Do risk factors for childhood infections and malnutrition protect against asthma? A study of Brazilian male adolescents

Subjective socioeconomic status: an alternative to objective socioeconomic status

BACKGROUND

Subjective "ladder" measurements of socio-economic status (SES) are easy-to-administer tools that ask respondents to rate their own SES, allowing them to evaluate their own material resources and determine where it places them relative to their community. Here, we sought to compare the MacArthur Scale of Subjective Social status to the WAMI, an objective measure of SES that includes data on water and sanitation, asset ownership, education, and income.

METHODS

Leveraging a study of 595 tuberculosis patients in Lima, Peru, we compared the MacArthur ladder score to the WAMI score using weighted Kappa scores and Spearman's rank correlation coefficient. We identified outliers that fell outside the 95^th percentile and assessed the durability of the inconsistencies between scores by re-testing a subset of participants. We then used Akaike information criterion (AIC) to compare the predictability of logistic regression models evaluating the association between the two SES scoring systems and history of asthma.

RESULTS

The correlation coefficient between the MacArthur ladder and WAMI scores was 0.37 and the weighted Kappa was 0.26. The correlation coefficients differed by less than 0.04 and the Kappa ranged from 0.26 to 0.34, indicating fair agreement. When we replaced the initial MacArthur ladder scores with retest scores, the number of individuals with disagreements between the two scores decreased from 21 to 10 and the correlation coefficient and weighted Kappa both increased by at least 0.03. Lastly, we found that when we categorized WAMI and MacArthur ladder scores into three groups, both had a linear trend association with history of asthma with effect sizes and AICs that differed by less than 15% and 2 points, respectively.

CONCLUSION

Our findings demonstrated fair agreement between the MacArthur ladder and WAMI scores. The agreement between the two SES measurements increased when they were further categorized into 3-5 categories, the form in which SES is often used in epidemiologic studies. The MacArthur score also performed similarly to WAMI in predicting a socio-economically sensitive health outcome. Researchers should consider subjective SES tools as an alternative method for measuring SES, particularly in large health studies where data collection is a burden.

Exclusive breast-feeding, the early-life microbiome and immune response, and common childhood respiratory illnesses

BACKGROUND

The impact of breast-feeding on certain childhood respiratory illnesses remains controversial.

OBJECTIVE

We sought to examine the effect of exclusive breast-feeding on the early-life upper respiratory tract (URT) and gut microbiome, the URT immune response in infancy, and the risk of common pediatric respiratory diseases.

METHODS

We analyzed data from a birth cohort of healthy infants with prospective ascertainment of breast-feeding patterns and common pediatric pulmonary and atopic outcomes. In a subset of infants, we also characterized the URT and gut microbiome using 16S ribosomal RNA sequencing and measured 9 URT cytokines using magnetic bead-based assays.

RESULTS

Of the 1949 infants enrolled, 1495 (76.71%) had 4-year data. In adjusted analyses, exclusive breast-feeding (1) had an inverse dose-response on the ⍺-diversity of the early-life URT and gut microbiome, (2) was positively associated with the URT levels of IFN-α, IFN-γ, and IL-17A in infancy, and (3) had a protective dose-response on the development of a lower respiratory tract infection in infancy, 4-year current asthma, and 4-year ever allergic rhinitis (odds ratio [95% CI] for each 4 weeks of exclusive breast-feeding, 0.95 [0.91-0.99], 0.95 [0.90-0.99], and 0.95 [0.92-0.99], respectively). In exploratory analyses, we also found that the protective association of exclusive breast-feeding on 4-year current asthma was mediated through its impact on the gut microbiome (P = .03).

CONCLUSIONS

Our results support a protective causal role of exclusive breast-feeding in the risk of developing a lower respiratory tract infection in infancy and asthma and allergic rhinitis in childhood. They also shed light on potential mechanisms of these associations, including the effect of exclusive breast-feeding on the gut microbiome.

Infant milk-feeding practices and food allergies, allergic rhinitis, atopic dermatitis, and asthma throughout the life span: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the USDA and Department of Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding prior to infant formula introduction, 4) feeding a lower versus higher intensity of human milk to mixed-fed infants, and 5) feeding a higher intensity of human milk by bottle versus breast with food allergies, allergic rhinitis, atopic dermatitis, and asthma.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published between January 1980 and March 2016, dual-screened the results according to predetermined criteria, extracted data from and assessed the risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

The systematic reviews numbered 1-5 above included 44, 35, 1, 0, and 0 articles, respectively. Moderate, mostly observational, evidence suggests that 1) never versus ever being fed human milk is associated with higher risk of childhood asthma, and 2) among children and adolescents who were fed human milk as infants, shorter versus longer durations of any human milk feeding are associated with higher risk of asthma. Limited evidence does not suggest associations between 1) never versus ever being fed human milk and atopic dermatitis in childhood or 2) the duration of any human milk feeding and allergic rhinitis and atopic dermatitis in childhood.

CONCLUSIONS

Moderate evidence suggests that feeding human milk for short durations or not at all is associated with higher childhood asthma risk. Evidence on food allergies, allergic rhinitis, and atopic dermatitis is limited.

