Does previous infection protect against atopic eczema and recurrent wheeze in infancy?

Association of antibiotics use in preschool age with atopic and allergic skin diseases in young adulthood: a population-based retrospective cohort study

BACKGROUND

Overuse and misuse of antibiotics is a public health problem in low-income and middle-income countries. Although the association of antibiotics with atopic and allergic diseases has been established, most studies focused on prenatal exposure and the occurrence of disease in infants or young children.

OBJECTIVE

To investigate the association of preschool use of antibiotics with atopic and allergic skin diseases in young adulthood.

DESIGN

Population-based retrospective cohort.

SETTING AND PARTICIPANTS

The first-year college students (n=20 123) from five universities were investigated. The sampled universities are located in Changsha, Wuhan, Xiamen, Urumqi and Hohhot, respectively.

METHODS

We conducted a dermatological field examination and a questionnaire survey inquiring the participants about the frequency of upper respiratory tract infection (URTI) and the preschool antibiotics use (prior to 7 years old). The two-level probit model was used to estimate the associations, and adjusted risk ratio (aRR) and 95% CI were presented as the effect size.

RESULTS

A total of 20 123 participants with complete information was included in the final analysis. The frequent antibiotics use intravenously (aRR 1.36, 95% CI 1.14 to 1.62) and orally (aRR 1.18, 95% CI 1.01 to 1.38) prior to 7 years old was significantly associated with atopic dermatitis in young adulthood. Similar trends could be observed in allergic skin diseases among those who use antibiotics orally and intravenously, with RRs of 1.16 (95% CI 1.01 to 1.34) and 1.33 (95% CI 1.13 to 1.57), respectively.

CONCLUSIONS

Preschool URTI and antibiotics use significantly increases the risk of atopic and allergic skin diseases in young adulthood.

Markers of microbial exposure lower the incidence of atopic dermatitis

BACKGROUND

The hygiene hypothesis proposes that reduced exposure to infectious agents in early life would explain the increase of allergic and autoimmune diseases observed over the past decades in high-income countries.

METHODS

We conducted a matched case-control study on incident atopic dermatitis (AD). Cases were 426 outpatient children with a first diagnosis of incident AD. Controls were 426 children attending a pediatric/dermatological visit for nonatopic disorders matched to cases (1:1). Particular attention was paid to the time elapsed between the markers of microbial exposure and disease onset, and we considered for controls the same time window of exposures from birth as his/her matched case. Odds ratios (ORs) were computed using multivariable conditional logistic regression models, according to center, sex, age, and period of enrollment, and including as potential confounders a family history of any allergy in parents, type of delivery, having siblings, keeping pets, age at weaning, and having had ≥4 infections.

RESULTS

The OR of AD first occurrence was 0.35 (P-value = .039) for children who had experienced ≥4 infections compared with those with no infections. A decreasing trend in risk was observed with increasing number of siblings (P-value = .023), the protective effect reaching about 40% for children with 2 or more siblings (OR = 0.62; P-value = .048). Pet keeping, in particular daily contact with dogs, was inversely associated with AD risk (OR = 0.40; P-value = .004).

CONCLUSIONS

These results support the hygiene hypothesis in its broad sense. Early-life environmental exposures, including pathogens and commensals, act as "microbes contact carriers" influencing immune system balance early in life.

Relationship between birth weight or fetal growth rate and postnatal allergy: A systematic review

BACKGROUND

Individual susceptibility to allergic diseases is developmentally programmed by early-life exposures. Evidence from preclinical studies suggests that intrauterine growth restriction is protective against later inflammatory responses to allergens.

OBJECTIVE

We sought to evaluate whether prenatal growth affects susceptibility to allergy in human subjects.

METHODS

We systematically searched for relevant studies in 11 databases, including Web of Science, ProQuest, EMBASE, and PubMed. We included only studies that corrected for gestational age or were restricted to full-term infants to separate effects of fetal growth from those of prematurity.

RESULTS

The 42 eligible studies included prospective and retrospective cohort, cross-sectional, and case-control studies. Only 2 studies reported allergic asthma. A birth weight increase of 1 kg was associated with a 44% greater risk of food allergy in children (odds ratio [OR], 1.44; 95% CI, 1.04-1.99; P = .001), a 17% greater risk of ever allergic dermatitis in children (OR, 1.17; 95% CI, 1.04-1.32; P = .008), and a 34% greater risk of ever or current allergic dermatitis in infants up to 2 years of age (OR, 1.34; 95% CI, 1.08-1.68; P = .009). Risks of allergic rhinitis were not associated with birth weight.

