Culture of intraluminal thrombus during abdominal aortic aneurysm resection: Significant contamination is rare

The significance of positive bacterial cultures from intraluminal thrombus in patients undergoing repair of abdominal aortic aneurysm remains controversial. Over the last 4 years, thrombus was cultured during aneurysm repair in 116 patients. All patients received cephalosporin antibiotic before and for 48 h after operation. Although none of the aneurysms appeared to be clinically infected, six patients (5.2%) had positive cultures. Four groups were identified based on the bacteria cultured: group I, coagulase-negative staphylococci, light growth (three patients); group II, coagulase-negative staphylococci, light growth and ‘Streptococcus viridans’ (one patient); group III, Bacillus sp., heavy growth (Gram-negative stain) (one patient); group IV, Clostridium perfringens, occasional growth (one patient). One of the six patients died during resection; the other five are alive without graft infection at 5–24 (mean 12) months after operation. The absence of graft infection suggests that positive cultures were not clinically significant or were adequately covered by the antibiotic prophylaxis. The incidence of positive cultures was lower than previously reported. Routine culture of aneurysm thrombus in the absence of clinical infection is probably not cost-effective.