Antibiotic selection for purulent skin and soft-tissue infections in ambulatory care: a decision-analytic approach.
OBJECTIVE
Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has caused a nationwide epidemic of skin and soft-tissue infections in ambulatory pediatrics. Antibiotic treatment recommendations suggest incorporating local epidemiology for the prevalence of CA-MRSA. We sought to identify the antibiotic strategy with the highest probability of activity and to identify threshold values for epidemiologic variables including bacterial prevalence and antibiotic resistance.


METHODS
We used decision analysis to evaluate 3 empiric antibiotic strategies: clindamycin, trimethoprim/sulfamethoxazole (T/S), and cephalexin. We calculated the probability of activity against the bacteria causing the infection (CA-MRSA, methicillin-sensitive S. aureus and group A Streptococcus [GAS]) by incorporating estimates of prevalence and antibiotic resistance to determine the optimal strategy. Sensitivity analysis was used to identify thresholds for prevalence and antibiotic resistance where 2 strategies were equal.


RESULTS
Clindamycin (0.95) and T/S (0.89) had substantially higher probability of activity than cephalexin (0.28) using baseline estimates for bacterial prevalence and antibiotic resistance. Cephalexin was the optimal antibiotic only when CA-MRSA prevalence was <10%. The probability of activity for clindamycin and T/S was highly sensitive to changes in the values for bacterial prevalence (both CA-MRSA and GAS) and CA-MRSA resistance to clindamycin.


CONCLUSIONS
Empiric treatment of skin and soft-tissue infections with either clindamycin or T/S maximizes the probability that the antibiotic will be active when CA-MRSA prevalence is >10%. Deciding between T/S and clindamycin requires consideration of antibiotic resistance and prevalence of GAS. This model can be customized to local communities and illustrates the importance of ongoing epidemiologic surveillance in primary care settings.
Hersh
Adam L
AL
Division of Pediatric Infectious Diseases, University of California, San Francisco, CA, USA. hershad@peds.ucsf.edu
Weintrub
Peggy S
PS
Cabana
Michael D
MD
D000553:Ambulatory Care / Q000592:standards* / Q000639:trends; D000704:Analysis of Variance; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D002506:Cephalexin / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D002981:Clindamycin / Q000627:therapeutic use; D017714:Community-Acquired Infections / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology; D003661:Decision Support Techniques; D004351:Drug Resistance; D004363:Drug Utilization; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D015999:Multivariate Analysis; D011336:Probability; D012680:Sensitivity and Specificity; D018461:Soft Tissue Infections / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D013207:Staphylococcal Skin Infections / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D002981:Clindamycin; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D002506:Cephalexin