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Modest rise in invasive pneumococcal pneumonia may be linked to seasonal influenza
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Seasonal influenza circulation may be associated with more than 10% of invasive pneumococcal pneumonia cases during the circulation period, according to results of a recent study.
Researchers from the CDC reviewed surveillance data for invasive pneumococcal pneumonia and seasonal influenza between 1995 and 2006. They estimated the weekly incidence of invasive pneumococcal pneumonia, which was defined by the isolation of pneumococci from normal sterile sites in individuals with clinical or radiographic pneumonia. The estimations were made using active population-based surveillance of three regions in the United States.
There were 21,239 episodes of invasive pneumococcal pneumonia observed among approximately 185 million person-years examined. There were 485,691 specimens examined for influenza.
During periods of influenza circulation, an association with influenza circulation was observed for 11% to 14% of pneumococcal pneumonia cases. Influenza circulation was linked to 5% to 6% of pneumococcal pneumonia cases overall.
In two of the three regions, the strongest associations between pneumococcal pneumonia and influenza circulation were detected when circulation data were lagged by one week. – by Rob Volansky
Walter N. Clin Infect Dis. 2010;50:175-183.
This report simply confirms and quantifies what most of us know to be true; that is, that influenza predisposes to secondary bacterial pneumonia, often pneumococcal. The data were collected during non pandemic years, from 1995-2006, with typical winter/spring influenza epidemics of varying etiology and severity. If anything, one might be surprised that the proportion of invasive pneumococcal pneumonia associated with influenza was so low, only 11% to 14%. Note, however, that this was invasive pneumococcal pneumonia, requiring positive blood, pleural fluid or other sterile site cultures. For every case of post-influenzal invasive pneumococcal pneumonia, there were likely six to 12 cases of non-invasive pneumococcal pneumonia.
The data on “lagging” makes perfect clinical sense; the time of greatest risk of post-influenzal bacterial pneumonia is five to eight days after the onset of influenza. Hence, bacterial pneumonia (and P & I mortality) are lagging indicators.
– Theodore C. Eickhoff, MD
Infectious Disease News Chief Medical Editor