Breastfeeding and the Developmental Origins of Asthma: Current Evidence, Possible Mechanisms, and Future Research Priorities

Breastfeeding has many established health benefits, but its impact on asthma development is uncertain. Breastfeeding appears to have a positive and dose-dependent impact on respiratory health, particularly during early childhood and in high-risk populations; however, the strength and causality of these associations are unclear. It is challenging to compare results across studies due to methodological differences and biological variation. Resolving these inconsistencies will require well-designed, prospective studies that accurately capture asthma diagnoses and infant feeding exposures (including breastfeeding duration, exclusivity, and method of feeding), account for key confounders, evaluate dose effects, and consider effect modification and reverse causality. Mechanistic studies examining human milk bioactives and their impact on lung health and asthma development are beginning to emerge, and these will be important in establishing the causality and mechanistic basis of the observed associations between breastfeeding and asthma. In this review, we summarize current evidence on this topic, identify possible reasons for disagreement across studies, discuss potential mechanisms for a causal association, and provide recommendations for future research.

Breastfeeding and asthma and allergies: a systematic review and meta-analysis

AIM

To systematically review the association between breastfeeding and childhood allergic disease.

METHODS

Predetermined inclusion/exclusion criteria identified 89 articles from PubMed, CINAHL and EMBASE databases. Meta-analyses performed for categories of breastfeeding and allergic outcomes. Meta-regression explored heterogeneity.

RESULTS

More vs. less breastfeeding (duration) was associated with reduced risk of asthma for children (5-18 years), particularly in medium-/low-income countries and with reduced risk of allergic rhinitis ≤5 years, but this estimate had high heterogeneity and low quality. Exclusive breastfeeding for 3-4 months was associated with reduced risk of eczema ≤2 years (estimate principally from cross-sectional studies of low methodological quality). No association found between breastfeeding and food allergy (estimate had high heterogeneity and low quality). Meta-regression found differences between study outcomes may be attributable to length of breastfeeding recall, study design, country income and date of study inception. Some of the protective effect of breastfeeding for asthma may be related to recall bias in studies of lesser methodological quality.

CONCLUSION

There is some evidence that breastfeeding is protective for asthma (5-18 years). There is weaker evidence for a protective effect for eczema ≤2 years and allergic rhinitis ≤5 years of age, with greater protection for asthma and eczema in low-income countries.

Breastfeeding duration and asthma in Puerto Rican children

RATIONALE

Little is known about breastfeeding and asthma in Puerto Ricans, the ethnic group most affected by this disease in the US. We examined the relation between the currently recommended duration of breastfeeding and asthma in school-aged Puerto Rican children.

METHODS

Case-control study of 1,127 Puerto Rican children aged 6-14 years living in Hartford, Connecticut (n = 449) and San Juan, Puerto Rico (n = 678). Parental recall of breastfeeding was categorized based on duration and according to current guidelines (i.e., none, 0-6 months, and >6 months). Asthma was defined as parental report of physician-diagnosed asthma and wheeze in the previous year. We used logistic regression for the multivariate analysis, which was conducted separately for each study site and for the combined cohort. All multivariate models were adjusted for age, gender, household income, atopy, maternal asthma, body mass index, early-life exposure to environmental tobacco smoke, and (for the combined cohort) study site.

RESULTS

After adjustment for covariates, children who were breastfed for up to 6 months had 30% lower odds of asthma (95% CI = 0.5-1.0, P = 0.04) than those who were not breastfed. In this analysis, breastfeeding for longer than 6 months was not significantly associated with asthma (OR = 1.5, 95% CI = 1.0-2.4, P = 0.06).

CONCLUSIONS

Our results suggest that breastfeeding for up to 6 months (as assessed by parental recall) is associated with decreased odds of asthma in Puerto Rican children, and that there is no additional beneficial effect of breastfeeding for over 6 months. These results support current recommendations on the duration of breastfeeding in an ethnic group at risk for asthma.

Social determinants of childhood asthma symptoms: an ecological study in urban Latin America

Asthma is an important public health problem in urban Latin America. This study aimed to analyze the role of socioeconomic and environmental factors as potential determinants of asthma symptoms prevalence in children from Latin American (LA) urban centers. We selected 31 LA urban centers with complete data, and an ecological analysis was performed. According to our theoretical framework, the explanatory variables were classified in three levels: distal, intermediate, and proximate. The association between variables in the three levels and prevalence of asthma symptoms was examined by bivariate and multivariate linear regression analysis weighed by sample size. In a second stage, we fitted several linear regression models introducing sequentially the variables according to the predefined hierarchy. In the final hierarchical model Gini Index, crowding, sanitation, variation in infant mortality rates and homicide rates, explained great part of the variance in asthma prevalence between centers (R(2) = 75.0 %). We found a strong association between socioeconomic and environmental variables and prevalence of asthma symptoms in LA urban children, and according to our hierarchical framework and the results found we suggest that social inequalities (measured by the Gini Index) is a central determinant to explain high prevalence of asthma in LA.

Exclusive breastfeeding is associated with reduced cow's milk sensitization in early childhood

BACKGROUND

Although breastfed infants have consistently been reported as having fewer infections and respiratory morbidity during infancy, none have reached a definitive conclusion as to whether breastfeeding is an effective strategy to prevent allergic diseases. This study aims to investigate the relationship between exclusive breastfeeding and sequential changes of several biomarkers of allergy, such as absolute eosinophil count, total IgE level, and specific IgE level during the first 3 yrs of life.

