Respiratory infections in the first year of life in children at risk of developing atopy

The management of acute bronchitis in children

Acute bronchitis is one of the most common infections reported in children under 5 years of age, and is a leading cause of hospitalisation. In general practice, confusion surrounds the clinical diagnosis of acute bronchitis, especially when distinguishing it from asthma. The microbiological causes are mostly known, but the contribution of each is much less clear, and they are non-specific in their clinical expression in individual cases. Viral pathogens, particularly respiratory syncytial virus and rhinoviruses are cited as the leading agents in the development of serious episodes, but other pathogens may also be important. This article covers a range of issues surrounding acute bronchitis, including epidemiology and pathogenesis, as well as the management, prevention and treatment of disease in children.

A birth cohort study of subjects at risk of atopy: twenty-two-year follow-up of wheeze and atopic status

This study describes the natural history of atopic and wheezy disorders from birth to adult life in a cohort at risk of atopy. One hundred subjects born in Poole, England, were selected at birth in 1976 on the basis that at least one parent was atopic. Subjects were examined annually in the preschool years, and at the ages of 11 and 22 yr. Skin prick tests and total serum immunoglobulin E (IgE) were performed at each visit, and at 11 and 22 yr, bronchial hyperresponsiveness (BHR) to inhaled histamine was measured. Sixty-three subjects remained on follow-up at 22 yr. The annual prevalence of both wheeze and atopy increased with age. Twenty-five percent of adults showed both wheeze and BHR (asthma). Remission of wheeze was common in subjects younger than 5 yr of age and likely if wheezing occurred on less than two occasions, but wheeze at 11 yr was likely to persist. Sixty percent of the adult subjects with asthma developed sensitivity to common allergens by the age of 2 yr and were showing BHR by mid-childhood. Sensitization to dietary allergens occurred in infancy and waned after early childhood but predicted the early sensitization to inhalant allergens. In conclusion, adults with asthma can begin wheezing at any age but tend to sensitize early and have abnormal airway characteristics by the age of 11 yr.

Viruses in asthma

Current evidence suggests that the overall load of infectious agents, including respiratory viruses, encountered early in life is an important factor influencing maturation of the immune system from a type 2 bias at birth towards predominantly type 1 responses, thus avoiding atopic diseases. The 'hygiene hypothesis' proposes that the relatively sterile environment present in industrialised Western countries has contributed to the recent epidemic of asthma and atopy. Whether specific infections are of greater or lesser protective value is an important question if strategies are to be derived to mimic the beneficial effects of childhood infection whilst avoiding morbidity and potential mortality of the natural pathogens. Infection by respiratory viruses is a major trigger of wheezing in infants and of exacerbations of asthma in older children. Viruses are detected in up to 85% of such episodes. Rhinovirus is common in all age groups; respiratory syncytial virus (RSV) is most important in infants and young children. Knowledge of the immunopathogenetic mechanisms of virus infection in the asthmatic airway will lead to the development of new treatments for virus-induced asthma.

Evaluation of the wheezy infant

BACKGROUND

The infant with persistent or recurrent wheezing during the first 2 years of life poses a diagnostic dilemma, which can be a source of anxiety to both physicians and parents. A suggested diagnostic approach to the causes of infantile wheezing is outlined.

OBJECTIVES

1. To review the physiologic considerations of the infant's airways that predispose to wheezing. 2. To discuss the key physical findings, family history, and risk factors associated with wheezing in infants. 3. To develop a rational approach to the differential diagnosis and management of infantile wheezing.

DATA SOURCES

The MEDLINE database as well as our clinical experience pertaining to infantile wheezing.

CONCLUSIONS

This review discusses the diagnostic evaluation and treatment of the wheezing infant. We suggest that infant pulmonary function testing may be used as one diagnostic aid in the workup of the wheezing infant.

The role of viral infections in the natural history of asthma

Viral infections have been related to the inception of recurrent wheezing illnesses and asthma in infants and are probably the most frequent cause of exacerbations of established disease in older children and adults. The well-recognized clinical effects of viral infections are mainly caused by virus-induced immune responses. Clinical studies of natural and experimentally induced viral infections have led to the identification of mechanisms of inflammation that could be involved in producing airway obstruction and lower airway symptoms. In addition, host factors that are associated with more vigorous viral replication or severe clinical illness are beginning to be identified. Advances in molecular virology and our understanding of immune responses to viral infections may lead to the development of new strategies for the prevention and treatment of virus-induced respiratory disorders.

