2,423 patients (1,272 males and 1151 females) were studied. The average age at admission was 55 years (SD 19; range 18–96). The average length of the surgical procedure was 117 min (SD 85; range 5–935). 1,059 patients were classified as ASA class 1, 1,079 patients as class 2, 280 patients as class 3, and 5 patients as class 4. The average BMI on admission was 23 (SD 3.9; range 15–36). The average follow-up period was 26 (13–38) months. Of these patients, 63 (2.6%) had preoperative nasal cultures that were positive for MRSA. Overall, 15 patients (0.6%) developed SSI with MRSA postoperatively. The mean time of onset of SSI with MRSA was 1.1 months (range 4 days to 3 months). No other organisms were detected in these 15 patients. According to the criteria defined by CDC, 6 patients had superficial incisional SSI, 1 patient had deep incisional SSI, and 8 patients had organ/space SSI. 1 patient had removal of a joint prosthesis, and 2 patients had limb amputation (). 3 patients with joint prostheses (1 femoral head prosthesis and 2 total knee prostheses) had SSI with MRSA. The latter 2 patients who had total knee replacement could retain their prostheses by debridement and antibiotic treatment. For the 1 patient who had replacement of a femoral head prosthesis, debridement and antibiotic treatment were not effective and removal of prosthesis was required.
Demographic and clinical data of 16 patients with MRSA surgical site infection.
Patients with preoperative nasal cultures that were positive for MRSA had a higher occurrence of SSI with MRSA (6.3%) than patients who were negative for nasal MRSA preoperatively (0.5%), by crude rate analysis (p < 0.001) (). Patients with nasal cultures that were positive for MRSA preoperatively were statistically significantly older than patients who were negative for MRSA in nasal cultures, both in the total group (median age: 69 vs. 59, p = 0.001) and in the SSI negative group (median age: 69 vs. 59, p = 0.001). However, in the SSI-positive group, the difference in age between patients who were positive or negative for MRSA in nasal swabs preoperatively was not statistically significant (median age: 69 vs. 59, p = 0.5). There was no significant association between gender and preoperative nasal culture status in any of the 3 groups.
Crude and adjusted ORs and 95%CIs for surgical site infection with MRSA using logistic regression model.
Possible associations between SSI with MRSA and perioperative factors (sex, age, history of diabetes mellitus, history of rheumatoid arthritis, the site of operation, use of a prosthesis, length of the surgical procedure, the existence of open fracture(s), ASA class, and BMI), as well as preoperative culture of nasal MRSA, were examined. By crude rate analysis, sex, age, history of diabetes mellitus and rheumatoid arthritis, the site of operation, use of a prosthesis, length of the surgical procedure, existence of open fracture(s), an ASA class of 1 or 2, and BMI were not statistically significant factors for SSI with MRSA. Nasal cultures that were positive for MRSA preoperatively and an ASA class of 3 or 4 were associated with SSI with MRSA by crude rate analysis (OR: 15; 95% CI: 4.5–47; p < 0.001; and OR: 6, 95% CI: 1.5–27; p = 0.01, respectively). Multivariate logistic regression analysis showed that preoperative culture of nasal MRSA was only statistically significantly associated with SSI with MRSA even after controlling for perioperative factors (adjusted OR: 11; 95% CI: 3–37; p < 0.001). Thus, positive culture of nasal MRSA independently increased the risk of SSI with MRSA by 11 times ().
Concerning the 4 patients who had positive results of culture of nasal MRSA preoperatively and SSI with MRSA subsequently, the susceptibility patterns of the MRSA isolates obtained from the nasal cavity and from the surgical site were the same.