Atopic conditions other than asthma and risk of the 2009 novel H1N1 infection in children: a case-control study.

A recent study showed an increased risk of 2009 novel H1N1 influenza (H1N1) infection among asthmatic children. Little is known whether this is true for other atopic conditions. This study was designed to determine the association between atopic dermatitis and/or allergic rhinitis and the risk of H1N1 infection among children. We conducted a case-control study in Olmsted County, MN. We randomly selected children ≤18 years of age with a positive test for H1N1. Controls were randomly selected from a pool of residents with negative H1N1 tests and were matched to cases with regard to birthday, gender, clinic registration date, diagnostic test, and month of influenza testing using frequency matching. We compared the frequency of atopic conditions other than asthma between cases and their matched controls. We enrolled 168 cases and 172 controls. Among cases, 91 (54.2%) were male patients, and 106 (63.1%) were white. The median age of cases was 6.3 years (interquartile range, 3.1-11.5). Among cases, 79 (47.0%) had atopic dermatitis and/or allergic rhinitis diagnosed before or after the index date, whereas 54 (31.4%) controls had such conditions (odds ratio [OR], 1.89; 95% CI, 1.15-3.12; p = 0.012, adjusting for asthma status, 2008-2009 seasonal influenza vaccine, time of illness at index date, and other comorbid conditions). History of receiving 2008-2009 seasonal influenza vaccine was associated with H1N1 infection (adjusted OR, 2.06; 95% CI, 1.32-3.28; p = 0.002). Our results suggest an association between H1N1 infection and atopic conditions other than asthma. The association between 2008-2009 seasonal influenza vaccinations and the risk of H1N1 requires further investigation.