Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Ilorin, Nigeria

Nosocomial infections caused by methicillin-resistant strains of Staphylococcus aureus constitute significant epidemiologic problems. Defining an outbreak requires the use of rapid and highly discriminatory epidemiologic methods to determine the epidemic strains involved in such outbreak.

A descriptive laboratory based surveillance study for MRSA was undertaken. One hundred and forty seven Staphylococcus aureus isolates from clinical specimens were screened for methicillin resistance at the University of Ilorin Teaching Hospital between January and December 2001. Fifty one (34.7%) methicillin resistant strains recovered were epidemiologically characterized using Eco R1 restriction enzyme analysis of their plasmid DNAs.

Forty five (88.2%) MRSA isolates were associated with infections and 6 (11.8 %) were colonizing strains; 36 (70.6%) and 15 (29.4%) were hospital and community acquired respectively. Skin and soft tissues were sites of infection in 36 (70.6 %) cases and surgical, emergency and ICU accounted for 33 (64.7%) isolates. All isolates were resistant to more than two antibiotics but sensitive to vancomycin. Forty two (82.4 %) isolates contained plasmids including 9 (21.4 %) that contained more than one plasmid. Restriction Enzyme Analysis of the Plasmid DNA (REAP) divided the isolates into 9 Eco R1 profiles, with profile 2 accounting for 41.7% of all nosocomial infections in the wards, implying that it is endemic. The remaining nosocomial profiles occurred less frequently, suggesting that they are sporadic strains originating from outside the hospital. The community strains showed diverse digestion pattern indicating that they are from different clones.

The spread of MRSA can be controlled through reinforcement of appropriate use of antibiotics, hand washing and laboratory surveillance for MRSA, particularly in the surgical wards and intensive care units, in order to identify sources of outbreaks.