Objective: To determine the prevalence and genotypes of MRSA isolates from among groups of HCW, and the results of eradiation therapy with nasal mupirocin and chlorhexidine baths.
Methods: In parallel with universal surveillance of admitted patients for MRSA, HCW were voluntarily screened via nasal swab beginning January 2007 to determine the prevalence of MRSA carriage. Isolates were grown on ChromAgar, and DNA was extracted and amplified by a DiversiLab Staphylococcus aureus DNA fingerprinting kit (bioMerieux). Dendograms were constructed using Diversilabs software, and the MRSA genotypes were compared to a library for USA types. The range of genotypes of MRSA isolates from those in direct patient care vs those in non-patient care were compared. Mupirocin susceptibility testing was performed using disc diffusion, broth microdilution and e-tests. Statistical analysis of MRSA genotypes carried between the study groups was by Pearson Chi Square tests.
Results: Among 7894 HCWs, 3638 (46.1%) were tested with 4.3% positive. Among those in direct patient care, 2136-of-4640 (46.0%) were tested with 100-of-2136 positive (4.6%). Among non-clinical staff, 1502-of-3254 (74-of-1502 (46.1%) were screened, with 74-of-1502 positive (4.2%). Genotyping of isolates from those in direct patient care identified 75% as healthcare-associated (HA) MRSA strains (USA 100, 200, 800), 14% as community associated (CA) MRSA strains (USA 300, 500) and 11% as non-typeable. Among MRSA genotypes isolated from HCW in non-direct patient care, 54% were HA-MRSA strains, 27% were CA-MRSA strains and 19% were non-typeable. The differences in carriage of USA types approached statistical significance ( p ≤ 0.052) between clinical and non-clinical HCW. Mupirocin eradiation treatment cleared 75% for ≥ 3 months, while 25% had carriage detected within 3 months. Mupirocin susceptibility testing revealed 7/78 (8.9%) high-level resistance and 8/78 (10.3%) low level resistance of their initial isolates. Development of resistance was detected among only 1/38 ( 2.6%) of those previously treated with mupirocin.
Conclusions: 1) The almost 4000 HCW voluntarily screened for MRSA represents the largest ongoing study of MRSA carriage among HCW in the US, with an overall carriage rate of 4.3%. 2)While the majority of HCW were cleared of MRSA carriage for ≥ 3 mo, 25% were detected as recurrent carriers. 3)The successful eradication of MRSA carriage and minimal induction of mupirocin resistance observed among those treated reinforces the efficacy of this approach in eradicating carriage of MRSA among HCW, as part of an overall strategy of Search and Destroy for MRSA at a healthcare facility.