CONCLUSIONS

The results of these meta-analyses suggest that intrauterine growth restriction protects against allergic diseases in human subjects consistent with preclinical evidence but that effects might differ between allergic diseases. The strongest evidence is available for infancy and early childhood, and additional studies in older children and adults are needed to determine whether the effects of prenatal growth on each allergic disease persist or differ between those with severe and mild phenotypes.

Antimicrobial therapy in childhood asthma and wheezing

There is an increasing number of viral and bacterial pathogens suspected of contributing to asthma pathogenesis in childhood, making it more difficult for the practitioner to make specific therapy decisions. This review discusses the role of viruses, e.g. respiratory syncytial virus, human metapneumovirus, influenza viruses and rhinoviruses, as well as the role of the atypical bacteria Chlamydophila pneumoniae and Mycoplasma pneumoniae, as contributors to childhood asthma. Diagnosis, prevention, and therapy are discussed, including a summary of drugs, i.e. macrolide antibacterials, antivirals, and vaccine regimens already available, or at least in clinical trials. For the practitioner dealing with patients every day, drug regimens are assigned to the individual pathogens and an algorithm for the management of atypical infections in patients with asthma or recurrent wheezing is presented.

Infectious illness in children subsequently diagnosed with acute lymphoblastic leukemia: modeling the trends from birth to diagnosis

Although there is increasing evidence that immune dysregulation in children who develop acute lymphoblastic leukemia (ALL) is detectable from birth, debate about the role of infectious exposures in infancy continues. With the aim of quantifying children's infectious exposures, investigators have used a number of infection exposure proxies, but there is a lack of consistency in findings, with some markers indicating increased ALL risks and others decreased risks, the disparity being evident both within and between studies. Accordingly, the authors conducted an in-depth analysis of key infection exposure proxies used in the United Kingdom Childhood Cancer Study, a national population-based case-control study conducted over the period 1991-1996, which combined data from medical records, parental interview, and population census. This longitudinal approach revealed the marked deterioration in immune response that emerged around 5 months prior to ALL diagnosis and confirmed that infectious diagnoses in the first year of life were significantly increased (P < 0.05) in children who developed leukemia between 2 and 14 years of age, as well as in those who had birth orders >1, were not breastfed, lived in deprived areas, or were diagnosed with eczema. By contrast, no association between infectious illness and preschool activity was detected, the lower infection levels among controls whose mothers reported attendance contributing to a significantly reduced ALL odds ratio.

What do Kramer's Baby-Friendly Hospital Initiative PROBIT studies tell us? A review of a decade of research

BACKGROUND

Kramer et al's PROBIT (Promotion of Breastfeeding Intervention Trial) research in Belarus studied effects of the Baby-Friendly Hospital Initiative (BFHI) training on breastfeeding duration, exclusivity, and health outcomes.

AIMS

To critique inclusion criteria, context, approaches to data analysis, and health outcome results.

METHOD

Twenty-two articles were retrieved from PubMed and the PROBIT Website for 2001-2010; 6 were excluded as not focusing on breastfeeding and health outcomes.

RESULTS

PROBIT data from the cluster randomized hospital comparisons included only breastfed babies since all non-breastfed babies were excluded from the research. Context may affect outcomes, knowing that Belarus has good basic health services, 3-year maternity leaves with little use of daycare, 95% breastfeeding initiation rate, and a well-educated population. PROBIT data were analyzed in 2 ways: (a) intent-to-treat analyses of breastfeeding and health differences by cluster randomized intervention and control site mother/baby pairs; and (b) as an observational cohort study of health outcomes for all mother/baby pairs, analyzed by various breastfeeding categorizations and controlling for biases. PROBIT demonstrated links between BFHI and longer breastfeeding duration (19.7% vs 11.4% at 12 months, P < .001) and exclusivity (43.3% vs 6.4% at 3 months, P < .001), reductions in gastrointestinal episodes and rashes, higher verbal IQ scores, and longer exclusive breastfeeding rates for subsequent children but no statistically significant differences in the child's body mass index, blood pressure, or dental health.

