Eighteen-month outcomes of house dust mite avoidance and dietary fatty acid modification in the childhood asthma prevention study (CAPS)☆☆☆

Article Outline

• Abstract
• Methods
  • Participants
  • Randomization
  • Interventions
    • HDM avoidance intervention
    • Dietary intervention
  • Outcomes
  • Skin prick testing
  • Assessment of HDM exposure
  • Fatty acid analysis
  • Lymphocyte cytokine responses to allergen stimulation
  • Blinding
  • Statistical methods
• Results
• Discussion
• Acknowledgements
• References
• Copyright

Abstract 

Background: Observational studies have linked house dust mite (HDM) exposure and dietary fatty acid intake with asthma in childhood. However, definitive evidence of their role in the etiology of asthma requires a randomized controlled trial. Objective: We hypothesized that the incidence of asthma and allergy in high-risk children would be reduced by avoidance of HDM allergens, supplementation with omega-3 fatty acids, or the combination of these strategies. We present the results of an interim analysis reporting outcomes assessed at 18 months. Methods: A total of 616 pregnant women were randomized to an HDM avoidance intervention, comprising the use of impermeable mattress covers and an acaricide or control and the use of an oil supplement, margarines, and cooking oils containing high levels of omega-3 fatty acids or control. Atopic status was measured by skin prick testing. Symptoms, diagnoses, and medication histories were elicited by means of parental interviews. Results: The diet intervention resulted in a 9.8% absolute reduction (95% CI, 1.5-18.1; P = .02) in the prevalence of any wheeze and a 7.8% absolute reduction (95% CI, 0.5-15.1, P = .04) in prevalence of wheeze of >1 week, but it had no effect on serum IgE, atopy, or doctors' diagnosis of asthma. The HDM avoidance intervention did not affect these outcomes but was associated with a lower use of oral steroids. Conclusion: Increasing dietary omega-3 fatty acids might have a beneficial effect on the prevalence of wheeze during the first 18 months of life. Follow-up to age 5 years, when the effect of the interventions on asthma risk will be assessed, is underway. (J Allergy Clin Immunol 2003;111:162-8.)

Keywords:  Allergen avoidance, asthma, atopy, fatty acids, house dust mite, primary prevention

Abbreviations:  HDM , House dust mite

The etiology of asthma is thought to be largely environmental. Sensitization to house dust mite (HDM) allergen in childhood is an established modifiable risk factor for asthma attacks, there being a dose-response relation between allergen exposure and risk of current asthma.¹ A reduced intake of fish in the diet is also a risk factor for asthma; case control data indicate that children who do not eat fish have a 3-times-higher prevalence of asthma.² If the association is causal, the high content of omega-3 fatty acids present in fish might reduce airway inflammation. Thus, reducing exposure to HDM allergen and increasing intake of omega-3 fatty acids need to be tested as primary preventive strategies. Although there are other risk factors that are important for asthma, such as parental smoking, infections, breast-feeding, family history, birth size, and sex, the magnitude of the risk is not as high and/or the exposure or risk factor is not as easily modified.³

The effectiveness of modifying dietary omega-3 fatty acids as a primary preventative measure has not been investigated. There have been 3 randomized trials in which the effectiveness of allergen avoidance for the primary prevention of asthma in high-risk infants has been tested.⁴, ⁵, ⁶ The results of these studies have been encouraging; all of them showed a reduction in respiratory symptoms in the first years of life.

The Childhood Asthma Prevention Study (CAPS) was established in 1997 in Sydney, Australia. The primary aims were to test whether in children at high risk of allergic disease the incidence of allergy and asthma at age 5 years could be reduced by the implementation of interventions directed at avoidance of HDM allergens, diet supplementation with omega-3 fatty acids, or a combination of these 2 interventions. In this article we present the results of this study as of when the children reached 18 months of age.

Back to Article Outline

Methods 

The study hypotheses were tested in a parallel-group randomized controlled trial in which the 2 interventions were tested separately and then together through use of a factorial design. The details of the study design and recruitment procedure, which have been reported elsewhere,⁷, ⁸ are described briefly here.

Participants 

Pregnant women whose unborn children were at high risk of developing asthma because of a parent or a sibling with a current diagnosis of asthma or with frequent wheeze were recruited from the antenatal clinics of 6 hospitals in Sydney, Australia. The selection criteria were as follows: at least 1 parent or sibling with symptoms of asthma, as assessed by means of a screening questionnaire; a reasonable fluency in English; a telephone at home; and residence within 30 km of the recruitment center. Exclusion criteria were as follows: a pet cat at home; the family's being on a strict vegetarian diet; multiple births; and babies born earlier than 36 weeks' gestation.

