Prevalence of anaerobic bacteria in surgical site infections in Lagos University Teaching Hospital

Surgical site infection (SSI) is the second most common cause of nosocomial infection, after urinary tract infection. Sequelae of SSI include increased healthcare costs and worse patient outcomes. There is a paucity of research studies on the impact of anaerobic organisms on SSIs in Nigeria. The aim of this study was to determine the role of anaerobic bacteria in SSI encountered at the Lagos University Teaching Hospital (LUTH).

A total of 438 patients were consecutively recruited into this study from general surgery, obstetrics and gynaecology and paediatric units of the LUTH from 1 July through 31 December 2019. Two surgical wound specimens were collected from all patients with suspected SSIs. One was for anaerobic culture using Brucella blood agar incubated in an anaerobic jar that secured anaerobiosis using the anaerobic gas pack. The other swab was used for aerobic culture on blood agar incubated on air at 37^oC. Identifications and antibiotic sensitivity testing were performed according to standard laboratory procedures.

The overall incidence of SSI in the study was 12.3%. The incidence of anaerobic SSI was 1.1%. The distribution of anaerobic infections by medical specialty unit was as follows; general surgery (1.6%), obstetrics and gynaecology (0.8%) and paediatrics (0.9%). Bacteroides species was the only anaerobic isolate. The risk factors associated with the development of SSI by multiple logistic regression analysis were duration of surgery greater than 2 h (OR 1.418; 95% CI 1.834-9.286; P = 0.001) and NNIS risk index 2 and 3 - (OR 2.165; 95% CI 2.366-32.086; P = 0.001).

The prevalence of anaerobic SSI was 1.1%. Duration of surgery greater than 2 h and NNIS risk index 2 and 3 were independent predictors of SSI.