Epidemiology of new colonization with multiple drug resistant organisms in long-term care facilities

Background: New acquisition of antimicrobial resistance in long-term care facilities (LTCF) is not well studied.

Objective: To define incidence, persistence of and time to new colonization with methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), ceftazidime- (CTZ-R) and quinolone-resistant (CIP-R) gram-negative bacteria (CEFT-R) in LTCFs.

Methods: After obtaining informed consent, LTCF residents were enrolled and prospectively cultured every month.  Monthly cultures were obtained from nares, oropharynx, groin, peri-anal area, and wounds (if present). Standard microbiological tests were used to identify MRSA, VRE, CTZ-R and CIP-R.  In order to qualify for analyses, residents had to have at least 90D follow-up.  Residents were categorized into 2 groups: a) resistant organism present at the start of the study (transient if they were cleared on subsequent culturing and persistent if remained colonized subsequently) and b) new acquisition at the facility (transient if they were cleared on subsequent culturing and persistent if remained colonized subsequently).  We also calculated time-to-colonization for any new acquisition within the facility.

Results:

We cultured 75 residents monthly for 3 – 12 months.  Of these, 47 (63%) were colonized with MRSA, 13 (17%) were colonized with VRE, 25 (34%) were colonized with CTZ-R, 53 (71%) were colonized with CIP-R. 

 

Of 47 residents with MRSA, 42% were colonized at the start of the study (21% transient and 21% persistently) and 58% acquired MRSA at the facility (26% transient and 32% persistent).  Of 13 residents with VRE, a majority (54%) transiently acquired the organism from the facility that cleared on subsequent culturing.  Of 25 residents with CTZ-R, 24% were admitted with a CTZ-R organism (4% transient, 20% persistent) and 76% acquired CTZ-R within the facility (44% transient and 32% persistent).  Of 53 residents with CIP-R GNB, 47% were admitted with CIP-R organism (32% transient, 15% persistent), 53% acquired CIP-R within the facility (23% transient and 30% persistent).  E. coli (45% of all CIP-R GNB) and P. mirabilis (30%) were the two most common CIP-R colonizing LTCF residents. As expected, majority of CIP-R GNB (85%) were isolated from peri-anal and groin areas.

 

Average time to new acquisition was the shortest for CIP-R at a mean of 68.5 days, with MRSA at 121.1 days (p = 0.006 vs. CIP-R), VRE at 150 days (p = 0.008 vs. CIP-R) and CTZ-R at 180 days (p< 0.0001 vs. CIP-R).

Conclusions: Contrary to prior studies, new acquisition of multiple drug-resistant organisms, in particular MRSA and CIP-R, is common in LTCFs.  Quinolone resistance is acquired rapidly and could be related to antimicrobial exposure at LTCFs.