Commentary: The end of the hygiene hypothesis?

Understanding asthma phenotypes: the World Asthma Phenotypes (WASP) international collaboration

The World Asthma Phenotypes (WASP) study started in 2016 and has been conducted in five centres, in the UK, New Zealand, Brazil, Ecuador and Uganda. The objectives of this study are to combine detailed biomarker and clinical information in order to 1) better understand and characterise asthma phenotypes in high-income countries (HICs) and low and middle-income countries (LMICs), and in high and low prevalence centres; 2) compare phenotype characteristics, including clinical severity; 3) assess the risk factors for each phenotype; and 4) assess how the distribution of phenotypes differs between high prevalence and low prevalence centres. Here we present the rationale and protocol for the WASP study to enable other centres around the world to carry out similar analyses using a standardised protocol. Large collaborative and integrative studies like this are essential to further our understanding of asthma phenotypes. The findings of this study will help elucidate the aetiological mechanisms of asthma and might potentially identify new causes and guide the development of new treatments, thereby enabling better management and prevention of asthma in both HICs and LMICs.

Risk factors for acute asthma in tropical America: a case-control study in the City of Esmeraldas, Ecuador

BACKGROUND

Despite the high asthma rates described in Latin America, asthma risk factors in poor urban settings are not well established. We investigated risk factors for acute asthma among Ecuadorian children.

METHODS

A matched case-control study was carried out in a public hospital serving a coastal city. Children with acute asthma were age- and sex-matched to non-asthmatics. A questionnaire was administered, and blood, as well as stool, and nasopharyngeal swabs were collected.

RESULTS

Sixty cases and 119 controls aged 5-15 were evaluated. High proportions of cases were atopic with population-attributable fractions for atopy of 68.5% for sIgE and 57.2% for SPT. Acute asthma risk increased with greater titers of mite IgE (3.51-50 kU/l vs. <0.70kU/l - OR 4.56, 95% CI 1.48-14.06, p = 0.008; >50kU/l vs. <0.70kU/l - OR 41.98, 95% CI: 8.97-196.39, p < 0.001). Asthma risk was significantly independently associated with bronchiolitis (adj. OR: 38.9, 95% CI 3.26-465), parental educational level (adj. OR 1.26, 95% CI: 1.08-1.46), and presence of sIgE (adj. OR: 36.7, 95% CI: 4.00-337), while a reduced risk was associated with current contact with pets (adj. OR: 0.07, 95% CI: 0.01-0.56). Rhinovirus infection was more frequent in cases (cases 35.6% vs. controls 7.8%, p = 0.002). None of the cases were on maintenance therapy with inhaled corticosteroids and most relied on emergency department for control.

CONCLUSIONS

A high proportion of children presenting to a public hospital with acute asthma were allergic to mite, particularly at high IgE titer. Poor asthma control resulted in overuse of emergency care.

The human microbiome. Early life determinant of health outcomes

The development of new technologies to isolate and identify microbial genomes has markedly increased our understanding of the role of microbiomes in health and disease. The idea, first proposed as part of the hygiene hypothesis, that environmental microbes influence the developmental trajectories of the immune system in early life, has now been considerably extended and refined. The abundant microbiota present in mucosal surfaces, especially the gut, is actively selected by the host through complex receptor systems that respond differentially depending on the molecular patterns presented to mucosal cells. Germ-free mice are more likely to develop allergic airway inflammation and show alterations in normal motor control and anxiety. These effects can be reversed by neonatal microbial recolonization but remain unchanged if recolonization occurs in adults. What emerges from these recent studies is the discovery of a complex, major early environmental determinant of lifetime human phenotypes. To change the natural course of asthma, obesity, and other chronic inflammatory conditions, active manipulation of the extensive bacterial, phage, and fungal metagenomes present in mucosal surfaces may be required, specifically during the developing years. Domesticating the human microbiome and adapting it to our health needs may be a challenge akin to, but far more complex than, the one faced by humanity when a few dozen species of plants and animals were domesticated during the transition between hunter-gatherer and sedentary societies after the end of the Pleistocene era.

