancer was 2.85 (95% CI 1.39 to 5.86), breast cancer 1.59 (95% CI 1.10 to 2.31), lymphoid and hematopoietic cancer 1.64 (95% CI 1.00 to 2.66), and non-Hodgkins lymphoma 3.25 (95% CI 1.73 to 6.07). The HR for basal cell carcinoma of the skin was 1.61 (95% CI 1.10 to 2.35). The HRs were increased for cancers of the nasal cavities, larynx, lung, prostate, thyroid gland and for soft tissue sarcoma; however the 95% CIs included unity.

CONCLUSIONS

More precise information on chemical and physical exposures are needed to draw firm conclusions from the findings. The significant excess risk of breast cancer, and basal cell carcinoma of the skin, and the suggested excess risk of other radiation-sensitive cancers, calls for measurement of the content of the gas emissions and the hot water, which have been of concern in previous studies in volcanic areas. There are indications of an exposure-response relationship, as the risk was higher in comparison with the cold than with the warm reference area. Social status has been taken into account and data on reproductive factors and smoking habits show that these do not seem to explain the increased risk of cancers, however unknown confounding can not be excluded.

Pelvic endometriosis diagnosed in an entire nation over 20 years

The annual incidence of pelvic endometriosis among women aged 15-49 years and up to age 69 years was ascertained for the Icelandic population between 1981 and 2000 by using Iceland's extensive record linkage systems. Comprehensive, state-financed health care and unique personal identification numbers enabled care to be tracked from first diagnosis. To identify cases, a centralized discharge-code registry was searched, as well as all hospital databases and, for individual patients, all hospital records. Each case of visually diagnosed and histologically verified endometriosis was cross-checked against the nationwide pathology registry. The revised American Society for Reproductive Medicine classification system was used for staging. Recorded was type of operation at diagnosis and presence of disease at 5 sites: deep pelvis, appendages, central pelvis, vesicouterine pouch, and ovaries. A total of 1,383 women were diagnosed surgically, with histologic verification of 811 (58.6%). All but 6 cases could be staged; 297 (36.9%) had minimal/mild and 508 (63.1%) had moderate/severe disease. The estimates of crude annual incidence were 0.1% for visually confirmed and 0.06% for histologically verified endometriosis, and respective age-standardized annual incidence was 0.1% and 0.05% for women aged 15-49 years. The most common site was the ovary, followed by deep pelvis, central pelvis, appendages, and vesicouterine pouch.

Non-causative discharge diagnosis from the emergency department and risk of suicide

Approximately 20% of Emergency Department (ED) users discharged home receive a non-causative discharge diagnosis in the category of "Symptoms, signs, abnormal findings, and ill-defined causes," according to the International Classification of Diseases. The objective of this study was to evaluate the association of these non-causative discharge diagnoses with mortality in general and with violent death and suicide in particular. This is a prospective study; the primary source of data was computer records from the ED at Landspitali University Hospital, Hringbraut, Reykjavik, Iceland over the period 1995-2001. The main discharge diagnoses were recorded according to the International Classification of Diseases. Individuals with a non-causative discharge diagnosis were followed-up for cause-specific mortality through national registries by record linkage and were compared to national mortality rates and the rates of those with causative physical diagnoses. The standardized mortality ratios, hazard ratios, and 95% confidence intervals (CI) were calculated. The data on individuals with a non-causative discharge diagnosis from the ED revealed that the standardized mortality ratio for all causes was 1.57 (95% CI 1.39-1.77) among men and 1.83 (95% CI 1.61-2.08) among women. The hazard ratio for violent death was 1.64 (95% CI 1.07-2.52) and for suicide 2.08 (95% CI 1.02-4.24), adjusted for age and gender, among individuals with a non-causative discharge diagnosis compared to those having causative physical discharge diagnoses. Through analysis of the discharge diagnoses "Symptoms, signs, abnormal findings and ill-defined causes," this study has identified an association between the group of patients discharged from the ED with a non-causative diagnosis who are at high risk of suicide and who may, through further studies, become subjects for suicide prevention strategies.

Death within 8 days after discharge to home from the emergency department

BACKGROUND

Deaths within 8 days after discharge have, in previous studies, been evaluated retrospectively based on review of hospital records and the cause of death. The aim of the study was to evaluate the association of death within 8 days after discharge to home from the emergency department with a non-causative diagnosis in a prospective cohort study.

METHODS

The records from the emergency department were filed by personal identification number and included information on gender, age, admission, discharge and diagnosis. The cause of death was obtained from a nation-wide registry by record linkage. Mortality per 100,000 within 8 days and the hazard ratio and 95% confidence intervals (CIs) were calculated for all causes of death in a time-dependent analysis.

