Does early exposure to cat or dog protect against later allergy development?

The role of immunoglobulin E in allergy and asthma

It has been nearly a century since the first suggestion that a soluble factor in plasma or serum might be responsible for the symptoms of allergic disease and asthma, and more than 30 yr since immunoglobulin E (IgE) was identified as the key molecule in mediating what are now described as type 1 hypersensitivity reactions (allergic asthma, allergic rhinitis, food allergy, atopic dermatitis, some forms of drug allergy, and insect sting allergy). Since that time, many of the details of the inflammatory cascade underlying allergy and asthma have been elucidated, and IgE is now known to play a key upstream role. The goals of this report are to review the cellular and molecular events set in motion by IgE and to examine the evidence for its participation in both the immediate allergic response and the late-phase or chronic inflammatory response in the skin and lungs.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Decreased prevalence of sensitization to cats with high exposure to cat allergen

We investigated the relationship between current exposure to cat allergen and sensitization to cats. A questionnaire was administered and skin prick testing and home visits for collection of dust samples (Fel d 1; ELISA) were performed in 2502 adults (mean age, 31.8 years; age range, 18-58 years; 1251 women). The results for Fel d 1 in relation to sensitization to cats were analyzed for 10 deciles of cat allergen exposure (cut points [microg/g]: 0.05, 0.34, 0.48, 0.72, 1.13, 1.92, 7.2, 44, 151). The prevalence of sensitization to cat was significantly decreased in the lowest and the highest exposure groups. In the multivariate regression analysis (age, sex, socioeconomic status, and current smoking being adjusted for), the risk of sensitization to cats was significantly increased with medium exposure to Fel d 1 (3rd centile, OR 2.3, 95% CI 1.2-4.4, P =.01; 4th centile, OR 2.1, 95% CI 1.1-4.0, P =.03; 5th centile, OR 2.2, 95% CI 1.2-4.3, P =.04, 6th centile, OR 2.5, 95% CI 1.3-4.9, P =.005). These results indicate that the prevalence of sensitization to cat is decreased in the lowest and highest cat allergen exposure groups.

Factors related to allergic sensitization to aeroallergens in a cross-sectional study in adults: The Copenhagen Allergy Study

BACKGROUND

The factors underlying recent increases in the prevalence of respiratory allergy are largely unknown.

OBJECTIVE

To assess the association between allergic sensitization and several lifestyle/environmental factors.

METHODS

A cross-sectional population-based study of 15-69-year-olds in Copenhagen was carried out in 1990. The participation rate was 77.5% (1112/1435). Different lifestyle/environmental factors (explanatory variables) were defined based on questionnaire data. Dependent (outcome) variables were skin prick test (SPT) positivity or specific IgE positivity to common aeroallergens. Explanatory variables associated with outcome in univariate analysis (P < 0.25) were selected for multivariate analysis. Subsequently, a final model for each dependent variable was obtained by stepwise regression analysis (cut-off for entry/removal of variables: P < 0.1).

RESULTS

Male sex, young age, low number of siblings, a positive family history of hay fever and never smoking, were independently associated with both SPT positivity and specific IgE positivity. Furthermore, SPT positivity was positively associated with alcohol consumption (dose-response relationship only), and negatively associated with previous keeping of a dog in the household. The association between alcohol consumption and SPT positivity was mainly due to the consumption of wine and remained after adjustment for educational level. Specific IgE positivity was furthermore associated with body mass index with no apparent dose-response relationship.

CONCLUSION

Being male, young age, a positive family history of hayfever, low number of siblings and never smoking, were independently associated with allergic sensitization. In addition, the results indicated a possible relationship of alcohol consumption, body mass index and previous keeping of a dog in the household to allergic sensitization. There is a need for prospective studies of risk factors for respiratory allergy.

Pet allergen levels in homes in Ghana and the United Kingdom

The frequency of cat and/or dog ownership in Ghana is comparable to that in the United Kingdom (approximately 50%). However, in Ghanaian communities pets are predominantly kept outdoors. Levels of pet allergens (Fel d 1 and Can f 1) in 100 Ghanaian homes (49 without pets) were compared with levels in 410 homes in the United Kingdom (258 without pets). Homes with pets in the United Kingdom contained much higher allergen levels than homes with pets in Ghana (for Fel d 1: mean difference, 275-fold; 95% CI, 129-fold to 594-fold; P <.0001; for Can f 1: mean difference, 75-fold; 95% CI, 33-fold to 169-fold; P <.0001). Homes without cats in the United Kingdom contained significantly higher levels of Fel d 1 than homes with cats in Ghana (mean difference, 3.7-fold; 95% CI, 2.0-fold to 7.2-fold; P <.0001). In the United Kingdom, homes with dogs contained 75-fold (95% CI, 47-fold to 139-fold) more Can f 1 than homes without dogs, whereas in Ghana, homes with dogs contained 3.1-fold (95% CI, 1.5-fold to 6.1-fold; P =.003) more Can f 1 than homes without dogs. In the United Kingdom, homes with cats contained 77-fold more Fel d 1 (95% CI, 46-fold to 129-fold; P <.0001) than homes without cats; there was no difference in cat allergen levels between homes with cats and homes without cats in Ghana. In conclusion, levels of pet allergens in Ghanaian homes with pets were (1) between 75-fold (dog) and 275-fold (cat) lower than levels in homes with pets in the United Kingdom and (2) lower than or comparable to levels in homes without pets in the United Kingdom.