CONCLUSION

PROBIT provides foundational evidence for BFHI policy and follow-up care. Knowing that non-breastfed babies were excluded, caution must be exercised for health comparisons.

The retrospective evaluation of pneumonia and bronchitis cases in infants and small children with atopic dermatitis in the practice of a family doctor - personal observations

PURPOSE

The purpose of the work is to estimate the occurrence of lower respiratory tract infections in infants and small children with atopic dermatitis and to compare them with a group of children at the same age without features of allergy.

MATERIAL AND METHODS

The study has been conducted on the basis of the retrospective analysis of medical documentation of individual history of disease among children born in 2005 - 2008 treated in an outpatient clinic.

RESULTS

Children suffering from atopic dermatitis are more prone to pneumonia and bronchitis. They are also more often hospitalized due to these reasons. Also, this group of patients is more liable to wheezing in the time of infection.

CONCLUSIONS

Infants and small children with atopic dermatitis are more prone to lower respiratory tract infections. Recurrence of infections within the respiratory system may be an important risk factor for asthma.

Neonatal sepsis and later development of atopy

BACKGROUND

The role of infections on the development of atopy is still widely debated. We aimed to evaluate the effects of neonatal severe sepsis and consequent antibiotic treatment on the development of atopy and allergic diseases.

MATERIAL AND METHODS

A retrospective enrollment at school age of children with a clear history of neonatal sepsis (NS) was performed from registers of neonatal intensive care units. A normal control was assigned to each patient with sepsis. Thirty six cases with sepsis (18 males, 18 females) and 36 controls (21 males, 15 females) were selected (8.5+/-3.6 yrs). Physical examination and lung function evaluation were performed. Atopic status was verified by blood eosinophil count, total IgE serum level and skin prick tests (SPT).

RESULTS

SPT positivity for at least one allergen was present in 30% of subjects in both groups. No difference for all investigated parameters between groups and no influence by other factors such as familiarity or gender was observed. No correlation was associated to NS history.

CONCLUSIONS

Neonatal sepsis, even if clinically severe and dramatic, could represent an event too limited and really precocious in life to influence the development of immune response. Furthermore, other factors, besides infections, may influence the atopic future of newborns.

The low prevalence of allergic disease in Eastern Europe: are risk factors consistent with the hygiene hypothesis?

BACKGROUND

The prevalence of allergic disease is known to be low in Eastern Europe.

OBJECTIVE

To assess the association of suspected risk factors, including several closely linked to the hygiene hypothesis, with allergic symptoms and atopic sensitization in young school-aged children.

METHODS

Observational study of 13 889 Belarusian children followed up at age 6.5 years in the Promotion of Breastfeeding Intervention Trial (PROBIT). Allergic symptoms and diseases were based on parental responses to the International Study of Asthma and Allergy in Childhood questionnaire, and prick tests to five common inhalant allergens were performed using standard methods.

RESULTS

Significantly increased risks of wheezing and hayfever symptoms in the past 12 months, and of recurrent itchy rash were observed in boys, children with a positive first-degree family atopic history, and those who had received probiotics (especially as prophylaxis with antibiotic use). Pet ownership, contact with farm animals, the presence and number of younger and (especially) older siblings, and residency in rural areas of Western Belarus were associated with reduced risks. Maternal postnatal smoking was associated with wheezing and hayfever symptoms, while the duration of exclusive breastfeeding was not protective against any of the studied outcomes. The risk factors for allergic symptoms were similar in children with positive skin-prick tests to those in the overall cohort.

CONCLUSION

Many of the risk and protective factors we identified are consistent with those reported in Western countries and with the hygiene hypothesis. Further research on dietary and other environmental and genetic factors is necessary to understand the low prevalence of allergic disease in Belarus and other Eastern European countries.

