Researchers have discovered that the incidence of serious infections caused by gram-negative bacteria climbs in line with the temperature outside.

Dr E Perencevich and colleagues and colleagues found that the incidence of serious infections caused by gram-negative bacteria among hospitalized patients increased by as much as 17% for every 10ºF rise in external temperature. Thus, meaning that the incidence of such infections could be as much as 46% higher in summer than in winter.

The researchers studied the effect of temperature on a number of pathogens, including Escherichia coli (E. coli) and Staphylococcus aureus, however the weather had the greatest effect upon the incidence of infections caused by P. aeruginosa, a common cause of external ear, urinary tract, and lung infections, and A. baumannii, an opportunistic pathogen that can cause death and serious illnesses, particularly in people with compromised immune systems.

"Gram-negative bacteria are a frequent cause of urinary tract, gastrointestinal and respiratory infections, as well as more serious things like pneumonia, wound or blood infections," said Jessina McGregor, in a news release. "Everyone knows there is a seasonality to some viral infections such as influenza or the common cold, but we're now finding that some of these bacterial infections peak in the heat of summer."

The researchers concluded: “Significantly higher rates of gram-negative infection were observed during the summer months, compared with other seasons. For some pathogens, higher temperatures were associated with higher infection rates, independent of seasonality. These findings have important implications for infection prevention, such as enhanced surveillance during the warmer months, and for choice of empirical antimicrobial therapy among hospitalized adults.”

Perencevich EN, McGregor JC, Shardell M, Furuno JP, Harris AD, Morris JG, Fisman DN, Johnson JA. Summer Peaks in the Incidences of Gram-Negative Bacterial Infection Among Hospitalized Patients. Infect Control Hosp Epidemiol. 2008;29:1124–1131. doi: 10.1086/592698

News release: Winter brings flu, summer brings bacterial infections. Oregon State University. November 26th 2008.