Six children who had been randomized were withdrawn for medical reasons immediately after birth. These reasons included the following: a birthweight of <2.5 kg; babies requiring major surgery or hospitalization for >1 week; and babies with congenital malformations or other significant neonatal disease. At the completion of recruitment in January 2000, a total of 616 pregnant women had been enrolled.

The study was approved by the ethics committees of the University of Sydney, the Children's Hospital at Westmead, and the Western and South Western Sydney Area Heath Services.

Randomization 

Each woman was randomized to 1 of the 4 study groups before the first home visit at 36 weeks' gestation through use of a randomized block design with a block size of 4. The allocation was made through use of sequentially numbered sealed envelopes. The research nurses who were responsible for recruiting participants and assigning participants to groups were blinded to the methods of randomization until recruitment was complete.

Interventions 

HDM avoidance intervention 

The HDM avoidance intervention involved the use of both physical and chemical methods for the reduction of HDM allergen concentrations in homes. The allergen avoidance procedures were focused on the infant's bed and main play area as the major sites for allergen exposure during infancy. For the active intervention groups, the mattress of the infant's cot or bed was covered in an allergen-impermeable cover. Parents were asked to avoid leaving soft toys in the child's bed and to avoid using sheepskin underlays. If the child slept for more than 2 hours per day in the parents' bed, a zippered impermeable mattress cover and impermeable pillow covers were provided for the parents' bed. A washable play mat was provided to reduce the child's contact with carpeted floors. Parents were asked to wash the child's bedding and play mat and their own bedding (if the infant slept in their bed) in an acaricid-al washing detergent before the birth and then every 3 months. Parents were asked to record this information in a laundry diary.

The participants in the control group for the HDM avoidance intervention were given standard advice on simple cleaning, vacuuming, dusting, and maintaining adequate ventilation. Placebo mattress covers were not provided.

Dietary intervention 

Families in the dietary intervention groups were provided with a daily omega-3–rich tuna fish oil supplement (500 mg, Clover Corporation, Sydney, Australia), to give to the child from the age of 6 months. If the child was breast-feeding before the age of 6 months, no supplement was given, because the concentration of omega-3 in breast milk was equivalent to that of the supplement. If bottle-feeding was introduced before the age of 6 months, the parents were asked to add the oil supplement to the child's formula. The dose was standardized according to the fluid intake and thus according to the age of the child. In addition, each family was provided with canola-based oils and spreads, which are rich in omega-3 fatty acids, for use in food preparation. The control group received placebo supplements made of Sunola oil (Clover Corporation, Sydney, Australia) and were provided with polyunsaturated oils and margarines for use in food preparation. Adherence to the interventions was assessed at each visit through use of a questionnaire that included both self-reported and nurses' ratings of compliance.

Outcomes 

At the age of 18 months, each child underwent a clinical assessment performed by a nurse who was blinded to treatment group allocation. This assessment included an interviewer-administered questionnaire designed to collect information on symptoms, diagnoses, and treatment of asthma and eczema and an examination for the presence of eczema. The questions on eczema had been validated for use in epidemiologic studies.⁹ Procedures included an allergen skin prick test and blood collection for total serum IgE, PBMCs, and plasma fatty acids. All laboratory analyses were undertaken by research assistants who were blinded to treatment group allocation.

Skin prick testing 

Allergy was assessed through use of skin prick tests to ingested allergens (salmon, tuna, peanut, cow's milk, and egg) and inhaled allergens (HDM, grasses, cockroach, cat, and Alternaria ). Glycerine and histamine (6 mg/mL) were used as negative and positive controls, respectively. Any allergen wheal with a diameter of ≥2 mm and larger than the negative control was regarded as positive. When there were no positive allergen wheals and the histamine wheal was also negative, the test was regarded as void.

Assessment of HDM exposure 

Dust was collected from the child's bed at 1, 3, 6, 9, 12, and 18 months of age. The concentration of HDM allergen in fine dust was estimated on each occasion.¹⁰ Values were log-transformed for analysis, and these data were used to estimate the time-weighted average concentration of HDM allergen for each subject.

Fatty acid analysis 

Plasma phospholipids were estimated from blood collected at the 18-month assessments through use of gas chromatography. The proportions of total fatty acids that were omega-3 and omega-6, respectively, were estimated for each subject.