RESULTS

A non-causative diagnosis had been given to 11% of those who died within 8 days after discharge home. The mortality per 100,000 within 8 days was 208.5, within 15 days 347.4 and within 30 days 648.6. In the analysis of deaths within 8 days, the hazard ratio was higher for men than women and increasing age was significantly associated with high mortality. The hazard ratio for non-causative diagnosis was 0.44 (95% CI 0.20-0.96) as compared to causative diagnosis, adjusted for gender and age.

CONCLUSION

The mortality rate within 8 days of discharge found in the present study is considerably higher than findings in previous studies. Death shortly after discharge of patients with non-causative diagnosis may indicate a misjudgement of the patients' condition at the time of discharge.

Autism spectrum disorders in children with a history of infantile spasms: a population-based study

The objective of this article is to describe autistic spectrum disorders in children diagnosed with infantile spasms in the first year of life. The source of data was the records of all 3 pediatric departments in Iceland. Twenty children born between 1981 and 1998 who had infantile spasms were invited to participate. When appropriate, the parents of these children were asked to complete the Social Communication Questionnaire. Children scoring 10 points or higher on the questionnaire were selected for further examination using the Autism Diagnostic Interview- Revised and either the Autism Diagnostic Observation Schedule or the Childhood Autism Rating Scale. All participants were given appropriate cognitive tests or measures of adaptive behavior. The parents of 17 children (10 boys, 7 girls) agreed to participate in the study. Age at assessment ranged from 5 to 19 years with a mean age of 11 years and 6 months. Fourteen children had at least one neurodevelopmental disorder. Six (6/17), or 35.3%, were diagnosed with autism spectrum disorder (3 boys, 3 girls), five of these had a history of symptomatic infantile spasms, and four were profoundly mentally retarded (IQ/DQ<20). If the diagnosis of autism spectrum disorder was restricted to children with a developmental age of 24 months or more (3 cases), the prevalence was 17.6%. The estimates found in this study exceed the estimated prevalence of autism spectrum disorder in the general population.

Seven-year evolution of discharge diagnoses of emergency department users

OBJECTIVES

To describe the pattern of main diagnoses of persons discharged home from the emergency department.

METHODS

This was a descriptive study, using data from computer records of the emergency department at Landspitali University Hospital Hringbraut in Reykjavik, Iceland, over a 7-year period, 1995-2001. The main diagnoses of those discharged were registered according to the International Classification of Diseases and were transferred to the European shortlist, 'main categories'. Changes in the pattern of discharge diagnoses during the study period (1995-2001) were analyzed by calculating chi for the linear trend in each category.

RESULTS

The proportion of users discharged each year increased through the period. In 1995, 54.5% were sent home (not admitted to hospital) and in 2001, 72.5%. Diagnoses in the diagnostic category 'symptoms, signs, abnormal findings, and ill-defined causes', were the most frequently applied to both men and women; this was the classification in more than 20% of cases on average. The most significant change during the study period was the increase in frequency of this category among both men and women.

CONCLUSIONS

The proportion of emergency-department users, who are discharged without admission to hospital, increased and exceeded 70% of total cases received. On average, 20% of the discharge diagnoses were in the category 'symptoms, signs, abnormal findings, and ill-defined causes'. The pattern of discharge diagnoses can be assumed to reflect an increased load on the emergency department.

Autism Spectrum Disorders in Children with Seizures in the First Year of Life-A Population-Based Study

PURPOSE

To describe autistic spectrum disorders (ASDs) in a cohort of children with history of unprovoked seizures other than infantile spasms in the first year of life.

METHODS

The source of data was computer records from all the three pediatric departments in Iceland. Children diagnosed 1982-2000 with unprovoked seizures with onset between 28 days and 12 months of age (N = 102) were invited to participate in a study. Children with known developmental disorders and those whose parents had concerns regarding their child's development or behavior were investigated for possible ASD. Parents were asked to complete the Social Communication Questionnaire and children scoring 10 points or higher were further examined with the Autism Diagnostic Interview-Revised and observational measures.

RESULTS

Eighty-four children (82.4%), 28 boys and 56 girls, participated in the study and 36.9% (31/84) were investigated for possible ASD. Twenty-four (28.6%) had at least one neurodevelopmental disorder, 14.3% had mental retardation (MR), and six (7.1%) were diagnosed with ASD, all of whom also had MR and three of whom had congenital brain abnormalities.

CONCLUSION

These results suggest that the estimated prevalence of ASD is higher in children with history of seizure in the first year of life than it is in the general population. There are indications that support the view that children with ASD and history of seizure in the first year of life have higher prevalence of congenital brain abnormalities and are more often female, than other children with ASD.