A parental history of asthma is a risk factor for wheezing and nonwheezing respiratory illnesses in infants younger than 18 months of age

The relationship between respiratory infection and allergy as risk factors for the development of wheezing illnesses in infants has been in dispute. We hypothesized that a parental history of allergic diseases would be associated with an increased rate of respiratory infections as well as an increased rate of wheezing during infectious episodes. We prospectively evaluated 1,193 infants from birth to 18 mo of age, using bi-weekly telephone surveillance to document all respiratory events. The overall rate of respiratory illness (all RI) increased to a maximum of 10.6 illnesses/infant/year in the 7- to 9-mo age group and then leveled off in the older infants. Multivariable models adjusting for demographic variables, breast feeding, month of illness, number of siblings, and attendance at day care showed an increase in the rate of all RI in infants older than 7 mo of age who had a parental history of asthma (OR = 1.24, CI = 1.09 to 1.41) or a parental history of atopy (OR = 1.14, CI = 1.03 to 1.26). The rate of lower respiratory illnesses accompanied by wheezing was related only to a parental history of asthma (OR = 2.06, CI = 1.36 to 3.11). We conclude that all RI, most of which represent viral infections, are increased in otherwise normal infants with a parental history of asthma or atopy, whereas wheezing is related only to a parental history of asthma.

[Factors associated with the development of atopy in young adults]

BACKGROUND

To determine the risk factors for the development of atopy in Spanish young adults.

SUBJECTS AND METHODS

Case-control study over prevalent cases. Carried out in general population between the ages of 20 to 44 years old. Spanish participants of the ECRHS, a random representative sample of Spanish young adults (n = 16,884), and a 20% randomised subsample made by those who answered to a short respiratory questionnaire and had atopy assessed, was studied. Atopy was defined as having serum specific IgE positivity to the following aeroallergnes: cat dander, Cladosporium herbarum, Dermatophagoides pteronyssinus, Parietaria judaica and Phleum pratense.

RESULTS

Several factors had a statistically significant effect. In addition to male gender and lower age, maternal allergy (OR = 1.63; 95% CI = 1.11-2.40), having allergic siblings (OR = 1.40; 95% CI = 1.06-1.90) and a higher educational level (OR = 1.69; 95% CI = 1.22-2.34) were associated with the presence of high levels of specific IgE in our sample. Moreover, having had older siblings, especially older brothers appears to be a protective factor to the development of atopy but not in a statistically significant way, while having had pet birds during childhood appears to enhance the risk.

CONCLUSIONS

In addition to the familial variables that indicates both environmental and genetic factors, educational level seems to have low degree of association with atopy; this feature shows that variables related with life style are involved in atopy development.

Viral and bacterial infections in the development and progression of asthma

Viral respiratory infections produce wheezing illnesses in patients of all ages. In infancy, infections with respiratory syncytial virus and parainfluenza virus are the major cause of bronchiolitis and croup, whereas infections with common cold viruses such as rhinoviruses are the principal triggers for wheezing in older children and adults with asthma. In addition to causing increased wheezing in asthma, there is mounting evidence that infections early in childhood can affect the development of the immune system and thereby modify the risk for the subsequent development of allergies and asthma. Both of these effects appear to be mediated by virus-induced immune responses. Early during the course of viral infection, resident cells in the airway are activated in an antigen-independent fashion, triggering antiviral responses but also activating and recruiting cells to the airway that could contribute to airway obstruction and respiratory symptoms. Virus-specific T- and B-cell responses may also have dual effects in the presence of preexisting airway inflammation. Finally, there is evidence of synergistic interactions between allergen- and virus-induced airway inflammation. It is likely that greater definition of mechanisms of virus-induced inflammation will provide therapeutic targets for the treatment and possibly the prevention of allergies and asthma.

Investigation of seroprevalence of respiratory virus infections in an infant population with a multiantigen fluorescence immunoassay using heel-prick blood samples collected on filter paper

Respiratory viruses are an extremely common cause of childhood morbidity. However, the current seroprevalence of viruses in infant populations is difficult to establish because invasive venipuncture may be technically and ethically unacceptable. This prospective study aimed to establish the seroprevalence of respiratory viruses in an infant population by use of a novel multiantigen fluorescence immunoassay against common respiratory viruses, using heel-prick blood samples collected on filter paper. Mothers and babies were recruited in the immediate peripartum period in the Royal Maternity Hospital, Belfast. Cord blood samples at birth and heel-prick filter paper blood samples at 7 mo were collected for measurement of virus-specific IgG to respiratory syncytial virus, influenza A virus, adenovirus, and parainfluenza virus type 1, type 2, and type 3 by indirect immunofluorescence using a multiviral assay developed for this purpose. Of 386 mothers approached, 325 (84%) permitted follow-up at 7 mo, and of these, 256 (79%) agreed to the heel prick. From 234 paired samples, 125 infections were documented. Adenovirus infections were commonest, 53 (22.6%), followed by respiratory syncytial virus, 32 (13.7%); influenza A virus, 22 (9.4%); parainfluenza virus type 3, 14 (6%); parainfluenza virus type 1, 2 (0.85%); and parainfluenza virus type 2, 2 (0.85%). These results demonstrate the seroprevalence of a range of respiratory viruses in an infant population, using a novel multiviral immunoassay. The filter paper collection of blood samples and multiantigen assay format has implications for easy, widespread viral serodiagnosis in both seroepidemiology studies and in the diagnosis of pediatric viral illnesses. Filter paper permits recovery of respiratory virus-specific IgG and can be used as a simple and acceptable epidemiologic and diagnostic tool.