METHODS

This is an unselected, population-based study that is part of a prospective birth cohort called the PATCH (Prediction of Allergy in Taiwanese Children). Blood analysis was performed at ages 6, 12, 18, 24, and 36 months. Clinical records of breastfeeding and detailed questionnaires regarding to allergic diseases were also obtained.

RESULTS

Analysis comparing exclusive breastfeeding ≥4 months with those <4 months and those partially breastfed showed a decreased risk of sensitization toward cow's milk protein up to the age of 2 yr (adjusted OR for cow's milk sensitization at 12 months was 0.2 [95% CI, 0.07-0.5]), at 18 months of age it was 0.2 [95% CI, 0.07-0.5], and at 24 months of age it was 0.2 [95% CI, 0.04-0.7]). In addition, although not significant, children of the exclusive breastfeeding group showed a trend of lower absolute eosinophil counts than their counterparts at all ages, and a lower total IgE level at the age of 3 yr.

CONCLUSIONS

Results of this study suggest that exclusive breastfeeding is associated with a reduced risk of cow's milk protein sensitization during early childhood.

Breastfeeding and childhood asthma: systematic review and meta-analysis

Asthma and wheezing disorders are common chronic health problems in childhood. Breastfeeding provides health benefits, but it is not known whether or how breastfeeding decreases the risk of developing asthma. We performed a systematic review and meta-analysis of studies published between 1983 and 2012 on breastfeeding and asthma in children from the general population. We searched the PubMed and Embase databases for cohort, cross-sectional, and case-control studies. We grouped the outcomes into asthma ever, recent asthma, or recent wheezing illness (recent asthma or recent wheeze). Using random-effects meta-analyses, we estimated pooled odds ratios of the association of breastfeeding with the risk for each of these outcomes. We performed meta-regression and stratified meta-analyses. We included 117 of 1,464 titles identified by our search. The pooled odds ratios were 0.78 (95% confidence interval: 0.74, 0.84) for 75 studies analyzing "asthma ever," 0.76 (95% confidence interval: 0.67, 0.86) for 46 studies analyzing "recent asthma," and 0.81 (95% confidence interval: 0.76, 0.87) for 94 studies analyzing recent wheezing illness. After stratification by age, the strong protective association found at ages 0-2 years diminished over time. We found no evidence for differences by study design or study quality or between studies in Western and non-Western countries. A positive association of breastfeeding with reduced asthma/wheezing is supported by the combined evidence of existing studies.

The association of the 'additional height index' with atopic diseases, non-atopic asthma, ischaemic heart disease and mortality: a population-based study

OBJECTIVE

Intrauterine growth has been associated with atopic conditions. Growth and adult height have been associated with cardiovascular disease, cancers and mortality but are highly genetic traits. The objectives of the study were as follows: first, to define a height measure indicating an individual's height below or above that which could be expected based on parental height (genetic inheritance) and growth charts. It was named 'the additional height index' (AHI), defined as (attained-expected) height; second, to investigate possible associations of AHI with atopic versus non-atopic health outcomes and with ischaemic heart disease (IHD) and IHD mortality.

DESIGN

General population-based study.

SETTING

Research centre.

PARTICIPANTS

A random sample of 2656 men and women living in greater Copenhagen took part in the MONICA10 study (the Danish monitoring trends and determinants of cardiovascular disease). In total, 1900 participants with information of parental height were selected.

OUTCOME MEASURES

Atopic sensitisation (serum IgE), questionnaire information of atopic dermatitis, rhinoconjunctivitis, asthma or wheezing, and registry-based diagnoses of IHD/IHD mortality from National Registries.

RESULTS

Increasing levels of AHI were inversely associated with non-atopic asthma, non-atopic wheezing, IHD and IHD mortality (IHD-all). For one SD increase of AHI, the OR or HR with CI in adjusted analyses was non-atopic asthma OR=0.52 (0.36 to 0.74), non-atopic wheezing OR=0.67 (0.51 to 0.89), and IHD-all HR=0.89 (0.78 to 1.01). The level of AHI was higher among individuals with atopic dermatitis, allergic rhinoconjunctivitis and atopic sensitisation (all p values <0.001) compared with individuals without those conditions; however, the associations were not confirmed in adjusted analyses.

CONCLUSIONS

Individuals with childhood conditions that led them to attain tallness higher than expected from their parents' height may be at lower risk of non-atopic asthma/wheeze and IHD/IHD mortality but possibly at higher risk of atopic conditions. The measure of tallness below or above the expected height could be a sensitive alternative to normal height in epidemiological analyses.

Breastfeeding, asthma, and allergy: a tale of two cities

BACKGROUND

The effect of breastfeeding duration on subsequent asthma and allergy remains the subject of much controversy.

OBJECTIVE

To investigate whether differences in study design or disease-related exposure modification were the cause of the differences in study findings.

METHOD

The data from two cohorts, the Childhood Asthma Prevention Study (CAPS) from Australia and the Barn Allergi Miljo Stockholm cohort from Sweden, which had reported different findings on the association between breastfeeding and asthma, were combined. For this analysis, the definitions for breastfeeding, asthma, and allergy were harmonized. Subjects were included if they had at least one parent with wheeze or asthma and had a gestational age of more than 36 wks (combined n = 882). The risk of disease-related exposure modification was assessed using survival analysis.

