Age at childhood infections and risk of atopy

Infection-exposure in infancy is associated with reduced allergy-related disease in later childhood in a Ugandan cohort

Background

Lack of early infection-exposure has been associated with increased allergy-related disease (ARD) susceptibility. In tropical Africa, little is known about which infections contribute to development of ARDs, and at which time.

Methods

We used latent class analysis to characterise the early infection-exposure of participants in a Ugandan birth cohort and assessed ARDs in later childhood.

Results

Of 2345 live births, 2115 children (90%) had data on infections within the first year of life while 1179 (50%) had outcome data at 9 years. We identified two latent classes of children based on first-year infection-exposure. Class 1 (32% membership), characterised by higher probabilities for malaria (80%), diarrhoea (76%), and lower respiratory tract infections (LRTI) (22%), was associated with lower prevalence of wheeze, eczema, rhinitis, and Dermatophagoides skin prick test (SPT) positivity at 9 years. Based on 5-year cumulative infection experience, class 1 (31% membership), characterised by higher probabilities for helminths (92%), malaria (79%), and LRTI (45%), was associated with lower probabilities of SPT positivity at 9 years.

Conclusions

In this Ugandan birth cohort, early childhood infection-exposure, notably to malaria, helminths, LRTI, and diarrhoea, is associated with lower prevalence of atopy and ARDs in later childhood.

Funding

This work was supported by several funding sources. The Entebbe Mother and Baby Study (EMaBS) was supported by the Wellcome Trust, UK, senior fellowships for AME (grant numbers 064693, 079110, 95778) with additional support from the UK Medical Research Council. LL is supported by a PhD fellowship through the DELTAS Africa Initiative SSACAB (grant number 107754). ELW received funding from MRC Grant Reference MR/K012126/1. SAL was supported by the PANDORA-ID-NET Consortium (EDCTP Reg/Grant RIA2016E-1609). HM was supported by the Wellcome's Institutional Strategic Support Fund (grant number 204928/Z/16/Z).

Is Adenoidectomy and/or Tonsillectomy a Risk Factor for Allergic Diseases and Asthma in Adulthood?

Objective

To determine the relationship between adenoidectomy and/or tonsillectomy in childhood and allergic diseases in adulthood.

Materials and Methods

A survey investigating the history of adenoidectomy and/or tonsillectomy was administered to patients that were followed-up by our department between January and June 2014 with the diagnosis of asthma, allergic rhinitis, urticaria-angioedema, drug allergy, food allergy, and venom allergy; patients willing to participate were included in the study. The relationship and risk ratios were analyzed.

Results

Totally, 510 (female/male: 379/131) patients were included in the study: 248 with asthma, 205 with rhinitis, 82 with drug allergy, 73 with urticaria, 24 with food allergy, and 14 with venom allergy. Of these, 65 (12.7%) had undergone adenoidectomy and/or tonsillectomy. Of these 65 patients, 41 had asthma, 33 had allergic rhinitis, and 28 had other allergic diseases. No relation between the history of atopy and adenoidectomy and/or tonsillectomy (p=0.129) was detected; however, there was a positive correlation between asthma and patients aged <15 years having a history of tonsillectomy and/or adenoidectomy (p=0.020). The risk of asthma was determined to be increased by 1.96 fold among the patients, provided the patient had undergone adenoidectomy and/or tonsillectomy (confidence interval [CI]:1.14-3.36). No connection was observed between atopic and non-atopic asthmatic patients in relation to adenoidectomy and/or tonsillectomy (p=0.46). No relationship was observed between allergic rhinitis and adenoidectomy and/or tonsillectomy.

Conclusion

Adenoidectomy and/or tonsillectomy in childhood increase the risk of asthma in adulthood, whereas it does not increase the risk of atopy. This result signifies the criticality of adenoidectomy or tonsillectomy in the pathogenesis of asthma.

Early daycare attendance increase the risk for respiratory infections and asthma of children

OBJECTIVES

To study the impact of daycare attendance on airways infections and "allergic" symptoms of children aged 1-8 years in Northeast Texas.

METHODS

Self-administrated questionnaires were distributed to parents through Women, Infants and Children offices, daycare centers, elementary schools, clinic centers, hospitals, and churches. The health outcomes consisted of "allergic" symptoms, and respiratory tract disorders. Questions on child care included; type of daycare settings (proxy for the number of children in daycare), time spent at daycare centers per week, and age of entry to a daycare center.