PEDIATRIC ALLERGY

The current paradigm of allergy pathogenesis is that allergy develops in individuals with a genetic predisposition only after they are exposed to allergens (Fig. 1). This hypothesis implies that factors in the environment can determine the initiation of allergic sensitization and can potentially influence the clinical manifestations and severity of disease. Because the prevalence of atopic diseases such as allergic rhinitis, asthma, atopic dermatitis, and food allergy have increased worldwide in the past several decades, and there is no mechanism for changes in population genetics over this short period of time, changes in the human environment are most likely responsible for these trends. From this line of reasoning, it follows that if the factors responsible for the increasing prevalence can be identified, then there would be an opportunity to develop strategies to reverse these trends. It also would be helpful to identify infants who are at risk for developing allergy, so that preventive strategies could be used most effectively.

In this article, studies to determine the contributions of genetics and the environment to the development of allergic diseases in childhood are explored. In addition, progress in identifying risk factors for allergy and preventive therapies for those children at risk are also addressed.

Meta-analysis on the association between environmental tobacco smoke (ETS) exposure and the prevalence of lower respiratory tract infection in early childhood

The aim of this study was to obtain quantitative information from published data on the association between environmental tobacco smoke (ETS) exposure and the prevalence of serious lower respiratory tract infections (LRTI) in infancy and early childhood. We identified 21 relevant publications on the relation between ETS and the prevalence of serious LRTI by reviewing reference lists in relevant reports and by conducting manual and computer searches (Medline database; Dissertation abstracts index of Xerox University Microfilms) of published reports between 1966 and 1995. Thirteen studies were included in a quantitative overview using random effects modeling to derive pooled odds ratios. Sensitivity analyses were conducted to test the decision rules used in extracting odds ratio data. The results of community and hospital studies are broadly consistent and show that the child of a parent who smokes is at approximately twice the risk of having a serious respiratory tract infection in early life that requires hospitalization. This association was pronounced in children younger than age two and diminished after the age of two. The combined odds ratio for hospitalization for lower respiratory tract infections in infancy or early childhood is 1.93 (95% CI 1.66-2.25); the combined odds ratio of prevalence of serious LRTI at age less than 2 years, between 0 and 6 years, and between 3 and 6 years were 1.71 (95% CI 1.33-2.20); 1.57 (1.28-1.91), and 1.25 (0.88-1.78), respectively. There was no evidence of heterogeneity across the studies in these combined odds ratios. We conclude that this meta-analysis provides strong evidence that exposure to ETS causes adverse respiratory health outcomes such as either a serious LRTI or hospitalization for LRTI. New public health campaigns are urgently needed to discourage smoking in the presence of young children.

Skin sensitization in asthmatic children less than 36 months of age

BACKGROUND

Atopy is reported to play an insignificant role in wheezing during infancy in contrast to later childhood. For this reason skin testing may not be included in a workup of wheezing infants.

OBJECTIVE/METHOD

In order to evaluate the degree and evolution of skin sensitization to allergens in infants with asthma, we have retrospectively analyzed the skin test results from 40 referred asthmatic children less than 36 months of age, who had had more than three wheezing episodes and whose symptoms improved on treatment with beta-agonist and anti-inflammatory agents.

RESULTS

Skin sensitization (epicutaneous) to common indoor and outdoor aeroallergens and foods were demonstrated in 23 (58%) of these patients. Asthmatic children with the onset before 12 months of age and duration of less than 12 months were sensitive predominantly to foods. Those with later onset asthmas and longer duration developed sensitivity first to indoor and then to outdoor allergens. The most common food, indoor, and outdoor allergens were egg, dust mite, and pollens, respectively. Six of these patients had repeat skin tests later. Two demonstrated a decrease in skin sensitivities to foods, one gained a new sensitivity to grass, while three remained unsensitized.

CONCLUSION

Skin sensitization to allergens was common in selected asthmatic infants and evolves in the order of exposures: foods, indoor allergens, and outdoor allergens. Repeat skin tests showed changing skin test patterns in some patients.

Measles and atopy in Guinea-Bissau

BACKGROUND

Epidemiological studies have led to speculation that infections in early childhood may prevent allergic sensitisation but evidence to support this hypothesis is lacking. We investigated whether measles infection protects against the development of atopy in children of Guinea-Bissau, West Africa.

