Seasonal variation in Klebsiella pneumoniae bloodstream infection on 4 continents

Background. Klebsiella pneumoniae causes serious, life-threatening infections in humans in endemic and epidemic settings. The objective of this study was to determine whether the incidence of K. pneumoniae bloodstream infection (BSI) was higher during warm months. Methods. We analyzed surveillance data from 2001-2006 at 4 hospitals located on 4 continents. Incidence rates (IRs) and IR ratios (IRRs) were determined using multivariable Poisson regression. Results. In total, 1189 cases of K. pneumonia BSIs occurred during 6,671,337 patient-days. The IR of K. pneumoniae BSI during the 4 warmest months of the year was 2.23/10,000 patient-days, whereas the IR of K. pneumoniae BSI for the other 8 months was 1.55/10,000 patient-days (IRR, 1.46 [95% confidence interval, 1.04-2.06]; P = .03). In contrast, no seasonal variation was identified in rates of BSI due to Enterobacter or Serratia species. Using Poisson regression, we showed that temperature (P < .0001) and dew point (a marker for relative humidity; P < .0001) were both linearly predictive of increasing rates of K. pneumoniae BSI. Conclusions. Environmental pressures may lead to an increase in the IR of K. pneumoniae BSI during the warmest months of the year.