Study procedures
A questionnaire was used to collect data on socio-demographic factors, family history of allergy, and home environment by interview of the child’s mother around the time of the child’s birth. Questionnaires were repeated periodically to collect data on wheeze and asthma symptoms. Wheeze was defined as any episode of parentally-reported wheeze during the previous 12 months at 8 years. Asthma was defined as parentally reported wheeze during the previous 3 years plus one or both of parentally reported wheeze up to 5 years and a doctor diagnosis of asthma ever.
Stool samples to detect geohelminths were collected from mothers before birth of the child, and from children periodically from birth. Samples were examined using of a combination of methods: saline mounts, modified Kato-Katz, formol-ether concentration, and carbon-coproculture methods.18 A positive sample was defined by the presence of at least one egg or larva from any of the four detection methods. A. lumbricoides and T. trichiura infection intensities were expressed as eggs per gram (epg) of faeces using results of Kato-Katz.
Spirometry was done at 8 years using a Microloop spirometer (CareFusion, UK) before and after 200 ug of salbutamol administered through a spacer. A positive test for bronchial hyperreactivity was an increase in FEV1 of ≥12%. Fractional exhaled nitric oxide was measured in parts per billion using NObreath (Bedfont Scientific, UK) at a flow rate of 50 ml/sec. Nasal wash samples were collected at 8 years using a standardized protocol as described.19
Allergic sensitization was measured by SPTs with 9 allergen extracts (Greer laboratories, Lenoir, North Carolina, USA): house dust mites (Dermatophagoides pteronyssinus/Dermatophagoides farinae mix), American cockroach (Periplaneta americana ), cat, dog, grass pollen (9 southern grass mix), fungi (New stock fungi mix), egg, milk, and peanut, with positive histamine and negative saline controls. A positive reaction was defined as a mean wheal diameter at least 3 mm greater than the saline control 15 min after pricking the allergen onto the forearm with lancets. Positive SPT was defined as a positive reaction to any of the allergens tested.