Farming and prostate cancer

Commentary on paper by Meyer et al (see page 155)

Risk of non-Hodgkin's lymphoma and exposure to hexachlorocyclohexane, a nested case-control study

Organochlorines have been linked with non-Hodgkin's lymphoma (NHL) in epidemiological studies. We elucidate the importance of hexachlorocyclohexane (HCH), an organochlorine insecticide, in the aetiology of NHL among individuals with dermal exposure to HCH. This is a case-control study nested in a cohort of sheep owners, collected from records on sheep dipping. The number of dipped sheep was used as surrogate for exposure. No other insecticide was used in sheep dip in Iceland during the study period. Cases (n=45) were identified by record linkage with the national cancer registry (through 1962-2003) and controls (n=221) were selected at random from the cohort. In logistic regression analysis the odds ratio for NHL was 3.86 (95% CI 1.59-8.53), adjusted for age, for individuals who had 100 sheep or more as compared to those who had less than 100 sheep. The results indicate that HCH may be linked to the development of NHL.

Cancer incidence among farmers exposed to lindane while sheep dipping

OBJECTIVES

The objective of this study was to determine whether site-specific cancer incidence among farmers exposed to the insecticide lindane (g-hexachlorocyclohexane) while dipping sheep differs from that of the general population in Iceland.

METHODS

Cohorts of 7882 men and 429 women, who, according to records on sheep dipping, were sheep owners, were followed from 1962 to 2003 in the Cancer Registry for cancer incidence. The observed number of cancers was compared with expected values, calculated on the basis of person-years of risk and cancer incidence in the general population of Iceland.

RESULTS

For men the standardized incidence ratio (SIR) for all cancer sites was 0.79, with a 95% confidence interval (95% CI) of 0.76-0.83. For both the men and the women a significantly increased risk for lip cancer was found, with SIR of 1.50 (95% CI 1.08-2.04) and 9.09 (95% CI 1.02-32.82), respectively. The SIR for several cancer sites were lower than unity for both the men and women. Examples were cancers of the colon, rectum, pancreas, stomach, lungs, kidney, bladder, and brain and nervous system.

CONCLUSIONS

The decreased risk of most cancers among these sheep farmers agrees with findings reported previously among farmers from other countries, as well as in Iceland. Cancer of the lip was the only cancer type in significant excess among both genders, and the stomach cancer rates were near unity, but, in previous studies on Icelandic farmers, an increase had been found for stomach cancer. The site-specific cancer incidence for sheep-dipping farmers did not differ substantially from that of the general population.

Mortality of the users of a hospital emergency department

OBJECTIVE

To ascertain the annual number of users who were discharged home after visits to the emergency department (ED), grouped by age, sex, and number of visits during the calendar year, and to assess whether a higher number of visits to the department predicted a higher mortality.

METHODS

This was a retrospective cohort study, with follow up of cause specific mortality through a national registry, in the Reykjavik area of Iceland. In total, 19 259 patients who visited the ED during the period 1995-2001 and who were discharged home at the Landspítali University Hospital, Reykjavik, Iceland, were enrolled. The main outcome measures were the standardised mortality ratio, with expected number based on national mortality rates, and hazard ratio calculations using time dependent multivariate regression analysis.

RESULTS

The annual increase in visits to the ED among the patients discharged home was 7-14% per age group during the period 1995-2001, with the highest increase among older men. When emergency department users were compared with the general population, the standardised mortality ratio was 1.81 for men and 1.93 for women. Among those attending the ED two, three, or more times in a calendar year, the mortality rate was higher than among those coming only once in a year. The causes of death that led to the highest mortality among frequent users of the ED were neoplasm, ischaemic heart diseases, and external causes, particularly drug intoxication, suicides, and probable suicides.

CONCLUSIONS

The mortality of those who had used the ED and been discharged home was found to be higher than that of the general population. Frequent users of the ED had a higher mortality than those visiting the department no more than once a year. As the ED serves general medicine and surgery patients, not injuries, the high mortality due to drug intoxication, suicide, and probable suicide is interesting. Further studies are needed into the diagnosis at discharge of those frequently using the ED, in an attempt to understand and possibly prevent this marked mortality rate.

Cosmic radiation increases the risk of nuclear cataract in airline pilots: a population-based case-control study

BACKGROUND

Aviation involves exposure to ionizing radiation of cosmic origin. The association between lesions of the ocular lens and ionizing radiation is well-known.

OBJECTIVE

To investigate whether employment as a commercial airline pilot and the resulting exposure to cosmic radiation is associated with lens opacification.