RESULTS

A total of 3766 children participated in this study, giving a response rate of 71%. Daycare attendance was associated with more frequent respiratory tract infections and "allergic" symptoms, compared to home care. A dose-response relationship between time spent at daycare centers and prevalence of respiratory tract disorders and asthma and allergies was observed. Earlier age exposure at daycare centers was a risk factor for rhinitis up to 7-8 years.

CONCLUSIONS

Daycare attendance had a substantial negative influence on health status of children aged 1-8 years in Northeast Texas.

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.

Effects of early measles on later rhinitis and bronchial hyperresponsiveness

BACKGROUND

The hygiene hypothesis suggests that infectious diseases in early life reduce the risk of allergic diseases.

OBJECTIVE

To investigate the association between measles infection during early childhood and the prevalence of allergic diseases, lung function, bronchial hyperresponsiveness (BHR), and sensitization in later childhood.

METHODS

A survey was conducted 5 years after a nationwide measles outbreak in Korea. From September 1 through November 30, 2006, we obtained information on history of measles and allergic diseases but not of measles vaccination through a questionnaire completed by 1004 schoolchildren aged 6 to 7 years. Furthermore, we measured measles antibody titers and performed skin prick tests, pulmonary function tests, and methacholine challenge tests. Children were divided into groups based on their history of measles infection and antibody titers.

RESULTS

Prevalence of measles infection was 8.2%. Children with both a positive measles history and a positive antimeasles antibody had significantly higher antimeasles antibody levels than those without a measles history. The prevalence of current rhinitis (adjusted odds ratio [aOR], 1.86; 95% confidence interval [CI], 1.02-3.40), rhinitis ever (aOR, 2.17; 95% CI, 1.19-3.94), and current BHR (aOR, 1.98; 95% CI, 1.04-3.78) was significantly higher in the group with a positive measles history compared with the group with a negative measles antibody. No differences were found among groups in the prevalence of asthma, lung function, provocation concentration that caused a decrease in forced expiratory volume of 1 second of 20%, or sensitization.

CONCLUSION

Early measles infection was associated with increased prevalence of rhinitis and BHR at the age of 7 years but has no effect on the development of asthma and allergy at the age of 7 years. This study indicates that common childhood infections such as measles in early age do not protect against later development of allergic diseases.

Allergic disease and atopic sensitization in children in relation to measles vaccination and measles infection

OBJECTIVE

Our aim was to investigate the role of measles vaccination and measles infection in the development of allergic disease and atopic sensitization.

METHODS

A total of 14 893 children were included from the cross-sectional, multicenter Prevention of Allergy-Risk Factors for Sensitization in Children Related to Farming and Anthroposophic Lifestyle study, conducted in 5 European countries (Austria, Germany, the Netherlands, Sweden, and Switzerland). The children were between 5 and 13 years of age and represented farm children, Steiner-school children, and 2 reference groups. Children attending Steiner schools often have an anthroposophic (holistic) lifestyle in which some immunizations are avoided or postponed. Parental questionnaires provided information on exposure and lifestyle factors as well as symptoms and diagnoses in the children. A sample of the children was invited for additional tests, and 4049 children provided a blood sample for immunoglobulin E analyses. Only children with complete information on measles vaccination and infection were included in the analyses (84%).

RESULTS

In the whole group of children, atopic sensitization was inversely associated with measles infection, and a similar tendency was seen for measles vaccination. To reduce risks of disease-related modification of exposure, children who reported symptoms of wheezing and/or eczema debuting during first year of life were excluded from some analyses. After this exclusion, inverse associations were observed between measles infection and "any allergic symptom" and "any diagnosis of allergy by a physician." However, no associations were found between measles vaccination and allergic disease.

CONCLUSION

Our data suggest that measles infection may protect against allergic disease in children.

Incidence of chickenpox in young South Korean soldiers and correlation with atopic dermatitis

BACKGROUND

In South Korea, military service is compulsory for all healthy young men and provides specific environmental factors, with groups working and living together in specific places for several years making varicella more transmissible to susceptible individuals. Studies of people serving in the South Korean military may provide information about the young adult male population in Korea.

