Comparison of local risk factors for children's atopic symptoms in Hanoi, Vietnam

Neonatal, atopic and infectious disease outcomes among children born to mothers with latent tuberculosis infection

Exposure to microbes may result in maternal immune responses that can affect fetal immune development. Several lines of evidence have shown that mycobacterial antigens can change the onset of atopic disease. We hypothesized that infants born to mothers with a positive tuberculosis (TB) test and a negative chest radiograph, may exhibit differential development of atopic disease during early childhood. The study was designed as a case control study. Birth records for infants born to untreated mothers with a positive TB skin test (TST), as defined by ≥10 mm induration were reviewed (n = 145 cases) and compared to a randomly selected unmatched control cohort of 46 women with a negative TST who delivered during the same time period at Scripps Hospital in San Diego, CA, USA. Childhood outcome parameters reviewed were: (1) the onset of physician diagnosed asthma; (2) lower respiratory tract infection (LRTI) with wheezing, latent tuberculosis infection/wheezing diagnosed on physical examination; (3) nonsurgical hospitalization; (4) atopic disease (eye/skin/nasal-sinus disease); (5) infections: ear, LRTI, sinus. LRTI was defined as an infection of the lower airways, eg, pneumonia. Outcomes at the end of years 1, 2, and 3–5 years combined were analyzed. Fisher exact test, Chi-square analysis or Poisson regression analysis were used as appropriate and a P-value of <0.05 was defined as significant. The cases and controls had similar birth weights, gestational ages, maternal ages: 3.34 versus 3.35 kg; 38.3 versus 39.2 weeks, 27.4 versus 26 years (P = non-significant). The childhood outcome parameters of the new onset of asthma was significantly higher than controls by age 2 years, but not at other ages studied, based on available clinic follow up data (P = 0.02). There was a difference in the risk for lung infection at age 2 and 3–5 years (P < 0.0001). There were no differences in the other outcome parameters studied (P = ns). There were no cases of infants with a positive TST, maternal Bacille Calmette-Guerin vaccination or active maternal TB, based on our study findings. There was a higher occurrence of asthma and lung infections at age 2 years among controls (P = 0.02). Our study defines for the first time a possible influence of maternal latent TB infection on fetal and childhood illness.

Exposure to farming environments in childhood and asthma and wheeze in rural populations: a systematic review with meta-analysis

Asthma is a chronic respiratory disorder that has become substantially more common over the past decades. One environmental factor for which particularly strong associations with asthma and allergic diseases have been described is exposure to farming environments in childhood. The aim of this systematic review was to update and extend existing narrative reviews, test for heterogeneity of effect across studies, and conduct a meta-analysis to report a summary effect measure. Published relevant literature was searched through PubMed including all articles added to PubMed before September 1, 2011. Articles were included if they reported an epidemiological study on the exposure to a farming environment in childhood and subsequent wheeze or asthma. Heterogeneity of effect measures across studies was evaluated using Cochran's Q and I(2). Random-effects meta-analysis was performed to summarize effect measures for various outcome definitions. In total, 357 retrieved abstracts revealed 52 original articles from 39 studies with data considered for the meta-analysis. Most studies were conducted among children or on childhood onset of disease. Most data were published on doctor-diagnosed asthma or current wheeze. The meta-analysis showed substantial heterogeneity across studies with similar outcome definitions. Nonetheless, the combined effects were statistically significant and showed an approximate 25% lower asthma prevalence among exposed subjects compared with unexposed subjects. The protective 'farm-effect' on asthma was reported in numerous studies. Its underlying factors ought to be studied, and promising efforts have been already made. However, the heterogeneity of the effect across studies should also be investigated because whatever causes it is a potential threat to valid synthesis of evidence and to the detection of specific protective factors.

Early probiotic supplementation for the prevention of atopic disease in newborns-probiotics and the hygiene hypothesis-

Environmental factors during early infancy could theoretically affect immune system development and subsequent risk of allergic disease. One potentially helpful exposure is early infant supplementation with specific probiotic strains. Unlike other exposures, probiotic supplementation is feasible and has a good safety profile. A review of recent randomized, controlled trials suggests that the effect of supplementation with probiotics on preventing the development of allergic disease is mixed. Further studies are needed to define potential mechanisms of action, such as effects on infant microbiota, as well as potential subgroups of patients that may benefit from these interventions.

Increase in asthma and a high prevalence of bronchitis: results from a population study among adults in urban and rural Vietnam

BACKGROUND

While a large amount of data about the epidemiology of asthma, COPD, chronic bronchitis and respiratory symptoms are available from developed countries, the information about these diseases in developing countries in south-east Asia are scarce.

AIM

Assess the prevalence of respiratory diseases and symptoms and their relation with demographic data including smoking habits among adults in rural and urban Vietnam.

METHODS

A random sample of subjects aged 21-70 years were invited; 3008 subjects living in an inner city area of Hanoi and 4000 in a rural area of Bavi in northern Vietnam. An internationally used questionnaire was delivered by field workers to the study subjects. The questionnaire was completed by the subjects, or when necessary, by the field workers after reading the questions for the study participants.

RESULTS

The response rate was 92% in Bavi and 70% in Hanoi. Of men in Bavi 67.8% (Hanoi 49.7%; p < 0.001) were smokers, while of women 4.2% were smokers in Hanoi (Bavi 1.2%; p < 0.001). The prevalence of ever asthma was in Hanoi 5.6% (Bavi 3.9%; p = 0.003) with no major gender difference. The most common symptom was longstanding cough (Hanoi 18.1%, Bavi 12.0%; p < 0.001) followed by sputum production, while the prevalence of symptoms common in asthma was considerably lower. Although the large difference in smoking habits, respiratory symptoms tended to be only slightly more common in men than women. Family history of asthma and chronic bronchitis, respectively, were strongly associated with both diseases.