Lymphocyte cytokine responses to allergen stimulation 

Samples of 7 to 8 mL of venous blood were collected in heparin. PBMCs were separated by centrifugation over Ficoll-Hypaque, resuspended at 10⁶/mL in serum-free AIM-V medium, and cultured in 5% CO₂ at 37°C. The PBMCs were cultured with the mitogen phytohemagglutinin (10 μg/mL, Sigma, St Louis, Mo), an aqueous sonicated extract of HDM (50 μg/mL, CSL, Melbourne, Australia), or medium alone for 48 hours. Supernatants were then harvested and stored at –70°C before analysis. Cytokine levels for IL-4, IL-5, IL-10, and IFN-γ were measured by means of 2-site capture immunoassays; OptEIA monoclonal antibody sets (Pharmingen, San Diego, Calif), streptavidin-horseradish peroxidase conjugate, and recombinant cytokines were used as standards. The limits of detection of these assays are 3.1 pg/mL for IL-4 and IL-5, 6.2 pg/mL for IL-10, and 31.25 pg/mL for IFN-γ. When a subject's cytokine response to polyclonal (phytohemagglutinin) stimulation was less than 3 times the control (medium only) level, the subject's results for that cytokine after specific stimulation with HDM were considered void. Assay results below the detection limit were assigned a value equal to the detection limit for purposes of analysis.

Blinding 

The HDM reduction intervention was not blinded, because families in the placebo groups did not receive impermeable mattress coverings, play mats, or washing detergent. The use of bedding materials that are impermeable to HDM in Australia is considered standard care for children with asthma. Providing placebo materials, such as cotton covers not impermeable to HDM allergens, could have been considered to compromise families' decisions to obtain standard care and might have been considered unethical. Parents in the placebo groups were free to choose their own bedding, and for this reason we monitored the use of bedding materials.

The use of placebo supplements, oils, and margarines helped to ensure single blinding for the diet intervention. The slight fishy smell of the active supplements meant that some participants in the intervention groups might have been aware of the constituency of the supplements; however, because the supplements for both groups have been described as natural food oil supplements, the participants' awareness of their group status (active versus control) might have been reduced. Because information about compliance was collected in each group, we were able to detect differences in the use of supplements between groups.

For this study it was not possible to blind the research nurses to group allocation, because they were responsible for explaining the study and giving different advice to each group. However, the research nurses who undertook the outcome assessments and the statistician who conducted the analyses were blinded to the group allocation of the participants.

Statistical methods 

Our sample size was sufficient to allow the detection of a difference of 12% between the control and intervention groups at 80% power and an α of 0.05. We conducted a planned interim analysis of the data collected on all participants when they were 18 months of age. The primary outcomes were as follows: any positive skin prick test result (≥2 mm) to inhaled or ingested allergens; a positive skin prick test result to HDM allergen; and the level of serum IgE. Secondary outcomes were as follows: the prevalence of symptoms, including number of episodes of wheeze or cough; episodes of wheeze or cough lasting for >1 week not associated with colds; historical or physical evidence of eczema; and the level of cytokine responses of PBMCs to stimulation with HDM. Data on adherence to diet and HDM avoidance procedures, HDM allergen concentrations, and plasma fatty acid profiles were used as measures of adherence to the interventions.

For binary outcomes, χ² tests were used to test whether the interventions, categorized as diet (active versus placebo) and HDM reduction (active versus control), had independent effects on outcome. For normally distributed outcome variables, the effect of intervention was calculated as the ratio of the means or geometric means with 95% CIs. For cytokine data, which could not be transformed to a normal distribution, groups were compared by means of the Wilcoxon 2-sample rank-sum test.

Back to Article Outline

Results 

Fig 1 shows the trial profile.

• 
  • View Large Image
  • Download to PowerPoint

• Fig. 1. 

  CAPS trial profile.

Fifty-six participants withdrew after randomization and before the 12-month visit, and an additional 6 participants withdrew before the 18-month assessment. A total of 554 participants completed the 18-month assessment. Table I shows the characteristics of the participants and their families in each of the 4 intervention groups.

Table I. Demographic data for all groups

Potential confounders, such as exposure to environmental tobacco smoke, male sex, maternal history of asthma, breast-feeding, low birthweight, and young maternal age, were equally distributed among the groups.

With regard to the participants who withdrew after randomization, the parents were significantly younger, the mothers were less likely to be tertiary-educated, and the fathers were less likely to be employed full-time than those in the continuing group. Parental smoking status was similar between the 2 groups, and there was no significant difference in weight, length, or head circumference at birth.