AIM

To determine the relationship between chickenpox and atopic dermatitis (AD) in young adults over a period of 3 years.

METHODS

The computerized database of the Armed Forces Medical Command was examined to identify the number of reported cases of chickenpox, AD, and AD associated with chickenpox.

RESULTS

In total, 588 cases of chickenpox (183, 182 and 223 in the periods November 2004 to October 2005, November 2005 to October 2006, and November 2006 to October 2007, respectively) were reported. A greater number of patients were found to be infected with chickenpox in January and November, with fewer patients in August and September (P < 0.0001). Within the same periods, 1890, 2417 and 2779 patients diagnosed with AD were recorded in the Defense Medical Information System. Only 3 of 588 patients with chickenpox also had AD (0.5%).

CONCLUSION

In this population-based study, the epidemiological trend of chickenpox and AD over a period of 3 years within the military personnel of South Korea is shown.

Asthma and infectious respiratory disease in children--correlation to residence near hazardous waste sites

Rates of hospitalization for asthma and respiratory infectious disease in children were modeled as a function of residence: (1) in a zip code containing a hazardous waste site with persistent organic pollutants ('POPs'); (2) in a zip code with a waste site that did not contain POPs ('other'); or (3) in a zip code without any identified waste site ('clean'), as well as other demographic covariates. After adjustment, living in a zip code containing a POPs waste site significantly increased the frequency of hospitalization for asthma and infectious respiratory disease. Living in a zip code with an 'other' waste site also increased hospitalization frequencies for both diseases. The association was strongest for zip codes whose residents were in the lowest quartile of medium family income. This evidence supports the hypothesis that living near a hazardous waste site increases risk of respiratory disease in children.

Vaccinations, infections and antibacterials in the first grass pollen season of life and risk of later hayfever

BACKGROUND

It has been hypothesized that early-life exposure to vaccinations, infections or antibacterials influence allergic disease development. Concurrent exposure to grass pollens may alter any effect.

OBJECTIVE

To test the hypothesis that exposure to antibacterials, vaccinations (DTP or MMR) or specific infections during the first grass pollen seasons of life influences the risk of hayfever more than at any other time of the year.

METHODS

Nested case-control studies were based on birth cohorts within two large databases of computerized patient records from UK general practices: the General Practice Research Database (GPRD) and Doctors' Independent Network (DIN). Seven thousand ninety-eight hayfever cases, diagnosed after age 2, were matched to controls for practice, age, sex and follow-up of control to case ascertainment date. Conditional logistic regression was used to compare exposure by age 1 (age 2 for MMR) inside vs. outside the grass pollen season (May, June, July). Odds ratios (ORs) were pooled across databases.

RESULTS

There were no associations in either database between MMR during vs. outside the grass pollen season and later hayfever. Of 23 infections studied, none were statistically significant; although analyses for the less common conditions were limited by low statistical power. The pooled OR for hayfever comparing exposure to antibacterials only in the grass pollen season with only outside it was 1.20 (95% CI 0.98-1.47) and for DTP was 0.84 (95% CI 0.72-0.98).

CONCLUSION

Although an interaction between early exposure to microbial agents and concurrent grass pollen exposure on hayfever risk seemed plausible, there was little evidence to support it across a range of analyses. However, the effect of DTP though weak deserves further study.

Allergic sensitization and microbial load--a comparison between Finland and Russian Karelia

Epidemiological data have indicated that some infections are associated with a low risk of allergic diseases, thus supporting the idea (hygiene hypothesis) that the microbial load is an important environmental factor conferring protection against the development of allergies. We set out to test the hygiene hypothesis in a unique epidemiological setting in two socio-economically and culturally markedly different, although genetically related, populations living in geographically adjacent areas. The study cohorts included 266 schoolchildren from the Karelian Republic in Russia and 266 schoolchildren from Finland. The levels of total IgE and allergen-specific IgE for birch, cat and egg albumen were measured. Microbial antibodies were analysed against enteroviruses (coxsackievirus B4), hepatitis A virus, Helicobacter pylori and Toxoplasma gondii. Although total IgE level was higher in Russian Karelian children compared to their Finnish peers, the prevalence of allergen-specific IgE was lower among Russian Karelian children. The prevalence of microbial antibodies was, in turn, significantly more frequent in the Karelian children, reflecting the conspicuous difference in socio-economic background factors. Microbial infections were associated with lower risk of allergic sensitization in Russian Karelian children, enterovirus showing the strongest protective effect in a multivariate model. The present findings support the idea that exposure to certain infections, particularly in childhood, may protect from the development of atopy. Enterovirus infections represent a new candidate to the list of markers of such a protective environment. However, possible causal relationship needs to be confirmed in further studies.

