Clinical and epidemiologic characteristics as predictors of treatment failures in uncomplicated skin abscesses within seven days after incision and drainage.

Background: Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is now the leading cause of superficial abscesses seen in the Emergency Department.

Study Objectives: Our primary aim was to determine if an association exists between three predictor variables (abscess size, cellulitis size, and MRSA culture) and treatment failure within 7 days after incision and drainage in adults. Our secondary aim was to determine if an association exists between two clinical features (abscess size and size of surrounding cellulitis) and eventual MRSA diagnosis by culture.

Methods: Logistic regression models were used to examine clinical variables as predictors of treatment failure within 7 days after incision and drainage and MRSA by wound culture.

Results: Of 212 study participants, 190 patients were analyzed and 22 were lost to follow-up. Patients who grew MRSA, compared to those who did not, were more likely to fail treatment (31% to 10%, respectively; 95% confidence interval [CI] 8-31%). The failure rates for abscesses ≥ 5 cm and < 5 cm were 26% and 22%, respectively (95% CI -11-26%). The failure rates for cellulitis ≥ 5 cm and < 5 cm were 27% and 16%, respectively (95% CI -2-22%). Larger abscesses were no more likely to grow MRSA than smaller abscesses (55% vs. 53%, respectively; 95% CI -22-23%). The patients with larger-diameter cellulitis demonstrated a slightly higher rate of MRSA-positive culture results compared to patients with smaller-diameter cellulitis (61% vs. 46%, respectively; 95% CI -0.3-30%), but the difference was not statistically significant.

Conclusion: Cellulitis and abscess size do not predict treatment failures within 7 days, nor do they predict which patients will have MRSA. MRSA-positive patients are more likely to fail treatment within 7 days of incision and drainage.