Journal of Infectious Diseases
Volume 205 Issue 3 February 1, 2012
http://www.journals.uchicago.edu/toc/jid/current

Editorial Commentaries
Carlos G. Grijalva and Marie R. Griffin
Unveiling the Burden of Influenza-Associated Pneumococcal Pneumonia
J Infect Dis. (2012) 205(3): 355-357 doi:10.1093/infdis/jir753

Extract
In the United States alone, seasonal (interpandemic) influenza is responsible for an average of 226 000 hospitalizations and >23 000 deaths per year [1, 2]. Although all age groups are susceptible to influenza virus infections, children experience the highest disease incidence, whereas older adults suffer the most serious disease-related complications and mortality. Many of these events are secondary bacterial pneumonias, most of which are thought to be caused by Streptococcus pneumoniae (the pneumococcus). Although several observations have suggested that influenza plays an important role in the pneumococcal pneumonia incidence, its contribution has been difficult to appreciate. In this issue of the Journal, Weinberger and colleagues present an elegant assessment that helps to clarify the contribution of influenza virus infections to pneumococcal pneumonia hospitalizations during the 2009 influenza pandemic [3].

Several lines of evidence indirectly support an interaction between influenza virus and the pneumococcus: First, pneumococcal nasopharyngeal acquisition patterns mirror the seasonal patterns of influenza outbreaks [4]. Second, increases in pneumococcal pneumonias during previous influenza pandemics have been documented [5, 6]. Third, concurrent influenza infections and pneumococcal pneumonias have been described [7, 8], and prevention of these pneumonias has been demonstrated in an efficacy trial of a 9-valent pneumococcal conjugate vaccine in South African children. In that randomized study, vaccination with pneumococcal conjugate vaccine reduced the incidence of influenza-associated pneumonia (ie, pneumococcal pneumonia with concurrent influenza infection) by 45% compared with controls [9]. This decline, however, was seen only in human immunodeficiency virus–infected children, and significant reductions were also observed for concurrent infections with parainfluenza viruses and human metapneumovirus [9 …

VIRUSES
Daniel M. Weinberger, Lone Simonsen, Richard Jordan, Claudia Steiner, Mark Miller, and Cécile Viboud
Impact of the 2009 Influenza Pandemic on Pneumococcal Pneumonia Hospitalizations in the United States
J Infect Dis. (2012) 205(3): 458-465 doi:10.1093/infdis/jir749

Abstract
Background. Infection with influenza virus increases the risk for developing pneumococcal disease. The A/H1N1 influenza pandemic in autumn 2009 provided a unique opportunity to evaluate this relationship.

Methods. Using weekly age-, state-, and cause-specific hospitalizations from the US State Inpatient Databases of the Healthcare Cost and Utilization Project 2003–2009, we quantified the increase in pneumococcal pneumonia hospitalization rates above a seasonal baseline during the pandemic period.

Results. We found a significant increase in pneumococcal hospitalizations from late August to mid-December 2009, which corresponded to the timing of highest pandemic influenza activity. Individuals aged 5–19 years, who have a low baseline level of pneumococcal disease, experienced the largest relative increase in pneumococcal hospitalizations (ratio, 1.6 [95% confidence interval {CI}, 1.4–1.7]), whereas the largest absolute increase was observed among individuals aged 40–64 years. In contrast, there was no excess disease in the elderly. Geographical variation in the timing of excess pneumococcal hospitalizations matched geographical patterns for the fall pandemic influenza wave.

Conclusions. The 2009 influenza pandemic had a significant impact on the rate of pneumococcal pneumonia hospitalizations, with the magnitude  of this effect varying between age groups and states, mirroring observed variations in influenza activity.