Allergic rhinoconjunctivitis, eczema, and sensitization in two areas with differing climates

In this 5-year follow-up study we compared the prevalence of allergic rhinoconjunctivitis, eczema, and sensitization, in relation to several background factors, in two Swedish regions (Göteborg and Kiruna). In Göteborg, a city on the southwest coast, the climate is mild and humid. Kiruna is a town north of the Arctic Circle. Questionnaire replies and results of interviews were collected from all 412 7-8-year-old children of a population-based sample (203 in Göteborg and 209 in Kiruna); in addition, 192 children from Göteborg and 205 from Kiruna were skin-prick tested for sensitization to common aero-allergens. After 5 years, at 12-13 years of age, almost all of the initial study cohort were re-investigated. At follow-up the prevalence of allergic rhinoconjunctivitis was 17%, eczema 23%, and sensitization 32%. Allergic rhinoconjunctivitis and eczema were as common in Göteborg as in Kiruna, whereas sensitization was far more common in Kiruna. Children born during the pollen season had allergic rhinoconjunctivitis less often -- and were sensitized to pollen and animal protein less often -- than those born during the rest of the year. Sensitization to birch pollen, cat protein, and horse protein was less common in children living in Göteborg, the region with the highest frequency of cat ownership and horseback riding, and with the longest birch-pollen season. The girls were more commonly horseback riders but the boys were more often sensitized to horses. The results reinforce our previous findings: indoor climate may affect the development of sensitization and allergic diseases, to some extent independently; and if exposure to antigen is unavoidable, high doses might be better than low doses.

Effect of environmental manipulation in pregnancy and early life on respiratory symptoms and atopy during first year of life: a randomised trial

BACKGROUND

Asthma places huge demands on health-care services, and its prevalence is increasing. Reduction of exposure to environmental allergens could offer a realistic chance for primary prevention. Our aim was to ascertain whether or not living in a low-allergen environment reduces the risk of asthma and atopic diseases in infants.

METHODS

We assigned infants to four risk groups according to parental atopic status. We enrolled 291 high-risk couples (both parents atopic, no pets) into a prospective, prenatally randomised, cohort study, and allocated them to environmental manipulation, in which measures to reduce prenatal and postnatal allergen exposure were undertaken (active HRA) (n=145) or no intervention (control HRC) (n=146). Two further prospective groups were studied: 161 high-risk infants with pets in the home (HRP group) and 168 low-risk infants, whose parents were both non-atopic (LR group). The main outcome measures were signs and symptoms of atopic disease at 1 year of age.

FINDINGS

103 families dropped out or were lost to follow up. At age 1 year we followed-up 133 HRA, 118 HRC, 140 HRP, and 126 LR infants. Children in the HRA group were less likely to have respiratory symptoms during the first year of life than those in the HRC group. The most pronounced differences were in the relative risks for severe wheeze with shortness of breath (relative risk 0.44 [95% CI 0.20-1.00]), prescribed medication for the treatment of wheezy attacks (0.58 [0.36-0.95]), and wheezing after vigorous playing, crying, or exertion (0.18 [0.04-0.79]). Probability of respiratory symptoms in HRC and HRP infants was similar, whereas it was much lower in the LR than in the HRC group. Cat ownership was significantly associated with sensitisation to cats (24.6 [3.04-199.05]; p=0.003).

INTERPRETATION

Environmental manipulation reduces some respiratory symptoms in the first year of life in high-risk infants. Further follow up is needed, however, to ascertain whether living in a low-allergen environment reduces allergy and asthma in later life.

Asthma and indoor environment in Nepal

BACKGROUND

The development of asthma seems to be influenced by the adoption of a Western lifestyle. A study was undertaken to assess the importance of indoor environmental factors in Nepal where the lifestyle and home environment differ from that in the West.

METHODS

The home environment of 121 schoolchildren with asthma and 126 controls aged 11-17 years was studied. The homes of all participants were investigated and the children and their mothers were interviewed using a standardised questionnaire. Cases and controls were identified from an ISAAC (International Study of Asthma and Allergy in Childhood) based population study of 2330 schoolchildren in Kathmandu, Nepal.

RESULTS

Keeping cattle inside the house during the night was related to a lower risk for having asthma (adjusted odds ratio (OR) 0.2 (95% CI 0.1 to 0.5)) while there was no association between asthma and cattle kept outside. Asthma was associated with cigarette smoking by two or more family members (OR 1.9 (95% CI 1.0 to 3.9)) and with the domestic use of smoky fuels (OR 2.2 (95% CI 1.0 to 4.5)). In analyses stratified by sex, passive smoking and the use of smoky fuels were significantly associated with asthma only in boys.

CONCLUSIONS

The risk of asthma in Nepalese children was lower in subjects exposed to cattle kept inside the house and higher in subjects exposed to passive smoking and indoor use of smoky fuels. Childhood exposure to microorganisms or allergens from cattle may protect against the development of atopic disease.

Influence of early and current environmental exposure factors on sensitization and outcome of asthma in pre-school children

BACKGROUND

Exposure to furred pets in early life has been considered to increase the risk of allergic sensitization and consequent development of asthma later in children. However, recently, it has been suggested that early exposure to pets prevents sensitization. The aim of this study was to evaluate the importance of early exposure to pets and other environmental risk factors in asthmatic children.

METHODS

This is a follow-up study after 2 years of a previously investigated group of 193 asthmatic children, aged 1-4 years. The study was completed by 181 children, who were clinically examined; serum IgE antibodies were also measured and a questionnaire was answered.

RESULTS

Children with reported exposure to cats during the first 2 years of life were more likely to have developed sensitization to cat by 4 years of age than unexposed children. High levels of cat allergen (Fel d 1> or =8 microg/g dust) were associated with an increased risk of sensitization to cat and, in combination with tobacco smoke, also with the development of more severe asthma.

CONCLUSION

In young asthmatic children, early exposure to cat and tobacco smoke increased the risk of allergic sensitization and further development of more severe asthma later in childhood.

Asthma and indoor environment in Nepal

BACKGROUND

The development of asthma seems to be influenced by the adoption of a Western lifestyle. A study was undertaken to assess the importance of indoor environmental factors in Nepal where the lifestyle and home environment differ from that in the West.