Do vaccines modify the prevalence of asthma and allergies?

Epidemiological studies suggest the hypothesis that the increase in asthma and allergies in the industrialized world can be explained by a decline in the number of infectious diseases occurring during childhood. In the context of this 'hygiene hypothesis', is immunization in early life a risk factor for promoting allergic diseases? The majority of studies, especially those conducted with more extensive populations, have not found an increased risk, and although 'not finding an increased risk' is not the same as 'the non-existence of any risk at all', it seems that the evidence is tipped in favor of the absence of risk. Conversely, although some surveys have described a protective effect of vaccination, the majority refuted this result. If there is any effect, it is probably a weak one.

Childhood asthma and measles vaccine response

BACKGROUND

Asthmatic patients have a TH2-predominant milieu that is associated with humoral immunity. However, little is known about whether humoral immune responses to viral antigens differ between asthmatic and nonasthmatic children.

OBJECTIVE

To determine whether humoral immune response differs in asthmatic patients vs nonasthmatic patients.

METHODS

Measles virus specific IgG antibody levels were determined for the Rochester Family Measles Study cohort (n = 876), a convenience sample of healthy children 5 to 12 years of age in Rochester, MN. We conducted comprehensive medical record reviews of 838 children who were eligible for this study. We determined the child's asthma status at the time of determination of antibody levels by applying predetermined criteria for asthma. Comparisons were made using the 2-sample t test or chi2 test.

RESULTS

Of the 838 children, 156 (18.6%) had asthma at the time of the determination of antibody levels and were not taking systemic steroids within 14 days of specimen collection. Among those with a nonequivocal antibody reading, the seropositive response rates were similar in asthmatic patients and nonasthmatic patients (89.7% vs 90.3%, respectively; P = .83). However, the equivocal response rates were slightly higher among asthmatic patients than nonasthmatic patients (6.4% vs 4.7%, respectively).

CONCLUSION

Asthmatic children seem to have similar humoral immune responses to measles vaccine as those without asthma. Although the findings reassure health care practitioners, whether this finding is generalizable to other vaccines and whether asthmatic patients with low antibody levels have normal cell-mediated immunity need to be elucidated in future studies.

The role of respiratory viruses in the pathogenesis of pediatric asthma

The role of respiratory viral infection in the development of asthma remains unclear. A number of factors play crucial roles, including the type of virus, the severity of the disease, the time of the infection, and, most important, the host predisposition. On the other hand, there is little doubt that a strong association exists between viral respiratory infections and induction of wheezing illnesses and asthma exacerbations. The underlying mechanisms, although not fully clarified, are likely to be multifactorial, involving inflammation of the bronchial mucosa, which interacts under certain circumstances with allergic inflammation. In addition, repetitive infections play an important role in perpetuating inflammation and airway hyperresponsiveness, especially in the presence of atopy, leading from childhood asthma to a more persistent asthma phenotype.

Frequency of allergic diseases following measles

OBJECTIVE

Viral and bacterial infections in childhood decrease the likelihood of allergic diseases in later life. The frequency of allergic diseases in patients with a history of measles has been reported to be low but some studies still suggest that measles can increase the frequency of allergic diseases. The aim of this study was to investigate the frequency of allergic diseases following measles in childhood.

METHODS

Fifty-two children hospitalized in our clinic with measles were compared with 51 children without measles. Allergic diseases were investigated in both groups by using the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. In all children, allergy skin tests were performed with the four most common allergens.

RESULTS

Sensitivity to Dermatophagoides pteronyssinus was less frequent in children with measles than in those without (p < 0.05). A history of nebulized salbutamol use in the emergency room in the previous 12 months was also less frequent in the measles group (p < 0.05). Inhaled corticosteroid use was more common in the group without measles (p < 0.05).