A total of 543 infants (88% of the total sample size) were successfully skin-tested at 18 months of age. Table II shows that the interventions were not associated with any significant reductions in specific sensitization.

Table II. Sensitization to inhaled and ingested allergens by skin prick testing at 18 months of age

There were no significant differences in geometric mean IgE concentrations between any of the groups. IgE concentrations were 18.8 IU/L (95% CI, 15.6 to 22.7) in the active diet intervention group, 22.4 IU/L (95% CI, 18.1 to 27.6) in the control diet group (P = .23), 18.6 IU/L (95% CI, 15.1 to 23.0) in the active HDM avoidance group, and 22.4 IU/L (95% CI, 18.6 to 27.2) in the control HDM group (P = .19). There was no significant interaction between the 2 interventions (P = .24).

Table III shows the frequency of early symptoms of asthma and allergic disease.

Table III. Symptoms of wheeze, cough, and eczema at 18 months of age

The prevalence of wheeze-ever was 9.8% lower and the prevalence of wheeze for >1 week 7.8% lower in the active diet intervention group than in the control group. Although the prevalence of most other wheeze indicators was lower in the active diet intervention group, the differences were small and not statistically significant. The prevalence of wheeze for >1 week without a cold was 2.0% lower and the prevalence of doctor visits for wheeze 6.3% lower in the active diet intervention group. The intervention had no significant effect on the prevalence of reported diagnosed asthma at this age. The prevalence of diagnosed asthma was 12.5% in the control diet group compared with 14.7% in the active diet group (95% CI for the difference, −7.9% to 3.5%); the prevalence was 13.8% in the control HDM group compared with 13.6% in the active HDM avoidance group (95% CI for the difference, −5.5% to 6.0%). The prevalence of reported eczema was 8.2% higher and the prevalence of visible eczema 6.9% higher in the active HDM avoidance intervention group than in the control HDM group. There was a lower prevalence of use of oral steroids in the active HDM avoidance group (Table IV), which might indicate a trend toward a lower prevalence of severe disease in this group.

Table IV. Medication use at 18 months of age

However, there were no significant differences in the use of other medications. There were no significant interactions between the diet and HDM avoidance interventions in the effect on any of these outcomes.

The cytokine responses by PBMCs to HDM stimulation in vitro were compared between active and control HDM avoidance groups. The median levels of cytokine in culture supernatant were less than the detection limit for both groups for IL-4, IL-5, and IFN-γ. Median concentrations for IL-10 were 12.2 pg/mL in the control HDM group and 13.4 pg/mL in the active HDM avoidance group. The distribution of levels of cytokines detected after in vitro HDM stimulation did not differ between the active and control HDM avoidance groups (P > .05 in all cases).

We also investigated the extent to which the interventions were successfully implemented. The time-weighted mean Der p 1 concentration in the participants' beds was 15.4 μg/g for the control HDM group and 4.6 μg/g in the active HDM avoidance group. This represents a 70% (95% CI, 64% to 75%) reduction attributable to the intervention. The average concentration for the playroom floor was 15.11 μg/g (95% CI, 12.27-18.60) for the control HDM group and 10.45 μg/g (95% CI, 8.39-12.88) for the active HDM avoidance group. The proportion of plasma fatty acids that were omega-3 plasma fatty acid was higher in the active diet intervention group (6.7%; 95% CI, 6.5-7.0) than in the control diet group (5.0%; 95% CI, 4.8-5.2; P < .0001). The proportion of omega-6 fatty acids was higher in the control diet intervention group (35.0%; 95% CI, 34.6-35.4) than in the active diet intervention group (32.5%; 95% CI, 32.1-32.9; P < .0001). The ratio of omega-3 to omega-6 was 1:5.00 in the active diet intervention group and 1:7.14 in the control diet group (P < .0001).

Back to Article Outline

Discussion 

The early results of this study suggest that increasing omega-3 fatty acids in the diet in the first 18 months of life might have a beneficial effect on wheezing in high-risk infants. The prevalence of parental report of wheeze-ever was 9.8% lower and the prevalence of wheeze for >1 week 7.8% lower in the active diet intervention group. The prevalence of other indicators of wheeze and allergic disease, such as rhinitis, also tended to be reduced in this group. However, we found no benefit for the active HDM avoidance intervention on symptoms at this age.

