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Background: Various studies have linked periods of warmer temperatures to an increased occurrence of surgical site infections （SSIs） and healthcare-associated infections in general. In an observational study, we sought to determine the pathogens for which this association was especially strong. Method: Patient- and procedure-related data of the SSI-module of the German nosocomial infection surveillance system were linked with monthly aggregated meteorological data from the German Meteorological Service for a period from 2000 to 2016. Due to high correlation with other meteorological parameters, analyses were executed focusing on the outside ambient temperature. Temperature was regarded as both a continuous variable and a categorical variable with different temperature intervals （5°C steps ranging from 5°C to ≥20°C）. Through multivariable logistic regression analysis, adjusted odds ratios （OR） with 95% confidence intervals were calculated for SSI rates relating to temperature. SSIs were stratified by pathogen and depth of infiltration. Result: Altogether, 2,004,793 procedures, conducted in 1,455 German surgical departments and resulting in 32,118 SSIs, were included. A general association of warmer mean temperatures in the month of surgery with an increased SSI-risk was observed, particularly for SSIs caused by gram-negative pathogens. Stratification by pathogen revealed that the association was especially prominent for Acinetobacter spp, Pseudomonas aeruginosa, and certain Enterobacteriaceae. Per additional 1°C, we observed a 6% increase in the risk for SSIs caused by Acinetobacter spp （OR, 1.06; 95% CI, 1.04–1.09）, and a 4% increase in the risk for SSIs caused by Enterobacter spp （OR, 1.04; 95% CI, 1.03–1.05）. Among gram-positive pathogens, temperature-association was strongest for Staphylococcus aureus. Superficial SSIs showed a higher temperature-association than deeper SSIs. The risk for superficial SSIs with Acinetobacter spp significantly increased >10-fold after surgeries conducted in months with a mean temperature of ≥20°C in reference to 5°C. For Pseudomonas aeruginosa, we observed a >2-fold statistically significant increase in the risk for superficial SSIs, when comparing the same temperature categories （≥20°C vs 5°C）. Conclusions: Our study demonstrated that higher temperatures were associated with increased SSI-rates caused by gram-negative bacteria. As a consequence, future SSI-prevention measures should place a higher emphasis on the parameter season as part of a more tailormade, personalized approach at infection prevention. For instance, it may be conceivable to seasonally adjust decolonizing regimes and certain prophylaxes. Underlying shifts in microbiome composition due to meteorological factors should be considered in further analyses. Given the expected rise of global temperatures until the end of the century, the topic gains relevance from multiple perspectives. Funding: None Disclosures: None
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