Increased H1N1 Infection Rate in Children With Asthma

Abstract

In 2009, H1N1 influenza resulted in 87 000 hospitalizations among children. The most common comorbidity for patients hospitalized as a result of H1N1 infection was asthma. Were children with asthma more likely to be infected with H1N1 influenza?A total of 161 children aged 4 to 12 years, 95 with asthma and 66 without asthma, were recruited from within a study of 193 children being studied for the effects of rhinovirus infection on asthma.The children provided 8 weekly nasal mucus samples that were analyzed for respiratory viruses by polymerase chain reaction. Upper respiratory infection and asthma symptoms, morning peak expiratory flow rates, and albuterol use were recorded on daily diary cards. Loss of asthma control was defined as at least moderate asthma symptoms and either a decrease in peak expiratory flow of ≥20% or use of albuterol for ≥2 days per week.Three hundred forty-six infections were detected: rhinoviruses (62%), enterovirus (12%), H1N1 (10%), adenovirus (2%), and multiple viruses (13%). When multiple viruses were detected in a single sample, rhinovirus (80%) and H1N1 (51%) were the most common. Thirty-four percent of children were infected with H1N1; rates were higher in children with asthma (41%) than in children without asthma (24%) (odds ratio: 2.2; 95% confidence interval: 1.1–4.4; P = .03). Asthma did not affect rates of infection with rhinovirus (90% in each group), enterovirus (30% vs 24%), adenovirus (11% vs 12%), or other viruses (6% vs 5%). Rates of loss of asthma control per infection were as follows: H1N1, 38% (9 of 24); rhinovirus, 21% (27 of 127); and the combination of rhinovirus and H1N1, 44% (4 of 9).Given the increased susceptibility of children with asthma to infection, these findings reinforce the need for yearly influenza vaccination to prevent infection and raise new questions about the mechanism for enhanced susceptibility to influenza infection in asthma.Influenza infection is more likely to cause chest symptoms in a child with underlying asthma, but in addition, this study suggests that children with asthma also become infected at a higher rate. This increased susceptibility to infection appeared to be unique to influenza virus as opposed to rhinovirus and other viruses. Whereas the mechanism of this increased susceptibility to infection with a particular virus needs to be explored, infection with the particular virus involved (influenza) can often be prevented by vaccination.