No Difference in the Pathogenic Microorganisms Among Different Types of Anorectal Abscesses: A Retrospective Study.

Objective:  There is limited data on the pathogenic microorganisms associated with anorectal abscesses. The purpose of this study was to retrospectively analyze the types and quantities of pathogenic microorganisms in the pus cultures of patients with anorectal abscesses and to explore the correlation between pathogenic microorganisms and types of anorectal abscesses.

Methods:  A retrospective analysis was conducted on the microbiological data of 517 inpatient surgical patients with anorectal abscesses treated at a single center from January 2017 to December 2021. Chi-square tests were used to analyze whether there were differences in the types and quantities of pathogenic microorganisms among different types of anorectal abscesses.

Results:  Among the 517 patients, the mean age was 38.5 years, with an average duration of illness of 7.4 days. Of these, 440 (85.1%) were male and 77 (14.9%) were female. The types of anorectal abscesses included perianal abscesses (54 cases, 10.4%), intersphincteric abscesses (253 cases, 48.9%), ischiorectal abscesses (129 cases, 25.0%), deep posterior anal space (DPAS) abscesses (26 cases, 5.0%), supra-levator abscesses (10 cases, 1.9%), and horseshoe abscesses (45 cases, 8.7%). A total of 23 different microorganisms were cultured from the 517 pus specimens. The most common microorganism was Escherichia coli (323 cases, 62.5%), followed by Klebsiella pneumoniae (77 cases, 14.9%), Bacteroides fragilis (nine cases, 1.7%), Pseudomonas aeruginosa (eight cases, 1.5%), and Staphylococcus aureus (seven cases, 1.4%). Additionally, no microorganisms were cultured from 58 (11.2%) pus specimens. Nine patients (1.7%) were admitted with concomitant necrotizing fasciitis. Among the nine cases of concurrent necrotizing fasciitis, E. coli, K. pneumoniae, and S. aureus were cultured in six (66.7%), two (22.2%), and one (11.1%) case, respectively. Chi-square tests revealed no significant differences in the types and quantities of pathogenic microorganisms among different types of anorectal abscesses (P > 0.05).

Conclusion:  This study provides a large sample of pus culture microbiological data from patients with anorectal abscesses. Regardless of whether it is a simple anorectal abscess or concurrent necrotizing fasciitis, E. coli was the most common microorganism cultured from the pus of patients with anorectal abscesses. Other common microorganisms include K. pneumoniae, B. fragilis, and S. aureus. These results provide evidence for the precise antibiotic treatment of anorectal abscesses. Additionally, there were no differences in the types and quantities of pathogenic microorganisms among different types of anorectal abscesses.