CONCLUSION

The results of this study indicate that findings of allergic disease are less frequent in children with a history of measles. These children were less sensitive to D. pteronyssinus.

Too clean, or not too clean: the hygiene hypothesis and home hygiene

The 'hygiene hypothesis' as originally formulated by Strachan, proposes that a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings. Use of the term 'hygiene hypothesis' has led to several interpretations, some of which are not supported by a broader survey of the evidence. The increase in allergic disorders does not correlate with the decrease in infection with pathogenic organisms, nor can it be explained by changes in domestic hygiene. A consensus is beginning to develop round the view that more fundamental changes in lifestyle have led to decreased exposure to certain microbial or other species, such as helminths, that are important for the development of immunoregulatory mechanisms. Although this review concludes that the relationship of the hypothesis to hygiene practice is not proven, it lends strong support to initiatives seeking to improve hygiene practice. It would however be helpful if the hypothesis were renamed, e.g. as the 'microbial exposure' hypothesis, or 'microbial deprivation' hypothesis, as proposed for instance by Bjorksten. Avoiding the term 'hygiene' would help focus attention on determining the true impact of microbes on atopic diseases, while minimizing risks of discouraging good hygiene practice.

Day-care attendance and increased risk for respiratory and allergic symptoms in preschool age

BACKGROUND

The reported impact of day-care attendance on respiratory and atopic symptoms has varied between studies from different countries. Regarding to the 'hygiene-hypothesis', day-care attendance may lead to less sensitization later in life, but the question still is whether day-care attendance and subsequent exposure to more frequent early infections is a risk or a protection against future allergic disease or asthma (atopic and nonatopic).

METHODS

A cross-sectional postal questionnaire was replied by parents of 10,851 children, aged 1-6 years, in the year 2000 in a Swedish region (DBH-phase 1). The questionnaire focused on respiratory and atopic symptoms, the home environment and information on day care of the children.

RESULTS

Children in day care were reported to have more symptoms than children in home care: adjusted odds ratio (AOR) for wheezing last 12 months, AOR 1.33 (CI 95%: 1.12-1.58), cough at night apart from colds last 12 months AOR 1.56 (CI: 1.17-2.07), doctor diagnosed asthma AOR 1.23 (CI: 0.88-1.71), rhinitis last 12 months AOR 1.15 (CI: 0.92-1.44), doctor diagnosed hay fever AOR 1.75 (CI: 0.94-3.23), eczema last 12 months, AOR 1.49 (CI: 1.24-1.79), allergic reactions to foods, AOR 1.27 (CI: 1.07-1.52), >6 colds last 12 months of 2.57 (CI: 2.12-3.12) and ear infection ever AOR 2.14 (CI: 1.87-2.45). The increased risks were mainly seen and reached significance in the youngest group of children, aged 1-4 years. Adjusting and stratification for the number of airway infections last year did not change the risk associated with day-care attendance for allergic diseases.

CONCLUSIONS

Attending day care was associated with an increased risk of symptoms related to airways infections as well with eczema and allergic reactions to food. No sign of protection from day-care attendance for allergic diseases was found up to 6 years of age. Multiple airway infections and day-care attendance were found to be independently associated with asthma and allergic symptoms.

Atopy in Patients with Bronchiectasis: More than Coincidence

Bronchiectasis is common in developing countries, but its precise underlying mechanism can be detected in only about 40% of the cases. The studies reporting the frequency of atopy and its relation to radiological findings and lung function in bronchiectasis are limited in number, and the results are controversial. The present study was designed to investigate the relationship between atopy and bronchiectasis by means of high resolution computed tomography (HRCT) and pulmonary function tests. Skin prick test, HRCT and pulmonary function tests, including spirometric values of forced expiratory volume in one second (FEV1), FEV1/FVC (forced vital capacity) ratio were performed in 121 bronchiectatic patients of unknown etiology and in 68 healthy controls. Atopy and HRCT scores for the severity of atopy and extent of bronchiectasis respectively were determined for each patient. The rate of atopy (48.8% vs 11.8%) and mean atopy score (14.3 +/- 10.1 mm vs 5.5 +/- 2.1 mm) were significantly higher in patients with bronchiectasis than those in controls. Atopic patients had significantly worse spirometric values and more extended bronchiectasis than non-atopics. There is a significant correlation between atopy and HRCT scores (r = 0.54, p < 0.001), indicating that the more severe atopy is the more extended bronchiectasis. In conclusion, we suggest that the rate of atopy is higher in bronchiectatic patients than that in healthy controls. Bronchiectatic patients with atopy have lower spirometric values and higher HRCT scores. Atopy might be considered as a deteriorating and/or a causative or contributing factor for development of bronchiectasis.

