Methicillin-resistant Staphylococcus aureus: a ten-year survey in a Dublin hospital

Surveillance of hospital-acquired infection in the Republic of Ireland: past, present and future

There is increasing interest in the surveillance of hospital-acquired infection (HAI) in the Republic of Ireland due to a greater awareness of the consequences of antibiotic resistance, and consumer pressure in the form of public expectations of the quality of health care. To date there have been no nationwide prospective surveillance projects but surveillance has taken place in the form of participation in international and national studies, and the description of local outbreaks. Infection control teams and others have participated in projects such as a European study of HAI in intensive care units conducted in 1992, the second national prevalence study conducted in the UK in 1993 and two surveys of methicillin-resistant Staphylococcus aureus (MRSA) carried out in 1995 and 1999, the latter involving colleagues in Northern Ireland. There have been a number of local surveys of antibiotic-resistant bacteria including the molecular characterization of MRSA in Dublin hospitals, vancomycin-resistant enterococci, and Gram-negative bacteria such as Enterobacter spp. and Serratia spp. affecting compromised patients such as bone marrow transplant recipients. In the future, it is hoped to standardize case definitions, automate data entry, increase collaboration with surveillance initiatives in Northern Ireland and link in with European networks such as EARSS and HELICS. Apart from the need to improve the quality of health care in Irish hospitals, approximate costings suggest that there are potential savings of 7.5 pounds sterling -15 pounds sterling m to be made following a reduction of HAI rates of 15%.

Combined use of ribotyping, PFGE typing and IS431 typing in the discrimination of nosocomial strains of methicillin-resistant Staphylococcus aureus

We have previously reported the phenotypic characterization of methicillin-resistant Staphylococcus aureus (MRSA) clinical strains isolated in Malaya University Hospital in the period 1987 to 1989 using antibiogram, coagulase typing, plasmid profiles, and phage typing. Here, we report the analysis of the same strains with three genotyping methods; ribotyping, pulsed-field gel electrophoresis (PFGE) typing, and IS431 typing (a restriction enzyme fragment length polymorphism analysis using an IS431 probe). Ribotyping could discriminate 46 clinical MRSA strains into 5 ribotypes, PFGE typing into 22 types, and IS431 typing into 15 types. Since the differences of the three genotyping patterns from strain to strain were quite independent from one another, the combined use of the three genotyping methods could discriminate 46 strains into 39 genotypes. Thus, the powerful discriminatory ability of the combination was demonstrated.

Molecular epidemiology for local outbreaks of methicillin resistant Staphylococcus aureus (MRSA). The need for several methods

Subtyping isolates may be useful for epidemiological studies of methicillin-resistant-Staphylococcus aureus (MRSA) outbreaks. Among subtyping methods, DNA-based techniques have been applied very effectively for this purpose. An outbreak of MRSA infections took place in one hospital in Barcelona early during 1991. From the beginning of the outbreak to December 92, 70 MRSA isolates from different patients and sources were collected. All strains were evaluated by restriction endonuclease analysis of plasmid DNA (REAP) and macrorestriction endonuclease analysis of genomic DNA using Sma I and pulsed-field-gel-electrophoresis (PFGE). Plasmid screening and REAP using Hind III demonstrated two plasmid subtypes: subtype A showing a large plasmid, and subtype B showing the same large plasmid plus a smaller one. Subtypes A and B corresponded to the more recent and older isolates, respectively, suggesting the loss of the small plasmid during the epidemic. PFGE using Sma I displayed two closely related profiles (PFGE subtype A and A'; CS = 0.90). These subtypes were different from those subtypes exhibited from 4 methicillin-susceptible-Staphylococcus aureus (MSSA) isolates from the same hospital and from 2 epidemiologically unrelated MRSA isolates. Almost all isolates showing PFGE subtype A preceded those isolates showing PFGE subtype A'. This fact and the similarity between both subtypes suggested minor chromosomal DNA rearrangement during the outbreak from a unique strain. While PFGE using Sma I is a useful tool in evaluation of clonal dissemination, our data suggest epidemic or local outbreaks may need several methods to best delineate the source and spread of MRSA strains. The reproducibility and discriminatory power of REAP makes it a useful adjunct in this context.

Prospective study of infection, colonization and carriage of methicillin-resistant Staphylococcus aureus in an outbreak affecting 990 patients

In the three years between November 1989 and October 1992, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) affected 990 patients at a university hospital. The distribution of patients with carriage, colonization or infection was investigated prospectively. Nosocomial acquisition was confirmed in at least 928 patients, 525 of whom were identified from clinical specimens as being infected (n = 418) or colonized (n = 107) by MRSA. An additional 403 patients were identified from screening specimens, of whom 58 subsequently became infected and 18 colonized. Screening of the nose, throat and perineum detected 98% of all carriers. Of the 580 infections in 476 patients, surgical wound, urinary tract and skin infections accounted for 58% of the infections. Of the 476 infected patients, death was attributable to MRSA infection in 13%. Colonization with MRSA was found in 127 patients and 42% of 165 colonized sites were the skin. Auto-infection from nasal carriage or cross-infection, probably via staff hands, seemed to be the most common mode of acquisition of MRSA infections.

An outbreak of infection due to Staphylococcus aureus phage type 52 in a neonatal intensive care unit

An outbreak of infection due to Staphylococcus aureus phage-type 52, resistant only to penicillin, occurred in children's wards primarily in a neonatal intensive care unit. The outbreak involved 86 infants; the majority presented with conjunctivitis, wound infections, boils, omphalitis and otitis externa. Seven per cent of these infants (six of 86) also had septicaemia. In addition, 6% (five of 86) were colonized by this phage type and the most common site of carriage was the umbilicus. The outbreak was contained by eradication of nasal carriage among the staff members and also by standard infection control measures.

Comparative sensitivity to antibiotics and biocides of methicillin-resistant Staphylococcus aureus strains isolated from Saudi Arabia and Great Britain

Methicillin-resistant Staphylococcus aureus (MRSA) isolated in Saudi Arabia and Great Britain were examined for susceptibility to antibiotics and biocides. The strains differed in their sensitivity patterns. None of the Saudi strains showed resistance to propamidine isethionate, but most of the British gentamicin methicillin-resistant Staph. aureus (GMRSA) strains were highly resistant to this compound and to some other nucleic acid-binding (NAB) compounds. Both groups showed a low level of resistance towards quaternary ammonium compounds (QACs), but resistance to these compounds was not associated with resistance to gentamicin in the Saudi strains. The aminoglycoside-resistant determinants were non-conjugative in these strains. Natural MRSA strains were good recipients for pWG613, but transferred this plasmid in reciprocal crosses at significantly lower rates.