Pre-natal and post-natal exposure to respiratory infection and atopic diseases development: a historical cohort study

Background: According to the hygiene hypothesis, infections in
early life protect from allergic diseases. However, in earlier
studies surrogate measures of infection rather than clinical
infections were associated with decreased frequencies of atopic
diseases. Exposure to infection indicating sub-clinical infection
rather than clinical infection might protect from atopic diseases.
Objective: to investigate whether exposure to acute respiratory
infections within pregnancy and the first year of life is
associated with atopic conditions at age 5 - 14 years and to
explore when within pregnancy and the first year of life this
exposure is most likely to be protective. Methods: Historical
cohort study: Population level data on acute respiratory infections
from the routine reporting system of the former German Democratic
Republic were linked with individual data from consecutive surveys
on atopic diseases in the same region (n = 4672). Statistical
analyses included multivariate logistic regression analysis and
polynomial distributed lag models. Results: High exposure to acute
respiratory infection between pregnancy and age one year was
associated with overall reduced odds of asthma, eczema, hay fever,
atopic sensitization and total IgE. Exposure in the first 9 months
of life showed the most pronounced effect. Adjusted odds ratio's
for asthma, hay fever, inhalant sensitization and total IgE were
statistical significantly reduced up to around half. Conclusion:
Exposure to respiratory infection ( most likely indicating
sub-clinical infection) within pregnancy and the first year of life
may be protective in atopic diseases development. The postnatal
period thereby seems to be particularly important.