The prevalence, characteristics of and risk factors for eczema in Belgian schoolchildren

Childhood eczema is common in infants, but its nature and extent during later childhood remains unclear. In this cross-sectional study we examined the prevalence and characteristics of eczema in an unbiased community population of 2,021 Belgian schoolchildren, aged 3.4 to 14.8 years with skin prick testing and parental questionnaires. Our study identified an eczema prevalence of 23.3% and a considerable allergic comorbidity, mainly in sensitized children. The reported prevalence of eczema in infancy was 18.5% and for current eczema 11.6%. The overall sensitization rate (33.2%) as well as sensitization rates for the individual allergens were significantly higher in children with "eczema ever." Sensitization to Dermatophagoides pteronyssinus (19.6%), mixed grass pollen (15.1%), and cat (9.1%) were most common. Until the age of 6 years, boys with eczema were significantly more sensitized than girls (p = 0.007). Children with both eczema in infancy and current eczema show a tendency to be more sensitized than children with eczema in infancy only or current eczema only, but significance was only noted for a few individual allergens. Analysis of factors associated with eczema revealed a predominantly atopic profile characterized by family or personal history of allergy. Breastfeeding and environmental factors seemed to assume little relevance except for a protective effect of prematurity and having a dog at birth.

Dental caries and allergic disorders in Japanese children: the Ryukyus Child Health Study

BACKGROUND

Dental caries is an infectious disease and is highly prevalent among children. In the etiology of allergic diseases, the hygiene hypothesis contends that infections might confer protection against the development of allergic diseases. The aim of this cross-sectional study was to investigate the association between dental caries and the prevalence of allergic disorders.

METHODS

Study subjects were 21,792 children 6 to 15 years of age in Okinawa, Japan. Outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Data on dental caries were obtained from school records. Children were classified as having dental caries if one or more teeth had decayed and/or had been filled. Adjustment was made for sex, age, region of residence, number of siblings, smoking in the household, paternal and maternal history of asthma, atopic eczema, or allergic rhinitis, and paternal and maternal educational level.

RESULTS

The prevalence of wheeze, asthma, atopic eczema, and allergic rhinoconjunctivitis in the previous 12 months was 10.8%, 7.6%, 6.8%, and 7.6%, respectively. In an overall analysis, no measurable relationship was found between dental caries and the prevalence of wheeze, asthma, atopic eczema, or allergic rhinoconjunctivitis. However, dental caries was significantly inversely associated with the prevalence of allergic rhinoconjunctivitis only among children with a positive parental allergic history: The adjusted odds ratio was 0.84 (95% confidence interval: 0.72, 0.99).

CONCLUSIONS

The present findings do not support the hypothesis that dental caries was protective against allergic diseases. However, a parental allergic history may affect the association between dental caries and allergic rhinoconjunctivitis.

Probiotics and the skin

A review of the relationships between probiotics and the skin is presented. After a brief historical introduction, the main pathophysiological data on intestinal microflora, the immune system and the skin are presented. Clinical studies with probiotics in atopic children are discussed in detail. Many experimental studies have found that probiotics exert specific effects in the luminal lumen and on epithelial cells and immune cells with antiallergic potential. Not all probiotics have the same immunological properties. Moreover, although rarely, complications of probiotic use can occur and must be known and taken into account. This review underlines the potential interest in probiotics for the management of skin pathology.

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.

House cleaning with chlorine bleach and the risks of allergic and respiratory diseases in children

Chlorine bleach or sodium hypochlorite can inactivate common indoor allergens. In this cross-sectional study we evaluated to what extent regular house cleaning with bleach can influence the risks of respiratory and allergic diseases in children. We studied a group of 234 schoolchildren aged 10-13 yr among whom 78 children were living in a house cleaned with bleach at least once per week. Children examination included a questionnaire, an exercise-induced bronchoconstriction test and the measurement of exhaled nitric oxide (NO) and of serum total and aeroallergen-specific immunoglobulin (Ig)E, Clara cell protein (CC16) and surfactant-associated protein D (SP-D). Children living in a house regularly cleaned with bleach were less likely to have asthma (OR, 0.10; CI, 0.02-0.51), eczema (OR, 0.22; CI, 0.06-0.79) and of being sensitized to indoor aeroallergens (OR, 0.53; CI, 0.27-1.02), especially house dust mite (OR, 0.43; CI, 0.19-0.99). These protective effects were independent of gender, ethnicity, previous respiratory infections, total serum IgE level and of family history of allergic diseases. They were however abolished by parental smoking, which also interacted with the use of bleach to increase the risk of recurrent bronchitis (OR, 2.03; CI, 1.12-3.66). House cleaning with bleach had effect neither on the sensitization to pollen allergens, nor on the levels of exhaled NO and of serum CC16 and SP-D. House cleaning with chlorine bleach appears to protect children from the risks of asthma and of sensitization to indoor allergens while increasing the risk of recurrent bronchitis through apparently an interaction with parental smoking. As chlorine bleach is one of the most effective cleaning agent to be found, these observations argue against the idea conveyed by the hygiene hypothesis that cleanliness per se increases the risk of asthma and allergy.