Over the 18-month study period, levels of HDM allergen in the bedding of the active HDM intervention group were more than 3-fold lower than levels in the bedding of the control HDM group. However, HDM allergen concentrations might not have been low enough to influence the development of sensitization and symptoms. The active diet intervention achieved a significant shift in the ratio of omega-3 to omega-6 in the plasma of the children.

In the Manchester Asthma and Allergy Study, a randomized controlled trial designed to test the effectiveness of HDM allergen reduction, the study team was able to reduce HDM concentrations in the children's beds to <1 μg/g, a level that was more than 5 times lower than we achieved in our active HDM intervention group.¹¹ In the Manchester trial, a modest but significant reduction was found in attacks of severe wheeze with shortness of breath (8%), prescriptions of medication for wheeze symptoms (11%), and wheeze after exertion (7%), but there was no difference in atopy as measured by skin prick testing at the age of 12 months.¹²

In a randomized trial conducted in Winnipeg and Vancouver, Canada, a combined dietary and environmental modification intervention resulted in reduction in the risk of possible or probable asthma by 34%, of probable asthma by 46%, and of rhinitis without colds by 49% at age 12 months.¹³ The geometric mean level of allergen in the active group in this study at 12 months was 0.8 μg/g—more than 5 times lower than the levels in our active HDM intervention group (5 μg/g). Both the Manchester and the Canadian studies have provided evidence that primary preventative interventions can be beneficial to children at high risk of developing asthma. It is encouraging that a low allergen environment can be achieved and maintained during infancy and childhood. In both of these studies the children are being followed prospectively, and further evidence of effectiveness will become available when they are older.

Using a less rigorous HDM intervention strategy combined with diet modification, the Isle of Wight study achieved a reduction in HDM allergen levels similar to that seen in our study (from 25 μg/g to 6 μg/g), yet it showed a reduction in allergy (6%), asthma (12%), and eczema (12%) at 1 year of age.¹⁴ At the 4-year follow-up, allergen avoidance in the first 12 months of life was associated with a 20% lower prevalence of allergy and an 11% lower prevalence of both asthma and eczema in the active group. However, because of the small sample size there was limited certainty about these results.

We found a significantly higher prevalence of eczema in our active HDM intervention group. However, the prevalence of the use of steroid creams was identical in the 2 groups. Further studies are required to determine whether these findings could be explained by the reduction in HDM allergen levels, were a side effect of the intervention, or were simply artefactual.

Exposure to environmental tobacco smoke, male sex, maternal history of asthma, breast-feeding, low birthweight, and young maternal age are all risk factors associated with wheezing and asthma and were equally distributed among the groups.¹⁵ The advantages of our study include its factorial design (which allows us to examine the separate and combined effects of the interventions), its sample size, and its regular prospective follow-up visits. At 18 months, children are at an age when symptoms of asthma cannot be reliably categorized or diagnosed. In addition, prospective cohort studies have shown that early transient wheeze is not a good predictor of a child's developing wheeze and asthma later in life.¹⁶, ¹⁷ We also need to be cautious because we conducted a large number of statistical tests, leading to the possibility that effects on secondary outcome measures would be detected by chance. Further analysis will be conducted at 3 and 5 years of age, when allergy and asthma symptoms can be more reliably measured; by that time, transient food allergy will have subsided and persistent inhalant allergy will be established in many children.¹⁸ These analyses will provide more reliable information about whether the interventions, either separate or combined, have any effect on the current high rates of respiratory and allergic symptoms and medication use in our study groups.

Back to Article Outline

Acknowledgements 

The CAPS Study senior investigators are Jennifer K. Peat, Guy B. Marks, Craig M. Mellis and Stephen R. Leeder. Associate investigators are Euan R. Tovey and Karen Webb. The Study Coordinator is Seema Mihrshahi. The authors wish to thank the CAPS research team involved in the study. Data have been collected by Anne Tattam, Samantha Forbes, Nicola Vukasin, Craig Wainwright, William Krause, and Natalia Knezevic. Allergen assays were performed by Carl H. Vanlaar and Sally Criss. Fatty acid and cytokine assays were performed by Mark Neumann and Jie Zhou. Database managers are Elena Belousova and Rosario Ampon.

