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Warm weather increases risk of serious surgical site infections

Rates of infection post surgery rise in summer and fall in winter, study finds

Ingrid Torjesen

Wednesday, 17 May 2017

Surgical site infections increase in the summer and decrease in the winter, according to research published online by Infection Control & Hospital Epidemiology, the journal of the Society for Healthcare Epidemiology of America.

Temperatures above 90°F were associated with 28.9% increased odds for hospitalisation with a surgical site infection (SSI) compared to temperatures less than 40°F.

Researchers used data on millions of patients from the Nationwide Inpatient Sample, the largest database of discharges from hospitals in the United States, to identify every adult hospitalisation with a diagnosis of SSI from January 1998 to November 2011.

Each hospital's longitude and latitude were used to identify nearby weather stations, and monthly summary statistics from each station were included in the analysis, including temperature, rainfall and wind speed.

SSIs were found to be seasonal, with 26.5% more SSI-related hospital discharges in the peak month of August than at the low point of January.

Researchers estimated that a 25% reduction in the average number of at-risk surgeries in the months of July and August would be associated with a decrease of nearly 1,700 SSIs each year. Seasonality and incidence were similar across all regions, age groups, genders and hospital teaching categories, but the seasonal effect was greatest among patients in their 40s and 50s.

Senior author Dr Philip M Polgreen, director of the Innovation Lab at The Signal Center for Health Innovation and Associate Professor of Internal Medicine and Epidemiology at the University of Iowa, said the study had shown that seasonality of surgical site infections is strongly associated with average monthly temperature. As temperatures rise, risk increases.

'However, the odds of any one person getting an infection are still small, and due to the limitations of our data, we still do not know which particular surgeries or patients are at more risk from higher temperature.'

Anthony CA, Peterson RA(a2), Polgreen LA et al. The seasonal variability in surgical site infections and the association with warmer weather: a population-based investigation. Infect Control Hosp Epidemiol 2017 DOI:

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