Epidemiology of Respiratory Allergies and Asthma

Asthma has puzzled and confused physicians from the time of Hippocrates to the present day. The word “asthma” comes from a Greek word meaning “panting” (Keeney 1964), but reference to asthma can also be found in ancient Egyptian, Hebrew, and Indian medical writings (Ellul-Micallef 1976; Unger and Harris 1974). There were clear observations of patients experiencing attacks of asthma in the second century and evidence of disordered anatomy in the lung as far back as the seventeenth century (Dring et al. 1689).

Atopy and allergic respiratory disease in rural Poland before and after accession to the European Union

BACKGROUND

In 2003, we recorded a striking difference in the prevalence of atopy between village and small-town populations in southwest Poland. Nine years later, we undertook a second survey of the same area.

OBJECTIVE

We sought to assess whether rapid changes in farming practices, driven by accession to the European Union in 2004, were accompanied by an increase in atopy, asthma, and hay fever in these villages.

METHODS

In 2012, we surveyed 1730 inhabitants older than 5 years (response rate, 85%); 560 villagers and 348 town inhabitants who had taken part in the earlier survey. Participants completed a questionnaire on farm-related exposures and symptoms of asthma and hay fever. Atopy was assessed by using skin prick tests.

RESULTS

In 2012, far fewer villagers had contact with cows (4% vs 24.3% in 2003) or pigs (14% vs 33.5%), milked cows (2.7% vs 12.7%), or drank unpasteurized milk (9% vs 35%). Among the villagers, there was a significant increase at all ages in the prevalence of atopy between 2003 and 2012 both in the total population (7.3% vs 19.6%, P < .0001) and among those who took part in both surveys (7.9% vs 17.8%, P < .0001). Among the townspeople, the prevalence of atopy did not change substantially (20% vs 19.9% and 21.7% vs 18.5%, respectively). Hay fever increased 2-fold in the villages (3.0% vs 7.7%) but not in the town (7.1% vs 7.2%); there was little or no change in asthma prevalence in the villages (5.0% vs 4.3%) or town (4.3% vs 5.0%).

CONCLUSIONS

We report a substantial increase in atopy at all ages and in a remarkably short period of time in a Polish population whose farm-related exposures were dramatically reduced after their country's accession to the European Union.

Lifestyle changes and childhood asthma

In recent decades there have been marked increases in asthma prevalence in Western countries. More recently, asthma prevalence has peaked, or even begun to decline, in Western countries, but many low and middle income countries are now beginning to experience increases in prevalence (although there is no evidence of increases in prevalence in India to date). "Established" risk factors for asthma cannot account for the global prevalence increases, or the international patterns that have been observed, or the recent declines in prevalence in some Western countries. It seems that as a result of the "package" of changes in the intrauterine and infant environment that are occurring with "Westernization", we are seeing an increased susceptibility to the development of asthma and/or allergy. There are a number of elements of this "package" including changes in maternal diet, increased fetal growth, smaller family size, reduced infant infections and increased use of antibiotics and paracetamol, and immunization, all of which have been (inconsistently) associated with an increased risk of childhood asthma, but none of which can alone explain the increases in prevalence. It is likely that the "package" is more than the sum of its parts, and that these social and environmental changes are all pushing the infants' immune systems towards an increased risk of asthma.

Childhood infections and the risk of asthma: a longitudinal study over 37 years

BACKGROUND

Few studies have examined common childhood infections and adult asthma. We examined associations between childhood infectious diseases, childhood pneumonia, and current, persisting, and incident asthma to middle age.

METHODS

We analyzed data from the Tasmanian Longitudinal Health Study (TAHS). A history of pneumonia was ascertained from their parents when the TAHS participants were 7 years old. Measles, rubella, mumps, chickenpox, diphtheria, and pertussis were identified from school medical records. Associations with current, persisting, or incident asthma were examined using regression techniques.