METHODS

We conducted a historical cohort study in Bandim, a semi-rural district of Bissau, the capital of Guinea-Bissau. 395 young adults, first surveyed in 1978-80 aged 0-6 years, were followed up in 1994. Our analyses were restricted to 262 individuals still living in Bandim for whom a measles history, documented in childhood, was judged to be reliable. We defined atopy as skin-prick test positivity (> or = 3 mm weal) to one or more of seven allergens.

FINDINGS

17 (12.8 percent) of 133 participants who had had measles infection were atopic compared with 33 (25.6 percent) of 129 of those who had been vaccinated and not had measles (odds ratio, adjusted for potential confounding variables 0.36 [95 percent CI 0.17-0.78], p=O.O1). Participants who had been breastfed for more than a year were less likely to have a positive skin test to housedust mite. After adjustment for breastfeeding and other variables, measles infection was associated with a large reduction in the risk of skin-prick test positivity to housedust mite (odds ratio for Dermatophagoides pteronyssinus 0.20 [0.05-0.81], p=0.02; D farinae 0.20 [0.06-0.71], p=0.01).

INTERPRETATION

Measles infection may prevent the development of atopy in African children.

Respiratory syncytial virus infection: its role in aeroallergen sensitization during the first two years of life

Our aim was to study the influence of infection with the respiratory syncytial virus (RSV) in non-hospitalized infants on sensitization to aeroallergens and the early manifestation of atopy. Six hundred and nine infants from the prospective German Multicenter Cohort Study on Atopy were included, 38% of whom had an elevated atopic risk. RSV IgG and IgM antibodies were tested by ELISA with gradient purified RSV antigen. Specific IgE against mites, cat dandruff, birch and grass pollens and relevant nutritional antigens were tested with CAP-RAST-FEIA (Pharmacia, Sweden). Of the cord sera 99% were positive for RSV-IgG, 44.7% at one year and 64.2% (n = 265) at two years of age. The positivity rate after 12 months varied with the season of birth, the number of siblings and the degree of exposure to tobacco smoke; and correlated closely with attacks of wheezing during infancy. Twenty (2.8%) children were found to be sensitized against at least one aeroallergen at one year, and 28 (10.5%) at two years. By the first birthday, mite sensitization (n = 3) could only be seen in the RSV-infected children; grass pollen sensitization (n = 9) was associated with RSV seropositivity (logistic regression model including the confounders mentioned above: with RSV IgG < p = 0.048 > and IgM < p = 0.0006 >), as was birch sensitization (n = 5) with RSV IgM (p = 0.009). No such differences could be detected at two years. No correlation of RSV seropositivity to any allergic manifestation could be found. We conclude, that it is only in the first year of life, that RSV infection plays a significant role in promoting sensitization against aeroallergens, which do not at this time produce allergic symptoms.

Evidence for two unlinked loci regulating total serum IgE levels

Studies investigating the genetic control of total serum IgE levels are of major importance in understanding basic pathophysiologic mechanisms in atopy and asthma, since IgE levels predict onset and correlate with the clinical expression of these disorders. Previous analysis of data from 92 families, ascertained through a parent with asthma, showed evidence for recessive inheritance of high IgE levels with linkage to chromosome 5q. Since there was significant residual familial correlation in the one-locus segregation analysis, two-locus segregation and linkage analyses were performed. Segregation analyses provided evidence for a second major locus unlinked to the locus on 5q. Utilization of this two-locus model corroborates the previous evidence for linkage between this trait and markers on 5q31-q33. The LODs for the most informative marker D5S436 increased from 3.00 at 10% recombination to 4.67 at 9% recombination, when the two-locus model was used. Additional linkage studies are needed to map this second locus. These results demonstrate the importance of performing multilocus segregation and linkage analyses for quantitative traits that are related to the phenotype of a complex disorder. This approach has given further insight into the genetics of allergy and asthma by providing evidence for a two-locus model.

Viral infections and the development of asthma

The possible role of viral infections in the inception of asthma has been the matter of considerable debate. Older data suggested that viral respiratory infections occurring during early life could alter the lungs and the immune system, thus starting the process leading to allergic sensitization and persistent bronchial responsiveness. More recent studies suggest that infants who wheeze belong to two distinct groups, which at present can only be differentiated by the evolution of their illness. Most of these infants have a transitory tendency to wheeze during viral infections, and their lung function shortly after birth is significantly lower than that of infants who will not wheeze during similar infections. Most of these children become symptom-free during the preschool years, and their condition is not associated with higher serum IgE levels. A smaller group of children who wheeze as infants will still have wheezing episodes during the early school years. The factors that determine which infants will become persistent wheezers are not well understood, but viral infections per se are likely to play a minor role, if any. Early sensitization to aeroallergens in subjects genetically predisposed to having high serum IgE levels seems to be the main risk factor for this condition.