METHODS

The home environment of 121 schoolchildren with asthma and 126 controls aged 11–17 years was studied. The homes of all participants were investigated and the children and their mothers were interviewed using a standardised questionnaire. Cases and controls were identified from an ISAAC (International Study of Asthma and Allergy in Childhood) based population study of 2330 schoolchildren in Kathmandu, Nepal.

RESULTS

Keeping cattle inside the house during the night was related to a lower risk for having asthma (adjusted odds ratio (OR) 0.2 (95% CI 0.1 to 0.5)) while there was no association between asthma and cattle kept outside. Asthma was associated with cigarette smoking by two or more family members (OR 1.9 (95% CI 1.0 to 3.9)) and with the domestic use of smoky fuels (OR 2.2 (95% CI 1.0 to 4.5)). In analyses stratified by sex, passive smoking and the use of smoky fuels were significantly associated with asthma only in boys.

CONCLUSIONS

The risk of asthma in Nepalese children was lower in subjects exposed to cattle kept inside the house and higher in subjects exposed to passive smoking and indoor use of smoky fuels. Childhood exposure to microorganisms or allergens from cattle may protect against the development of atopic disease.

Metropolitan home living conditions associated with indoor endotoxin levels

BACKGROUND

Household endotoxin exposure in allergy and asthma has been gaining attention for its dual potential to exacerbate these conditions in individuals with established disease and to abrogate atopy before disease onset.

OBJECTIVE

We sought to better understand the home environmental and lifestyle factors influencing house dust endotoxin levels.

METHODS

From the homes of 86 infants with wheeze in metropolitan Denver, Colorado, house dust endotoxin (detected with a standardized Limulus Amebocyte Lysate assay) and common indoor allergen (Fel d 1, Can f 1, Der p 1, Der f 1, and Bla g 1) contents were quantified. Comprehensive home environment and lifestyle questionnaires were completed during home visits by trained study staff and parents.

RESULTS

House dust endotoxin levels were associated with only 2 home environmental features: animals in the home and the presence of central air conditioning. The strongest positive associations were found with animals in the home. Interestingly, the homes without cats or other animals revealed a negative correlation between house dust Fel d 1 and endotoxin (P =.03). Central air conditioning, especially during months of typical use, was associated with lower house dust endotoxin levels. No significant associations between house dust endotoxin levels and home dampness, number of household inhabitants or young children, cleaning frequency, or presence of tobacco smokers in the home were found.

CONCLUSIONS

Indoor endotoxin exposure can be increased by the presence of animals in the home and decreased with central air conditioning. In some homes without animals, where allergen exposure adequate for sensitization still occurs, there are lower levels of house dust endotoxin. Therefore in homes without animals, factors that influence allergen and endotoxin levels in house dust probably differ. Households with detectable allergen levels but low endotoxin levels may provide a predisposing environment for animal allergen sensitization.

Exposure to pets and atopy-related diseases in the first 4 years of life

BACKGROUND

It is still unclear how early-life exposure to pets is related to children's risk of developing atopy-related diseases. We estimated associations between early-life exposure to pets and atopy-related diseases at 0-4 years of life in a cohort of Norwegian children.

METHODS

A population-based cohort of 2531 children born in Oslo, Norway, was followed from birth to the age of 4 years. Information on early-life exposure to pets, a number of possible confounders, and atopy-related diseases was mainly collected by questionnaire.

RESULTS

In logistic regression analysis adjusting for potential confounders, the odds ratio for being exposed to pets in early life (reference category: not exposed) was, for bronchial obstruction at 0-2 years of life, 1.2 (95% confidence interval 0.9, 1.8); for asthma at the age of 4 years, 0.7 (0.5, 1.1); for allergic rhinitis at the age of 4 years, 0.6 (0.4, 1.0); and for atopic eczema at 0-6 months of life, 0.7 (0.5, 0.9).

CONCLUSIONS

The results indicate that early-life exposure to pets or lifestyle factors associated with exposure to pets reduce the risk of developing atopy-related diseases in early childhood. However, these findings might also be explained by selection for keeping pets.

Sensitisation, asthma, and a modified Th2 response in children exposed to cat allergen: a population-based cross-sectional study

BACKGROUND

Although asthma is strongly associated with immediate hypersensitivity to indoor allergens, several studies have suggested that a cat in the house can decrease the risk of asthma. We investigated the immune response to cat and mite allergens, and asthma among children with a wide range of allergen exposure.

METHODS

We did a population-based cross-sectional study of children (aged 12-14 years), some of whom had symptoms of asthma and bronchial hyper-reactivity. Antibodies to mite (Der f 1) and cat (Fel d 1) allergens measured by isotype (IgG and IgG4) specific radioimmunoprecipitation assays were compared with sensitisation and allergen concentrations in house dust.

FINDINGS

226 children were recruited, 47 of whom had symptoms of asthma and bronchial hyper-reactivity. Increasing exposure to mite was associated with increased prevalence of sensitisation and IgG antibody to Der f 1. By contrast, the highest exposure to cat was associated with decreased sensitisation, but a higher prevalence of IgG antibody to Fel d 1. Thus, among children with high exposure, the odds of sensitisation to mite rather than cat was 4.0 (99% CI 1.49-10.00). Furthermore, 31 of 76 children with 23 microg Fel d 1 at home, who were not sensitised to cat allergen had >125 units of IgG antibody to Fel d 1. Antibodies to Fel d 1 of the IgG4 isotype were strongly correlated with IgG antibody in both allergic and non-allergic children (r=0.84 and r=0.66, respectively). Sensitisation to mite or cat allergens was the strongest independent risk factor for asthma (p<0.001).

