The prevalence of nasal colonization and infection with methicillin-resistant Staphylococcus aureus (MRSA) among patients and staff was studied in a section of a Paediatric Surgical Unit in Lisbon between February and July 1985. Nasal colonization was demonstrated in 41% of burned patients, 5% of non-burned patients and 35 % of the nurses. Infection by MRSA occurred in 30% of the burns.
The isolates had identical serological patterns, slight differences on phage typing and were resistant to methicillin, cephalosporins, tetracycline, erythromycin and aminoglycosides. A chloramphenicol resistance plasmid of 3 Md was present in those isolates which were chloramphenicol resistant and a small plasmid of 1·7 Md which coded for constitutive erythromycin resistance was present in many isolates. Gentamicin, tetracycline and inducible erythromycin resistance were chromosomal.
Several reasons for the apparent low virulence of the isolates are discussed. Attempts to control the outbreak by the discharge of colonized or infected patients, improvement of nursing practices and treatment with temporary removal from work of the colonized nurses did not eliminate the organism from the unit.