Publication:

The value of microbiological analysis of pus swabs in perianal abscess. Have they stood the test of time and antibiotic usage?

Background Evaluation of perianal abscess bacteriology is useful in predicting anal fistula. We report on the predictive strength of pus swab microbiology in aiding future fistula identification and assess the impact of antibiotics.

Methods Consecutive peri-anal abscesses were reviewed retrospectively from the OPCS database between 2003-2012. Microbiological flora analysis, impact of antibiotics and clinical outcome at follow up were recorded.

Results 491 patients were identified in the study period. The age range was 4-81 with mean age being 40 years. 72 were female and 419 male patients. 152 patients received broad-spectrum oral antibiotics in the community for an average of 5 days duration (range 3 to 9). Microbiology revealed: polymircobial (mixed anaerobes, coliforms and Staph. aureus) in 58, monomicrobial in 76 (18 coliforms, 32 bacteroides and 26 Strep. milleri); sterile abscesses 70; no data available in 65 patients.43 patients had a fistula in the non-antibiotic group of which, enteric organisms were predictive in 32% at initial, and 67% at recurrent presentation. 18 patients in the antibiotic group had a fistula wherein enteric organisms were predictive in 16% at initial and 44% at recurrent diagnosis. 27% of these were associated with sterile abscesses.

Conclusions Enteric flora are predictive of anal fistula to a significant extent. Antibiotic usage impacts the microbiology of the flora and can influence the predictive nature of enteric flora in anal fistula. Presence of skin organisms or sterile abscesses does not necessarily exclude occurrence of a fistula in ano in future and use of antibiotics may reduce the risk of fistula formation.