INTERPRETATION

Exposure to cat allergen can produce an IgG and IgG4 antibody response without sensitisation or risk of asthma. This modified T-helper-2 cell response should be regarded as a form of tolerance and may be the correct objective of immunotherapy. The results may also explain the observation that animals in the house can decrease the risk of asthma.

The role and remediation of animal allergens in allergic diseases

Animal allergens are common causes of both acute and chronic allergic disease. The most important animal allergens are derived from mammals, principally cats, dogs, rats, mice, horses, and cows, which secrete or excrete allergens into the environment. Allergic sensitization may occur at home or in the workplace. Cat and dog allergens commonly cause allergies in the home and affect the general population. Laboratory animal handlers often have allergic reactions to rats and mice. Cow dander allergy is usually caused by occupational exposure and occurs in farmers and farm workers. Horse allergy occurs among people who regularly handle horses, either professionally or for recreational purposes. Over the past 20 years, the major animal allergens have been defined and characterized with regard to their molecular structure, immunogenicity, and environmental distribution. One remarkable finding has been the fact that most of the mammalian allergens that have thus far been cloned belong to a single family of proteins called the lipocalins. In addition to these molecular similarities, it has also been shown that most of the animal allergens are quite similar with regard to their aerodynamic properties. Although much is yet to be learned, progress is being made in our knowledge regarding the steps that may be necessary to control exposure to these allergens through environmental modifications in both homes and occupational settings. These measures include source control, air filtration devices, barrier devices, removal of carpeting and other reservoirs, and, in some cases, washing of the animal.

NAC Manchester Asthma and Allergy Study (NACMAAS): risk factors for asthma and allergic disorders in adults

Asthma and atopic disorders are the most common chronic diseases in the developed countries. Knowledge of the risk factors for these disorders may facilitate the development of preventive strategies aimed at reducing prevalence rates. To investigate the risk factors for asthma and allergic diseases in a large number of adults who are the parents of children in the National Asthma Campaign Manchester Asthma and Allergy Study. All pregnant women and their partners attending "Booking" antenatal clinics were invited to take part in the study. Questionnaire data were collected including the history of asthma and other atopic diseases, pet ownership and smoking habits, and skin prick tests were performed. The prevalence of atopy and the risk factors for asthma and allergic disorders were investigated in all subjects who completed the questionnaire and underwent skin testing. Statistical analysis was carried out using logistic regression. Initially, risk factors were assessed by univariate analysis to see how each potential explanatory variable affected the probability of having allergic disease. Variables were then tested in a forward stepwise multivariate analysis. In 5687 adult subjects there was a very high (48.2%) prevalence of atopy, and 9.7% of subjects had a diagnosis of asthma. In a multivariate regression analysis sensitization to dust mite, cat, dog and mixed grasses were all independently associated with asthma. The odds ratios for current asthma increased with the increasing number of positive skin tests (any two allergens - OR 4.3, 95% CI 3.3-5.5; any three allergens - OR 7.0 95% CI 5.3-9.3; all four allergens - OR 10.4, 95% CI 7.7-14; P < 0.00001). Dog ownership (OR 1.31, 95% CI 1.10-1.57; P = 0.003) and current smoking (OR 1.36, 95% CI 1.15-1.62; P = 0.0004) were significantly and directly associated with "asthma ever". Thirteen per cent of participants reported a history of eczema. In the multivariate analysis the strongest independent associate of eczema was sensitization to dog (OR 1.37, 95% CI 1.14-1.63, P < 0.0001). Apart from dog, the strength of the association between sensitization to common allergens and eczema appeared to be much lower than in the case of asthma. The prevalence of hay fever was high (20.6%), and in the multivariate analysis the association between sensitization to pollen and hay fever was extremely strong (OR 13.6, 95% CI 11.3-16.3; P < 0.0001). The results of the current study emphasize the importance of sensitization to indoor allergens in asthma. However, evidence of a possible direct role of allergen exposure in asthma causation remains unclear.

Incidence and remission of asthma in schoolchildren: report from the obstructive lung disease in northern Sweden studies

OBJECTIVE

An increasing prevalence of asthma has been reported worldwide as well as in Sweden. In 1996, the prevalence of asthma and type 1 allergy was investigated in a cohort of 3525 children 7 and 8 years old in 3 areas of northern Sweden. The aim of the present study was to estimate the incidence of asthma and to identify risk factors for incident cases over 1 year.

METHODS

The study started with a parental questionnaire, the International Study of Asthma and Allergies in Childhood questionnaire with additional questions, a skin prick test, and a validation study. The cohort was followed up after 1 year with the same questions. The response rate to the questionnaire was 97% in 1996, and 3339 children (97%) participated both in 1996 and 1997.

RESULTS

The incidence of physician-diagnosed asthma was 0.9/100/year; of wheezing, 3.8/100/year; and of new frequent or daily users of asthma medicines, 1.1/100/year. There was no difference by sex. The risk factor pattern based on incident cases of asthma was different from that based on prevalent cases. Significant risk factors for incident asthma were a positive skin test (odds ratio [OR]: 9.3; 95% confidence interval [CI]: 3.8-22.7); low birth weight (OR: 7.4; 95% CI: 2.2-24.5); and family history of asthma (OR: 2.6; 95% CI: 1.1-6.3). Having or having had pets at home was associated with a decreased risk for asthma and wheezing based on prevalent cases, although it was associated with an increased risk for incidence of wheezing (OR: 2.9; 95% CI: 1.3-6.2). Remission of asthma, which was reported by 10% of the children with current asthma during 1 year, was associated with a negative skin test.

CONCLUSION

The incidence of asthma at the age of 8 years was high, but remission was also common. Important risk factors for the development of asthma at this age were type 1 allergy, low birth weight, and family history of asthma. Furthermore, the results suggest that in a region where sensitivity to domestic animals is a strong risk factor for asthma, the presence of pets in the home may have different effects in early childhood compared with later in childhood.

