Results
Through the electronic data warehouse, 737 of 46,045 encounters were identified that met all inclusion criteria. After chart review, 6 were excluded due to missing data in the EHR. Thus 731 encounters were included in the final analysis dataset. Of these, 54.4% were for female patients and the mean patient age was 39.1 years (standard deviation, ±23.7 years); 70.3% of the encounters were the initial visit for diagnosis and treatment of the SSTI (Table 2). Family medicine had the largest proportion of visits (61.4%) of the three outpatient departments and 13.2% of those visits were in patients under age 18. Cellulitis/abscess was the most common SSTI (68.3%) identified through chart review, followed by folliculitis (8.9%) and impetigo (8.9%), carbuncle/furuncle (6.0%), and other SSTIs (7.8%). Of the 100 wound cultures performed among the 617 SSTIs confirmed through chart review, 66 (66.0%) were positive cultures. S. aureus was the most frequently isolated pathogen. Among initial encounters for SSTIs, antibiotic treatment alone was prescribed in 68.4% of visits, IND alone was performed in 3.9%, IND and antibiotics were given in 11.9%, and neither IND nor antibiotic treatment was given in 15.8% of encounters. Trimethoprim/sulfamethoxazole (28.0%), cephalexin (19.2%) and mupirocin (16.2) were the most commonly prescribed antibiotics.
"True" SSTIs were confirmed in 617 of the encounters, a prevalence of 1.3%. Table 3 presents the positive predictive value for each of the SSTI identification algorithms calculated among all encounters and among only initial encounters for the SSTI. The highest PPV was for detecting cellulitis/abscess based on ICD-9 codes at (PPV = 91.5%; 95% CI: 88.9–94.1%), and the lowest was for the identification cellulitis/abscess specific to body site (PPV = 52.6%; 95% CI: 47.6–57.6%). PPVs were lower overall when the SSTI identification algorithm was restricted to initial visits.