Decreasing Incidence of Skin and Soft Tissue Infections With a Seasonal Pattern at an Academic Medical Center, 2006–2014

Background.  The incidence of skin and soft tissue infections (SSTIs) in the United States increased sharply after 2000 with the emergence of USA300 methicillin-resistant Staphylococcus aureus. We examined trends in SSTI incidence in 2006-2014 at the University of Chicago Medicine (UCM). Methods.  Data were obtained for patient encounters at UCM with an International Classification of Diseases, Ninth Revision-coded SSTI diagnosis between January 1, 2006 and March 31, 2014. Incidence density was calculated per 1000 encounters by quarter and year. Encounters were stratified by inpatient, outpatient clinic and emergency department (ED) encounters and by age group, gender, and race. Poisson regression was used to assess change over time. Results.  In 2006-2014, data were collected for 38 201 SSTI-associated encounters among 31 869 subjects. Among all patients treated at UCM, there was a decrease of 1% per year in the incidence of SSTIs during 2006-2013, with an overall decrease of 16%. There was a significant decrease in SSTI-related encounters among inpatients (rate ratio [RR] = 0.97; 95% confidence interval [CI], .96-.98), ED patients (RR = 0.98; 95% CI, .97-.98), adults (RR = 0.98; 95% CI, .97-.98), children (RR = 0.96; 95% CI, .95-.97), and African Americans (RR = 0.99; 95% CI, .98-.99). There was an annual seasonal trend, with the peak incidence occurring during the late summer. Conclusions.  The incidence of SSTIs at UCM decreased in children and adults with seasonal variation, peaking during the summer months. This suggests a reversal of the massive increase in SSTI incidence in the United States after 2000.