Seasonal and Environmental Variation of Lower Extremity Cellulitis Incidence Among Emergency Department Patients in Three Geographic Locations

BACKGROUND: Recent investigation has suggested a higher incidence of lower extremity cellulitis (LEC) during the summer, but it is not clear if this phenomenon is limited only to certain climates or locations. We sought to investigate this phenomenon and further elucidate the relationship with environmental climate factors in three different geographic locations. METHODS: This was a retrospective study of all patients with at least 1 ICD-9 code recorded during an emergency department (ED) visit at Mayo Clinic in Scottsdale, AZ; Jacksonville, FL; and Rochester, MN; between January 1, 2009 and December 12, 2014. Demographics were defined using ICD-9 data. Temperature data was obtained from the National Oceanic and Atmospheric Administration website. The climates of each location were classified according to the Köppen Climate Classification System as hot desert (AZ), humid subtropical (FL) or humid continental (MN) climate types. The primary outcome was LEC (ICD-9 code 682.7) expressed as a proportion of 1000 ED visits (LEC visits/1,000 EDV), to account for seasonal variation in ED usage. Univariate and multivariate regression were performed for analysis. RESULTS: There were 627,292 ED visits among 288,349 patients during the study period. The incidence of LEC visits/1,000 EDV was significantly different across sites (9.36 in FL, 7.95 in AZ, and 7.39 in MN, P <0.0001 for any difference). In the humid climate types (FL and MN), the peak incidences of LEC occurred in the warmest month; July in FL (11.77 LEC visits/1,000 EDV) and August in MN (9.69 LEC visits/1000 EDV). In AZ, the peak incidence occurred in November, the fourth coolest month (9.44 LEC visits/1000 EDV) (Figure 1). There was a significant positive correlation between the high daily temperature and the incidence of LEC cellulitis in all three sites (Figure 2). After controlling for total daily ED visits, gender, and age, the high temperature for the day was significantly associated with occurrence of LE cellulitis at each site (P <0.0001). CONCLUSION: The incidence of LEC presenting to the ED is associated with environmental temperature across different geographic locations and climate types, but slight variations in seasonality of infection was observed. Investigation to determine whether other environmental factors, in particular, humidity, are associated with the incidence of LEC is ongoing. DISCLOSURES: All authors: No reported disclosures.