Men's Health

Prevalence of Methicillin-Resistant Staphylococcus aureus Among Orthopedic Patients at a Large Academic Hospital

By Bennie Lindeque, MD, PhD; Jonathan Rutigliano, BS; Allison Williams, MD, PhD; Jodi McConnell, PA-C
ORTHOPEDICS 2008; 31:363

April 2008

Abstract

Community-based methicillin-resistant Staphylococcus aureus (MRSA) contributes to postoperative surgical site infections, and it is therefore important to eliminate nasal carriage of MRSA before surgery. A total of 678 nasal swabs were performed on elective orthopedic patients undergoing surgery with the usage of metal implants. Thirty-eight specimens (5.6%) were positive for MRSA and 146 (21.5%) were positive for methicillin-sensitive S aureus (MSSA). A slow increase in the number of MSSA was noted between 2006 and 2007. Positive cases of MRSA nasal carriage were treated with nasal mupirocin ointment and chlorhexidine baths or showers for 5 days prior to surgery.

Staphylococcus infections of orthopedic implants are the number one cause of wound infections.1,2 Methicillin-resistant Staphylococcus aureus (MRSA) in particular have proven to be a problem as the eradication and treatment of a MRSA infection is much more difficult, given its resistance to most antibiotics.

Staphylococcus aureus carriers have a 2- to 9-fold increased risk of developing a surgical site or intravenous infection.3 The costs of treating a failed infected joint arthroplasty or other orthopedic implant are high both financially as well as socially. This issue is further complicated by the Centers for Medicare and Medicaid Services (CMS), which announced it would no longer reimburse hospitals for preventable conditions. Two of these conditions include MRSA and surgical site infections. It is therefore imperative to not only monitor the incidence of these infections but also to try and eradicate skin carrier status before surgery.

This study evaluated the incidence of MRSA and methicillin-sensitive S aureus (MSSA) in orthopedic patients undergoing elective procedures with the intention of implanting metallic hardware and examined prophylactic treatment of patients who were nasal carriers of MRSA. Our hypothesis was that a gradual increase in the incidence of community-based MRSA and MSSA in orthopedic patients would necessitate routine screening with surveillance and prophylactic treatment to eradicate nasal carriage of MRSA before surgical implantation of hardware.

Materials and Methods

This study received institutional review board approval. Nose swabs routinely were obtained from all orthopedic patients undergoing implant surgery during their preoperative workup. This procedure was regarded as standard care, and all results were documented, with the intent to treat MRSA carriers before their elective procedures. All patients with a positive nasal swab for MRSA were notified and received a prescription for mupirocin nasal ointment and chlorhexidine soap to be used for a minimum of 3 days prior to surgery.

The results were submitted to one of the authors (A.W.) for statistical analysis. Particular attention was paid to any differences in gender, age, and monthly prevalence of MRSA and MSSA.

Data were analyzed using Statistical Package for Social Sciences version 11.5 (SPSS, Chicago, Illinois). A P value <.05 was considered statistically significant.

Results

A total of 678 samples were collected from April 2006 through November 2007. Samples were collected from 288 men (42.5%) and 390 women (57.5%). Thirty-eight specimens (5.6%) were positive for MRSA, and 146 specimens (21.5%) were positive for MSSA.

Data were cross-tabulated and Fisher exact tests were performed to analyze the differences by month and year for the period from July 2006 through November 2007. During this period, 9 of 224 (4%) specimens collected in 2006 were positive for MRSA and 9 of 93 (9.7%) specimens were positive for MRSA in 2007. The association between year collected and MRSA status approached statistical significance (P=.061). The association between year collected and MSSA status was statistically significant, with samples more likely to be positive for MSSA in 2007 (P<.01; odds ratio [OR]=9.627; 95% confidence interval [CI]=4.939 to 18.764). Fifteen samples (6.7%) collected in 2006 were positive for MSSA, and 38 samples (40.9%) collected in 2007were positive.

When compared by month, a statistically significant association between MRSA and year collected was found for October (P=0.043; OR=10; 95%CI=0.992 to 100.821). One (3.8%) of 26 samples collected during October 2006 was positive for MRSA, whereas 4 (28.6%) of 14 samples collected during October 2007 were positive. Thus, samples were more likely to be positive for MRSA in October 2007 than October 2006.

