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SSIs more common in warm weather

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May 22, 2017


The risk for surgical site infection varies by season and is linked with warm weather, according to findings recently published in Infection Control and Hospital Epidemiology.

“At the institutional level, the volume of procedures or institution size may increase the [surgical site infection (SSI)] risk, and other environmental-level risk factors may also exist,” Chris A. Anthony, MD, resident of the department of orthopedic surgery and rehabilitation at the University of Iowa Hospital, and colleagues wrote. “For example, some studies have demonstrated an increased incidence of SSIs for surgeries performed during the summer months. To date, most reports regarding the seasonality of SSIs are based on investigations in single centers, on specific procedures, or in specific geographic regions.”

Anthony and colleagues performed a retrospective cohort study using discharge data from the National Inpatient Sample database. The researchers reviewed all hospital discharges that included a diagnosis of SSI from 1998 to 2011, and used data from the National Climatic Data Center to estimate each month’s average temperature for the locations of all hospitals included in the study.

The incidence of SSIs was “highly seasonal,” Anthony and colleagues reported. Incidence was lowest in January and highest in August, with an average seasonal increase of 2,312 infections from January to August. This increase corresponded to 26.5% (95% CI, 23.3-29.7) more cases in August than in January. After the researchers controlled for hospital-level and demographic characteristics, they estimated that the likelihood of hospital admission for SSI increased by 2.1% per 5°F increase in average monthly temperature.

Average monthly temperatures of hotter than 90°F were associated with a 28.9% (95% CI, 20.2-38.3) increase in the odds of a SSI admission compared with temperatures below 40°F, the researchers wrote.

Anthony and colleagues acknowledged that the study was limited because it did not focus on individual procedures, did not include patient chart reviews and used only inpatient data.

“Despite these limitations, we have demonstrated that the incidence of hospitalizations for SSIs is seasonal and that the seasonality of SSIs can, at least in part, be explained by weather patterns,” the researchers wrote. “Our results suggest that further investigation is needed with more granular data including exact surgery dates and specific procedures. Such work will help determine whether shifting the timing of some surgeries away from peak SSI months can help reduce SSIs in patients with specific procedures.” – by Andy Polhamus

Disclosure: The researchers report no relevant financial disclosures.

itj+ Infographic

Infographic shows that surgical site infections rose by 28.9% in months when the average monthly temperature exceeded 90 degrees.

itj+ Perspective

Keith Kaye
Keith S. Kaye

SSIs can cause severe illness or death after surgery, so preventing and avoiding these infections is critical for patient safety. This study provides unique and important insight into the prevalence of SSIs, specifically the fact that there is an association between SSI incidence and season. This association was strongest among patients aged in their 40s and 50s.

The results show that reducing the number of at-risk surgeries in July and August by 25% could result in a decrease of almost 1,700 SSIs each year — an incredible and impactful reduction. It is important to note that the limitations of the data are that we often do not know which surgeries or patients are at the highest risk during peak summer months.

As a result of this study, researchers and infection control professionals within hospital settings should work to identify which surgeries and patients are most at risk for these SSIs and particularly, which regions in the country are most likely to increase patients’ risk due to high temperatures. By considering seasonality in conjunction with proven modalities of SSI prevention, SSI risk might be reduced and outcomes for patients notably improved.

Keith S. Kaye, MD, MPH

Infectious Disease News Editorial Board member

Professor of internal medicine at the University of Michigan Medical School

President-elect, SHEA

Disclosure: Kaye reports no relevant financial disclosures.