Influencia de la colonización del tracto urinario por bacilos gram negativos en el desarrollo de infección aguda de la herida quirúrgica tras cirugía vertebral instrumentada

Abstract

Influence of urinary tract colonization on surgical site infection by gram negative bacteria following instrumented spinal surgery. Surgical site infection (SSI) is a relative frequent complication following instrumented spinal surgery. Infection rates do vary depending on the type of surgery, the length of the instrumentation and the patient’s comorbidities among many other factors. The most common microorganism is S.aureus. During the last decade, an increasing rate of SSI due to gram negative bacteria (GNB) has been reported. GNB are common enteral microorganisms, which may colonize the urinary tract but are not likely to be isolated at the patient’s skin. Hence, contamination of the surgical wound by GNB might be related with the presence of these microorganisms at the urinary tract. This study focuses on the possible association between urinary tract colonization and further development of SSI. The first part of the study analyses the potential benefits of preoperative screening of urine tract colonization. Based on the literature, we established the following selection criteria for patients at risk of urinary tract colonization: indwelling catheter, incontinency, neurogenic bladder, preoperative stay length longer than seven days, history of repetitive urinary tract infections and admission from other health care facilities. All patients fulfilling one of these criteria had a preoperative urinary study. Those who finally had positive urinary cultures received antibiotic treatment before surgery. Personalized broad-spectrum perioperative antibiotic prophylaxis was administered covering the microorganisms isolated at the urine cultures. This measure showed a statistically significant decrease on the incidence of SSI by GNB. The second part of the study covers the potential relation between postoperative urinary tract infection (UTI) and SSI. The association found between both infections was strong (OR 3.54, CI 95% 1.9-6.5, p<0.001), but only in 40% of the patients were both infections caused by the same microorganism. However, 38% of the SSI by GNB had a urinary source, suggesting that preventing and treating UTI could be helpful in order to prevent SSI by GNBs. We additionally investigated the effect of the antibiotic treatment administered for UTI in the resistance patterns of the microorganisms isolated at the surgical wound. Interestingly, patients who received ciprofloxacin for the treatment of UTI had higher resistance rates to this agent at the wound isolates. Ciprofloxacin, in combination with other antibiotics is one of the best agents for treatment of infected wounds following muskuloskeletal surgery. Using alternative antibiotics to treat non-complicated UTIs is recommended in order to avoid resistances and reserve ciprofloxacin to treat a SSI if it finally occurs. The results of treatment after SSI following instrumented spinal surgery have not been deeply studied until now. We performed a survival analysis of patients treated for this complication following the Kaplan-Meier method. Terminal event was defined as the need for removal of the instrumentation. Implant removal before achieving fusion means that the goals of the index surgery have probably not been achieved due to the infectious complication. Survival rate decreased progressively during the first to years o follow-up until 73.2 %. More than half of the patients who had their implants removed continued to have infectious complications and needed significantly more additional surgeries than those whose implants could be retained. Outcomes were similar in patients with infection by GNB or by gram positive bacteria.

Date of Award	25 Nov 2013
Original language	Spanish
Supervisor	Enric Caceres Palou (Director), Ferran Pellise Urquiza (Director) & Rodriguez Pardo Maria Dolores (Director)