For MSSA, statistically significant associations between sample status and year collected were found for July (P<.01), September (P<.01), October (P<.01; OR=62.5; 95% CI=6.199 to 630.132), and November (P<.01; OR=87; 95% CI=9.627 to 786.243). Positive MSSA findings in 2006 were as follows: 0 (0%) in July, 0 (0%) in September, 1 (3.8%) in October, and 8 (8.4%) in November. In 2007, the number of positive MSSA samples was 12 (18.5%) in July, 4 (100%) in September, 10 (71.4%) in October, and 8 (88.9%) in November.

A statistically significant association was found between year and MRSA status for women, with samples collected from women in 2007 more likely to be MRSA positive than samples collected from women in 2006 (P=.024; OR=4.610; 95% CI=1.240 to 17.141). Six samples (12.8%) from women collected in 2007 and 4 samples (3.1%) in 2006 were positive for MRSA.

The association between year collected and MRSA status was not significant for specimens collected from men. However, for MSSA status, there was a significant association with year for both men and women. In 2006, 8 women (6.2%) were positive for MSSA, and in 2007, 19 women (40.4%) were positive for MSSA (P<.01; OR=10.348; 95% CI=4.114 to 26.032). Seven samples (7.4%) collected from men in 2006 were MSSA positive, and 19 samples (41.3%) collected from men in 2007 were MSSA positive (P<.01; OR=8.746; 95% CI=3.321 to 23.03)

Discussion

The high incidence of overall S aureus prevalence in the orthopedic population was surprising. A statistically significant increase in the incidence of MRSA per year occurred in women, whereas the increase in MRSA incidence was not significant for men. For MSSA, there was an increase in incidence in both men and women per year.

The high incidence of community-based MSSA and MRSA in our orthopedic population indicates postoperative MRSA and MSSA infections cannot be assumed to be caused nosocomially. Patients may carry MRSA in their noses and may infect themselves.4,5 Postoperative infections in patients with positive MRSA and MSSA nasal carriage cannot summarily be attributed to a nosocomial cause. It is therefore important to prove the presence of preexisting MRSA and MSSA carriage to defend a diagnosis of a non-nosocomial source of infection.

The prophylactic use of a combination of mupirocin nasal ointment and chlorhexidine soap bath or showers has proven effective in decreasing MRSA carriage.6,7 It is a cost-effective way to decrease the incidence of surgical site infections and is recommended. Preoperative nose swabs and prophylactic treatment of MRSA-positive patients form part of a comprehensive strategy in our hospital to minimize the incidence of postoperative infections.

References

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2. Buchholz HW, Elson RA, Engelbrecht E, Lodenkamper H, Rottger J, Siegel A. Management of deep infection of total hip replacement. J Bone Joint Surg Br. 1981; 63(3):342-352.
3. Perl TM. Prevention of Staphylococcus aureus infections among surgical patients: beyond traditional perioperative prophylaxis. Surgery. 2003; 134(5 suppl):S10-S17.
4. West TE, Guerry C, Hiott M, Morrow N, Ward K, Salgado CD. Effect of targeted surveillance for control of methicillin resistant Staphylococcus aureus in a community hospital system. Infect Control Hosp Epidemiol. 2006, 27(3):233-238.
5. Farr BM, Salgado CD, Karchmer TB, Shere4tz RJ, Can antibiotic-resistant nosocomial infections be controlled? Lancet Infect Dis. 2001; 1(1):38-45.
6. Wilcox MH, Hall J, Pike H, et al. Use of perioperative mupirocin to prevent methicillin-resistant Staphylococcus aureus (MRSA) orthopaedic surgical site infections. J Hosp Infect. 2003; 54(3):196-201.
7. Denton GW. Chlorhexidine. In: Disinfection, Sterilization, and Preservation. 4th ed. Philadelphia, PA: Williams and Wilkins; 1991:61-76.
   Authors

Drs Lindeque and Williams, and Mr Rutigliano are from the University of Colorado School of Medicine and Ms McConnell is from the University of Colorado Health Sciences Center, Denver, Colorado.

Drs Lindeque and Williams, Mr Rutigliano, and Ms McConnell have no relevant financial relationships to disclose.

Correspondence should be addressed to: Bennie Lindeque, MD, PhD, Department of Orthopedics, PO Box 6511, Mail Stop B202, Aurora, CO 80045.

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