Influenza-associated cystic fibrosis pulmonary exacerbations

Abstract

Background: Although cystic fibrosis (CF) is the most common inherited respiratory disease, the burden of influenza among individuals with CF is not well characterized.

Methods: We used the CF Foundation Patient Registry to determine the relationship between pulmonary exacerbation incidence rate and influenza virus season from July 2003 through June 2007. The outcome of interest, pulmonary exacerbation, was defined as treatment of a respiratory illness with IV antibiotics. Each influenza season was defined as all months during which >/= 15% of laboratory tests for influenza virus were positive in the US influenza virologic surveillance system. We calculated incidence rates of pulmonary exacerbation during the influenza and summertime seasons as well as relative rates with 95% CIs. A multivariate regression model adjusted for demographic and clinical predictors.

Results: In 2003, the patient cohort size was 21,506 patients, and 7,727 patients experienced at least one pulmonary exacerbation. The overall pulmonary exacerbation incidence rate in the influenza season was 595.0 per 10,000 person-months compared with a summertime baseline of 549.6 per 10,000 person-months. The incidence rate ratio was 1.08 (95% CI: 1.06, 1.10). Multivariate analysis did not change our estimate of risk (adjusted odds ratio: 1.07; 95% CI: 1.05, 1.10). An estimated annual excess of 147.6 per 10,000 person-months or an excess 2.1% of total exacerbations occur during the influenza season.

Conclusion: Our data demonstrate a substantial contribution of the influenza season to CF morbidity. Further studies to determine any causal link between influenza infection and CF pulmonary exacerbations are necessary.

Figure 1.

Cystic fibrosis (CF) pulmonary exacerbation incidence rates per 10,000 person-months by age group and US influenzalike illness rates, July 2003 through June 2007. Weekly influenzalike illness rates are from US influenza surveillance data.^, Influenzalike illness rates are plotted on the Wednesday of each week. CF exacerbation incidence rates are plotted on the 15th day of each calendar month.

Figure 2.

CF pulmonary exacerbation incidence rates per 10,000 person-months and US influenzalike illness rates among patients with < 2 pulmonary exacerbations, July 2003 through June 2007. Y-axis changed from Figure 1 to demonstrate seasonal variation. Smoothed function is a moving average of five data points: the two previous, the current, and the two subsequent incidence rates. See Figure 1 legend for expansion of abbreviation.