RESULTS

Breastfeeding reduced the risk of asthma at 4/5 and 8 yrs of age in children with a family history of asthma. The effect was stronger in the Swedish cohort. Breastfeeding had no effect on the prevalence of sensitization to inhaled allergens in this cohort with a family history of asthma but was a risk factor for sensitization to cow's milk, peanuts, and eggs in the CAPS cohort at 4/5 yrs and in the combined cohort at 8 yrs. There was no evidence to support the existence of disease-related exposure modification in either cohort.

CONCLUSION

These findings point to the importance of harmonization of features of study design, including subject selection criteria and variable definitions, in resolving epidemiological controversies such as those surrounding the impact of breastfeeding on asthma and allergic sensitization.

Systematic review and meta-analysis investigating breast feeding and childhood wheezing illness

There is conflicting evidence concerning the relationship between breast feeding and wheezing illness. The objective of this study was to investigate whether there is any association between breast feeding and wheezing in children aged over 5 years and to discover possible sources of heterogeneity. An electronic search of MEDLINE and EMBASE databases was conducted from January 2000 to June 2010. In addition, reference lists from relevant publications were searched. Birth cohort, cross-sectional and case-control studies were included if they measured any breast feeding or exclusive breast feeding for 3 or 4 months. Wheezing illness, including asthma, was identified based on symptoms, reported diagnosis or objective criteria. Thirty-one publications were identified for meta-analysis. There was no association found between any or exclusive breast feeding and wheezing illness, although there was a high level of heterogeneity between the studies. Subgroup analysis revealed that any breast feeding slightly lowers the odds of wheeze (pooled odds ratio 0.92 [0.86, 0.98]) but slightly increases the odds of asthma defined by specific criteria (pooled odds ratio 1.10 [1.00, 1.22]). This meta-analysis does not provide evidence that breast feeding is protective against wheezing illness in children aged 5 years and over. The difference in the effects of breast feeding according to the nature of the wheezing illness highlights the importance of the heterogeneity of illness phenotypes.

Poverty-associated risk factors for wheezing in the first year of life in Honduras and El Salvador

BACKGROUND

Risk factors for wheezing specifically during the first year of life have been studied in well-developed countries, but the information from developing countries is very scarce. There are no such studies focusing on factors derived from poverty. The aim of the present study was to determine if risk factors related to poverty are associated to wheezing during the first year of life in infants from Honduras and El Salvador.

METHODS

A survey, using a validated questionnaire, was carried out in the metropolitan area of San Pedro Sula (Honduras) and in La Libertad (El Salvador) in centres where infants attended for a scheduled vaccination shot or a healthy child visit at 12 months of age. Fieldworkers offered questionnaires to parents and helped the illiterate when necessary. The main outcome variable was wheezing during the first year of life, as reported by parents.

RESULTS

A total of 1047 infants in El Salvador and 780 in Honduras were included in the analysis. The prevalence of wheeze in the first year was higher in El Salvador (41.2%) than in Honduras (27.7%), as was recurrent wheezing defined as three or more episodes (18.4% vs. 11.7%). Wheezing and recurrent wheezing was associated to unpaved floor in the household (summary odds ratios for both countries 1.55, p=0.036 and 1.72, p=0.054 for any wheeze and recurrent wheezing, respectively); dust entering from streets (1.30, p=0.052 and 1.67, p=0.008); living in a heavily polluted area (1.33, p=0.037 and 1.52, p=0.033); and having mould stains on the household walls (1.36, p=0.072 and 1.76, p=0.007). Furthermore, marginal associations were found for additional person at home and use of kerosene as cooking fuel. University studies in the mother (0.34, p=0.046 and 0.32, p=0.022) and a professional occupation in the father (0.34, p=0.046 and 0.26, p=0.047) were associated to a lower risk.

CONCLUSIONS

The prevalence of wheezing and recurrent wheezing is notoriously high in El Salvador and Honduras. In those populations factors related to poverty are associated to a higher prevalence of wheezing and recurrent wheezing, whereas higher maternal education and paternal professional occupation behave as protective factors.

[Prevalence of wheezing in the chest among adults from the 1982 Pelotas birth cohort, Southern Brazil]

OBJECTIVE

To estimate the prevalence of wheezing in the chest among adults, and to explore the effect of some variables on the prevalence of this condition.

METHODS

This was a prospective cohort study on individuals born in the city of Pelotas (Southern Brazil) in 1982. A total of 4,297 subjects was traced in 2004-5, representing 77.4% of the original cohort. Data were collected by means of interviews using the ISAAC (International Study of Asthma and Allergies in Childhood Steering Committee) questionnaire. Associations between the outcome 'occurrence of wheezing in the chest within the 12 months prior to the interview' and the variables of socioeconomic, demographic and birth characteristics were tested by means of multivariable analyses, using Poisson regression.

RESULTS

The prevalence of wheezing over the preceding year was 24.9%. Among the individuals reporting wheezing, 54.6% reported difficulty in sleeping, and 12.9% reported difficulty in speaking due to wheezing. The prevalence of wheezing in the chest was significantly higher among women. This association was maintained in analyses adjusted for non-white skin color, family history of asthma and low socioeconomic level. Among men, there was no significant association in the analyses adjusted for skin color and family income at birth. Family histories of asthma and poverty throughout life presented significant associations with wheezing in the chest. For both sexes, there were no associations with the variables of birth weight and breastfeeding duration.

