Effect of the 2009 influenza A(H1N1) pandemic on invasive pneumococcal pneumonia

Abstract

Background: Because pneumococcal pneumonia was prevalent during previous influenza pandemics, we evaluated invasive pneumococcal pneumonia (IPP) rates during the 2009 influenza A(H1N1) pandemic.

Methods: We identified laboratory-confirmed, influenza-associated hospitalizations and IPP cases (pneumococcus isolated from normally sterile sites with discharge diagnoses of pneumonia) using active, population-based surveillance in the United States. We compared IPP rates during peak pandemic months (April 2009-March 2010) to mean IPP rates in nonpandemic years (April 2004-March 2009) and, using Poisson models, to 2006-2008 influenza seasons.

Results: Higher IPP rates occurred during the peak pandemic month compared to nonpandemic periods in 5-24 (IPP rate per 10 million: 48 vs 9 (95% confidence interval [CI], 5-13), 25-49 (74 vs 53 [CI, 41-65]), 50-64 (188 vs 114 [CI, 85-143]), and ≥65-year-olds (229 vs 187 [CI, 159-216]). In the models with seasonal influenza rates included, observed IPP rates during the pandemic peak were within the predicted 95% CIs, suggesting this increase was not greater than observed with seasonal influenza.

Conclusions: The recent influenza pandemic likely resulted in an out-of-season IPP peak among persons ≥5 years. The IPP peak's magnitude was similar to that seen during seasonal influenza epidemics.