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.