Towards prevention

The prevalence of atopy in asthmatic children correlates strictly with the prevalence of atopy among nonasthmatic children

BACKGROUND

Because asthma preferentially burdens persons with atopy, atopy is simplistically considered a primary 'cause' of asthma. Yet at the population level, the percentage of asthma cases 'attributable' to atopy ranges from less than 10% to more than 60%. Seeking to understand the rationale for the variability of atopy-attributable cases of asthma, we systematically reviewed the results of our own previous epidemiological studies and several studies conducted by others in children.

METHODS

From each of the 37 random pediatric populations selected by a Medline search combining the key words 'IgE or skin tests or hypersensitivity, immediate' with 'epidemiological studies, cross-sectional, case-control, prevalence, longitudinal, epidemiology of asthma' (12 from our previous pediatric surveys and a further 25 reported from 19 studies in children), we extracted the population prevalence of asthma and atopy among asthmatic subjects and among the nonasthmatic part of the population.

RESULTS

No correlation was found between the prevalence of asthma (range 1.8-44.1%) and atopy (range 5.8-63.9%) in these 37 populations of children (r = 0.052, p = 0.761). Nevertheless, the prevalence of atopy among asthmatics strictly correlated with the prevalence of atopy in nonasthmatics (r = 0.900, p < 0.001, slope 1.364).

CONCLUSION

The prevalence of asthma and atopy varies worldwide and at various time points and independently undergoes the influence of powerful environmental factors. The almost perfect correlation we found between atopy in asthmatics and atopy in the nonasthmatic part of the childhood population shows that the prevalence of atopy in asthma depends on environmental factors that simultaneously induce atopy in asthmatic and nonasthmatic subjects.

Asthma, smoking and chronic cough in rural and urban adult communities in The Gambia

BACKGROUND

Asthma is reported to be rare in traditional rural communities, but is thought to be increasing as lifestyles become more urbanized or 'western'.

OBJECTIVES

A community-based survey of non-communicable diseases was conducted from October 1996 to June 1997, and included comparison of the prevalence of asthma, smoking and chronic cough in rural and urban Gambia.

METHODS

A cluster sample survey was conducted in a random sample of rural and urban adults (> or = 15 years of age). Subjects were asked about respiratory symptoms using a locally adapted version based on the IULTD questionnaire. Spirometry (basal, methacholine provocation and reversibility with a bronchodilator) and skin prick tests were performed on a randomly selected subsample of all subjects and those who, when interviewed, said they wheezed or had been diagnosed as asthmatic by a doctor.

RESULTS

Out of 2166 participants in the urban population, 4.1% reported having had wheezing or whistling in the chest in the previous 12 months, 3.6% reported doctor-diagnosed asthma, and 0.6% chronic cough. In the rural population with 3223 participants these figures were 3.3%, 0.7% and 1.2%, respectively. Wheeze was more common in women, cough for 3 months of the year was more common in the age-groups 45+. Those who reported that they currently smoked accounted for 34% in urban and 42% in rural men. Figures were much lower for women (1.5% and 6.0%). Seven out of 574 randomly selected subjects (1.4%) exhibited bronchial hyper-responsiveness to methacholine challenge. Four of 133 (3.0%) people with self-reported wheeze and 3/69 (4.3%) participants with doctor-diagnosed asthma reacted positively on bronchial provocation with methacholine. There was a remarkably high prevalence of positive skin prick tests to aeroallergens: 38% in participants with a history of wheeze and 27% in those without.

CONCLUSION

The prevalence of wheeze (particularly in association with bronchial hyper-responsiveness) was low in both rural and urban Gambia. This is in contrast to the relatively high prevalence of positive skin prick tests to aeroallergens (in both wheezers and non-wheezers), questioning the mechanisms of interaction between allergy and asthma and the presence of protective factors against asthma in this West African population. The high smoking rates justify international concern about tobacco marketing in developing societies.

Dog exposure in infancy decreases the subsequent risk of frequent wheeze but not of atopy

BACKGROUND

Influence of household pets in the development of childhood asthma or atopy has been controversial.

OBJECTIVE

The purpose of this study was to investigate whether pet exposure in early life decreases the subsequent risk of frequent wheezing and/or allergic sensitization.

METHODS

This was a prospective observational birth cohort study. The setting was a large health maintenance organization in Tucson, Ariz; the subjects were a population sample of 1246 newborns enrolled at birth and followed prospectively to age 13 years. The main outcome measures were as follows: time to first report of frequent wheezing (>3 episodes in the past year), skin prick test reactivity at 6 years and 11 years of age, and total serum IgE at 9 months, 6 years, and 11 years of age.

