Strain of vancomycin-resistant enterococcus caused 10-fold increase in cases in a single year
Image credit: CDC/Janice Carr
Sweden saw a “dramatic” increase in the number of people colonised or infected with vancomycin-resistant enterococci (VRE) during 2007 and 2008, report researchers this week in Eurosurveillance.1 Most cases recorded during this period were caused by a strain of Enterococcus faecium vanB that seems to be unrelated to known VRE strains, they say.
“The cause of the dissemination is unknown,” write Tomas Söderblom, of the Swedish Institute for Infectious Disease Control, and colleagues. “No major changes in the general hospital infection control policies such as changes of nurses per bed ratios or antibiotic policies had been introduced that could explain the increased VRE prevalence.”
Cases of infection or colonisation with VRE have been notifiable in Sweden since 2000, which means that all detected cases are reported to the Swedish Institute for Infectious Disease Control. Since 2004, contact tracing has also been mandatory whenever VRE infection or colonisation is detected.
Before 2006, the incidence rate of VRE-affected people in Sweden was low — no more than 0.2–0.4 per 100,000 per year, according to the researchers. But as of the autumn of 2007, sharp increases were reported in Stockholm county followed by Västmanland and Halland. The total number of cases detected in Sweden increased 10-fold between 2007 and 2008, and 760 patients were found to be infected or colonised with the bacteria between July 2007 and February 2009. About 9% of these had clinical infections, including bloodstream infections.
The three counties affected are geographically separate, but genetic typing of the bacteria using pulsed-field gel electrophoresis (PFGE) revealed that most cases had a common cause, a strain of Enterococcus faecium vanB.
“The PFGE pattern of the current strain is seemingly new and has not been seen previously among vancomycin-resistant E. faecium isolates in Sweden,” say Söderblom and colleagues. They also compared the bacteria to a collection of reference strains of VRE kept in Germany, and found no related strains. They are now trying to determine if the new strain might have emerged from a vancomycin-susceptible strain, as outbreaks have been caused by such strains before.
“Although vancomycin-resistant enterococci are seldom encountered in serious clinical infections, they occasionally cause invasive infections notably in immunocompromised hosts,” the researchers write. “Some of these infections, particularly those caused by Enterococcus faecium, are often difficult to treat since only few antimicrobial treatment options are available.”
Vancomycin is the last line of treatment for many infections caused by Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA).
“Vigorous” countermeasures have reduced the number of new cases in the affected hospitals, the authors say. These include strict cleaning procedures, educating ward staff about proper infection-control practices, and removing food buffets, as well as introducing patient screening and contact tracing, Despite these measures, new cases of infection or colonisation with the new strain have been detected since the study, the authors say, and the incidence rate across Sweden for this year so far is still higher than the yearly average prior to 2007, according to figures from the Swedish Institute for Infectious Disease Control.2
Reference and links
1.
Söderblom T, Aspevall O, Erntell M, Hedin G, Heimer D, Hökeberg I, et al. Alarming spread of vancomycin resistant enterococci in Sweden since 2007. Euro Surveill. 2010;15:pii=19620. Article
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