CONCLUSIONS

The prevalence of asthma in adults may have increased in both urban and rural Vietnam, as the few previous estimates have found 2% of adults having asthma. Half of men in Hanoi and two-thirds in Bavi were smokers versus a few percent of women in both areas. Bronchitic symptoms were common in both men and women.

Allergen tolerance versus the allergic march: the hygiene hypothesis revisited

In addition to genetics, several environmental variables appear to impact allergic risk. Meta-analyses of epidemiologic studies presented in this article demonstrate a correlation between specific ambient exposures (eg, livestock, pets, endotoxin, and unpasteurized milk ingestion) and reduced allergic risk during childhood. Additional laboratory investigations discussed in this review characterized the intrinsic immunostimulatory activities of living environments. Considered together, results of these investigations suggest a novel paradigm by which early-life home exposures to microbial products and other allergen-nonspecific immunostimulants modify allergic risk.

The genetic and environmental basis of atopic diseases

The prevalence of atopic diseases has increased abruptly in recent years in most Westernized societies, making the question why this happened the topic of a heated debate. The best paradigm available to date to explain this steep rise, the 'hygiene hypothesis', supports that it is the excess 'cleanliness' of our environments that has led to the decline in the number of infectious stimuli that are necessary for the proper development of our immune system. Recent findings support that it is the combined effect that not only pathogenic, but also non-pathogenic microorganisms, and even their structural components,can exert on the immune system that deters from the development of atopic responses. Adding to these results are intriguing new findings on the effect different gene polymorphisms can have on an individual's predisposition to allergic diseases. The most important linkages produced, to date, include those among the genes for IL-4, IL-13, HLA-DRB, TNF, LTA,FCER1B, IL-4RA, ADAM33, TCR alpha/delta, PHF11, GPRA, TIM, p40, CD14, DPP10, T-bet, GATA-3, and FOXP3 and allergic disorders. The two parallel research efforts, epidemiologic and genetic, are only recently starting to converge,producing fascinating results on the effect particular gene-environment interactions might have in the development of atopy.The most important lesson learned through this tremendous research effort is that not only a small number but thousands and millions of separate risk factors act in concordance in the production of the allergic phenotype.

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.

Defining a role for ambient TLR ligand exposures in the genesis and prevention of allergic diseases

Environmental variables responsible for the increasing allergic disease burden observed in developed countries over the last century have yet to be adequately characterized. Meta-analyses of epidemiological studies presented in the first half of this paper demonstrate a correlation between farm-associated exposures (i.e., livestock, pets, unpasteurized milk, and endotoxin) and a reduction in allergic risk during childhood. Laboratory investigations discussed in the second half of the paper characterize the intrinsic immunostimulatory activities of living environments. Considered together, experimental findings presented herein suggest a novel paradigm by which early life home exposures to microbial products and other allergen-nonspecific immunostimulants modify allergic risk.

The influence of childhood infections and vaccination on the development of atopy: A systematic review of the direct epidemiological evidence

BACKGROUND

The 'hygiene hypothesis' has been used to justify a belief common among homeopaths, that the suppression of childhood infections and immunisation may lead to the development of chronic atopic diseases.

OBJECTIVES

To analyse the influence of childhood infections and immunisation on the development of atopy.

METHODS

Qualitative systematic review of direct epidemiological evidence (Medline 1993-2004) concerning the influence of childhood infections and immunisation on the development of atopy and discussion based on homeopathy.

CONCLUSIONS

(1) Childhood infections do not protect against atopy; on the contrary, they increase the risk of allergic diseases, in agreement to Hahnemann's observations, which included epidemic diseases among the factors capable of stimulating the development of chronic diseases. (2) Vaccination is not a risk factor for atopy, notwithstanding the allergenic effect of some vaccines.

The hygiene hypothesis: does it function worldwide?

PURPOSE OF REVIEW

This article intends to be a systematic review of papers published during 2003-2004 quoted in a Medline search for 'hygiene hypothesis'. The worldwide perspective of the article does not refer just to a geographical concept, but tries also to address the question of whether the consensus on the hypothesis is global or whether it applies to all types of allergic or immunologic disease, to any age sample or infectious agent. Furthermore, the article outlines those clinical and experimental studies which, in the authors' opinion, may represent significant contributions to a better understanding of the hygiene hypothesis and may guide further investigations on the subject.

RECENT FINDINGS

The association between a reduced exposure to infectious agents (as a part of a changed lifestyle) and a higher prevalence of atopy seems now to be confirmed by consistent evidence. Mechanisms underlying this association, however, are not yet completely clear (immune deviation or immune regulation).

SUMMARY

Further experimental and clinical studies are needed, with special reference to the time, duration and intensity of exposure to any specific infectious agent which is related to well-defined allergy outcomes. The background information for using microbial products in allergy prevention and treatment is still limited.

Signs of reversing trends in prevalence of asthma

Several recent reports have provided evidence that the burden of asthma may have levelled off, after increasing for decades. Implementation of the national and global asthma prevention and management guidelines that have led to earlier detection and improved treatment of asthmatics, is considered to be involved in this apparent change for the better. In addition, environmental influences associated with the modern life may have reached the maximum in inducing symptoms and disease in genetically susceptible individuals in some areas. Available data obtained from Canada and non-English-speaking countries in Europe show that the peak in asthma prevalence has been reached at the level of 8-12%. This review outlines the most recent literature on time trends in asthma prevalence and considers the possible causes of the current trends. Problems and pitfalls in appraising studies on time trends are also discussed.