METHODS

This is a population-based case-control study of 445 men. Lens opacification was classified into 4 types using the World Health Organization simplified grading system. These 4 types, serving as cases, included 71 persons with nuclear cataracts, 102 with cortical lens opacification, 69 with central optical zone involvement, and 32 with posterior subcapsular lens opacification. Control subjects are those with a different type of lens opacification or without lens opacification. Exposure was assessed based on employment time as pilots, annual number of hours flown on each aircraft type, time tables, flight profiles, and individual cumulative radiation doses (in millisieverts) calculated by a software program. Odds ratios were calculated using logistic regression.

RESULTS

The odds ratio for nuclear cataract risk among cases and controls was 3.02 (95% confidence interval, 1.44-6.35) for pilots compared with nonpilots, adjusted for age, smoking status, and sunbathing habits. The odds ratio for nuclear cataract associated with estimation of cumulative radiation dose (in millisieverts) to the age of 40 years was 1.06 (95% confidence interval, 1.02-1.10), adjusted for age, smoking status, and sunbathing habits.

CONCLUSION

The association between the cosmic radiation exposure of pilots and the risk of nuclear cataracts, adjusted for age, smoking status, and sunbathing habits, indicates that cosmic radiation may be a causative factor in nuclear cataracts among commercial airline pilots.

Risk factors for malignant melanoma in an Icelandic population sample

OBJECTIVES

To describe the constitutional risk factors for malignant melanoma and exposure to sunlight in a population sample in Iceland.

METHODS

Information on various risk factors for malignant melanoma was collected through mailed questionnaires sent to a random sample of the Icelandic population. The information collected was the first phase of a prospective study on malignant melanoma among aircrew members as compared to a population sample.

RESULTS

The overall participation rate was about 50%. Seven percent of women and six percent of men had red hair color. Blue or green eye color was reported among 89% of women and 87% of men. Sixteen percent of women aged 20 to 39 had used sun beds more than 100 times during their lifetime, while the corresponding figure was 12% for men of the same age. Younger age groups had more sunny vacations than the older age groups. The frequency of sunburn differed in the groups with reported different skin types according to Fitzpatrick classification.

CONCLUSION

The high prevalence of sun bed usage among young women is concurrent with the increased incidence of malignant melanoma among young women registered in the nationwide cancer registry. Young people have more often used sun beds and taken sunny vacation than the older, indicating a changed behavior in the population.

Cosmic radiation and cancer mortality among airline pilots: results from a European cohort study (ESCAPE)

Cosmic radiation is an occupational risk factor for commercial aircrews. In this large European cohort study (ESCAPE) its association with cancer mortality was investigated on the basis of individual effective dose estimates for 19,184 male pilots. Mean annual doses were in the range of 2-5 mSv and cumulative lifetime doses did not exceed 80 mSv. All-cause and all-cancer mortality was low for all exposure categories. A significant negative risk trend for all-cause mortality was seen with increasing dose. Neither external and internal comparisons nor nested case-control analyses showed any substantially increased risks for cancer mortality due to ionizing radiation. However, the number of deaths for specific types of cancer was low and the confidence intervals of the risk estimates were rather wide. Difficulties in interpreting mortality risk estimates for time-dependent exposures are discussed.

Breast cancer risk in airline cabin attendants: a nested case-control study in Iceland

AIMS

To investigate whether length of employment as a cabin attendant was related to breast cancer risk, when adjusted for reproductive factors.

METHODS

Age matched case-control study nested in a cohort of cabin attendants. The cases were found from a nationwide cancer registry (followed up to end of year 2000) and the reproductive factors (age at first childbirth and number of children) from a registry of childbirth, in both instances by record linkage with the cabin attendants' identification numbers. The employment time of the cabin attendants at the airline companies and the reproductive factors had been systematically recorded prior to the diagnosis of breast cancer in the cohort. A total of 35 breast cancer cases and 140 age matched controls selected from a cohort of 1532 female cabin attendants were included in the study.

RESULTS

The matched odds ratio from conditional logistic regression of breast cancer risk among cases and controls of cabin attendants was 5.24 (95% CI 1.58 to 17.38) for those who had five or more years of employment before 1971 compared with those with less than five years of employment before 1971, adjusted for age at first childbirth and length of employment from 1971 or later.

CONCLUSIONS

The association between length of employment and risk of breast cancer, adjusted for reproductive factors, indicates that occupational factors may be an important cause of breast cancer among cabin attendants; the association is compatible with a long induction period.

