The value of an operative wound swab sent in transport medium in the prediction of later clinical wound infection: A controlled clinical and bacteriological evaluation

Abstract

Operative wound swabs taken at 214 transperitoneal operations were examined during the course of three controlled clinical trails to determine the value of transport medium in the carriage of specimens. The use of Stuart's transport medium more than doubled the number of swabs yielding pathogens in the laboratory compared with a control series of duplicate swabs not sent in transport medium. Anaerobes were even more severely affected than aerobes by ‘dry’ carriage. A polyester foam swab was shown to have no advantage over the standard cottonwool variety. Bacteriological swabs from superficial wound fat were shown to be superfluous if a peritoneal wound swab had already been taken. We suggest that operative abdominal wound swabs should not be accepted for processing by a microbiological laboratory unless sent in transport medium. Wound infection, assessed on the fifth postoperative day, was shown to be related to the result of operative swab culture only when the swab was sent in transport medium. When the operative culture was negative at 48 h, only 1 per cent later became infected. When the operative swabs grew obligate anaerobes alone, 13 per cent became infected–aerobes alone, 23 per cent, and mixed aerobes plus anaerobes, 71 per cent. The growth of mixed aerobes plus anaerobes from the operative swab was a far superior predictive factor for later infection than the degree of operative contamination or the type of operation, and provided a simple, rapid means of identifying a subgroup of patients at high risk (71 per cent) of developing infection who might benefit from planned antibiotic therapy.