Wound infection rates: the importance of definition and post-discharge wound surveillance.

The importance of definition and post-discharge wound surveillance on reported wound infection rates have been studied, using data taken from a prospective, randomized, placebo-controlled, double-blind trial of the effect of whole body disinfection on postoperative wound infection rates. All patients admitted for an elective clean or potentially contaminated surgical procedure over a 32-month period were recruited into the study. Of the 3733 patients recruited, 3466 completed the study. Wound infection (which is defined for this study) is the main outcome that was examined. The effect of careful post-discharge follow-up of patients to look for wound infections was analysed for age, wound type and presence or absence of a drain. Sixty percent of postoperative wound infections occurred after discharge. A rising wound infection rate with increasing age was observed in the in-hospital cohort whereas the incidence of outpatient wound infections declined with age. This finding is attributed to the longer in-hospital stay encountered in patients above 50 years old (median, 3 vs. 5 days, P < 0.00001). Although clean operations had a significantly lower in-hospital infection rate, potentially contaminated procedures had a lower outpatient infection rate. A similar picture was observed in other subgroups of operations including horizontal versus vertical wounds and use of drains. When assessing reported wound infection rates, the definition of wound infection used and the extent of follow-up must be known to enable accurate assessment of the results.