Risk factors for cutaneous malignant melanoma among aircrews and a random sample of the population

AIMS

To evaluate whether a difference in the prevalence of risk factors for malignant melanoma in a random sample of the population and among pilots and cabin attendants could explain the increased incidence of malignant melanoma which had been found in previous studies of aircrews.

METHODS

A questionnaire was used to collect information on hair colour, eye colour, freckles, number of naevi, family history of skin cancer and naevi, skin type, history of sunburn, sunbed, all sunscreen use, and number of sunny vacations.

RESULTS

The 239 pilots were all males and there were 856 female cabin attendants, which were compared with 454 males and 1464 females of the same age drawn randomly from the general population. The difference in constitutional and behavioural risk factors for malignant melanoma between the aircrews and the population sample was not substantial. The aircrews had more often used sunscreen and had taken more sunny vacations than the other men and women. The predictive values for use of sunscreen were 0.88 for pilots and 0.85 for cabin attendants and the predictive values for sunny vacation were 1.36 and 1.34 respectively.

CONCLUSION

There was no substantial difference between the aircrew and the random sample of the population with respect to prevalence of risk factors for malignant melanoma. Thus it is unlikely that the increased incidence of malignant melanoma found in previous studies of pilots and cabin attendants can be solely explained by excessive sun exposure.

Cancer incidence among marine engineers, a population-based study (Iceland)

OBJECTIVES

Marine engineers are in their occupation exposed to different chemicals, organic solvents, exhaust gases, oils, and petroleum products, and were formerly exposed to asbestos. The aim was to study the cancer pattern, with particular attention to lung and bladder cancer, in an Icelandic cohort of marine engineers, indirectly controlling for their smoking habits.

METHODS

A cohort of 6603 male marine engineers was followed up from 1955 to 1998, a total of 167,715 person-years. The cohort was record linked by the engineers' personal identification numbers to population-based registers containing the vital and emigration status and cancer diagnosis. Standardized incidence ratios (SIRs) were calculated for all cancers and different cancer sites in relation to different lag time and year of graduation. Information on smoking habits was obtained by administering a questionnaire to a sample of the cohort (n = 1,501).

RESULTS

In the total cohort 810 cancers were observed, whereas 794 were expected (SIR 1.0, 95% CI 1.0-1.1), and significantly increased risk of stomach cancer (SIR 1.3, 95% CI 1.0-1.5) and lung cancer (SIR 1.2, 95% CI 1.0-1.5) was found. Increased risk of all cancers (SIR 1.2, 95% CI 1.1-1.3), stomach cancer (SIR 1.5, 95% CI 1.1-1.9), lung cancer (SIR 1.4, 95% CI 1.2-1.8), pleural mesothelioma (SIR 4.8, 95% CI 1.3-12.3), and urinary bladder cancer (SIR 1.3, 95% CI 1.0-1.8) were observed when a 40-year lag time was applied. The engineers' smoking habits were similar to those in a sample of the general population. The predictive value for lung cancer was 1.03.

CONCLUSIONS

The increased risk for mesothelioma is possibly attributable to the previous asbestos exposure. The excess of lung cancer could also be related to asbestos exposure. The high incidence of stomach cancer, lung cancer, and bladder cancer may be related to exposure to chemical risk factors, such as oils and petroleum products, as confounding due to smoking seems to be ruled out. In the light of the limited exposure information in the present study the importance of the different occupational exposures needs to be evaluated in further studies.

Overview of atmospheric ionizing radiation (AIR) research: SST-present

The Supersonic Transport (SST) program, proposed in 1961, first raised concern for the exposure of pregnant occupants by solar energetic particles (SEP), and neutrons were suspected to have a main role in particle propagation deep into the atmosphere. An eight-year flight program confirmed the role of SEP as a significant hazard and of the neutrons as contributing over half of the galactic cosmic ray exposures, with the largest contribution from neutrons above 10 MeV. The FAA Advisory Committee on the Radiobiological Aspects of the SST provided operational requirements. The more recent lowering of ICRP-recommended exposure limits (1990) with the classification of aircrew as "radiation workers" renewed interest in GCR background exposures at commercial flight altitudes and stimulated epidemiological studies in Europe, Japan, Canada and the USA. The proposed development of a High Speed Civil Transport (HSCT) required validation of the role of high-energy neutrons, and this resulted in ER-2 flights at solar minimum (June 1997) and studies on effects of aircraft materials on interior exposures. Recent evaluation of health outcomes of DOE nuclear workers resulted in legislation for health compensation in year 2000 and recent European aircrew epidemiological studies of health outcomes bring renewed interest in aircraft radiation exposures. As improved radiation models become available, it is imperative that a corresponding epidemiological program of US aircrew be implemented.