Perianal abscesses are frequent diseases in general surgery. Principles of standard patient care are surgical drainage with exploration and concomitant treatment of fistula. Antiinfective therapy is frequently applied in cases of severe local disease and perianal sepsis. However, the role of microbiologic testing of purulence from perianal abscesses is disputed and the knowledge concerning bacteriology and bacterial resistances is very limited. A retrospective cohort study was performed of consecutive patients (≥ 12 years of age) from a tertiary care hospital, who underwent surgical treatment for perianal abscess from 01/2008 to 12/2019. Subdividing the cohort into three groups regarding microbiological testing results: no microbiological testing of purulence (No_Swab, n = 456), no detection of drug resistant bacteria [DR(-), n = 141] or detection of bacteria with acquired drug resistances from purulence [DR(+), n = 220]. Group comparisons were performed using Kruskall-Wallis test and, if applicable, followed by Dunn´s multiple comparisons test for continuous variables or Fishers exact or Pearson's X2 test for categorical data. Fistula persistence was estimated by Kaplan Meier and compared between the groups using Log rank test. Corralation analysis between perioperative outcome parameters and bacteriology was performed using Spearman´s rho rank correlation. Higher pretherapeutic C-reactive protein (p < 0.0001) and white blood cell count (p < 0.0001), higher rates of supralevatoric or pararectal abscesses (p = 0.0062) and of complicated fistula-in-ano requiring drainage procedure during index surgery (p < 0.0001) reflect more severe diseases in DR(+) patients. The necessity of antibiotic therapy (p < 0.0001), change of antibiotic regimen upon microbiologic testing results (p = 0.0001) and the rate of re-debridements during short-term follow-up (p = 0.0001) were the highest, the duration until definitive fistula repair was the longest in DR(+) patients (p = 0.0061). Escherichia coli, Bacteroides, Streptococcus and Staphylococcus species with acquired drug resistances were detected frequently. High rates of resistances against everyday antibiotics, including perioperative antibiotic prophylaxis were alarming. In conclusion, the knowledge about individual bacteriology is relevant in cases of complex and severe local disease, including locally advanced infection with extended soft tissue affection and perianal sepsis, signs of systemic inflammatory response as well as the need of re-do surgery for local debridements during short-term and fistula repair during long-term follow-up. Higher rates of acquired antibiotic resistances are to be expected in patients with more severe diseases.
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