Drug-resistant bacteria in perianal abscesses are common and relevant

From 01/2008 to 12/2019 all consecutive patients (≥ 12 years), who underwent surgical treatment at the University Hospital Giessen for perianal abscess (c. in-ano and, if necessary, excision primary or fistula drainage) as well as for extensive surgical excision of advanced infected perianal/perineal soft tissue from perianal abscesses were retrospectively assessed and included in this study.

Patient data was retrospectively analyzed from the prospectively maintained institutional database. The present work focused mainly on the bacteriology of swabs obtained intraoperatively from the purulence of perianal abscesses and on the (acquired) resistance to drugs of the microorganisms detected. Intermediate antibiotic efficacy was not judged as drug resistance. Two microbiologists independently reviewed the results of bacterial cultures and susceptibility testing for intrinsic or acquired drug resistance against the current EUCAST (European Committee on Antimicrobial Susceptibility Testing) endpoint tables for interpretation of minimum inhibitory concentrations and zone diameters, v11.0, 2021, and intrinsic resistance and unusual phenotypes, v3.2, 2020, http://www.eucast.org. Isolates with at least one detected acquired resistance were interpreted as “drug resistant”, while the intrinsic resistances of the detected bacteria, indicated by the respective EUCAST documents, were filtered out. Bacteria with only intrinsic resistances were not interpreted as “drug resistant”.

The analysis of resistance to cefuroxime and metronidazole, two important drugs for routine perioperative antibiotic prophylaxis in colorectal surgery, was carried out independently of the acquired or intrinsic origin. The isolates detected were further classified according to the ESKAPE definition, which includes highly virulent and frequently drug-resistant pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter sp.15.

Duration of postoperative hospitalization and duration from initial surgery until surgical repair of the fistula were interpreted as surrogate parameters for postoperative outcomes. In addition, general patient characteristics, preoperative systemic markers of infection, including C-reactive protein (CRP) values ​​and peripheral blood white blood cell (WBC) count, procedure characteristics After surgery, the patient’s postoperative outcomes, including re-surgery, recurrence, and application of postoperative antibiotics were assessed.

Surgery and perioperative patient care

Perianal abscesses are treated as surgical emergencies. Therapeutic strategies follow German guidelines for anal abscess and cryptoglandular fistula16. Surgical drainage or excision of the abscess are standard treatment, followed by careful exploration of the fistula during index surgery. Primary fistulectomy is routinely performed during index surgery for superficial fistulas by experienced surgeons. In case of uncertain results or transsphincter and higher located fistulas, initial placement of loose setons for fistula drainage during index surgery is performed followed by permanent fistula repair in a second surgery after 4 to 6 weeks or as soon as possible beyond the infectious situation by trained surgeons.

During abscess drainage surgery, swabs of purulence were obtained according to the surgeon’s own judgment. Therefore, swabs of abscess pus and infected tissue are routinely taken in cases of more complicated and severe perianal disease, including locally advanced infection with extensive soft tissue disease, whereas, in patients with mild and uncomplicated disease, swabs are not obtained in clinical routine. .

All patients referred for surgical perianal abscess drainage procedure receive single-dose perioperative antibiotic prophylaxis with intravenous cefuroxime and metronidazole. However, antibiotic therapy is not systematically continued postoperatively. Indications for postoperative antibiotic therapy after surgical drainage of perianal abscesses with or without detection and subsequent drainage or excision of fistulas are complicated perianal infections and perianal and perineal sepsis with locally advanced phlegmonous or gangrenous infection of the soft tissues. Otherwise, the patients rinse the perianal wounds themselves and systematically go out as soon as possible on the first or second postoperative day.

statistical analyzes

The patient cohort was subdivided into three groups with respect to microbiological swab examination and diagnosis of drug-resistant bacteria: (1) patients in whom a microbiological swab was not obtained from the abscess intraoperatively (No_Swab group: n = 456), (2) patients with intraoperative microbiological swab without detection of DR bacteria [DR(−) group: n = 141] or (3) patients with intraoperative swab and detection of acquired drug resistance in bacteria during microbiological examination [DR(+) group, n = 220].

Statistical analyzes were performed using GraphPad Prism (Version 9 for Windows, GraphPad Software, San Diego, CA, USA, www.graphpad.com). The retrospective availability of the data presented was > 96%. For descriptive statistics, categorical data were analyzed using Fishers exact or Pearson’s X2 test. Group comparisons of continuous variables were made by the Kruskall-Wallis test for the overall effects between the three groups and, where appropriate, by Dunn’s multiple comparisons test of each group.

For patients with a perianal fistula discovered during index surgery with abscess drainage, the persistence of the fistula, i.e. the time between index surgery and permanent fistula repair surgery, was a calculated by Kaplan Meier estimation. Patients with initial fistula drainage at index surgery but lost to follow-up were censored from this analysis at last contact. This is indicated in the Kaplan–Meier curves by vertical tick marks. The day of the fistula surgery indicated “the event”. If the fistula was approached during the index surgery by any type of fistulectomy, postoperative day “0” was anticipated as the “event”. The log-rank test was used for comparisons of Kaplan-Meier curves between patient groups.

Spearman’s rho rank correlation was used to determine statistical dependencies across the entire patient cohort or in patients who underwent microbiologic examination by abscess swab between patient characteristics, microbiologic culture results and postoperative outcome indicators. The results are given as Spearman’s rank correlation coefficient (rPS) and their respective meanings.

Heatmaps display the correlation coefficients between the respective variables in the entire patient cohort or exclusively patients with abscess swab exams as well as the ratio of acquired resistances of microorganisms detected in the study .

Data are given as mean ± standard deviation for continuous variables as well as in n (%) for categorical data; p-values ​​≤ 0.05 indicate statistical significance. Due to the exploratory nature of the study, no adjustment of p-values ​​was made.

Ethics approval

This exploratory and retrospective single-center cohort study was performed in accordance with the latest version of the Declaration of Helsinki and was approved by the local ethics committee of the Faculty of Medicine of the University of Giessen (accreditation no. 66/ 19). Due to the retrospective nature of the study, the requirement for written informed consent was waived by the ethics committee. Data is collected, manuscript is written and submitted according to COPE and STROBE guidelines. All patients were treated according to the institution’s standard of care.

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