Prevalence and Trends in Postoperative S. aureus Cultures in the Veterans Health Administration during 2009-2013

Author(s):
William O’Brien; Kalpana Gupta; Kamal Itani

Background:

Postoperative Staphylococcus aureus (SA) infection is associated with morbidity and excess cost. Many of these events are preventable, and efforts are underway to develop a SA vaccine. This study describes the rate of postoperative SA positive cultures in 5 selected surgery types in the Veterans Health Administration (VA) during a 5-year period.

Hypothesis:

We hypothesize that rates of SA cultures varied among surgery type, and decreased over time.

Methods:

We obtained demographic and clinical data on Veterans undergoing elective surgery during FY09-13 (10/1/2008 – 9/30/2013), as well as cultures positive for SA one year postoperatively. Specimen topography was categorized as blood, urine, sputum, wound, or other, as a proxy for bloodstream infections, urinary tract infections, pneumonia, or surgical site infections, respectively. Surgeries were flagged as having a 1-year postoperative SA culture or not, independently by topography.

Results:

We identified 93,546 surgeries during the study period. Median patient age was 64 years, and 93.7% were male. Patients who had a positive SA culture, compared with those who did not, were more likely to be male (96.4% vs. 93.5%), were similar in age, and had a longer mean index length of stay (14.1 vs. 7.7 days). Mean time between surgery and positive culture was 89.6 days.

The positive culture rate was 5.1% among all surgeries. Rates varied by surgery type (5.7% in cardiac, 7.0% in colorectal, 1.2% in hysterectomy, 3.1% in orthopedics, and 11.5% in vascular). The most frequent topography was wound, and prevalence ranged from 0.7% in hysterectomy to 8.8% in vascular.

Overall, annual positive culture rates declined linearly, from 6.3% in FY09 to 4.0% in FY13. A similar trend occurred in cardiac (6.2% to 4.5%), colorectal (8.4% to 5.7%), and orthopedics (4.3% to 2.6%). Hysterectomy rates were flat, ranging from 0.6% in FY11 to 1.5% in FY10. The rate in vascular surgery varied but had a consistent decline from FY11-FY13 (12.8% to 9.5%).

Conclusions:

The rate of 1-year postoperative positive SA cultures declined by approximately a half percentage point per year during the study period. This improvement is similar to recent work showing an 8-year reduction through FY17 in MRSA hospital acquired infection rates in the VA. These may be attributable to better infection control practices such as the VA MRSA Prevention Initiative. Future work could examine the extent to which positive cultures represent true infections, and their association with the index surgery.