Seasonal variation in health care-associated bloodstream infection: Increase in the incidence of gram-negative bacteremia in nonhospitalized patients during summer

Objective: Recent research has suggested that episodes of gram-negative (GN) bloodstream infection (BSI) are more common in the population during summer months. Our objective was to determine if the same phenomenon could be observed in patients with health care-associated (HCA) BSI, and if so, whether a summer peak was less apparent in patients accommodated in a climate-controlled hospital environment. Methods: Data from episodes of HCA BSI spanning an 11-year period were analyzed. To test for seasonal variation in HCA BSI among hospitalized and nonhospitalized patients, and between GN and gram-positive organisms, the χ2 goodness-of-fit test was used. Results: There were 440 episodes of HCA GN BSI of which 259 (59%) occurred in inpatients and 181 (41%) occurred in noninpatients. A significant increase in the frequency of HCA GN BSI was observed in nonhospitalized patients during the summer months (P = .03) but not in climate-controlled hospitalized patients. The most common source of infection in these patents was an intravascular device (38%). Conclusions: We found an increased incidence of GN HCA BSI during summer that was not apparent in our inpatient cohort. The cause is unknown. It might be prudent to advise patients at risk of BSI (eg, those receiving intravascular infusions) to minimize exposure to high environmental temperature and to educate on possible behavioral factors that may increase risk.