CONCLUSIONS

The prevalence of wheezing in the chest was high, and subjects with low family income at birth were more likely to have had wheezing in the chest over the preceding year.

[Wheezing phenotypes from birth to adolescence: a cohort study in Pelotas, Brazil, 1993-2004]

OBJECTIVE

To study the prevalence of wheezing patterns and their associations with independent variables.

METHODS

Cohort study of live births in 1993 in Pelotas, Brazil. A systematic subsample (20%) of the original cohort was evaluated at 6 months, 12 months and 4 years. At 10-12 years, 87.5% of the original cohort was contacted. Wheezing was categorized: transient, wheezing at 4 years but not at 10-12; persistent, wheezing at all evaluations; late-onset, wheezing at 10-12 years. Independent variables were analyzed: gender; skin color; family income; smoking/asthma during pregnancy; breastfeeding; respiratory infection/diarrhea (during the 1st year); family members with asthma/allergy (at 4 years and at 10-12); physician-diagnosed rhinitis/eczema (at 10-12 years).

RESULTS

The subsample comprised 897 adolescents. Wheezing patterns were expressed as prevalence (95% CI): transient, 43.9% (40.7-47.2); persistent, 6.4% (4.8-8.0); and late-onset, 3.3% (2.2-4.5). The transient pattern was more common in children from low-income families, children breastfed for less time, children with a history of respiratory infections (during the 1st year) and children with asthma in the family (at 4 years). The persistent pattern was almost twice as common in males, in children whose mothers had asthma during pregnancy, in children with respiratory infections (during the 1st year) and in children with asthma in the family (at 4 and 10-12 years). The late-onset pattern was more prevalent among those with asthma in the family (at 10-12 years) and those diagnosed with rhinitis (at 10-12 years), being less prevalent among those reporting respiratory infections (during the 1st year) and those diagnosed with eczema (at 10-12 years).

CONCLUSIONS

Knowledge of the associations of wheezing patterns allows us to adopt preventive and therapeutic measures.

The use of maternal and child health services in three population-based cohorts in Southern Brazil, 1982-2004

This study aimed to describe indicators of health care assistance during antenatal care, delivery and in the first year of life in Pelotas, Rio Grande do Sul State, Brazil. In 1982, 1993, and 2004, all hospital newborns from the urban area of Pelotas were enrolled in a cohort study. In this period, the number of pregnant women that did not attend antenatal care fell from 4.9% to 1.9%; the mean number of appointments increased from 6.7 to 8.1; and the number of women who began antenatal care in the third trimester of pregnancy decreased from 14.8% to 7%; caesarean sections increased from 27.7% to 45.2% and the proportion of deliveries assisted by physicians increased from 61.2% to 89.2%. Improvements in immunization rates during the first year of life mainly occurred between 1982 and 1993, while the number of preventive medical appointments improved among those born in 2004. This increase in coverage was greater for low-income mothers and children, which may reflect the implementation of universal coverage in Brazil; however, coverage levels in 1982 were already high for wealthy mothers and children, reducing the scope for further gains.

Prospective study of breast-feeding in relation to wheeze, atopy, and bronchial hyperresponsiveness in the Avon Longitudinal Study of Parents and Children (ALSPAC)

BACKGROUND

Breast-feeding clearly protects against early wheezing, but recent data suggest that it might increase later risk of atopic disease and asthma.

OBJECTIVE

We sought to examine the relationship between breast-feeding and later asthma and allergy outcomes by using data from the Avon Longitudinal Study of Parents and Children, a large birth cohort in the United Kingdom.

METHODS

We used adjusted logistic regression models to evaluate the association between breast-feeding and atopy at age 7 years, bronchial responsiveness to methacholine at age 8 years, and wheeze at ages 3 and 7 1/2 years. Bayesian methods were used to assess the possibility of bias caused by an influence of early wheezing on the duration of breast-feeding, as well as selection bias.

RESULTS

Breast-feeding was protective for wheeze in the first 3 years of life (odds ratio [OR] of 0.80 [95% CI, 0.70-0.90] for > or = 6 months relative to never) but not wheeze (OR, 0.98; 95% CI, 0.79-1.22), atopy (OR, 1.12; 95% CI, 0.92-1.35), or bronchial hyperresponsiveness (OR, 1.07; 95% CI, 0.82-1.40) at ages 7 to 8 years. Bayesian models adjusting for the longer duration of breast-feeding among children with wheezing in early infancy produced virtually identical results.

CONCLUSIONS

We did not find consistent evidence for either a deleterious effect or a protective effect of breast-feeding on later risk of allergic disease in a large prospective birth cohort of children with objective outcome measures and extensive data on potential confounders and effect modifiers. Neither reverse causation nor loss to follow-up appears to have materially biased our results.

