CONTROL OF AN OUTBREAK OF AN EPIDEMIC METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS ALSO RESISTANT TO MUPIROCIN

An epidemic methicillin-resistant Staphylococcus aureus (EMRSA-3) appe ared in a District hospital in June 1989 as part of a regional outbrea k. The dynamics of the outbreak were complex and involved patient tran sfer between hospitals and wards. Control measures followed UK guideli nes and included the use of nasal mupirocin. During these efforts a mu pirocin-resistant MRSA [MuMRSA: mupirocin minimum inhibitor concentrat ion (MIC) >256 mg/L] emerged, probably in a patient who had been given eight mupirocin courses over nine months. The MuMRSA had a narrower p hage-typing pattern than EMRSA-3, but was indistinguishable by pulsed- field gel electrophoresis of SmaI chromosomal restriction enzyme diges ts and its susceptibility pattern to other antibiotics. The results of in vitro curing and gene probing indicated that mupirocin resistance was encoded on a 48 Md plasmid. MuMRSA spread occurred in 12 patients and 11 staff. The affected patients were nursed on the same ward. The strain was eradicated from patients with oral ciprofloxacin and rifamp icin, triclosan skin treatment and nasal fusidic acid and bacitracin c ream. The control of the outbreak had significant medical, social and financial implications. Fortunately, there were alternative topical ag ents to mupirocin,an agent which has played such a key role in MRSA er adication in recent years.