Benefits and risks of breastfeeding

In the absence of significant, unpreventable risks, breastfeeding should be the norm for the nourishment of human infants and should, therefore, be encouraged for populations in all countries. Continued efforts of international and national agencies and healthcare professionals to aid and abet breastfeeding, reduce the risks that occur in some women during breastfeeding, provide the safest substitutes for human milk when that is necessary, and encourage further research into the posed questions should considerably improve the health of many children.

Effect of neonatal sepsis on the development of allergies and asthma in later childhood

BACKGROUND

Exposure to large amounts of endotoxins and other bacterial products in early childhood may protect against the development of allergic diseases later in childhood. The aim of this study was to investigate the effects of neonatal sepsis on subsequent development of asthma, allergic rhinitis, and atopic dermatitis in children.

METHODS

We recruited 85 children (mean age 48.67 +/- 12.88 months) who had been hospitalized for sepsis in their neonatal period and their siblings (n = 85) as controls (mean age 61.81 +/- 21.34 months) to investigate the prevalences of asthma, atopic dermatitis and allergic rhinitis. After asking the questions in the International Study of Asthma and Allergies in Children (ISAAC) questionnaires to the parents, total IgE levels in sera were measured and skin prick tests were performed.

RESULTS

Children with neonatal sepsis had lower total IgE levels and less sensitivity to Dermatophagoides pteronyssinus than controls (25.9 vs. 9.4%, p = 0.003). In addition, wheeze ever, wheeze in the last 12 months, physician-diagnosed asthma, and use of asthma drugs were less common in these subjects. Prevalences of allergic rhinitis and atopic dermatitis were equal in both groups.

CONCLUSION

Exposure to severe infections such as sepsis in the neonatal period may decrease sensitization to environmental allergens and prevalence of asthma in later childhood.

Chlorinated pool attendance, atopy, and the risk of asthma during childhood

The pool chlorine hypothesis postulates that the rise in childhood asthma in the developed world could result at least partly from the increasing exposure of children to toxic gases and aerosols contaminating the air of indoor chlorinated pools. To further assess this hypothesis, we explored the relationships between childhood asthma, atopy, and cumulated pool attendance (CPA). We studied 341 schoolchildren 10-13 years of age who attended at a variable rate the same public pool in Brussels (trichloramine in air, 0.3-0.5 mg/m3). Examination of the children included a questionnaire, an exercise-induced bronchoconstriction (EIB) test, and the measurement of exhaled nitric oxide (eNO) and total and aeroallergen-specific serum IgE. CPA by children (range, 0-1,818 hr) emerged among the most consistent predictors of asthma (doctor diagnosed or screened with the EIB test) and of elevated eNO, ranking immediately after atopy and family history of asthma or hay fever. Although the risk of elevated eNO increased with CPA [odds ratio (OR) = 1.30; 95% confidence interval (CI), 1.10-1.43] independently of total or specific serum IgE, the probability of developing asthma increased with CPA only in children with serum IgE > 100 kIU/L (OR for each 100-hr increase in CPA = 1.79; 95% CI, 1.07-2.72). All these effects were dose related and most strongly linked to pool attendance before 6-7 years of age. Use of indoor chlorinated pools especially by young children interacts with atopic status to promote the development of childhood asthma. These findings further support the hypothesis implicating pool chlorine in the rise of childhood asthma in industrialized countries.

Atopic dermatitis, extrinsic atopic dermatitis and the hygiene hypothesis: results from a cross-sectional study

BACKGROUND

Atopic Dermatitis (AD), hayfever and asthma are commonly summarized as atopic diseases. The spatial distribution of AD differs from that of asthma and hayfever, suggesting that AD might follow a different risk pattern than these diseases. AD can be differentiated into an allergic extrinsic form (EAD) and a non-allergic intrinsic form (IAD). Only EAD might follow the distribution and risk pattern that have been ascribed to asthma and hayfever.