RESULTS

Greater infectious diseases load was negatively associated with persisting asthma at all ages. Individually, pertussis (adjusted OR [aOR], 0.53; 95% CI, 0.28-1.00) was negatively associated with asthma persisting to age 13 years, chickenpox (aOR, 0.58; 95% CI, 0.38-0.88) was negatively associated with asthma persisting to age 32 years, and rubella was negatively associated with asthma persisting to ages 32 (aOR, 0.61; 95% CI, 0.31-0.96) and 44 years (aOR 0.53; 95% CI, 0.35-0.82). Pertussis was associated with preadolescent incident asthma (adjusted hazard ratio [aHR], 1.80; 95% CI, 1.10-2.96), whereas measles was associated with adolescent incident asthma (aHR, 1.66; 1.06-2.56). Childhood pneumonia was associated with current asthma at ages 7 (aOR, 3.12; 95% CI, 2.61-3.75) and 13 years (aOR, 1.32; 95% CI, 1.00-1.75), an association stronger in those without than those with eczema (aOR, 3.46; 95% CI, 2.83-4.24 vs aOR, 2.08; 95% CI, 1.38-3.12).

CONCLUSIONS

Overall, childhood infectious diseases protected against asthma persisting in later life, but pertussis and measles were associated with new-onset asthma after childhood. Measles and pertussis immunization might lead to a reduction in incident asthma in later life.

Environmental Exposure and Nonadherence with Medicines Directly Correlate with Exacerbations and Hospitalization for Asthma: A Population-Based Survey from UAE

Acute severe exacerbation of asthma is directly related with the uncontrolled asthma including noncompliance with the medicines and exposure to the environmental factors. To our knowledge, none of the community-based study has explored the prevalence of asthma and other factors (namely, pattern of symptoms, environmental/occupational/housing/behavioral pattern/misperception about asthma, and educational factors) contributing to the exacerbation of asthma. We also studied the nonadherence issues related to the management of asthma in the United Arab Emirates (UAE). By using European Community Respiratory Health Survey (ECRHS) questionnaires and pooled data from AIRGNE (UAE) study, we aimed to determine the above-mentioned factors in the general population by means of a cross-sectional assessment of a random sample of 1,229 participants of which 62.97% were male and 20.01% were UAE nationals, with a mean age (±SD) of 32.9 (±14.1) years. Prevalence of individual respiratory symptoms from the ECRHS questionnaire in all participants ranged from 8 to 10%, while those participants aged 20–44 years presented a lower prevalence in all symptoms (P<0.05). Conclusion. Certain specific persistent environmental factor along with nonadherence to the controller medicines is a significant factor leading to uncontrolled asthma with consequent exacerbations, morbidity/mortality, and health care cost in UAE.

Association of allergic sensitization with infectious diseases burden in Roma and non-Roma children

The hypothesis whether exposure to certain infections protects from atopy remains equivocal. To further investigate this, we compared serologic markers of infection and allergic sensitization prevalence in Roma children, who live under unfavorable hygienic conditions that facilitate the spread of infections, and non-Roma children who live in the same area. Analyses included 98 Roma and 118 non-Roma children. Serum IgG antibodies for 13 foodborne- airborne- and bloodborne infectious agents were determined, and a cumulative index of exposure was calculated by adding one point for each positive infection. Specific serum IgE to certain common food- and aero-allergens was also tested. and positivity to any of them was defined as indication of atopy. Roma children were found significantly more seropositive for T. gondii, Hepatitis A, H. pylori, HSV-1, CMV, and Hepatitis B (p < 0.0001). Non-Roma children were found more seropositive for RSV and M. pneumonia (p < 0.0001). Regarding the overall prevalence of atopy or the specific IgE responses to the allergens tested, no statistically significant differences were found between Roma and non-Roma children. A positive association of the cumulative index of exposure to infections with atopy was found in the non-Roma children (OR: 1.38, 95% CI: 1.08-1.75, p = 0.01) and in the total population (OR: 1.42, 95% CI: 1.11-1.83, p = 0.01). Regarding the specific infectious agents tested, a statistically significant positive association of atopy with seropositivity was found for M. pneumoniae in the non-Roma children (OR: 3.93, 95% CI: 1.39) as well as in the total population studied (OR: 2.83, 95% CI: 1.32-6.07, p = 0.01). Despite the higher burden of exposure to the battery of the infectious agents tested among Roma children, no protective effect for allergic disease development was evident. On the contrary, a positive association of exposure to infections with evidence of atopy was found, especially evident in the non-Roma children.

