Researchers Describe Incidence, Microbiology and Patient Characteristics of SSTIs

Skin and soft tissue infections (SSTIs) are commonly occurring infections with wide-ranging clinical manifestations from mild to life-threatening. There are few population-based studies of SSTIs in the period after the rapid increase in community-acquired methicillin-resistant Staphyloccus aureus (MRSA). Ray, et al. (2013) used electronic databases to describe the incidence, microbiology, and patient characteristics of clinically-diagnosed SSTIs among members of a Northern California integrated health plan. They identified demographic risk factors associated with SSTIs and MRSA infection.
 
During the study period from 2009 to 2011, 376,262 individuals experienced 471,550 SSTI episodes, of which 23 percent were cultured. Among cultured episodes, 54 percent  were pathogen-positive. Staphylococcus aureus (S. aureus) was isolated in 81 percent  of pathogen-positive specimens, of which nearly half (46 percent) were MRSA. The rate of clinically-diagnosed SSTIs in this population was 496 per 10,000 person-years. After adjusting for age group, gender, race/ethnicity and diabetes, Asians and Hispanics were at reduced risk of SSTIs compared to whites, while diabetics were at substantially higher risk compared to non-diabetics. There were strong age group by race/ethnicity interactions, with African Americans aged 18 to <50 years being disproportionately at risk for SSTIs compared to persons in that age group belonging to other race/ethnicity groups. Compared to Whites, S. aureus isolates of African-Americans and Hispanics were more likely to be MRSA (Odds Ratio (OR): 1.79, Confidence Interval (CI): 1.67 to 1.92, and, OR: 1.24, CI: 1.18 to 1.31, respectively), while isolates from Asians were less likely to be MRSA (OR: 0.73, CI: 0.68 to 0.78).
 
The researchers conclude that SSTIs represent a significant burden to the healthcare system. The majority of culture-positive SSTIs were caused by S. aureus, and almost half of the S. aureus SSTIs were methicillin-resistant. They add that the reasons for African-Americans having a higher likelihood, and Asians a lower likelihood, for their S. aureus isolates to be methicillin-resistant, should be further investigated. Their research was published in BMC Infectious Diseases.

Reference: Ray GT, Suaya JA and Baxter R. Incidence, microbiology, and patient characteristics of skin and soft-tissue infections in a U.S. Population: a retrospective population-based study. BMC Infectious Diseases 2013, 13:252 doi:10.1186/1471-2334-13-252.