Risk Factors for Skin and Soft Tissue Infections (SSTIs) in HIV-Infected Patients

Background:  Studies have identified risk factors for SSTIs in HIV-infected patients in the era of community-associated MRSA, but patient cohorts were followed for brief periods of time.  These studies yielded conflicting findings about the association between immunologic markers of HIV disease progression and the development of SSTIs.

Objective:  To assess the incidence and risk factors for SSTIs caused by MRSA and other pathogens in HIV-infected outpatients in the University of Chicago Medical Center Infectious Diseases clinic.

Methods:  Retrospective cohort study of 94 HIV-infected outpatients followed between 1/1/2005 and 12/31/2009 with medical record review for data on presentation and etiology of all physician-diagnosed SSTIs, as well as patient demographics, comorbidities, sexually transmitted infection history, and putative risk factors for SSTIs.

Results:  Of 94 patients, 19 (20.2%) had ≥1 SSTI, with a mean number of SSTIs in these 19 patients of 1.63.  The mean follow-up period was 3.6 years.  We observed 92.2 SSTIs per 1000 patient-years.  Of a total of 31 SSTIs diagnosed, 13 (41.9%) were cultured.  Of 13 cultured cases, Staphylococcus aureus was the only isolated pathogen in 8 cases and was one of several pathogens cultured in 2 other cases.  S. aureus was methicillin-resistant in 90% (9/10) of cases.  Eight of 9 (89%) MRSA isolates were clindamycin-susceptible and all were susceptible to trimethoprim-sulfamethoxazole.  There was no significant difference in bivariate analysis between patients with and without SSTIs with regards to initial, last measured, and peak HIV viral loads; gender; race; insurance status; proportion of men who were MSM; and history of IVDU.  There was a significant association with the development of an SSTI and a history of presumptive HPV disease (p=0.01), diabetes (p=0.03), and longer duration of follow-up (p=0.03).  There was a trend for a history of syphilis to be associated with the development of an SSTI (p=0.06).  SSTI patients did not differ significantly from non-SSTI patients in initial (345/mm³ vs 318/mm³; p=0.7), nadir (218/mm³ vs 199/mm³; p=0.5), peak (633/mm³ vs 694/mm³; p=0.7), and last measured (439/mm³ vs 498/mm³; p=0.4) CD4+ T-cell counts.  In a multiple logistic regression model, age, race, gender, duration of follow-up, and history of chronic skin disease were not independently associated with SSTI risk, while history of presumptive HPV disease (OR 4.7, 95% CI 1.2-19.1) and history of diabetes (OR 12.3, 95% CI 1.9-80.2) were independent predictors of developing an SSTI.

Conclusions:  MRSA was the most common etiology of cultured SSTIs in HIV-infected patients.  Diabetes and HPV disease were risk factors for SSTIs.  HPV disease may be a marker for behavioral risk factors predisposing to MRSA infection or for immune status independent of markers of HIV disease progression.  These risk factors may allow physicians to target certain HIV patients for SSTI screening or preventative care.