Report finds increase in occurrence of MRSA bacteria in Denmark

In 2011, more Danes became infected with MRSA bacteria, and the number was the highest in over 25 years. The increase was primarily seen in otherwise healthy people without any hospital relation. Although the number of MRSA positive pig herds is on a par with the level seen in 2010, significantly more pigs at slaughter were found to be infected with the so-called pig MRSA, and the number of people infected with pig MRSA is increasing. This appears from the Danish surveillance report, DANMAP, for 2011.

MRSA bacteria are resistant to antimicrobial agents that are essential to treating life-threatening infections in humans. The number of people diagnosed with MRSA continues to rise, but compared with other countries, Denmark still experiences a low occurrence of infections caused by MRSA bacteria.

MRSA guideline works in hospitals
The number of new MRSA cases continued to increase to 1,292 in 2011, which was an 18% increase compared to 2010. The number is the highest seen in more than 25 years. The development from 2009 to 2010, when the number increased by 34%, thus continued in 2011.

The increase is seen primarily in community acquired cases (751 in 2011 compared with 578 in 2010). In about 12% of the cases, people had had contact with pigs, but in many of the cases there are no known risk factors. The number of cases acquired while abroad has also increased. However, the number of hospital-acquired cases remained low (61 cases in 2011 and 62 in 2010).

"It is an evident success that the number of hospital-acquired cases is still very low, but the continued rise in community acquired cases require, that we continue to do an effort at full strength," says Robert Skov, Consultant at Statens Serum Institut.

Increase in occurrence of pig MRSA
In 2011, the occurrence of MRSA was studied in approx. 80 pig farms and about 800 pigs and 180 cattle in slaughterhouses. MRSA was not found in cattle, but in 16% of pig herds, which was the same level as in 2010.

44% of the pigs tested positive for MRSA at slaughter, which was higher than in 2009, when the last survey of pigs in slaughterhouses was conducted. This suggests that there was a higher occurrence in the positive herds than previously which means that MRSA more frequently was transmitted between pigs during transport and before slaughter.

The number of people infected with MRSA of the so-called pig type, CC398, increased from 109 in 2010 to 164 in 2011. MRSA CC398 constituted 12.5% of all MRSA cases in 2011. The vast majority of new cases were still seen in persons in direct contact with pigs.

"We need to prevent increasing occurrence of MRSA in pigs because we have a large pig production in Denmark and pigs are the main source of MRSA CC398", says Yvonne Agersø, Senior Researcher at the National Food Institute, Technical University of Denmark.

Revision of MRSA guideline
As a consequence of the increasing occurrence of MRSA CC398 contact with live pigs is now included as a risk factor in the revised MRSA guideline for healthcare professionals which will be published this autumn.

"The continued increase of community acquired MRSA and the increasing occurrence in agriculture should be taken seriously and combated as it could otherwise lead to increased hospital incidence. The fact that contact with live pigs is added as a risk factor in the revised MRSA guideline and is an important step in the right direction", says Robert Skov.

FACTS

MRSA bacteria
MRSA is short for Methicillin-resistant Staphylococcus aureus.

Staphylococci are bacteria found in humans, animals and in our surrounding environment. Staphylococcus aureus is part of the normal nasal and skin flora in approx. 50% of the population. Staphylococcus aureus can cause a wide range of infections ranging from superficial wounds and abscesses to serious infections such as Osteitis and Endocarditis. In hospitals, Staphylococcus aureus is the most frequent cause of post-surgery infections. A large proportion of those infected with MRSA are just carriers of MRSA without being sick.

When bacteria are exposed to antimicrobial agents, they protect themselves by developing resistance in order to survive. The resistant bacteria have changed their hereditary material - their genes. The gene which primarily causes the resistance is called mecA. This makes the bacteria resistant to all so-called beta-lactam antimicrobial agents, including penicillin and the broad-spectrum antimicrobial agents cephalosporines. It is therefore important to only use antimicrobial agents as required to prevent overuse.

Researches are finding the same types of MRSA genes in both humans and a number of animals, including pigs and cows. In 2011, 16% of all pig herds were found positive with the so-called pig MRSA, which can be transmitted from pigs to humans.

Studies of approx. 800 meat samples from imported chicken, beef and pork and Danish chicken, beef and pork show the highest incidence of MRSA in imported chicken meat (31%) followed by Danish pork (10%), imported pork (5 %) and imported beef (4%).  For the first time, MRSA was found in Danish chicken. For now, consumption of meat is not considered a source of human infections.

The occurrence of MRSA in humans in Denmark is still low compared to many other countries in Europe.