Methods used in the 1982, 1993, and 2004 birth cohort studies from Pelotas, Rio Grande do Sul State, Brazil, and a description of the socioeconomic conditions of participants' families

Three birth cohorts are currently being followed in Pelotas, Southern Brazil, in order to assess changes in birth conditions, growth, development, morbidity, and infant mortality, as well as the influence of pre- and perinatal factors on the subsequent morbidity of participants in their adult lives. We provide a description of the methodology used for the cohort studies that began in 1982, 1993, and 2004 in Pelotas, and a description of the economic conditions of the families involved. For the three cohorts, similar strategies were used to recruit babies born to mothers living in the municipality's urban area. These included daily visits to maternity hospitals where births were identified, mothers interviewed, and newborns examined. Over this time frame, there has been a significant reduction in the number of births due to declining fertility rates amongst the target population. Salaries (measured as a multiple of the minimum wage) were stable across cohorts, but quality of life indicators - such as the availability of piped water, flushing toilets and refrigerators - showed clear improvements. Mothers' levels of education improved markedly. Important changes in the demographic profile of risk factors and health outcomes are being recorded by the Pelotas cohorts.

Environmental factors and allergic disorders

Despite numerous studies on possible associations between environmental exposure and allergic disorders, any conclusions made remain a matter of controversy. We conducted a review of evidence in relation to environmental and nutritional determinants and wheeze, asthma, atopic dermatitis, and allergic rhinitis. Identified were 263 articles for analysis after consideration of 1093 papers that were published since 2000 and selected by electronic search of the PubMed database using keywords relevant to epidemiological studies. Most were cross-sectional and case-control studies. Several prospective cohort studies revealed inconsistent associations between various environmental factors and the risk of any allergic disorder. Therefore, the evidence was inadequate to infer the presence or absence of a causal relationship between various environmental exposures and allergic diseases. However, evidence is suggestive of positive associations of allergies with heredity. Because almost all the studies were performed in Western countries, the application of these findings to people in other countries, including Japan, may not be appropriate. Further epidemiological information gained from population-based prospective cohort studies, in particular among Japanese together with other Asians, is needed to assess causal relationships between various environmental factors and allergic diseases.

Distinctive immunoglobulin E anti-house dust allergen-binding specificities in a tropical Australian Aboriginal community

BACKGROUND

There is evidence that the specificity of the IgE binding in allergy tests can vary for different populations.

OBJECTIVE

We aimed to examine the allergenic specificity of IgE binding in sera from house dust mite (HDM)-atopic subjects in a tropical Australian Aboriginal community.

METHODS

Sera shown to contain IgE antibodies to an HDM extract of Dermatophagoides pteronyssinus were examined for IgE binding to a panel of nine purified HDM allergens from this mite species by quantitative microtitre assays. IgG antibody binding (IgG1 and IgG4) was also measured.

RESULTS

The IgE-binding activity in the sera from the Aboriginal community was not directed to the expected major groups 1 and 2 HDM allergens but instead to the group 4 amylase allergen. There was also little IgE binding to the potentially cross-reactive tropomyosin (Der p 10) or arginine kinase (Der p 20) allergens. The IgG4 antibody was rarely detected and limited to the Der p 4 allergen. IgG1 antibody binding was frequently measured to all the allergens regardless of an individual's atopic status, whereas in urban communities it is restricted to the major allergens and to atopic subjects.

CONCLUSION

The high IgE anti-HDM response of Australian Aboriginals predominantly bound Der p 4 and not the Der p 1 and 2 allergens, showing a distinctive allergy that could affect the disease outcome and diagnosis.

Tele-education may be a valuable approach for educating patients with asthma in under-served communities

In Brazil, few people have access to asthma specialists. We conducted a survey in São Paulo city to evaluate the population's general knowledge about asthma. The results were used to guide the development of a 3-D video for patient education. The video presentation was about 12 min long. It used animated sequences to explain the pathophysiology of asthma (e.g. the anatomy of the respiratory system, the lung, the alveoli, mechanism of respiration). The object was to motivate the general public to change their habits. The motivation video can be delivered via the Internet or by DVD and can used by non-medical professionals. It will need to be tested formally in the context of primary care from the point of view of knowledge retention, cost and patient motivation.

Risk factors for wheezing in early adolescence: a prospective birth cohort study in Brazil

BACKGROUND

Many asthma studies are available in the literature, but few investigated whether risk factors for asthma differ by sex.

OBJECTIVE

To evaluate risk factors for wheezing in early adolescence, with emphasis on sex differences.

METHODS

A prospective birth cohort study was initiated in 1993; 87.5% of the original cohort was traced at 11 years, totaling 4,452 adolescents. Current wheezing was defined as at least 1 crisis in the previous 12 months. The following independent variables were analyzed: maternal smoking during pregnancy, wheezing at 4 years, maternal wheezing, and adolescent body mass index.

RESULTS

Current wheezing affected 13.5% (95% confidence interval [CI], 12.4%-14.5%) of the cohort. The prevalence of current wheezing was 15.3% (95% CI, 13.7%-16.8%) in boys and 11.7% (95% CI, 10.4%-13.1%) in girls (P < .001). Maternal smoking was related to an increased risk of wheezing for boys but not for girls. There was a significant tracking of wheezing from 4 to 11 years in both sexes, although the magnitude was stronger for boys. A dose-response association between maternal wheezing and adolescent wheezing was observed in boys but not in girls. Finally, obesity was associated with an increased risk of wheezing in boys but not in girls.

CONCLUSIONS

The variables explored in this investigation had a stronger effect on adolescent wheezing in boys than in girls. Public health strategies aimed at minimizing the burden of wheezing should take these sex differences into account.

