SAN FRANCISCO – During 2009's peak influenza season, children with asthma were nearly twice as likely to be infected with the novel H1N1 influenza virus compared with other viruses, results from a prospective single-center study demonstrated.
In addition, H1N1 influenza infection caused increased severity of both cold and asthma symptoms compared with other infections.
Although reasons for the association remain unclear, “this really proves that asthmatics need to be vaccinated for the flu, because we can see that they're more susceptible to be infected when they're exposed, and they're more susceptible to have loss of asthma control when they get it,” lead investigator Dr. Kirsten M. Kloepfer said in an interview during a poster session at the meetingo
Dr. Kloepfer, a fellow in allergy and clinical immunology at the University of Wisconsin, Madison, and her associates evaluated 161 children aged 4–12 years who provided at least six of eight consecutive weekly nasal samples between Sept. 5 and Oct. 24, 2009. The children also submitted daily cold symptom diaries, and when applicable, asthma symptom diaries including frequency of albuterol use and daily peak flow. The researchers used reverse transcriptase polymerase chain reaction testing to evaluate the nasal specimens.
Of these 161 children, 94 had asthma and 67 did not. Their mean age was 9 years, and 60% were male.
Dr. Kloepfer reported that the incidence of H1N1 influenza infection was 39% in asthmatics and 25% in nonasthmatics, a difference that was not statistically significant, with an odds ratio of 1.9 (P = .06).
However, after adjustment for race, sex, and allergic sensitization, the difference became statistically significant, increasing to an OR of 3.5 (P less than .002).
The incidence of human rhinovirus was statistically similar between the two groups (89% in asthmatics vs. 93% in nonasthmatics), as was the incidence of other viral infections (37% vs. 42%).
Both asthmatics and nonasthmatics reported significant increases in moderate and severe cold symptoms with H1N1, compared with human rhinovirus (63% vs. 28%).
Also, a significantly higher proportion of moderate to severe asthma severity was observed in patients infected with H1N1 influenza, compared with those infected with human rhinovirus (48% vs. 23%). This association held true for severe asthma symptoms as well (19% vs. 4%).
Dr. Kloepfer acknowledged certain limitations of the study, including its single-center design, the fact that it included only children aged 4–12 years, and the fact that it lasted only 8 weeks.
The study was supported by grants from the National Institutes of Health.
Dr. Kloepfer said that she had no other relevant financial disclosures.