Does the Risk for Postoperative Surgical Site Infection Increase During Heatwaves?

Rates of surgical site infection (SSI) after elective total knee replacement (TKR) or total hip replacement (THR) increase with respect to higher environmental temperature, according to results of a study published in the Journal of Hospital Infection.

Researchers evaluated the effect of environmental temperature and heatwaves on postoperative SSI risk among patients who underwent elective TKR or THR between January 2013 and September 2019. Data sourced from hospitals in Switzerland participating in the Swiss SSI surveillance program were evaluated in relation to climate data sourced from local weather stations. The primary endpoint was the rate of SSIs at 30 days and at 1 year, and the primary exposure was the presence of a heatwave on the day of the procedure. Heatwaves were defined as periods in which the daily mean temperature was at or above 25 °C for 3 consecutive days. Multivariable mixed-effects logistic regression models were used to assess risk factors for postoperative SSI, and Poisson mixed models were used to assess incident SSI trajectory over time.

A total of 116,981 procedures were performed across 122 hospitals during the study period, of which 0.8% occurred during a heatwave.

The overall SSI rate was 1.02%. Stratified by heatwave status, SSI rates were higher for procedures performed during heatwaves compared with those performed in nonheatwave periods (1.44% vs 1.01%, respectively; P =.2).

Using a mean monthly temperature interval of 5 to 10 °C as a reference, procedures performed when the mean monthly temperature was above 20°C were associated with increased SSI risk (odds ratio [OR], 1.59; 95% CI, 1.27-1.98; P <.001). However, this association was attenuated among a subset of patients with BMIs of 25 kg/m² and below (OR, 1.05; 95% CI, 0.51-2.01; P =.9).

Further analysis showed that the risk for SSI due to Gram-negative vs Gram-positive bacteria was higher for procedures performed during months in which the mean temperature was above 20 °C (OR, 3.10; 95% CI, 1.37-7.21; P =.007) or between 16 °C and 20 °C (OR, 2.85; 95% CI, 1.41-6.07; P =.005).

Risk factors for postoperative SSI included an American Society of Anesthesiology score of 3 and above (OR, 1.9; 95% CI, 1.5-2.2; P <.001), prolonged operating time (OR, 1.6; 95% CI, 1.3-2.0; P <.001), and larger hospital size (≥500 beds; OR, 1.4; 95% CI, 1.1-1.7; P =.01).

Postoperative SSI was less likely to occur among women compared with men (OR, 0.7; 95% CI, 0.6-0.8; P <.001) and after TKR compared with THR (OR, 0.7; 95% CI, 0.6-0.8; P <.001).

These data may not be generalizable for areas in which air conditioning systems are standard in hospitals. The researchers also noted the need for a standard definition of a heatwave to further validate these results.

“To establish if, and to which extent, heatwaves increase the risk of SSI, studies involving geographical areas with larger variability in temperatures are needed,” the researchers concluded.

This article originally appeared on Infectious Disease Advisor