Lung function, airway responsiveness, and respiratory symptoms before and after bronchiolitis

Acute viral respiratory illness during infancy has been implicated as a precursor for subsequent lower respiratory morbidity in childhood. A prospective, longitudinal study of respiratory function, airway responsiveness, and lower respiratory illness during early childhood was performed in a cohort of 253 healthy infants to characterise those who experienced bronchiolitis. Seventeen infants (7% of the cohort), were given a diagnosis of bronchiolitis during the first two years of life with two (1%) requiring hospital admission. Seventy one per cent of those infants with bronchiolitis had a family history of atopy, 53% of asthma, and 29% had a mother who smoked cigarettes. These family history characteristics in this group with bronchiolitis were not different from the rest of the cohort. There were also no differences in the number of older siblings, the number breast fed, the duration of breast feeding, or socioeconomic status of the families between those that did and did not get bronchiolitis. Respiratory function was assessed at 1, 6, and 12 months of age. Maximum flow at functional residual capacity (VmaxFRC) was measured using the rapid thoracic compression technique. Resistance (Rrs) and size corrected compliance (Crs/kg) were obtained from a single brief occlusion at end inspiration. Airway responsiveness was assessed by histamine inhalation challenge and the provocation concentration of histamine resulting in a 40% fall on VmaxFRC from baseline (PC40) was determined. Respiratory measurements were ranked into terciles to assess the distribution of infants who developed bronchiolitis through the cohort. Cough and wheeze were noted to be frequent before the episode of bronchiolitis. This study has demonstrated that infants who develop bronchiolitis have evidence of pre-existing reduced respiratory function and lower respiratory symptoms. It is proposed that bronchiolitis, although potentially contributory, is not usually causative of subsequent lower respiratory morbidity.

Sheepskins and bedding in childhood, and the risk of development of bronchial asthma

BACKGROUND

Sheepskin bedding might increase house dust mite exposure and so explain some of the increasing prevalence of severity of childhood asthma.

METHODS

Relationships between use of different types of bedding, and diagnoses of asthma, symptoms of wheezing, skin prick test evidence of house dust mite sensitivity, and airway responsiveness to methacholine, were examined retrospectively in a birth cohort of children followed longitudinally to age 15 years.

RESULTS

In the whole cohort, no associations were identified to suggest a causal relationship between use of any type of bedding and development of features of asthma. Although not an a priori hypothesis, we noted that among children with a family history of atopic disease, those who were house dust mite sensitive were more likely to have used an innerspring mattress (29.6% vs 10.2% who had not used an innerspring mattress, p = 0.005).

CONCLUSION

In this subgroup, increased airway responsiveness and mite sensitivity were significantly associated with use of innerspring mattresses, although whether this is a causal or secondary association is not certain. Use of a sheepskin in the bed in early childhood was not an additional risk factor for the development of asthma.

Effect of allergen avoidance on development of allergic disorders in infancy

There is much evidence that the development of allergic disorders may be related to early exposure of allergens, including those in breastmilk. We have tried to find out whether avoidance of food and inhaled allergens in infancy protects against the development of allergic disorders in high-risk infants. In a prenatally randomised, controlled study 120 infants with family history of atopy and high (greater than 0.5 kU/l) cord-blood concentrations of total IgE were allocated randomly to prophylactic and control groups. In the prophylactic group (n = 58), lactating mothers avoided allergenic foods (milk, egg, fish, and nuts) and avoided feeding their infants these foods and soya, wheat, and orange up to the age of 12 months; the infants' bedrooms and living rooms were treated with an acaricidal powder and foam every 3 months, and concentrations of Dermatophagoides pteronyssinus antigen(Der p l) in dust samples were measured by enzyme-linked immunosorbent assay. In the control group (n = 62), the diet of mothers and infants was unrestricted; no acaricidal treatment was done and Der p l concentrations were measured at birth and at 9 months. A paediatric allergy specialist unaware of group assignment examined the infants for allergic disorders at 10-12 months. Odds ratios were calculated by logistic regression analysis for various factors with control for other confounding variables. At 12 months, allergic disorders had developed in 25 (40%) control infants and in 8 (13%) of the prophylactic group (odds ratio 6.34, 95% confidence intervals 2.0-20.1). The prevalences at 12 months of asthma (4.13, 1.1-15.5) and eczema (3.6, 1.0-12.5) were also significantly greater in the control group. Parental smoking was a significant risk factor for total allergy at 12 months whether only one parent smoked (3.97, 1.2-13.6) or both parents smoked (4.72, 1.2-18.2).