Coorte de nascimentos de Pelotas, 2004: metodologia e descrição

OBJETIVO: Descrever uma coorte de nascimentos que teve início em 2004, para avaliar condições pré e perinatais dos recém-nascidos, morbi-mortalidade infantil, características e desfechos do início da vida e acesso, utilização e financiamento da atenção à saúde. MÉTODOS: Todas as crianças nascidas na zona urbana dos municípios de Pelotas e Capão do Leão (bairro Jardim América), no ano de 2004, foram identificadas e suas mães convidadas a fazer parte do estudo. No seu primeiro ano foram realizadas visitas às mães por ocasião do nascimento das crianças, aos três e aos 12 meses de idade. Nessas visitas um questionário foi aplicado às mães, com perguntas sobre saúde; hábitos de vida; utilização de serviços de saúde; situação socioeconômica; estimativa de idade gestacional; medidas antropométricas do recém-nascido (peso, comprimento, perímetros cefálico, torácico e abdominal); medidas antropométricas da mãe (peso e altura) e avaliação de desenvolvimento infantil. RESULTADOS: Do total de crianças elegíveis (4.558), mais de 99% foram recrutadas para o estudo logo após o nascimento. A taxa de seguimento foi de 96% aos três meses e de 94% aos 12 meses. Dentre os resultados iniciais destacaram-se: a taxa de mortalidade infantil de 19,7 por mil, sendo 66% dos óbitos infantis no período neonatal; freqüência de 15% de prematuros e 10% de baixo peso ao nascer; as cesarianas representaram 45% dos partos. CONCLUSÕES: A terceira coorte de nascimentos em Pelotas mostrou uma situação de estabilidade da mortalidade infantil nos últimos 11 anos, com predomínio da mortalidade neonatal, além de aumento da prematuridade e partos cesarianos.

Determinants of child morbidity in Latin America: A pooled analysis of interactions between parental education and economic status

Diarrhea and respiratory infections account for more than two-fifths of all deaths among children under five. Parental education and economic status are well-known risk factors for child morbidity, but little is known about whether education and economic status operate synergistically or independently to influence children's health. Confirming the presence and direction of such interactions is important to better target education and development policies. Our objective is to test for interactions between parental education and economic status in predicting the risk of diarrhea and respiratory illness among children under five, before and after adjusting for key proximate risk factors. We pool 12 Demographic and Health Surveys (DHS) and nine Living Standards Measurement Surveys (LSMS) from Latin America, creating two large databases. Quintiles of economic status are constructed from principal components asset indices. We use logistic regression to analyze episodes of diarrhea and respiratory illness, and interactions between economic quintile and maternal and paternal education are evaluated via likelihood ratio tests. We find that mother's education and quintile interact synergistically in the DHS data, while results are inconclusive in the LSMS data. The effect of increasing maternal education appears to be more protective for children in wealthy families than for children in poor families. Conversely, improvements in economic status reduce health risks more for children whose mothers are better educated. Father's education is protective and operates independently of economic status. Our findings imply that poverty alleviation efforts occurring in concert with programs to educate women and girls will be more effective for improving children's health than either approach alone.

Pesticides and respiratory symptoms among farmers

OBJECTIVE

Despite the intensive use of pesticides in agriculture there are few studies assessing the risk of respiratory conditions from this exposure. The study aimed at quantifying the prevalence of respiratory symptoms among farmers and evaluating its relationship with occupational use of pesticides and the prevalence of respiratory symptoms.

METHODS

A cross-sectional study was conducted among 1,379 farmers from two municipalities of Southern Brazil in 1996. Frequency and type of chemical exposure and pesticide poisoning were recorded for both sexes. All subjects aged 15 years or older with at least 15 weekly hours of agricultural activity were interviewed. An adapted questionnaire developed by the American Thoracic Society was used for the assessment of respiratory symptoms. Multivariate logistic regression analysis was carried out.

RESULTS

More than half (55%) of interviewees were male. The prevalence of asthma symptoms was 12% and chronic respiratory disease symptoms was 22%. Higher odds ratios for both asthma (OR=1.51; 95% CI: 1.07-2.14) and chronic respiratory disease (OR=1.34; 95% CI 1.00-1.81) symptoms were found in women. Logistic regression analysis identified associations between many forms of exposure to pesticides and increased respiratory symptoms. Occurrence of pesticide poisoning was associated with higher prevalence of asthma symptoms (OR=1.54; 95% CI: 1.04-2.58) and chronic respiratory disease symptoms (OR=1.57; 95% CI: 1.08-2.28).

CONCLUSIONS

In spite of causality limitations, the study results provide evidence that farming exposure to pesticides is associated with higher prevalence of respiratory symptoms, especially when the exposure is above two days per month.

The hygienic hypothesis and transformations in etiological knowledge: from causal ontology to ontogenesis of the body

The objective of this article is to systematize the principal recent research results pertaining to the so-called hygienic hypothesis, which establishes an etiological link between the increasing incidence of allergic diseases and the decreasing incidence of infectious diseases in the industrialized countries of the Western world. The author contends that the current debate on the hygienic hypothesis indicates significant transformations in the understanding of disease etiology, perhaps even as important as the transformations in the 19th century during the process leading to the constitution of modern medicine and the identification of infectious disease causal agents.

