TRACING THE ORIGIN OF AN OUTBREAK OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS INFECTIONS IN A PORTUGUESE HOSPITAL BY MOLECULAR FINGERPRINTING METHODS

Seventy-six methicillin-resistant Staphylococcus aureus (MRSA) isolate s were collected from July 1992 to May 1995 at a 400-bed district hosp ital in the northeast of Portugal, During the second half of the surve illance period, in July of 1994, an outbreak was detected in the ortho pedic ward, Thirty-three (out of the 76) MRSA strains were recovered o nly in this ward during the outbreak period, All strains were characte rized by a variety of genomic fingerprints, Hybridization of ClaI and SmaI restriction digests with the mecA- and Tn554-specific DNA probes was used to identify polymorphism and determine chromosomal location o f these determinants, and pulsed-field gel electrophoretic analysis of SmaI digests was used to determine chromosomal backgrounds, All strai ns recovered during the outbreak in the orthopedic ward were found to belong to a single clone that carried the mecA polymorph I, Tn554 type E in a macrorestriction background called H (clone I::E::H1), which w as identified in 18 patients, and 5 health care personnel and from a f omite sample, and was traced to a single transfer patient admitted to the hospital at the beginning of the outbreak, The new clone I::E::H1 differed only in the macrorestriction profile from the MRSA clone prev iously dominant in this hospital, known as Iberian epidemic clone I::E ::A, which has already been identified in several Spanish and Portugue se hospitals.