772. One-Year Risk of Methicillin Resistant Staphylococcus aureus Infection Following 211,339 MRSA Screening Tests
Session: Oral Abstract Session: Staph aureus: Screening and Prevention
Friday, October 21, 2011: 3:00 PM
Room: 157ABC

Background:

The risk of methicillin resistant Staphylococcus aureus (MRSA) infection in MRSA-colonized patients is unclear. Previous studies report rates of 30%, but may be biased by sampling largely high-risk patients. 

Methods:

We determined the 1-year risk of developing a positive MRSA clinical culture (CC) for all patients admitted to 4 affiliated study hospitals over 4.5 years when universal MRSA screening was in place. Each patient was screened with a nasal swab for MRSA PCR, and if positive, had a confirmatory nasal culture (NC) for MRSA. Patient encounters were divided into 3 groups: Group 1 (+ PCR, + NC), Group 2 (+ PCR, - NC) and Group 3 (- PCR). Positive NCs were tested for Panton Valentine Leukocidin (PVL) by PCR. A patient ‘episode' was defined as the time from PCR until the patient had a new PCR (i.e. on readmission) or 365 days. Microbiological databases were used to identify CCs with MRSA. To ensure minimal loss to follow up, we performed a sensitivity analysis restricting our data to patients with a primary care physician (PCP) in our network and at least one encounter within the subsequent year. Poisson regression was performed using STATA.

Results:

211339 episodes were included. Follow up for Groups 1, 2 and 3 included 3494, 2523 and 119777 patient-years respectively. The 1-year risk of MRSA positive CC in Groups 1, 2 and 3 was 11.8%, 4.9% and 0.7% respectively. Risk varied significantly based on patient history of MRSA colonization or past CC (Table). Patients with concurrent MRSA CC at the time of nasal testing had a 1-year risk of MRSA infection of 30%, regardless of Group.  Patients with PVL-positive MRSA had an infection rate of 14.4% vs. 10.9% for those with PVL-negative MRSA (p = 0.002).

Conclusion:

The 1-year risk of MRSA infection in colonized patients is likely lower than previously estimated, but still substantial. In the absence of a positive confirmatory NC, a positive nasal PCR is less predictive than positive NC of future MRSA CC.

Table. 1-year risk of MRSA infection following admission test

All patients

In-network PCP & encounter within a year

PCR+ NC+

History of MRSA

20.3%

20.9%

No history of MRSA

6.4%

7.7%

PCR+ NC-

History of MRSA

15.1%

22.2%

No history of MRSA

2.1%

2.4%

PCR-

History of MRSA

10.0%

11.6%

No history of MRSA

0.5%

0.5%

p<0.05 for all differences


Subject Category: N. Hospital-acquired and surgical infections, infection control, and health outcomes including general public health and health services research

Jessica Ridgway, MD1, Courtney Hebert, MD1, Lance Peterson, MD2 and Ari Robicsek, MD2, (1)University of Chicago, Chicago, IL, (2)NorthShore University HealthSystem, Evanston, IL

Disclosures:

J. Ridgway, None

C. Hebert, None

L. Peterson, Roche: Consultant, Grant Investigator and Investigator, Consulting fee, Grant recipient, Research grant and Speaker honorarium
BD GeneOhm: Consultant, Grant Investigator and Investigator, Consulting fee, Grant recipient, Research grant and Speaker honorarium
Cepheid: Consultant, Grant Investigator and Investigator, Consulting fee, Grant recipient, Research grant and Speaker honorarium
Syntezza: Grant Investigator and Investigator, Grant recipient and Research grant
Microphage: Grant Investigator and Investigator, Grant recipient and Research grant
Nanosphere: Grant Investigator and Investigator, Grant recipient and Research grant
3M: Grant Investigator and Investigator, Grant recipient and Research grant

A. Robicsek, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.