E-drug: Asthma associated with early antibiotic use (cont'd)
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[A while ago we had a discussion on asthma associated with early
antibiotic use. I contacted Chris Johnson, the author, and
asked her whether she could elaborate on her methodology, as
some of us wondered whether the study had been adequately
controlled. Her answer is below. HH]
Dear E-druggers,
Sorry to be so late with this response--it was in my mail-in-progress
folder and I forgot to mail it--
Yes, we controlled and/or stratified by child's gender, first-born
status, pet ownership, breast-feeding, maternal history of allergy or
asthma, day care use, lower respiratory infections and occurrence
of fever (first year). We eventually dropped gender, firstborn and
day care from the model as it helped increase our statistical power
and didn't materially change the estimates.
All the children were suburban whites.
We also repeated the analyses dropping kids who received
antibiotics in the first six months for any respiratory symptoms in
order to address the "reverse causation" bias--which didn't change
the estimates.
Timing seems to be important (not surprisingly). Repeating these
analyses considering 12 months or 2 years as the exposure period
pretty much wiped out any associations.
Chris Johnson
e-mail: cjohnso1@hfhs.org
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