Hope for the hygiene hypothesis: when the dirt hits the fan

The hygiene hypothesis was developed in response to data suggesting that the increase in allergic diseases as well as asthma was secondary to a reduced exposure to infectious stimuli. Indeed, the epidemiologic changes, resulting in an increase in atopic disease, have been impressive and intriguing. Furthermore, although there clearly is a genetic component to atopic diseases, genetics cannot account for a marked increase in the incidence and prevalence of allergic manifestations within a few generations. Thus, environmental factors have been suggested as responsible for the changing prevalence. There are two--not mutually exclusive--possibilities, namely, that substances that promote atopy have been added to the environment or that factors that provided protection from allergic disease were lost from the environment. Both outdoor and indoor pollution, along with a long list of other environmental factors, have been proposed. It is of interest that in many developed countries, certain types of pollution have decreased, whereas the prevalence of atopic disease has increased. In this review, we have explored a detailed analysis of a large number of studies that have focused on this issue and suggest that, although the hygiene hypothesis has merit, the stimuli responsible for the new epidemiology remain enigmatic.

Early respiratory infections, asthma, and allergy: 10-year follow-up of the Oslo Birth Cohort

OBJECTIVE

It has been hypothesized that early infections protect against the development of atopic disease, but there have been few long-term follow-up studies. We estimated the associations between early respiratory infections and doctor-diagnosed asthma, allergic rhinitis, and skin-prick sensitization in children at 10 years of age in the Oslo Birth Cohort, established in 1992-1993. We also considered birth order and attendance at a child care center as proxy measures of increased exposure to infections early in life.

METHODS

A total of 2540 children were followed from birth to the age of 10 years. Experiences of respiratory infections were recorded in follow-up surveys at 6 and 12 months. At age 10, questions were asked about current symptoms of asthma and allergic rhinitis and about having ever received a doctor diagnosis for these diseases. A subsample (n = 1740) of the cohort was tested for skin-prick test reactivity.

RESULTS

Current asthma was related to lower respiratory tract infection (adjusted odds ratio [OR]: 2.1; 95% confidence interval: 1.3-3.0) and croup (adjusted OR: 2.3; 95% confidence interval: 1.3-4.2) in the first year. ORs for allergic rhinitis and skin-prick sensitization were smaller but mainly positive. Birth order and child care attendance at age 1 year were not significantly associated with any of the studied outcomes.

CONCLUSIONS

Early respiratory infections did not protect against the development of asthma, allergic rhinitis, or sensitization to common allergens during the first 10 years of life but increased the risk for asthma symptoms at age 10 in this population.

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.

Ecological association between scarlet fever and asthma

One plausible explanation for the worldwide epidemic increase of asthma prevalence is the hygiene hypothesis, which suggests that better control of infections shifts the immune response toward an allergic phenotype. However, studies demonstrating an inverse association between asthma and infectious diseases are scarce and possess conflicting results. To explore the relationship between asthma and scarlet fever, an ecological analysis of their national trends was carried out. Association of both diseases in their annual (1996-2003), seasonal (by month) and geographic (by state) trends was evaluated using the Spearman's correlation coefficient (r(S)). Results showed a strong inverse association between asthma and scarlet fever in all settings. Thus, annual incidence rates of both diseases showed an r(S)=-0.93 (P=0.0009). Seasonal patterns showed a higher proportion of new asthma cases from September to January, while the number of scarlet fever cases increased from March to June (r(S)=-0.84, P=0.0006, 1-month lag). Among the 32 Mexican states, the higher the incidence of scarlet fever the lower the incidence of asthma (r(S)=-0.47, P=0.007). These results suggest that Streptococcus pyogenes, the causative agent of scarlet fever, might be one of the major protagonists of the hygiene hypothesis, a possibility deserving of further investigation.

