Continuing high prevalence of methicillin resistance amongst Staphylococcus aureus blood culture isolates

J Antimicrob Chemother 1999; 44: 300

N. H. O'Connell*, E. G. Smyth, C. Marshall and H. Humphreys

Department of Clinical Microbiology, Beaumont Hospital and Royal College of Surgeons in Ireland, Dublin 9, Ireland

Sir,

We read with interest a recent article in the Journal about the increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) blood culture isolates referred to the Public Health Laboratory Service in the UK. 1 Since the computerization of our laboratory in 1993, we too have been monitoring blood culture isolate data at Beaumont Hospital, Dublin, a 600 bed teaching hospital with a busy intensive care unit, and national neurosurgical and renal transplant reference centres. S. aureus was the second most common bloodstream isolate, accounting for, on average, 20% of positive blood cultures during this period. Our data reveal a relatively stable percentage of strains of MRSA among all episodes of bacteraemia caused by S. aureus, ranging from 26% in 1997 to 42% in 1994; the percentage for 1998 was 34%. These figures are similar to those reported by centres in Spain and the USA. 2,3 A national survey of MRSA isolates conducted in Ireland in 1995 showed that the period prevalence was 16.5/1000 hospital patient discharges and highlighted the endemicity of this bacterium in many Irish hospitals. 4

In common with Johnson et al., 1 we are concerned about the emerging threat of glycopeptide resistance among isolates of MRSA, as well as the controversy regarding the relative virulences of MRSA and methicillin-susceptible S. aureus (MSSA). Comparing the mortality rate in patients with MRSA bacteraemia with that in patients with MSSA bacteraemia can be unreliable, as patients with MRSA infection tend to be older and more debilitated, and the administration of appropriate antimicrobial therapy is often delayed if the initial empirical therapy is, as is often the case, a ß-lactam. None the less, the authors of a recent report from Spain demonstrated a higher mortality rate amongst patients with MRSA bacteraemia and we have also documented a higher mortality rate in patients with hospital-acquired MRSA bacteraemia (22% compared with 3% in patients with MSSA bacteraemia). 5

The cost of a 1 week course of treatment of a patient with MSSA bacteraemia in Ireland, i.e. iv flucloxacillin 1 g qds, is IR£136.08, compared with IR£293.16 (excluding drug assay costs) for a comparable course of therapy of a patient with a bloodstream infection caused by MRSA, i.e. vancomycin 1 g bd. Therefore, bacteraemic episodes caused by MRSA have important cost implications and, in our hospital, therapy and preventative measures consume considerable financial resources. In contrast, the prevalences of MRSA bacteraemia in other countries such as Denmark (0.2%) 6 are strikingly low. This may be the result of higher standards of infection control, more appropriate use of antibiotics and/or better medical facilities. Those countries in which the prevalences of MRSA are high or increasing should learn from those in which MRSA is rarely encountered. Therefore, while allowing for contrasting demographics and risk factors, a comparison of surveillance data from various countries should help to highlight differences in approach and facilitate greater efforts to prevent bacteraemias and other serious infections caused by MRSA.

Notes

* Tel: +353-1-809-2667; Fax: +353-1-809-2995. Back

References

1 . Johnson, A. P., James, D. & Livermore, D. M. (1999). Increasing prevalence of methicillin resistance amongst Staphylococcus aureus blood culture isolates. Journal of Antimicrobial Chemotherapy 43, 160.

2 . Steinberg, J. P., Clark, C. C. & Hackman, B. O. (1996). Nosocomial and community-acquired Staphylococcus aureus bacteremias from 1980 to 1993: impact of intravasular devices and methicillin resistance. Clinical Infectious Diseases 23, 255–9.[ISI][Medline]

3 . Romero-Vivas, J., Rubio, M., Fernandez, C. & Picazo, J. J. (1995). Mortality associated with nosocomial bacteremia due to methicillin-resistant Staphylococcus aureus. Clinical Infectious Diseases 21, 1417–23.

4 . Johnson, Z., Fitzpatrick, P. Hayes, C., Sayers, G., Pelly, H., McDonnell, B. et al. (1995). National survey of MRSA: Ireland, 1995. Journal of Hospital Infection 35, 175–84.

5 . Cunney, R. J., McNamara, E. B., Al Ansari, A. & Smyth, E. G. (1996). Community and hospital acquired Staphylococcus aureus septicaemia: 115 cases from a Dublin teaching hospital. Journal of Infection 33, 11–3.[ISI][Medline]

6 . 6.Kristensen, B., Smedegaard, H. H., Pedersen, H. M., Anderson, M. F., Dahlerup, J. F., Sorenson, H. T. et al. (1999). Antibiotic resistance patterns among blood culture isolates in a Danish county 1981–1995. Journal of Medical Microbiology 48, 67–71.[Abstract]





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