Epidemiology in a changing world: variation, causation and ubiquitous risk factors

We are all living in the era of globalization and, like it or not, it is going to change the way we practise epidemiology, the kinds of questions we ask and the methods we use to answer them. However, the methods, and ways of thinking about the health of populations, that will be required for epidemiology in the 21st century are in some instances quite different from the standard epidemiological techniques that are taught in most textbooks and courses today. As we develop epidemiological methods for addressing the scientific and public health problems of the 21st century, it is important that we consider, once again, the distinction between the analysis of variance and the analysis of causes. This has primarily been considered with respect to genetic research, and also with regard to the problems of making comparisons between different populations and environments at the same point in time. It has not been considered in depth with regard to the issues of conducting epidemiological research in a world that is changing over time. In this article, I first consider the statistical and scientific issues involved in the distinction between the analysis of variance and the analysis of causes. I then discuss some examples of the implications of this distinction for the theory and practice of epidemiology in a changing world, particularly with regard to risk factors that become ubiquitous over time. Sometimes the most important causes of disease are invisible because they are everywhere.

Childhood asthma, air quality, and social suffering among Mexican Americans in California's San Joaquin Valley: "Nobody talks to us here"

Nearly one in five Mexican American children residing in California's San Joaquin Valley (the Valley) in 2007 had an asthma attack at some point in their life. Numerous epidemiological studies have suggested that compared with other ethnic groups and Latino subgroups residing in the United States, Mexican origin children have the lowest rates of pediatric asthma. Ethnographic research conducted in central California, however, suggests otherwise. Known for its agricultural produce, extreme poverty, and poor air quality, the Valley is a magnet for the Mexican immigrant farm worker population. We conducted an exploratory ethnographic study to examine health disparities, social suffering, and childhood asthma in the Valley. Many Valley residents believe that their children's health concerns are being ignored. Open-ended interviews uncovered a largely rural community suffering not only from the effects of childhood asthma but the inability to have their experiences taken seriously.

Asthma: time to confront some inconvenient truths

Despite major advances in the understanding of the pathogenesis of asthma and improvements in management, the accompanying benefits from public health initiatives and clinical practice have arguably been less than expected. For example, there are no effective public health strategies or treatment regimes that reduce the risk of developing asthma or influence its natural history. These represent priority areas for future translational research, which would need to investigate genetic and environmental interactions and vaccine strategies. In terms of asthma management it is tempting to focus on novel drug therapies; however, a case can be made that the priority is to undertake research that leads to improvements in the use of existing treatments through public health and primary care initiatives. Guidelines represent an important component of this approach, with recommendations for asthma imbedded within respiratory guidelines that can be implemented in the developing world where other acute and chronic respiratory disorders are common. This approach offers the best opportunity to close the gap between what is currently achieved in asthma management and that which is potentially achievable.

Allergies in Asia: differences in prevalence and management compared with western populations

There is wide variability in the epidemiology and management of childhood asthma and related atopic diseases globally. Urbanized, affluent Western countries tend to have a higher prevalence of these diseases compared with Asian nations. However, recent studies have shown that the prevalence in Asia is increasing, although the rate of increase has slowed in the more developed Asian cities. Some possible causes for these differences are socioeconomic status, degree of urbanization, rates of infection, healthcare practices and genetic factors. Importantly, there are significant differences in the way asthma and allergic diseases are managed within Asia. This is of great concern because of the health implications, as these diseases are some of the most common chronic conditions that affect both adults and children. This review compares the differences in prevalence and management between Asia and the West, and discusses some of the possible reasons behind these variations.

Early life factors associated with incidence of physician-diagnosed asthma in preschool children: results from the Canadian Early Childhood Development cohort study