Childhood infections and risk of wheezing and allergic sensitisation at age 7-8 years

BACKGROUND

Childhood atopic disease has been associated with exposure to infections early in life. There is however considerable controversy on this issue, since evidence exists for both protective and adverse effects of infections. Aim of this study was to investigate the association between childhood infections and the occurrence of wheeze and allergic sensitisation in 7-8-year-old Dutch and German children.

METHODS

A nested case-control study was conducted among German and Dutch children participating in a large longitudinal study on respiratory health. Parents of 510 7-8-year-old children with respiratory complaints and an equal number of children without respiratory complaints were asked to complete a questionnaire. Blood samples were collected for specific serum Immunoglobulin E (IgE) analysis. Data on childhood infections were collected through records of the participating Municipal Health Services.

RESULTS

No association was found between recent wheeze and any of the childhood infections investigated. For scarlet fever infection an increased risk of allergic sensitisation (OR: 2.82; 95% CI: 1.40-5.72) and sensitisation against grasses (OR: 3.00; 95% CI: 1.35-6.69) at the age of 7-8 years was found. Varicella infection tended towards increased risk of sensitisation against grasses (OR: 1.88; 95% CI: 0.99-3.58). For allergic sensitisation and sensitisation against grasses the odds ratios increased with increasing number of infections.

CONCLUSIONS

The results do not lend support to the suggestion that childhood infection protects against wheezing or allergic sensitisation at age 7-8 years. Scarlet fever or varicella infection presented an increased risk of allergic sensitisation.

Influence of MMR-vaccinations and diseases on atopic sensitization and allergic symptoms in Swiss schoolchildren

The prevalence of asthma and allergic disease has increased in many countries. It has been proposed that vaccinations may contribute to the development of allergic disease by reducing clinical infections in infancy or through the direct IgE-inducing effects of the vaccines. Evidence for a potential role of immunizations in the development of allergic disease is scarce. Therefore the objective was to study the associations between vaccinations against measles, mumps and rubella (MMR), natural infections of these diseases and atopic sensitization to indoor and outdoor allergens and allergic symptoms in schoolchildren. The cross-sectional study including 1537 8(th) grade school children aged 13-15 years living in 10 communities across Switzerland was organized in the framework of an environmental health surveillance program within the School Health Services (Swiss Surveillance Program of Childhood Asthma and Allergies with respect to Air Pollution and Climate, SCARPOL). Main outcome measures were asthma and sneezing during pollen season assessed by parental questionnaires and atopic sensitization determined by IgE concentrations to various allergens. It was found that parents' reported history of measles or mumps was associated with a stronger immune response than two or more vaccinations against the respective infection (measles: geometric mean IgG titers (GMT) lU/ml (95% Cl) 2.8 (2.0-3.9) vs. 1.2 (1.0-1.4), mumps: GMT PE/ml (95% Cl) 16.3 (13.9-19.1) vs. 8.5 (6.1-11.7). With respect to atopic sensitization similar associations for exposure by natural MMR-infections or MMR-vaccinations were found: measles: OR (95% Cl) 1.02 (0.53-1.96) vs. 1.22 (0.69-2.16), mumps: 0.59 (0.38-0.93) vs. 0.79 (0.49-1.27), rubella: 0.93 (0.61-1.43) vs. 0.95 (0.66-1.37), respectively. Inverse relationships were found between the risk of asthma and a positive disease history or vaccination of measles 0.36 (0.14-0.91) vs. 0.45 (0.21-0.98) or a positive serum titer against measles 0.65 (0.35-1.20). From the present study can be concluded that exposure by MMR-vaccinations or natural MMR-infections in childhood does not increase the risk of sensitization to common allergens as well as to allergic respiratory diseases. MMR-vaccinations or natural MMR-infections are therefore an unlikely factor contributing to the increase in atopic disease in developed countries.

The hygiene hypothesis of atopic disease--an extended version

The hygiene hypothesis of atopic disease suggests that environmental changes in the industrialized world have lead to reduced microbial contact at an early age and thus resulted in the growing epidemic of atopic eczema, allergic rhinoconjunctivitis, and asthma. The epidemiological findings have been combined with the Th1/Th2 paradigm of immune responsiveness to provide a coherent theory. Recent advances in epidemiology and immunology demonstrate, however, that the hygiene hypothesis may need to be extended in three respects. First, the importance of infections in causing immune deviance may be outweighed by other sources of microbial stimulation, perhaps most importantly by the indigenous intestinal microbiota. Second, immunomodulatory and suppressive immune responses complement the Th1/Th2 paradigm. Third, in addition to protection against atopy, protection against infectious, inflammatory, and autoimmune diseases may also depend upon healthy host-microbe interactions implicated in the hygiene hypothesis.