Systematic review: Exposure to pets and risk of asthma and asthma-like symptoms

BACKGROUND

Studies of exposure to pets and risk of asthma have yielded conflicting results.

OBJECTIVES

We performed a systematic review to synthesize the evidence of the effect of exposure to pets in the home on the risk of asthma and asthma-related symptoms. We also assessed differences between the studies as sources of heterogeneity of the results.

METHODS

We conducted a MEDLINE search (until the end of 1999) using the following boolean search command: (asthma[all] OR wheez*[all]) AND (domestic animal*[all] OR pets[all]). The outcome was limited to either diagnosis of asthma or the symptom of wheezing. The exposure of interest was domestic animals in the home. Appropriate temporal relationship was defined as present in studies with either pet keeping within the first 2 years of life, in the past, or exposure to pets preceding the outcome.

RESULTS

Thirty-two of the 217 retrieved articles fulfilled the eligibility criteria. Inappropriate time sequence of the exposure and outcome information was an important source of heterogeneity and an indication of potential selection bias. Therefore we analyzed studies focusing on early exposure or ensuring appropriate temporal sequence. The pooled risk estimates for both asthma (fixed-effects odds ratio, 1.11; 95% CI, 0.98-1.25; heterogeneity, P =.04; random-effects odds ratio, 1.09; 95% CI, 0.89-1.34) and wheezing (fixed-effects odds ratio, 1.19; 95% CI, 1.05-1.35; heterogeneity, P =.03; random-effects odds ratio, 1.17; 95% CI, 0.95-1.44) indicated a small effect, which was limited to studies with a median study population age of over 6 years (fixed-effects odds ratio, 1.19; 95% CI, 1.02-1.40; heterogeneity, P =.04; random-effects odds ratio, 1.15; 95% CI, 0.86-1.56; fixed-effects odds ratio, 1.29; 95% CI, 1.12-1.48; heterogeneity, P =.31). In younger children the harmful effect disappeared for wheezing (odds ratio, 0.80; 95% CI, 0.59-1.08; P =.38).

CONCLUSION

Exposure to pets appears to increase the risk of asthma and wheezing in older children. The observed lower risk among exposed than among unexposed young children is consistent with a protective effect in this age group but could also be explained by selection bias.

Residential exposures associated with asthma in US children

OBJECTIVE

Residential exposures are recognized risk factors for childhood asthma, but the relative contribution of specific risk factors and the overall contribution of housing to asthma in US children is unknown. The objective of this study was to identify risk factors and estimate the population attributable risk of residential exposures for doctor-diagnosed asthma for US children.

METHODS

A cross-sectional survey was conducted from 1988 to 1994. Survey participants were 8257 children who were <6 years old and who participated in the Third National Health and Nutrition Examination Survey, a survey of the health and nutritional status of children and adults in the United States. The main outcome measure was doctor-diagnosed asthma, as reported by the parent.

RESULTS

Six percent of children had doctor-diagnosed asthma. The prevalence of asthma was higher among boys (6.7%) than girls (5.1%) and was higher among black children (8.9%) than white children (5.2%). Risk factors for doctor-diagnosed asthma included a family history of atopy (odds ratio [OR]: 2.2; 95% confidence interval [CI]: 1.5, 3.1), child's history of allergy to a pet (OR: 24.2; 95% CI: 8.4, 69.5), exposure to environmental tobacco smoke (OR: 1.8; 95% CI: 1.2-2.6), use of a gas stove or oven for heat (OR: 1.8; 95% CI: 1.02-3.2), and presence of a dog in the household (OR: 1.6; 95% CI: 1.1, 2.3). The population attributable risk of >/=1 residential exposure for doctor-diagnosed asthma in US children <6 years old was 39.2%, or an estimated 533 000 excess cases, whereas having a family history of atopy accounted for 300 000. The attributable cost of asthma as a result of residential exposures for children <6 years old was $402 million (95% CI: $296-$507 million) annually.

CONCLUSIONS

The elimination of identified residential risk factors, if causally associated with asthma, would result in a 39% decline in doctor-diagnosed asthma among US children <6 years old.

Sensitization and exposure to pet allergens in asthmatics versus non-asthmatics with allergic rhinitis

In sensitized subjects with allergic rhinitis (AR) or asthma, allergen exposure provokes symptoms. Among non-asthmatics with AR, an association between allergen sensitization, pollen season and lower airway inflammation has been demonstrated. Our aims were to compare AR and asthma with regard to patterns of allergen sensitization, the degree of airway hyperresponsiveness (AHR) and levels of exhaled nitric oxide (ENO). Finally, we wanted to relate our findings to previous or current exposure to household pets. Four hundred and thirty-one adolescents with different clinical phenotypes were randomly selected from a large-scale epidemiological survey. They were investigated with allergy screening, measurements of ENO and a methacholine bronchoprovocation test. Sensitization to pet allergens (cat, dog and horse) was associated with increased AHR and ENO both in asthmatics and non-asthmatics with AR. The risk of being sensitized to cat allergens was significantly reduced in those who had kept cats vs. those who had never kept them. Keeping dogs or horses did not influence the risk of being sensitized to the respective allergens. Only in steroid-naive, non-smoking asthmatics, a trend towards increased ENO in those sensitized and exposed to cat or dog allergens was seen. Although sensitization towards pet allergens was associated with inflammation in the lower airways irrespective of clinical phenotype, keeping pets did not increase the risk of being sensitized to pet allergens.