Back to Article Outline

References 

1. Peat JK, Tovey E, Toelle BG, Haby MM, Gray EJ, Mahmic A, et al.  House dust mite allergens. A major risk factor for childhood asthma in Australia. Am J Respir Crit Care Med. 1996;153:141–146
   • View In Article
   • MEDLINE
2. Peat JK, Salome CM, Woolcock AJ. Factors associated with bronchial hyperresponsiveness in Australian adults and children. Eur Respir J. 1992;5:921–929
   • View In Article
   • MEDLINE
3. Peat JK, Li J. Reversing the trend: reducing the prevalence of asthma. J Allergy Clin Immunol. 1999;103:1–10
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (144 KB)
   • CrossRef
4. Arshad SH, Matthews S, Gant C, Hide DW. Effect of allergen avoidance on development of allergic disorders in infancy. Lancet. 1992;339:1493–1497
   • View In Article
   • Abstract
   • CrossRef
5. Chan-Yeung M, Manfreda J, Dimich-Ward H, Ferguson A, Watson W, Becker A. A randomized controlled study on the effectiveness of a multifaceted intervention program in the primary prevention of asthma in high-risk infants. Arch Pediatr Adolesc Med. 2000;154:657–663
   • View In Article
   • MEDLINE
6. Custovic A, Simpson BM, Simpson A, Kissen P, Woodcock A. Effect of environmental manipulation in pregnancy and early life on respiratory symptoms and atopy during first year of life: a randomised trial. Lancet. 2001;358:188–193
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (89 KB)
   • CrossRef
7. Mihrshahi S, Peat JK, Webb K, Tovey ER, Marks GB, Mellis CM, et al.  The childhood asthma prevention study (CAPS): design and research protocol of a randomized trial for the primary prevention of asthma. Control Clin Trials. 2001;22:333–354
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (323 KB)
   • CrossRef
8. Mihrshahi S, Vukasin N, Forbes S, Wainwright C, Krause W, Ampon R, et al.  Are you busy for the next 5 years? Recruitment in the Childhood Asthma Prevention Study (CAPS). Respirology. 2002;7:147–151
   • View In Article
   • MEDLINE
   • CrossRef
9. Williams H, Burney P, Hay R, Archer C, Shipley M, Hunter J, et al.  The U.K. Working Party's diagnostic criteria for atopic dermatitis. I. Derivation of a minimum set of discriminators for atopic dermatitis. Br J Dermatol. 1994;131:383–396
   • View In Article
   • MEDLINE
   • CrossRef
10. Mihrshahi S, Marks G, Criss S, Tovey E, Peat J. Effectiveness of an intervention to reduce house dust mite allergen levels in infant's beds. Allergy. 2003; In press
    • View In Article
11. Custovic A, Simpson BM, Simpson A, Hallam C, Craven M, Brutsche M, et al.  Manchester Asthma and Allergy Study: low-allergen environment can be achieved and maintained during pregnancy and in early life. J Allergy Clin Immunol. 2000;105:252–258
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (67 KB)
    • CrossRef
12. Custovic A, Simpson BM, Simpson A, Kissen P, Woodcock A. Effect of environmental manipulation in pregnancy and early life on respiratory symptoms and atopy during first year of life. Lancet. 2001;358:188–193
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (89 KB)
    • CrossRef
13. Chan-Yeung M, Manfreda J, Dimich-Ward H, Ferguson A, Watson W, Becker A. A randomized controlled study on the effectiveness of a multifaceted intervention program in the primary prevention of asthma in high-risk infants. Arch Pediatr Adolesc Med. 2000;154:657–663
    • View In Article
    • MEDLINE
14. Hide DW, Matthews S, Tariq S, Arshad SH. Allergen avoidance in infancy and allergy at 4 years of age. Allergy. 1996;1:89–93
    • View In Article
15. Sherriff A, Peters TJ, Henderson J, Strachan D. Risk factor associations with wheezing patterns in children followed longitudinally from birth to 3¹/² years. Int J Epidemiol. 2001;30:1473–1484
    • View In Article
    • MEDLINE
    • CrossRef
16. Martinez FD, Wright AL, Taussig LM, Holberg CJ, Halonen M, Morgan WJ. Asthma and wheezing in the first six years of life. N Engl J Med. 1995;332:133–138
    • View In Article
    • MEDLINE
    • CrossRef
17. Rhodes HL, Thomas P, Sporik R, Holgate ST, Cogswell JJ. A birth cohort study of subjects at risk of atopy: twenty-two-year follow-up of wheeze and atopic status. Am J Respir Crit Care Med. 2002;165:176–180
    • View In Article
    • MEDLINE
18. Van Asperen PP, Kemp A, Mellis CM. Skin test reactivity and clinical allergen sensitivity in infancy. J Allergy Clin Immunol. 1984;73:381–386
    • View In Article
    • MEDLINE
    • CrossRef