Viruses as precipitants of asthma symptoms. I. Epidemiology

The epidemiological studies cited have indicated that viruses are commonly associated with wheezing illnesses in populations, in individuals, and in time, but, unlike bacteria, are rarely found during asymptomatic periods. Viruses have been identified in up to 50% of wheezing illnesses and asthma exacerbations occurring in childhood, and in up to 20% of those in adults. In childhood the predominant organisms identified have been rhinoviruses. RSV and parainfluenza viruses, but coronaviruses have not been studied adequately. Wheezing appears to be more common during rhinovirus and RSV than other virus infections in children spontaneously presenting with respiratory infections to medical care, but all virus groups have been incriminated, and in general, wheezing occurs in upwards of 50% of viral infections in asthmatics followed prospectively. The few adult studies available show little difference between viruses in identification rates during wheezing, or propensity to result in wheezing. The predominant viruses change with age, and children with asthma seem to be more prone to symptomatic virus infections than other children, although the presence of atopy alone does not appear to be important. There are important gaps in our knowledge of the epidemiology of virus-associated wheezing attacks, and further prospective studies are required, using early investigation and sensitive methods for identifying rhinoviruses and coronaviruses, to study severe asthma in children and adults. It is hoped that the use of nucleic acid hybridization and newer antigen-detection techniques will improve the ability to identify difficult viruses such as coronaviruses and rhinoviruses in the future. The ability to identify subclinical infections and compare the ratio of subclinical to clinical infections in normal and asthmatic children would be useful but would require intense monitoring of both groups for an extended period (minimum 12 months to cover seasonal variation) with full virological studies every 2-4 weeks-a difficult and expensive task. Another important line of study would be to prospectively document indoor aeroallergen exposure and virus infections in the same individuals, and compare their importance as precipitants of acute severe asthma attacks. With a clearer understanding of the groups at risk for asthma attacks, and the factors which put them at risk and precipitate their attacks, effective preventive strategies will become more feasible.

Natural history of asthma in childhood--a birth cohort study

A cohort of 67 babies at risk of developing atopic disorders was followed up prospectively for 11 years. Clinical assessment and skin prick allergen sensitivity testing were performed annually over the first five years. At 11 years the cohort was restudied, symptoms were assessed by questionnaire, and bronchial reactivity (BHR) to histamine was measured. On the basis of skin testing, 35 children were atopic and 32 remained non-atopic. The expression of atopy increased with age. The lifetime prevalence of eczema, wheeze, and hay fever were 46%, 63%, and 56% respectively. The yearly period prevalence of hay fever increased with age, that of eczema declined, while that for wheeze showed a bimodal distribution with a peak before the age of 2 years and a gradual increase thereafter. Of the 21 children who wheezed before their second birthday, most never wheezed again and did not show BHR at 11 years. Of the 21 children whose first wheezing was after 2 years of age, 17 were still wheezing at 11 years and 12 showed BHR. Of the children who wheezed before 2 years of age, 10 were or became atopic, compared with 20 of the 23 children who wheezed at 11 years. These findings suggest that childhood asthma is a heterogeneous condition with atopy being strongly associated with the persistence of wheeze.

Clinical observations on lower respiratory tract infections with special reference to serum IgE levels

To examine if the occurrence of wheezing among children with lower respiratory tract infections is associated with atopic predisposition, serum levels of IgE were determined for groups of children with or without wheezing, during infection with Mycoplasma pneumoniae or respiratory syncytial virus (RSV). In M. pneumoniae infection, more than 60% of wheezy children over 2 years of age showed a high IgE level (200 IU/mL or more), while IgE levels were less than 200 IU/mL in 73% of non-wheezy children. In RSV infection, the incidence of high IgE levels among wheezy children was nearly double that of non-wheezy children, although the difference was not significant. These results suggest that in children an allergic disposition is involved in the occurrence of wheezing during the course of lower respiratory tract infections.

Exposure to house-dust mite allergen (Der p I) and the development of asthma in childhood. A prospective study

BACKGROUND AND METHODS

Children with asthma commonly have positive skin tests for inhaled allergens, and in the United Kingdom the majority of older children with asthma are sensitized to the house-dust mite. In a cohort of British children at risk for allergic disease because of family history, we investigated prospectively from 1978 to 1989 the relation between exposure to the house-dust mite allergen (Der p I) and the development of sensitization and asthma.

RESULTS

Of the 67 children studied in 1989, 35 were atopic (positive skin tests), and 32 were nonatopic. Of the 17 with active asthma, 16 were atopic (P less than 0.005), all of whom were sensitized to the house-dust mite, as judged by positive skin tests and levels of specific IgE antibodies (P less than 0.001). For house-dust samples collected from the homes of 59 of the children in 1979 and from 65 homes in 1989, the geometric means for the highest Der p I exposure were, respectively, 16.1 and 16.8 micrograms per gram of sieved dust. There was a trend toward an increasing degree of sensitization at the age of 11 with greater exposure at the age of 1 (P = 0.062). All but one of the children with asthma at the age of 11 had been exposed at 1 year of age to more than 10 micrograms of Der p I per gram of dust; for this exposure, the relative risk of asthma was 4.8 (P = 0.05). The age at which the first episode of wheezing occurred was inversely related to the level of exposure at the age of 1 for all children (P = 0.015), but especially for the atopic children (r = -0.66, P = 0.001).

