UC Davis

Background

A major risk factor for the development of surgical site infections is Staphylococcus aureus carriage. Compared with non-carriers, S. aureus carriers have up to a 14-fold greater risk for post-surgical infections. Pre-operative screening for S. aureus carriage is controversial. Yet, targeted screening in high-risk patients or from clinically relevant sites may be beneficial. We aimed to determine whether S. aureus detection in high-risk surgical patients would be increased by culturing surgical sites, in addition to the nares, vs. nares-only culturing.

Methods

Adults undergoing pre-operative evaluations in orthopedic and neurosurgical clinics were eligible for participation. For each subject, specimens were collected from the anterior nares and from the proposed surgical site. Samples were inoculated onto methicillin-resistant S. aureus-selective chromogenic agar plates and blood agar plates.

Results

Of 150 subjects, 80 (53.3%) were women and 70 (46.7%) men. The mean age was 61 years and 77/150 (51.3%) had a BMI≥30. Culture results were available for 147/150 subjects. Of the 147 surgical site cultures, 54 (36.7%), 51 (34.7%), and 28 (19.0%) were collected from knee, hip, and lumbar sites, respectively; the remaining 14 (9.5%) were from cervical, thoracic, or infra-clavicular sites. Overall, 35/147 (23.8%) nasal cultures grew S. aureus; 29/147 (19.7%) grew methicillin-susceptible S. aureus (MSSA), and 6/147 (4.1%) grew methicillin-resistant S. aureus (MRSA). Only 2/147 (1.4%) surgical site cultures grew S. aureus; both grew MSSA and MSSA was cultured also from the nasal swabs of these subjects. Using nasal culture+surgical site culture as "true positive," the percentage of additional S. aureus carriers detected by the addition of surgical site screening was zero as compared to nasal screening alone.

Conclusions

The detection of S. aureus carriage in high-risk surgical patients is not improved by swabbing surgical sites in addition to the nares.