Atopy among schoolchildren in northern and southern Sweden in relation to pet ownership and early life events

Studies have suggested a higher prevalence of asthma and allergies in northern, as compared to southern, Scandinavia. The aim of this study was to evaluate regional differences in atopy in relation to pet ownership and certain early life events among schoolchildren (n=2108) aged 10-11 years from Linköping in southern Sweden and Ostersund in northern Sweden. The parents completed a questionnaire, comprising questions on home environment, heredity, socio-economic conditions, and the core questions on symptoms from the International Study of Asthma and Allergies in Childhood. The children were skin-prick tested to eight common inhalant allergens. Information on maternal smoking habits, gestational age, and anthropometric measures were obtained from the Swedish Medical Birth Registry. The prevalence of atopic symptoms and sensitization to pollen were similar in Ostersund and in Linköping. A higher prevalence of sensitization to animal dander among children in Ostersund could be linked to a higher occurrence of pets in the community. Current cat ownership was related to less sensitivity to cat allergen but only in children with an atopic heredity. Ponderal index >30 kg/m3 was related to an increased risk of atopic sensitization, both in Linköping (adjusted odds ratio 2.1; 95% confidence interval 1.1-4.0) and in Ostersund (adjusted odds ratio 2.0; 95% confidence interval 1.1-3.5). Maternal smoking during pregnancy was related to an increased risk of atopic sensitization among children in Linköping, whereas current smoking was associated with a decreased risk of sensitization in Ostersund. In conclusion, we demonstrated that a high occurrence of pets in the community was associated with sensitization, whereas atopic symptoms were essentially unaffected. This study has also suggested an association between body size at birth and atopic sensitization at 10-11 years of age.

Predictors of asthma three years after hospital admission for wheezing in infancy

OBJECTIVE

To evaluate the influence of early antiinflammatory therapy in the development of asthma 3 years after hospitalization for wheezing in infancy. In addition, the effects of allergic sensitization and respiratory syncytial virus (RSV) infection on the development of asthma were investigated.

DESIGN AND SETTING

A randomized, controlled follow-up study in a university hospital that provides primary hospital care for all pediatric patients in a defined area.

PATIENTS

Eighty-nine infants under 2 years of age who had been hospitalized for infection associated with wheezing and followed up for 3 years.

INTERVENTION

Early antiinflammatory therapy was given for 16 weeks; 29 patients received cromolyn sodium and 31 received budesonide. Twenty-nine control patients received no therapy.

OUTCOME MEASURES

Clinical diagnosis of current asthma, defined as having at least 3 episodes of physician-diagnosed wheezing and either a wheezing episode during the preceding year or ongoing antiinflammatory medication for asthma.

RESULTS

Fourteen (48%) patients in the former cromolyn group, 15 (48%) in the former budesonide group, and 16 (55%) in the control group had current asthma. The significant predictors of asthma were age over 12 months (risk ratio [RR] 4.1; 95% confidence interval [CI] = 1.59-10.35), history of wheezing (RR 6.8; CI = 1.35-34.43), and atopic dermatitis on study entry (RR 3.4; CI = 1.17-9.39). Skin prick test positivity at the age of 16 months significantly predicted asthma (RR 9.5; CI = 2.45-36.72). In addition, all of the 18 (20%) children sensitized with furred pet developed asthma. RSV identification (RR 0.3; CI = 0.08-0.80) and early furred pet contact at home (RR 0.3; CI 0.10-0.79) were associated with the decreased occurrence of asthma.

CONCLUSIONS

Antiinflammatory therapy for 4 months has no influence on the occurrence of asthma 3 years after wheezing in infancy. Early sensitization to indoor allergens, especially to pets, and atopic dermatitis predict subsequent development of asthma. RSV infection in wheezing infants may have a better outcome than other infections.

The role of intervention in established allergy: avoidance of indoor allergens in the treatment of chronic allergic disease

Avoidance of exposure to indoor allergens is an important element in the treatment of allergic disease. The results of several studies provide strong evidence in support of a role for allergen avoidance; however, strategies that optimize allergen reduction in houses have not been determined. Complex issues regarding the efficacy of physical and chemical measures that target house dust mite, pet, and cockroach allergens in the home are discussed. The greatest challenge is to educate allergic patients so that they can play an important role in controlling their own disease.

Pets and cockroaches: two increasing causes of respiratory allergy in indoor environments. Characteristics of airways sensitization and prevention strategies

The increasing prevalence of allergic sensitization to indoor allergens such as dust mites, pets and cockroaches is the result of the changes in indoor environments induced by human activities. The Westernized lifestyle and the increasing time spent indoors determine a reduction in natural air ventilation and, consequently, higher levels of allergen concentrations and longer exposure to allergens. The major cat allergen Fel d 1 is carried by small-dimension particles (< 5 microm diameter) that readily become airborne and persist immodified for a long time. Fel d 1 must be considered a ubiquitous allergen because it has been found in indoor environments and even in public places where a cat has never been kept. Recent research has demonstrated that clothing of cat owners may contribute to the dispersal of Fel d 1 in cat-free environments. Therefore, washing Fel d 1-contaminated clothes should be considered a simple and effective method for removing this allergen from clothing and, consequently, reducing the risk of Fel d 1 dispersion. Cockroach allergens constitute another important cause of environment-related respiratory allergy and may trigger asthma exacerbations in sensitized individuals. In the prevention of cockroach allergy, the use of chemical agents associated with an intensive vacuum cleaning of indoor environments is an important tool in removing cockroach material containing allergenic proteins. Early recognition of allergy-predisposed babies, monitoring indoor allergens and adequate strategies of allergen avoidance are likely to be important means for reducing the prevalence of bronchial asthma.

Early exposure to house-dust mite and cat allergens and development of childhood asthma: a cohort study. Multicentre Allergy Study Group

BACKGROUND

In a prospective birth-cohort study, we assessed the relevance of mite and cat allergen exposure for the development of childhood asthma up to age 7 years.

METHODS

Of 1314 newborn infants enrolled in five German cities in 1990, follow-up data at age 7 years were available for 939 children. Assessments included repeated measurement of specific IgE to food and inhalant allergens, measurement of indoor allergen exposure at 6 months, 18 months, and 3 years of age, and yearly interviews by a paediatrician. At age 7 years, pulmonary function was tested and bronchial hyper-responsiveness was measured in 645 children.

