Incidence and Effects of Seasonality on Nonpurulent Lower Extremity Cellulitis After the Emergence of Community-Acquired Methicillin-Resistant Staphylococcus aureus.

Nonpurulent lower extremity cellulitis (NLEC) is a common clinical diagnosis, with β-hemolytic streptococci and Staphylococcus aureus considered to be the most frequent causes. In 1999, the US Public Health Service alerted clinicians to the presence of community-acquired methicillin-resistant S aureus (CA-MRSA) infections in 4 children in the upper Midwest. Since then, it has become a well-recognized cause of skin and soft-tissue infections, in particular, skin abscess. A previous population-based study of NLEC in Olmsted County, Minnesota, reported an unadjusted incidence rate of 199 per 100,000 person-years in 1999, but it is unknown whether CA-MRSA subsequently has affected NLEC incidence. We, therefore, sought to determine the population-based incidence of NLEC since the emergence of CA-MRSA. Age- and sex-adjusted incidence (per 100,000 persons) of NLEC was 176.6 (95% CI, 151.5-201.7). Incidence differed significantly between sexes with age-adjusted sex-specific rates of 133.3 (95% CI, 104.1-162.5) and 225.8 (95% CI, 183.5-268.0) in females and males, respectively. Seasonal incidence differed, with rates of 224.6 (95% CI, 180.9-268.4) in warmer months (May-September) compared with 142.3 (95% CI, 112.8-171.9) in colder months (January-April and October-December). Despite emergence and nationwide spread of CA-MRSA since 1999 in the United States, the incidence of NLEC in Olmsted County was lower in 2013 than in 1999, particularly in females. This suggests that CA-MRSA is not a significant cause of NLEC and that NLEC cases are seasonally distributed. These findings may be important in formulation of empirical therapy for NLEC and in patient education because many patients with NLEC are prone to recurrent bouts of this infection.