RESULTS

Children living in households with > or =1 indoor dogs at birth were less likely to develop frequent wheeze than those not having indoor dogs (P =.004). This inverse association was confined to children without parental asthma (hazard ratio = 0.47; P <.001 [Cox regression]) and was not evident for children with parental asthma (hazard ratio = 0.96; P =.87). Adjustment by potential confounders did not change the results. Indoor cat exposure was not significantly associated with the risk of frequent wheezing. Neither cat exposure in early life nor dog exposure in early life was associated with skin prick test reactivity or total serum IgE at any age.

CONCLUSION

Dog exposure in early life might prevent the development of asthma-like symptoms, at least in low-risk children with no family history of asthma. Nevertheless, early pet exposure does not seem to significantly influence the development of allergic sensitization.

Problems and possibilities in understanding the natural history of asthma

In early life, asthma symptoms can occur intermittently or may not be severe enough to limit normal activities, which makes it difficult for the clinician to make reliable predictions and administer therapy with some precision. In the case of pediatric asthma, the identification of children who will experience the development of a clinically important illness that will impair their quality of life can be a complex process. The usual methods for describing this information include the prognostic statistics of sensitivity, specificity, likelihood ratio, and positive predictive value. The sensitivity, specificity, and likelihood ratio of various early markers of asthma have been calculated from several cohort studies.

What are the candidate groups for pharmacotherapeutic intervention to prevent asthma?

Despite the development of many new therapies for the treatment of asthma, the prevalence of this disease is still increasing in many areas of the world. Today no intervention is able to completely cure asthma but chronic therapies could decrease its severity. Moreover, asthma is one of the most common chronic diseases of childhood and its pharmacoeconomic burden is huge. Epidemiologic studies have identified some of the major factors involved in the pathogenesis and evolution of asthma. Several prevention programs have been developed in different countries with various success rates. Most of those interventions were based on allergen avoidance. From studies aimed at controlling early asthma and from epidemiologic data, we have learned to identify high-risk groups, e.g, the atopic child with allergic asthma, with a family history of asthma or allergy-related disease and early sensitization to aeroallergens. Only a few prospective studies aimed at preventing the onset of asthma have been published. With ketotifen, Iikura et al. could prevent the onset of asthma after a 1-year period in patients suffering from atopic dermatitis. Another study has been published by Bustos et al. concerning children with a family history of allergy and high total IgE levels. Those studies involved about 100 patients. No follow-up data has been published for either of them. Recently, the first results from the ETAC (Early Treatment of the Atopic Child) trial have been reported. This study involved 817 atopic children with atopic dermatitis and a family history of atopy: cetirizine halved the number of patients developing asthma in the subgroups (200 children) sensitized to house dust mite (51.5% versus 28.6%) or pollen (58.8% versus 27.8%). The optimal target for pharmaceutical intervention to prevent asthma would seem to be high risk patients: children with atopic dermatitis, a family history of asthma or atopic disease and early sensitization to aeroallergens. Primary prevention in whole populations (e.g. starting even before the onset of atopic dermatitis or allergen sensitization) does not at present appear to be a realistic approach.

Dust mites and asthma

Dust mite proteins have been implicated as a predominant cause of the current increase in asthma prevalence. Recent advances in the understanding of these allergens have vastly increased the potential for more effective treatment and prophylaxis. In the absence of vaccines, environmental controls aimed at allergen avoidance are currently the best defense against the disease.

Asthma prevalence and deprivation: a small area analysis

STUDY OBJECTIVE

To investigate the relation between the prevalence of asthma symptoms in adults and deprivation in the area of residence.

DESIGN

Two complementary surveys carried out between 1991-1993 yielding adult asthma symptom prevalence throughout New Zealand. Deprivation is measured by the NZDep91 index of deprivation for small areas.

SETTING

New Zealand.

PARTICIPANTS

A random sample of 25,042 adults aged 20-50 years.

MAIN RESULTS

After controlling for possible confounding by age, gender, and ethnicity, the 12 month period prevalence rates of asthma in this representative sample of New Zealand adults are significantly higher in the three most deprived area categories than in the least deprived (tenth) category. The prevalence ratio for the most deprived category compared with the least deprived category is 1.29 with 95% confidence intervals (CI) 1.14, 1.47. There is a linear increase in asthma prevalence with increasing area deprivation (chi 2(1) = 32.20, p < 0.001). Independently, the rates are also 1.41 (95% CI 1.29, 1.54) times higher among Maori and 1.29 (95% CI 1.10, 1.52) times higher among the Pacific Island group than among the remaining, mostly European, respondents.

CONCLUSIONS

The relation between asthma in adults and area deprivation is unlikely to be attributable to study biases or confounding. Further work should examine the possible role of modifiable deprivation factors in this relation.