No 46 - 2011

MRSA 2010

In 2010, a total of 1,097 new MRSA cases were detected (Methicillin-Resistant Staphylococcus Aureus). This was a 34% increase from the 817 cases detected in 2009, Figure 1.

The majority of the MRSA cases were infected in Denmark. Foreign infection was stated for 247 cases (23%).

The median age was 66 years for hospital-acquired cases and 34 years for community-acquired cases.

In 647 (59%) cases, a clinical infection caused the sampling and among these, MRSA was primarily detected from skin and sores: 489 cases (74%). In 21 cases, MRSA was isolated from blood.
In 244 cases, information about predisposing factors was given: the most frequent factors were sores (151 cases), chronic skin disorders (38) and foreign objects, e.g. drains, urinary tract or intravenous catheters (37).

As in 2009, the number of hospital-acquired infections was low (34), while an increase was seen in the number of infections acquired abroad and the number of community-acquired cases for which contact to a nursing home/hospital was stated, Figure 2.

In 40 cases, MRSA exposure was known, Table 1.

Outbreaks

A total of 21 outbreaks were recorded comprising a total of 94 cases. The largest outbreak comprised nine nursing home residents. Several outbreaks were observed at the Neonatal Department of the Copenhagen University Hospital, including among others eight (CC30) and seven (CC22) cases in patients, relatives and staff. Outbreaks at neonatal departments were previously, EPI-NEWS 48/08.

Epidemiological classification

The epidemiological classification based on presumed infection conditions established from epidemiological and microbiological information is presented in Table 1. The number of hospital-acquired cases remained low. The majority of cases were acquired in the community by persons who had no known contact to hospitals or nursing homes (578 cases). A total of 331 cases (57%) had a known exposure to an MRSA case, most frequently a family member (69%) followed by exposure to pigs (the CC398 clone, see below).

Typing

The 1,097 isolates represented 180 spa types from 18 different clonal complexes (CC groups). The two primary CC groups, CC8 (n = 212) and CC5 (n = 195), comprised 37% of the isolates and represented 18 and 24 different spa types, respectively. The ten most frequent spa types comprised 55% of the isolates; among these the two most frequently observed types were t002 (n = 110; CC5) and t034 (n = 93; CC398). Further details on typing and resistance profiles related to the spa types are available in the DANMAP 2010 report at www.danmap.org.

MRSA CC398

As previously, 2010 saw a considerable increase in the number of persons infected with MRSA CC398, which is primarily found in persons who have had contact to pigs (n = 109). This should be compared with the 40 cases detected in 2009. However, in 15 cases the affected persons neither had direct contact with pigs nor had anyone in their household.

New MRSA variant found

In 2011, a new variant was found of the mecA gene (the gene causing the MRSA phenotype). The variant was called mecA_LGA251. Previously, the gene could not be detected with the employed confirmatory methods, and the isolates have therefore tested as resistant, but without being classified as MRSA. Retesting of older isolates has detected the gene in an isolate from 1975. In 2010, a total of 21 cases were detected with this type which seems to have continued its increase in 2011. The gene was found in two CC groups (C130, C1946) also related to cows and sheep.

Commentary

In 2010, the number of newly detected MRSA cases was the highest recorded since the mid-1970s. The number of hospital-acquired cases remained low as previously, which may be interpreted to mean that the 2006 action plan is effective. However, a continued increase was observed for both community-acquired and imported cases.

The considerable number of different spa types indicates that MRSA is repeatedly imported to Denmark. Once introduced, the types spread, particularly within households.

2010 also saw a considerable increase in cases related to pigs. These now comprise a total of 10% of new cases nationwide and in some regions as much as 30%. It is therefore recommended that contact to pigs be stated as a risk factor in the ongoing amendment of the MRSA action plan, and that follow-up after treatment of carrier cases be intensified; this last measure to decrease the spreading of MRSA in the society.

(A. Petersen, A.R. Larsen, M. Sørum, R.L. Skov, Staphylococcus Laboratory) (L.K. Knudsen, P. Valentiner-Branth, Department of Epidemiology)

European Antibiotic Awareness day

Worldwide there is considerable overuse of antibiotics causing the development of bacteria resistant to antibiotics. For more information about the European Antibiotic Awareness Day and antibiotic resistance, please see www.ssi.dk and www.ecdc.europa.eu.

(A.M. Hammerum, Dept. for Microbiological Monitoring and Research)

16 November 2011