Age at bacille Calmette-Guérin vaccination and risk of allergy and asthma

BACKGROUND

It has been proposed that early age at bacille Calmette-Guérin (BCG) vaccination protects against the development of allergy.

OBJECTIVE

To study whether early age at BCG vaccination was associated with a decreased risk of atopy, allergic rhinitis, and asthma compared to BCG vaccination at later ages in childhood.

METHODS

The occurrence of atopy, allergic rhinitis, and asthma was studied in nearly 2000 women participating in the Danish National Birth Cohort study. Detailed information on age at BCG vaccination (age 0-15 years) was available from school health records. Atopic status was assessed serologically by a specific response to 11 common inhalant allergens using serum samples obtained from the women during the period 1997-2001. Information on allergic rhinitis and asthma was available from telephone interviews.

RESULTS

Approximately 85% of the women had been BCG-vaccinated. Age at BCG vaccination was not associated with risk of atopy, allergic rhinitis, or asthma. The odds ratio of atopy, allergic rhinitis, and asthma associated with being vaccinated during the first year of life was 1.05 (95% CI 0.71-1.56), 1.42 (95% CI 0.85-2.36), and 1.71 (95% CI 0.91-3.20), respectively, compared with being vaccinated at the age of 7 years. Adjustment for birth cohort, sibship size, age of the woman's mother at birth, and social class in childhood did not affect the results.

CONCLUSION

Our findings suggest that age at BCG vaccination in childhood does not influence the development of allergy or asthma.

Adenoidectomy during early life and the risk of asthma

The objective of the study was to evaluate the risk of asthma in children who had undergone an adenoidectomy, an operation frequently performed on children with glue ear or recurrent otitis media. Two surveys were carried out, a nation-wide questionnaire returned by 483 individuals (survey A) and a survey of hospital discharge records involving 1616 children who had undergone an adenoidectomy and 161 control children who had undergone probing of the nasolacrimal duct due to congenital obstruction (survey B). The questionnaire (survey A) showed that an adenoidectomy before the age of 4 years was associated with asthma (OR 3.19, 95% CI 1.25; 8.13) and with allergy to animal dust (OR 2.50, 95% CI 1.27; 4.95). In survey B, asthma diagnosis was retrieved from the national asthma register. It showed also that adenoidectomy at an early age was associated with an increased risk of asthma (OR 6.74, 95% CI 2.99; 15.2). There was an association between asthma and adenoidectomy, even before adenoidectomy had actually been performed. The risk of asthma was highest among children who had had adenoidectomy because of recurrent otitis media. The observed association between an adenoidectomy and asthma may be explained by an underlying factor predisposing to both recurrent otitis media and asthma.

The role of respiratory viruses in the origin and exacerbations of asthma

PURPOSE OF REVIEW

The present review focuses and comments on the increasing body of evidence correlating respiratory viral infections with asthma onset and exacerbations.

RECENT FINDINGS

Recent data suggest multiple and some time contrasting roles for viral infection in the origin of asthma. These data also indicate that the immune status of the host, including atopy, may interactively contribute to this process, conferring susceptibility or even resistance to the development of asthma in virus-infected individuals. In the presence of asthma, the role of viral infection in triggering exacerbations is clearly established. Chemokine and cytokine responses of the respiratory epithelium, a biased type 1/type 2 cytokine balance, defective costimulation, as well as abnormal neural control have been suggested as possible mechanisms. The importance of concurrent or synergistic effects of allergen exposure is currently under scrutiny.

SUMMARY

Viruses may initiate and certainly exacerbate asthma. Mild repeated infections early in life could also stimulate type 1 immune responses conferring protection from atopy and asthma. The host's immune status, the type of viral infection and the timing of exposure to various environmental stimuli are probably the key factors in this process. Mechanistic insights deduced from recent work should allow for the development of intervening strategies in the near future.