CONCLUSIONS

In addition to genetic factors, exposure in early childhood to house-dust mite allergens is an important determinant of the subsequent development of asthma.

Acute respiratory tract infections in children. A three-year follow-up from birth

Respiratory tract infections (RTIs) in small children account for a considerable proportion of health care expenditure. In 113 children, followed for the first three years of life, we studied the frequency of acute RTI and its relationship to the factors: type of day-care, age, sex, family size, living conditions, allergic predisposition, family smoking habits, and season. To elucidate the influence of age, the frequency of acute RTI and its relationship to type of day-care was longitudinally studied on a quarterly basis. The frequency of acute RTI diagnosis increased gradually from birth culminating in a peak at the beginning of the second year. Besides age and season, type of day-care was the only factor studied to show any relationship with the frequency of acute RTI diagnosis. Up to the age of almost 2 1/2 years, children attending day-care centres accounted for more RTI diagnoses than did those in home care or family day-care, categories with comparable frequencies.

Atopy in children with and without a family history of atopy. I. Clinical manifestations, with special reference to diet in infancy

The influence of a family history of atopy on atopic morbidity, and relationships between diet in infancy and allergic manifestations at the ages of one and five years were prospectively studied in 91 children. A control group consisted of 72 children with no family history of atopy. At the age of one year, atopic manifestations were found in 19% of 163 children, in 23% of those with a family history of atopy and in 14% of those with no such history. Skin problems were more common in children with a family history of atopy (43%) than in the control children (19%). Of the children with a family history of atopy, 23% had prolonged rhinorrhoea during infancy. The corresponding figure in children with no family history of atopy was 10%. Prolonged rhinorrhoea during infancy correlated with parental smoking only in children with a family history of atopy (47% vs. 18%). At the age of five years, atopic disease was found in 17% of 128 children, 24% of those with a family history of atopy and 9% of those with no such history. Atopic eczema was more common in children with a family history of atopy, irrespective of the diet consumed during infancy. Atopic signs were found in about half of all the children with a family history of atopy. If atopy had been present in the family, the child usually exhibited the same manifestation. Onset of atopic manifestations was not prevented or delayed.

Parental smoking, breast feeding, and respiratory infection in development of allergic diseases

Environmental factors were examined as determinants of clinical disease in a five year prospective study of 73 children born to atopic parents. Clinical follow up for evidence of eczema and wheezing was combined with regular skin testing, immunoglobulin assay, and respiratory viral culture where appropriate. Thirty six children developed eczema, which was often associated with a positive result of a skin test to ingestants in the first year and inhalants by the fifth year. Thirty two children developed one or more episodes of wheeze. Fifteen children wheezed once only, and not all of these developed atopy. No pattern of respiratory infection in early life was characteristic of children with recurrent wheeze. There was a significant difference in parental smoking habits between children with and without episodes of wheeze at the fifth birthday. No protective effect of breast feeding could be shown. The development of allergic disease in susceptible children is influenced by many environmental factors. Advice to families about reduction of environmental allergens continues to pose problems, but parents should be advised to avoid smoking in the child's presence.

Breast feeding conditions a differential developmental pattern of mucosal immunity

A prospective study of 146 children was conducted to evaluate the influence of infant feeding patterns on the development of mucosal immunity. First, there was a trend towards lower IgG concentrations in the breast-fed neonate, indicating a possible earlier 'closure' mechanism of membrane permeability. Second, the post-natal increase in IgA was earlier and greater in formula-fed infants. Third, IgM was detected earlier, more frequently, and at higher levels in formula-fed infants.

The relationship between atopy and salivary IgA deficiency in infancy

In a prospective study, infants born to atopic parents had a significantly higher prevalence of salivary IgA deficiency at all ages studied than control infants, and the mean non zero IgA level of the potentially atopic infants was significantly lower at 8 and 12 months than of control infants. Of the infants with atopic parents, the prevalence of IgA deficiency was not significantly greater in those who manifested atopic disease during the study period than in those who did not, but the levels were significantly lower at 4 months.

Nebulised sodium cromoglycate in recurrently wheezy preschool children

A double blind crossover study of nebulised sodium cromoglycate in 27 asthmatic preschool children was carried out over a one year period. All subjects had sufficiently severe asthma to have had at least one admission to hospital. The active treatment was sodium cromoglycate 20 mg (in 2 ml) administered by a nebuliser four times daily. Assessment was made by a diary card and clinical examination. Results were analysed in 24 subjects who completed the study. Statistical analysis allowed for order of treatment and seasonal effects. Significant results in favour of treatment with sodium cromoglycate were obtained for night cough, day activity, percentage of symptom free days, and overall severity of asthma. During active treatment there was no reduction in the rate of admissions to hospital or intravenous drugs used. The wheeze score during the week after an upper respiratory tract infection was not reduced during treatment with sodium cromoglycate. Nebulised sodium cromoglycate is a tedious prophylactic treatment for the young asthmatic child but is useful when other treatments have failed.

