Effect of the 2009 Influenza A(H1N1) Pandemic on Invasive Pneumococcal Pneumonia

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 20062008 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.