Socioeconomic risk factors for asthma in Chilean young adults

OBJECTIVES

We studied the association between socioeconomic status (SES) and asthma symptoms, severity of asthma, atopy, and bronchial hyperresponsiveness (BHR) to methacholine.

METHODS

We studied 1232 men and women born between 1974 and 1978 in a semirural area of Chile. We assessed asthma symptoms with a standardized questionnaire, atopy with a skin-prick test to 8 allergens, and BHR to methacholine with the tidal breathing method. SES was derived from several indicators: education, occupation, completion of a welfare form, belongings, housing, number of siblings, and overcrowding.

RESULTS

Those with fewer belongings had more asthma symptoms. Those who had higher education and those who owned cars had fewer asthma symptoms and BHR. Overcrowding was negatively related to atopy, atopy with asthma symptoms, and BHR. Higher education and noncompletion of a welfare form were risk factors for atopy.

CONCLUSION

The strength and direction of the association between asthma and SES depended on what definition of asthma was analyzed. Asthma symptoms were more common among poor people. There was some support for the hygiene hypothesis, as overcrowding was associated with less wheezing with atopy, less atopy, and less BHR.

The hygiene hypothesis and asthma

PURPOSE OF REVIEW

Reduced exposure to childhood infections may explain the increased prevalence of allergic diseases in industrialized countries (the hygiene hypothesis). This review will examine recent epidemiologic studies of the hygiene hypothesis and asthma.

RECENT FINDINGS

Recent studies have confirmed previous findings of an inverse association between increased exposure to other children during childhood and either allergen sensitization or hay fever. However, there is conflicting evidence regarding the relation between exposure to other children and asthma. Although it has been hypothesized that vaccinations may influence the development of asthma, recent findings do not support this association. Serologic evidence of exposure to certain gastrointestinal pathogens (eg, hepatitis A virus) has been inversely associated with either allergen sensitization or asthma in some, but not all, recent studies. Although heavy infestation with certain parasites (eg, helminths) is protective against allergen sensitization, there is conflicting evidence regarding the relation between parasitic infection and asthma. The results of recent studies suggest that the relation between endotoxin exposure and asthma is complex and likely influenced by factors related to the exposure itself, the host, and other covariates. Although it has been postulated that antibiotic use in early life is a risk factor for asthma, this hypothesis is not supported by recent findings.

SUMMARY

For every exposure studied with regard to the hygiene hypothesis, there are inconsistent findings in relation to asthma. The hygiene hypothesis is not likely to be the sole explanation for the ongoing asthma epidemic in industrialized nations.

The hygiene theory: fact or fiction?

PURPOSE OF REVIEW

The "hygiene hypothesis" offers a potentially credible and parsimonious explanation for the increasing prevalence of allergy noted in many westernized populations. The authors review recent evidence both for and against this hypothesis.

RECENT FINDINGS

A strong body of epidemiologic evidence indicates that the original observations, namely of a birth order effect and increased risk of atopic disorders in those born into small, affluent households, are robust findings. Improved hygiene is believed to mediate its effect through decreased exposure to infectious agents in early life, and recent evidence has focused attention on the importance of the gastrointestinal microbial environment. In particular, infection with hepatitis A, Helicobacter pylori, and toxoplasma in those living in temperate climates, and geoheminths in those living in endemic areas, have been shown to be associated with reduced risk of atopic manifestations. It is postulated that these infections exert their effect through critically altering T-helper (Th)1/Th2 regulation, which is supported by the examination of the cytokine profiles of cord mononuclear cells when exposed to gastrointestinal flora and, furthermore, emerging evidence on the benefits of probiotics on symptoms of atopic dermatitis. Attempts to identify an inverse relation between Th1- and Th2-mediated disorders (as might be predicted by the Th1/Th2 paradigm) have, however, yielded conflicting results, raising the possibility that this model may be something of an oversimplification.

SUMMARY

The hygiene hypothesis remains a credible but nonspecific explanation for observed variations over time, place and persons at risk for developing atopic allergic disorders. More prospective studies are needed to unravel which infectious agents exert a protective effect and the time period of importance for sensitization. The clinical implications of these advances in our understanding of the etiology of atopic allergic disorders are currently limited.

The Pelotas birth cohort study, Rio Grande do Sul, Brazil, 1982-2001

Given the growing recognition of the importance of the life course approach for the determination of chronic diseases, birth cohort studies are becoming increasingly important. This paper describes the methods used in the 1982 Pelotas (Brazil) birth cohort study, one of the largest and longest studies of this type in developing countries. All 5,914 hospital births occurring in Pelotas in 1982 (over 99% of all deliveries) were studied prospectively. The main stages of the study took place in 1983, 1984, 1986, 1995, 1997, 2000, and 2001. More than two thousand variables are available for each subject who participated in all stages of the study. Recent phases of the study included the examination of 2,250 males when presenting for the army recruitment exam in 2000, the study of a 27% sample of men and women in 2001 through household visits, and the study of over 400 children born to the cohort women. Follow-up rates in the recent stages of the cohort were 78.9% for the army examination and 69.0% for the household visits. Ethnographic and oral health studies were conducted in sub-samples. Some recent results on blood pressure, adolescent pregnancy, and asthma are presented as examples of utilization of the data. Suggestions on lessons learned for other cohort studies are proposed.