Background. Asthma is a common childhood illness. The objective of this study is to determine the incidence of physician-diagnosed asthma in preschool years and its relationship to host, prenatal and postnatal factors, early childhood factors, parental factors, household factors and demographic factors. Methods. The study sample was comprised of 8,499 infants and toddlers (<2 years at baseline) enrolled in the Canadian Early Childhood Development Study. Incidence of asthma was determined when the children were in preschool age (2 to 5 years). Results. The 4-year cumulative incidence at preschool age was 13.7% for physician-diagnosed asthma. History of early childhood wheezing before 2 years of age was a significant risk factor for incidence of asthma in preschool years (hazard ratio (HR): 2.32; 95% confidence interval (CI): 2.04-2.65). Factors that were protective for the development of asthma were breastfeeding more than 3 months (HR: 0.82; 95% CI: 0.69-0.97); history of nose or throat infection often in childhood (HR: 0.79; 95% CI: 0.67-0.93); early daycare attendance (HR: 0.85; 95% CI: 0.74-0.98); presence of two or more siblings at birth, (HR: 0.79; 95% CI: 0.64-0.97); and dwelling in rural non- central metropolitan areas (HR: 0.81; 95% CI: 0.69-0.95). Male sex, low birth weight, childhood allergy, single parent, maternal smoking during pregnancy, maternal medication use, parental atopy, and low SES at baseline were significant risk factors for the incidence of physician-diagnosed asthma in preschool years. Conclusion. This study emphasizes the role of wheezing in infant and toddler age on early onset of asthma during preschool years. The results also provide additional importance of early exposures to environmental factors such as early infections, daycare attendance, and rural environment in the development of proper immune dynamics to prevent asthma.

Antibiotic use in infancy and symptoms of asthma, rhinoconjunctivitis, and eczema in children 6 and 7 years old: International Study of Asthma and Allergies in Childhood Phase III

BACKGROUND

Phase III of the International Study of Asthma and Allergies in Childhood measured the global prevalence of symptoms of asthma, rhinoconjunctivitis, and eczema in children.

OBJECTIVE

To investigate the associations between the use of antibiotics in the first year of life and symptoms of asthma, rhinoconjunctivitis, and eczema in children 6 and 7 years old.

METHODS

Parents or guardians of children 6 and 7 years old completed written questionnaires on current symptoms and possible risk factors. Prevalence odds ratios (ORs) were estimated by using logistic regression.

RESULTS

A total of 193,412 children from 71 centers in 29 countries participated. Reported use of antibiotics in the first year of life was associated with an increased risk of current asthma symptoms (wheezing in the previous 12 months) with an OR (adjusted for sex, region of the world, language, and per capita gross national income) of 1.96 (95% CI, 1.85-2.07); this fell to 1.70 (1.60-1.80) when adjusted for other risk factors for asthma. Similar associations were observed for severe asthma symptoms (OR, 1.82; 95% CI, 1.67-1.98), and asthma ever (OR, 1.94; 95% CI, 1.83-2.06). Use of antibiotics in the first year of life was also associated, but less strongly, with increased risks of current symptoms of rhinoconjunctivitis (OR, 1.56; 95% CI, 1.46-1.66) and eczema (OR, 1.58; 95% CI, 1.33-1.51).

CONCLUSION

There is an association between antibiotic use in the first year of life and current symptoms of asthma, rhinoconjunctivitis, and eczema in children 6 and 7 years old. Further research is required to determine whether the observed associations are causal or are a result of confounding by indication or reverse causation.

Environmental factors in the development of chronic inflammation: a case-control study on risk factors for Crohn's disease within New Zealand

The role of environmental factors in the risk for Crohn's disease (CD), an inflammatory bowel disease (IBD), was investigated in a North Island-based New Zealand case-control cohort. A total of 315 CD patients and 536 controls were recruited through various sources to the Auckland CD Risk Factor Study. As well as demographic characteristics, the self-reported questionnaire included (1) smoking and drinking alcohol, (2) breastfeeding in infancy, (3) early life exposures to allergens and microbes, (4) health conditions lasting 6 months or longer and (5) taking antibiotics and any medications. There was strong evidence for familial associations of the disease, and minor effects of birth order and number of siblings. Being a smoker, especially over a long time period, and exposure to smoking during childhood and adolescence periods increased risk, whereas drinking alcohol at least once per week showed a slight protective effect. Long term use of the oral contraceptive pill increased the risk of developing CD, but breastfeeding and immunisation during infancy showed no significant association. Long term and debilitating illness (lasting 6 months or more), taking antibiotics prior to developing CD, or taking four or more antibiotics or any regular medication in a year during adolescence substantially increased the CD risk. Having a pet during childhood was a protective factor, but regularly feeding an animal was not sufficient to protect. Many of these significant factors are likely to impact on the colonic microflora and/or immune system. We conclude that, in addition to strong evidence for genetic associations, factors likely to impact on immune response or reduce early exposure to microbes provide a main risk factor for CD in this New Zealand population.