Invasive Pneumococcal Disease and Pandemic (H1N1) 2009

Invasive Pneumococcal Disease and Pandemic (H1N1) 2009, Denver, Colorado, USA CME

Abstract and Introduction

Abstract

Pneumococcal pneumonia was a complication during previous influenza pandemics but was not evident initially during pandemic (H1N1) 2009. During October 2009 in Denver, Colorado, USA, invasive pneumococcal disease (IPD) and pandemic (H1N1) 2009 peaked simultaneously, which suggests a link. We compared cases of IPD in October 2009 with cases in February 2009, the most recent peak month of seasonal influenza. During October 2009, we observed 58 IPD cases, which was 3× the average number of IPD cases that usually occur in October in Denver. Patients with IPD in October 2009 were younger and more likely to have chronic lung disease than patients who had IPD in February 2009; a total of 10/47 patients had influenza, and 33/53 patients had influenza-like illness. Thus, ≈17%–62% cases of IPD may have been associated with pandemic (H1N1) 2009. Pneumococcal disease prevention strategies should be emphasized during future influenza pandemics.

Introduction

Pneumonia caused by Streptococcus pneumoniae (pneumococci) was a frequent complication of influenza during previous pandemics. In 1 autopsy series, ≈20% of deaths during the 1918 influenza pandemic were associated with pneumococci.^[1] Pandemic (H1N1) 2009 was the first pandemic in which pneumococcal and influenza vaccines and antiviral drug treatment had the potential to change the interaction between pneumococcal infection and influenza.

Among early cases of pandemic (H1N1) 2009, pneumococcal complications were rarely reported.^[2–4] However, in October 2009, the Colorado Department of Public Health and Environment identified a substantial increase in cases of invasive pneumococcal disease (IPD) in the Denver metropolitan area, concurrent with a peak in pandemic (H1N1) 2009–associated hospitalizations, raising the question of the role of this pandemic (H1N1) 2009 virus. We evaluated the IPD cases in October 2009 in terms of age, prevalence of concurrent conditions, severity of illness, evidence of co-infection with pandemic (H1N1) 2009 virus, use of antiviral drugs, and influenza and pneumococcal vaccination. We also assessed the possible contribution of changes in laboratory practices to the increase in reported IPD cases.