Emergence of hetero-vancomycin-intermediate Staphylococcus aureus (hVISA) in Sydney

To the Editor: Methicillin-resistant Staphylococcus aureus (MRSA) with reduced susceptibility to glycopeptides (vancomycin-intermediate S. aureus, or VISA) was initially described in Japan,1 then the United States,2 and subsequently other regions of the world. Recently, Ward and colleagues reported the initial Australian isolate — a heteroresistant VISA (hVISA) strain — in Melbourne, Victoria.3 We report the first isolation of hVISA in Sydney, New South Wales.

A 79-year-old man underwent mitral valve annuloplasty in April 2002. Post-operative complications included MRSA bacteraemia, which resolved. He was discharged at the end of July 2002, but 12 days later was admitted to a second hospital with endocarditis caused by Streptococcus viridans. A month later, he developed a third episode of septicaemia, and MRSA was isolated from blood cultures. Despite two weeks' treatment with intravenous vancomycin, blood cultures again yielded MRSA. A transoesophageal echocardiogram confirmed endocarditis. Resistance screening of the MRSA isolate by E test (AB Biodisk, Solna, Sweden)4 gave minimum inhibitory concentrations of 16 mg/L for vancomycin and 32 mg/L for teicoplanin, suggesting resistance to glycopeptides. The patient was then treated with intravenous linezolid and underwent vegetectomy. Subsequent blood cultures were negative for MRSA, but the patient died seven days after surgery from nosocomial pneumonia caused by Escherichia coli. Population analysis of the MRSA isolate showed that it was heterogeneously resistant to vancomycin (hVISA).

The emergence of hVISA in Sydney is a sentinel event, with ramifications for clinicians, laboratories and infection control. Routine susceptibility testing will not detect this resistance. Hence, clinicians and laboratories should consider VISA and hVISA if a patient with a proven MRSA infection fails to respond to vancomycin or teicoplanin, or has had several courses of vancomycin/teicoplanin and continuing positive cultures. If alerted that specimens could contain VISA or hVISA, the laboratory should perform glycopeptide resistance screening using E tests or other methods. Isolates that screen positive should be confirmed with population analysis profile testing.4

Treatment of hVISA and VISA infections, particularly bacteraemia and endocarditis, with vancomycin and/or teicoplanin is likely to fail. Alternative antibiotics include linezolid and quinupristin–dalfopristin, which are both very expensive. There is limited information on the success or otherwise of these agents in treating serious staphylococcal infections, especially bacteraemia and endocarditis.5

As a number of outbreaks of VISA and hVISA infection have already been described in other countries, we must ensure that these organisms do not become established in Australian institutions.

• Strict attention to infection control must be observed, particularly handwashing and use of alcohol hand rubs before and after patient contact.

• Attention to rational prescribing of antibiotics is required, avoiding broad-spectrum agents whenever possible.

• Vancomycin and teicoplanin should be used only when necessary: when there is resistance to other agents, and only when infection is present. Colonisation is not an indication to use glycopeptides, nor is minor allergy to β-lactams.