OBJECTIVE

To investigate the distribution and risk factor profile of AD and EAD focusing on environmental factors relating to the hygiene hypothesis.

METHODS

Population-based cross-sectional study on 12,601 children aged 5-7 and 9-11 years from Dresden (Eastern Germany) and Munich (Western Germany). Information was obtained by International Study of Asthma and Allergic Childhood questionnaires, dermatological examinations and skin prick testing. AD-diagnosis ever, current AD-symptoms and visible eczema were investigated with their respective extrinsic forms.

RESULTS

Maternal and paternal history of AD were equally strong determinants of the child's AD status. Factors related to the hygiene hypothesis like day-care attendance and number of older siblings were not associated with a decreased risk of AD. The proportion of EAD within AD was higher in Eastern than in Western Germany. The determinants of the diseases appeared to be similar for both EAD and IAD.

CONCLUSIONS

There was no evidence of the hygiene hypothesis holding true for AD or EAD. AD might be a separate entity than respiratory atopic diseases. Little is known about the risk factors of AD and factors different from those of respiratory allergic diseases should be considered in future research.

Hospital admission with neonatal sepsis and development of atopic disease: Is there a link?

The role of suspected or confirmed neonatal sepsis in modifying the risk of atopic disease during childhood was assessed. Children with early-onset neonatal sepsis were identified from a cohort of neonates, hospitalized between 1990 and 1995. Of 196 individuals, 140 were recruited (71.4%). Pre- and postnatal history was ascertained from neonatal medical records. Based on clinical symptoms and a positive blood culture or at least three of initially defined laboratory or bacteriological criteria, they were stratified in either confirmed neonatal sepsis (CS) or suspected sepsis (SS) group. A control group (C) comprised children who were never hospitalized during infancy (n = 696). Primary end-point was the development of atopic dermatitis, bronchial asthma or allergic rhinitis during childhood (mean age 8.4 yr, range 5.7-12.4). CS and SS children had a higher prevalence of atopic dermatitis (CS 15.7%, SS 21.4%) compared with controls (C 5.2%, p < 0.001). Similarly, children with SS (7.1%), but not with CS (4.3%) had significantly more often a doctor's diagnosis of bronchial asthma compared to controls (1.9%, p = 0.02). No difference in the prevalence of allergic rhinitis was observed (CS 4.3%, SS 10%, C 8.3%). After adjusting for parental history of atopic disease and demographic factors, no significant difference for the risk to develop atopic dermatitis, asthma or allergic rhinitis among the groups was calculated in children with normal birth weight (>2500 g). Our data failed to show a possible link between hospital admission with SS and development of atopic disease.

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.

The asthma epidemic and our artificial habitats

Background

The recent increase in childhood asthma has been a puzzling one. Recent views focus on the role of infection in the education of the immune system of young children. However, this so called hygiene hypothesis fails to answer some important questions about the current trends in asthma or to account for environmental influences that bear little relation to infection.

Discussion

The multi-factorial nature of asthma, reflecting the different ways we tend to interact with our environment, mandates that we look at the asthma epidemic from a broader perspective. Seemingly modern affluent lifestyles are placing us increasingly in static, artificial, microenvironments very different from the conditions prevailed for most part of our evolution and shaped our organisms. Changes that occurred during the second half of the 20th century in industrialized nations with the spread of central heating/conditioning, building insulation, hygiene, TV/PC/games, manufactured food, indoor entertainment, cars, medical care, and sedentary lifestyles all seem to be depriving our children from the essential inputs needed to develop normal airway function (resistance). Asthma according to this view is a manifestation of our respiratory maladaptation to modern lifestyles, or in other words to our increasingly artificial habitats. The basis of the artificial habitat notion may lie in reduced exposure of innate immunity to a variety of environmental stimuli, infectious and non-infectious, leading to reduced formulation of regulatory cells/cytokines as well as inscribed regulatory pathways. This could contribute to a faulty checking mechanism of non-functional Th2 (and likely Th1) responses, resulting in asthma and other immuno-dysregulation disorders.

Summary

In this piece I discuss the artificial habitat concept, its correspondence with epidemiological data of asthma and allergy, and provide possible immunological underpinning for it from an evolutionary perspective of health and disease.