LONDON – Being obese increased the risk of surgical site infection nearly fourfold among patients who underwent operations in the United Kingdom from 2006 through 2010.
The findings pose questions such as whether preoperative dosing of antibiotics might be adjusted upward or whether preoperative weight loss should be advocated, said Dr. Simon Thelwall of the Health Protection Agency, London.
Dr. Simon Thelwall
The analysis was done using nationwide data from the UK’s Health Protection Agency (HPA) Surgical Site Infection Surveillance Service, comprising data submitted from all 212 of the National Health Service hospitals in England on a cumulative total of 326,880 adult patients who underwent one of five operations: abdominal hysterectomy, coronary artery bypass graft (CABG), hip replacement, knee replacement, and large bowel surgery.
Of those, surgical site infections (SSIs) were detected in inpatients and at readmission for 4,453, and body mass index (BMI) data were available for 43%. Of these 112,048 (79.3%) were overweight or obese, said Dr. Thelwall.
The rates of SSIs didn’t differ among those with and without available body mass index data except among CABG patients, for whom the rate of SSIs was double among those with and without BMI data (5.17% vs. 2.71%). The CABG patients with BMI data were also significantly more likely to have received implants (85% vs. 61%), to have undergone emergency operations (1.29% vs. 0.76%), and to have had significantly longer operations (205 vs. 220 minutes).
Thus, "CABG patients with BMI data are more likely to have risk factors predisposing them to SSI," Dr. Thelwall noted.
Obesity significantly increased the risk for SSI in all surgical groups except for abdominal hysterectomy, with risk ratios ranging from 1.62 for knee replacement to 1.87 for large bowel surgery. Obesity still increased the SSI risk among abdominal hysterectomy patients with a risk ratio of 1.81, but that did not reach statistical significance, he said.
Overall, the SSI risk increased with increasing BMI. In multivariate analysis adjusting for a variety of potential confounders including age, trauma, category of surgery, implant, and emergency surgery, the odds ratios for SSI increased from 1.44 among the overweight patients to 1.89 for those with BMIs of 30-34.99 kg/m2, to 2.94 for BMIs of 35-39.99 kg/m2, and to 3.73 for BMIs greater than 40 kg/m2. In the highest BMI category, even the SSI rate for abdominal hysterectomy became significantly greater, compared with that of patients of normal weight (risk ratio, 3.90), Dr. Thelwall said.
Among the morbidly obese (BMI greater than 40 kg/m2), between 65% and 78% of the risk for SSI was attributable to being very obese. And in that group of morbidly obese patients, the risk of SSI among abdominal hysterectomy patients became significantly elevated three- to fivefold, compared with that of women of normal weight, he noted.
Dr. Thelwall declared that he had no disclosures.