NEW ORLEANS, LA—Having an elevated body mass index (BMI) and/or a diagnosis of heart failure increases the likelihood of treatment failure for skin and soft tissue infection (SSTI), Erin Conway, PharmD, from the VA Western New York Healthcare System, Buffalo, NY, presented at IDWeek 2016.

Incidence of SSTIs increased from 8.6 million outpatient visits in 1997 to 14.2 million in 2005, with hospitalization rates also rising due to poorly managed or untreated infections. In addition, antimicrobial resistance can make appropriate oral antibiotic selection a challenge, especially if bacterial cultures are unavailable.

The goal of the quality improvement study was to evaluate risk factors for failure of antibiotic treatment within 30 days for uncomplicated SSTI among outpatients treated at a Veterans Affairs hospital.

Dr. Conway and colleagues conducted a retrospective chart review of 293 outpatients who received an ICD-9 coded diagnosis of cellulitis or abscess by a primary care provider or emergency department physician and were treated with an oral antibiotic between January 1, 2006, and July 1, 2015. The two primary outcomes were failure rate of the antibiotic, defined as another antibiotic prescribed or hospitalization within 30 days, and risk factors for failure of treatment.

At baseline, 67% of the patients were overweight/obese (BMI 25–40kg/m2) and 16% had extreme obesity (BMI >40kg/m2), while 17% were normal weight (BMI <25kg/m2). The type of infection was cellulitis in 62%, abscess in 23%, and mixed in 15%.

Of the total cohort, 224 were successfully treated, while 69 patients were deemed to be treatment failures. Among those who failed, the type of infection among 45 patients (64.3% had MRSA and 28.6%, MSSA) was statistically significant (P<0.01), as was hospitalization within 30 days (P<0.0001).

Of the subgroup of patients who failed oral antibiotics, mean BMI was elevated at 34.2kg/m2 (P=0.01), 47.8% had diabetes (P=0.03), and 15.9% had heart failure (P=0.03); elevated mean Charlson Comorbidity Index was also significant (P=0.05).

However, there were no statistically significant differences in antibiotic regimens or treatment duration in the patients that failed vs. patients who did not fail.

A multivariate logistics regression indicated that BMI and heart failure were determined to be significant predictors of antibiotic failure. Overall, an elevated BMI raised the chances of failure by 1.05 (1.01–1.1; P<0.009)) for every 1kg/m2 unit increment. A diagnosis of heart failure raised the chances of failure by 2.56 (1.1–5.8; P<0.03).

If a patient had a BMI of 40kg/m2 and heart failure, risk of antibiotic failure was 49.7%; this increased to 70.9% for a BMI of 60kg/m2. In contrast, those with a BMI of 40kg/m2 or 60kg/m2 without heart failure had antibiotic failure rates of 28.7% and 48.7%, respectively.

More studies are warranted in the subset of obese patients to find solutions for the “unacceptably high failure rates,” the authors concluded.

Dr. Conway’s study co-authors were Kari Kurtzhalts, PharmD, John A. Sellick, DO, and Kari A. Mergenhagen, PharmD, BCPS AQ-ID.