FINDINGS

At age 7, the prevalence of wheezing in the past 12 months was 10.0% (94 of 938), and 6.1% (57 of 939) parents reported a doctor's diagnosis of asthma in their children. Sensitisation to indoor allergens was associated with asthma, wheeze, and increased bronchial responsiveness. However, no relation between early indoor allergen exposure and the prevalence of asthma, wheeze, and bronchial hyper-responsiveness was seen.

INTERPRETATION

Our data do not support the hypothesis that exposure to environmental allergens causes asthma in childhood, but rather that the induction of specific IgE responses and the development of childhood asthma are determined by independent factors.

Exposure to endotoxin or other bacterial components might protect against the development of atopy

BACKGROUND

Several recent studies have shown that growing up on a farm confers significant protection against the development of atopy. These findings point particularly towards the importance of exposure to stable dust and farm animals. It has furthermore been reported that endotoxin, an intrinsic part of the outer membrane of gram negative bacteria, is abundant in environments where livestock and poultry is kept. The aim of this study was therefore to measure the level of environmental endotoxin exposure in homes of farmers' children, children with regular contact to livestock and control children with no contact to farm animals.

METHODS

Eighty-four farming and nonfarming families were identified in rural areas in Southern Germany and Switzerland. Samples of settled and airborne dust were collected in stables, and of settled dust indoors from kitchen floors and the children's mattresses. Endotoxin concentrations were determined by a kinetic Limulus assay.

RESULTS

Endotoxin concentrations were highest in stables of farming families, but were also significantly higher indoors in dust from kitchen floors (143 EU/mg vs 39 EU/mg, P < 0.001) and children's mattresses (49479 EU/m2 vs 9383 EU/m2, P < 0.001) as compared to control children from nonfarming families. In addition, endotoxin levels were also significantly higher in mattresses and dust from kitchen floors in households where children had regular contact to farm animals (38.6 EU/mg and 23340 EU/m2, respectively) as compared to control subjects.

CONCLUSION

We propose that the level of environmental exposure to endotoxin and other bacterial wall components is an important protective determinant for the development of atopic diseases in childhood.

Is prevention of allergy and asthma possible?

Allergy and asthma are common diseases today. Ways to stop the ongoing increase in incidence of these diseases are highly desired. In this review the scientific basis for allergy and asthma prevention is discussed.

RESULTS

Although secondary preventive measures are generally regarded as important, the views regarding the possibility of primary prevention vary. There is today only weak evidence that breastfeeding may reduce the risk of developing allergy, and if it does the effect is limited in degree and duration. There is some evidence that prolonged breastfeeding reduces the risk of developing asthma, at least in allergy-risk infants. There is also some evidence indicating that withholding solid foods in children at risk may have a beneficial effect. A dose-dependent risk of becoming sensitized to house dust mite and pet animal allergens has clearly been shown, but to what extent this sensitization is combined with asthma or clinical allergy is less well elucidated. Passive smoking increases the risk of wheezing problems and the indoor environment in damp houses seems to act synergistically with passive smoke.

CONCLUSION

Primary prevention is rarely possible, but the risk of developing asthma and allergy may to some extent be reduced by taking certain measures, such as avoidance of tobacco smoke and damp houses. Breastfeeding seems to reduce the risk of wheezing, but as allergy-preventive measures, breastfeeding and avoiding pet animals have only marginal effects.

Asthma in children: prevalence, treatment, and sensitization

This study compares the prevalence of asthma and sensitization in children from two Swedish regions with different climates: Göteborg on the southwest coast and Kiruna in the northern inland, north of the Arctic Circle. The 412 children of a population-based sample, 203 in Göteborg and 209 in Kiruna, were investigated at age 7-8 and 12-13 years. Questionnaire reports and interviews were obtained from all children at 7-8 years of age, and 192 children were skin-prick tested for common aeroallergens in Göteborg and 205 in Kiruna. At the follow-up, 5 years later, almost all the children were re-investigated. The prevalence of asthma, wheeze, and sensitization had increased with increasing age during the follow-up period. The questionnaire reports revealed that the prevalence of asthma was 8.5% at 12-13 years of age. All children who in the questionnaire reported current asthma, were using asthma medication. The interviews indicated that the prevalence of a clinically significant asthma might be even higher, reaching approximately 12%. Asthma and wheeze were as common in Göteborg as in Kiruna despite large differences in prevalence of sensitization. Sensitization, and especially sensitization to animals, was far more common in Kiruna than in Göteborg. This study shows that asthma and wheeze are increasingly prevalent even in school age children and that sensitization does not necessarily reflect the prevalence of asthma in a population.

Is allergen exposure the major primary cause of asthma?

In recent decades a number of authors have argued that allergen exposure is the major primary cause of asthma, and that the global increases in asthma prevalence are due to increases in exposure to aeroallergens. We have assessed the epidemiological evidence in support of this hypothesis. No longitudinal studies were identified in which allergen exposure during infancy in a random population sample has been related to asthma risk after the age of six years. Two studies have been conducted in selected populations chosen on the basis of a family history of asthma or allergy; one study found a non-statistically significant association whereas the other study found no association. Many of the identified prevalence studies in children showed negative associations between allergen exposure and current asthma, and the weighted averages of the population attributable risks in children were 4% for Der p 1, 11% for Fel d 1, -4% for Bla g 2, and 6% for Can f 1. There was little change in these estimates in studies in which children whose parents had adopted allergen avoidance measures were excluded. Furthermore, evidence from population studies is equivocal and provides little consistent evidence that allergen exposure is associated with the prevalence of asthma at the population level. Population-based cohort studies are clearly required, but currently available evidence does not indicate that allergen exposure is a major risk factor for the primary causation of asthma in children.