Development of IgE and IgG antibodies to food and inhalant allergens in children at risk of allergic disease

In a prospective study of 92 children with at least one atopic parent, the development of the specific antibody responses to food and inhalant allergens during the first 5 years of life were assessed. By the radioallergosorbent test egg specific IgE antibody occurred in about 30% of the children with the mean peak concentration at 12 months. By the second year the prevalence of this antibody had increased whereas the mean concentration had decreased. Milk specific IgE antibody could not be shown in any subject, including four whose skin tests yielded positive results. Food specific IgG antibody was noted by antigen binding radioimmunoassays at 3 months in most children. These responses had peaked and began to fall by the fifth year. In contrast few children had detectable IgE or IgG antibody to inhalant allergens before the first 2 years of life. Both the concentration and prevalence of specific antibody, however, increased from the second to the fifth year and was greater in children whose skin tests yielded positive results. Breast feeding was associated with an increase in the prevalence of positive results from skin tests but was not associated with detectable IgE antibody to both food proteins, a lower concentration of IgG antibody to cows' milk, and was not associated with protection against the development of disease. A high level of exposure to dust mite was associated with an increased prevalence of positive results from skin tests to dust mite and appreciably higher antibody concentration. This study indicates differences in the humoral responses to food and inhalant allergens. Environmental factors appear to influence the development of these responses.

Relationship of diet in the development of atopy in infancy

We examined the relationship of diet to the development of atopic manifestations in a group of infants with an immediate family history of atopy, followed prospectively from birth for up to 20 months of age. There was no relationship between the development of atopic dermatitis, rhinitis and wheeze and either 2 or 4 months exclusive breast feeding, or the introduction of cow's milk or solids in the first 4 months of life. In addition there was no relationship between the introduction of milk, egg or wheat into the diet and the development of skin-test positivity to these foods. In fact, five infants developed positive skin tests to the food prior to its introduction into the diet, suggesting exposure via maternal breast milk. Thus we have been unable to show a protective effect of either breast feeding or cow's milk or solid avoidance on the development of atopic disease in infancy.

Long-term prospective study in children after respiratory syncytial virus infection

We have prospectively evaluated for the past 8 years 29 children who were hospitalized during infancy with acute lower respiratory tract illness caused by respiratory syncytial virus (RSV). No differences in the prevalence of a family history of atopy or breast-feeding in these infants compared with controls were noted. However, a history of parental smoking was significantly associated with hospital admission for RSV lower respiratory tract disease. Evidence of atopy, as defined by serum IgE levels and radioallergosorbent testing, have developed in only three (10%) of 29 children. Six children (21%) continue to have recurrent lower respiratory tract disease. Fifty-five percent of these children had abnormally low oxyhemoglobin levels (SaO2) measured by ear oximetry for the first 3 to 4 years after the acute illness. Twenty-one percent have persistently low SaO2 levels during the eighth year of follow-up. Spirometric values indicate evidence of peripheral airway obstruction. These studies suggest that an association between RSV lower respiratory tract infections and chronic abnormalities of pulmonary function may be detected sequentially through the first 8 years of life. These abnormalities are not limited to those children developing an atopic state during that same time period.

A prospective study of the clinical manifestations of atopic disease in infancy

We prospectively followed a group of infants with a family history of atopy, from birth for up to 20 months of age. All infants were seen every 4 months and a history, physical examination and skin tests obtained. Atopic dermatitis and rhinitis occurred in about half the infants at some time during the study, while wheezing occurred in about a quarter. Both atopic dermatitis and rhinitis were more common in the first 12 months whereas wheezing occurred later and increased in prevalence with age. Defining atopy by the presence of atopic dermatitis or positive skin tests, only immediate food reactions were significantly associated with atopic infants. In contrast, rhinitis, a single episode of wheezing, colic, vomiting and delayed food reactions were not associated with atopy and thus are unlikely to be due to IgE-related mechanisms during infancy.

A common congenital immunodeficiency predisposing to infection and atopy in infancy

Twenty six infants with a congenital immunodeficiency, characterised by failure of their sera to opsonise heat killed bakers' yeast for phagocytosis by normal polymorphonuclear leucocytes, were studied during infancy to determine the frequency of infection and development of atopy. They were compared with controls, matched prospectively for birth date, sex, parental smoking, and atopy and in whom feeding patterns were similar. In 18 of 26 infants the serum defect persisted at age one year. The incidence of infection and atopy, was appreciably greater in the study group than in controls. The 8 children in whom the defect was transient had a similar incidence of infection but a higher incidence of atopy than controls. Eight of 26 mothers and four of 9 fathers tested also had the serum defect, suggesting a strong genetic component. We support the hypothesis that immunodeficiency predisposes to infection and atopy, and that transient immunodeficiency predisposes to atopy.