Nordic consensus report on asthma management. Nordic Asthma Consensus Group

The work with the Nordic consensus report on asthma management started some years ago. The Nordic countries have common socioeconomic conditions. We acknowledge the international as well as other European guidelines providing valuable recommendations. Nevertheless, we felt the need to combine the common Nordic experiences in order to have a local statement of asthma and asthma care, based upon Nordic clinical science and tradition. The work has been rewarding and we acknowledge many valuable contributions from paediatricians, allergologists and lung physicians in all Nordic countries. The response has so far been positive and we feel that the present material reflects the main opinion of Nordic physicians taking care of asthma patients of all ages. However, the asthma and allergy research field is rapidly developing. Thus, this document should merely be regarded as a time-limited contribution to the continuing scientific discussion of this fascinating field.

Exposure to foodborne and orofecal microbes versus airborne viruses in relation to atopy and allergic asthma: epidemiological study

OBJECTIVE

To investigate if markers of exposure to foodborne and orofecal microbes versus airborne viruses are associated with atopy and respiratory allergies.

DESIGN

Retrospective case-control study.

PARTICIPANTS

240 atopic cases and 240 non-atopic controls from a population sample of 1659 participants, all Italian male cadets aged 17-24.

SETTING

Air force school in Caserta, Italy.

MAIN OUTCOME MEASURES

Serology for Toxoplasma gondii, Helicobacter pylori, hepatitis A virus, measles, mumps, rubella, chickenpox, cytomegalovirus, and herpes simplex virus type 1; skin sensitisation and IgE antibodies to relevant airborne allergens; total IgE concentration; and diagnosis of allergic asthma or rhinitis.

RESULTS

Compared with controls there was a lower prevalence of T gondii (26% v 18%, P=0.027), hepatitis A virus (30% v 16%, P=0.004), and H pylori (18% v 15%, P=0.325) in atopic participants. Adjusted odds ratios of atopy decreased with a gradient of exposure to H pylori, T gondii, and hepatitis A virus (none, odds ratio 1; one, 0. 70; two or three, 0.37; P for trend=0.000045) but not with cumulative exposure to the other viruses. Conversely, total IgE concentration was not independently associated with any infection. Allergic asthma was rare (1/245, 0.4%) and allergic rhinitis infrequent (16/245, 7%) among the participants (245/1659) exposed to at least two orofecal and foodborne infections (H pylori, T gondii, hepatitis A virus).

CONCLUSION

Respiratory allergy is less frequent in people heavily exposed to orofecal and foodborne microbes. Hygiene and a westernised, semisterile diet may facilitate atopy by influencing the overall pattern of commensals and pathogens that stimulate the gut associated lymphoid tissue thus contributing to the epidemic of allergic asthma and rhinitis in developed countries.

Indoor allergen exposure in west and East Germany: a cause for different prevalences of asthma and atopy?

West and East Germans have been living in two different political systems for 40 years. These two populations have become a classic epidemiological example for the hypothesis that lifestyle changes accompanying the industrial and economic development of modern societies are responsible for an increase in the prevalence of atopic diseases. A higher prevalence of atopic sensitization, asthma, and hay fever was found in young West Germans after the unification. It has been hypothesized that this phenomenon was at least partially due to the installation of insulating windows and central heating systems in Western homes, favoring the growth of microorganisms like mites and moulds and increasing indoor allergen exposure. This review summarizes studies that have investigated reservoir concentrations of indoor allergens in public buildings and private homes in East and West Germany. Whereas a higher prevalence of atopic sensitization in West Germans was found for nearly all tested allergens (cat, mite, pollen), allergen exposure was higher only for cat allergens, but probably not for mite and cockroach allergens or moulds. The published data do not support the view that the differences in specific sensitization are caused by differences in the exposure to specific allergens.

Breastfeeding provides passive and likely long-lasting active immunity

OBJECTIVES

The reader of this review will learn about the mechanisms through which breastfeeding protects against infections during and most likely after lactation, as well as possibly against certain immunologic diseases, including allergy.

DATA SOURCES

I have followed the literature in the area closely for the last 30 to 40 years and have made repeated literature searches through MEDLINE, most recently in 1998. Textbooks and peer-reviewed journals have been sought for, as well as books representing meeting reports in English, French, German, and Spanish.

RESULTS

Human milk protects against infections in the breastfed offspring mainly via the secretory IgA antibodies, but also most likely via several other factors like the bactericidal lactoferrin. It is striking that the defense factors of human milk function without causing inflammation, some components are even directly anti-inflammatory. Protection against infections has been well evidenced during lactation against, e.g., acute and prolonged diarrhea, respiratory tract infections, otitis media, urinary tract infection, neonatal septicemia, and necrotizing enterocolitis. There is also interesting evidence for an enhanced protection remaining for years after lactation against diarrhea, respiratory tract infections, otitis media, Haemophilus influenzae type b infections, and wheezing illness. In several instances the protection seems to improve with the duration of breastfeeding. Some, but not all studies have shown better vaccine responses among breastfed than non-breastfed infants. A few factors in milk like anti-antibodies (anti-idiotypic antibodies) and T and B lymphocytes have in some experimental models been able to transfer priming of the breastfed offspring. This together with transfer of numerous cytokines and growth factors via milk may add to an active stimulation of the infant's immune system. Consequently, the infant might respond better to both infections and vaccines. Such an enhanced function could also explain why breastfeeding may protect against immunologic diseases like coeliac disease and possibly allergy. Suggestions of protection against autoimmune diseases and tumors have also been published, but need confirmation.

CONCLUSIONS

Breastfeeding may, in addition to the well-known passive protection against infections during lactation, have a unique capacity to stimulate the immune system of the offspring possibly with several long-term positive effects.