Frequently asked questions about MRSA

What is MRSA?

MRSA, or methicillin-resistant Staphylococcus aureus, refers to bacterial strains that differ from typical strains of S. aureus only in their resistance to antibiotics. Methicillin resistance does not increase the pathogenicity of the bacteria. MRSA strains are resistant to beta-lactam antibiotics such as penicillins and other betalactams. Like other S. aureus bacteria, MRSA may survive in the environment for extended periods of time.

What does it cause?

MRSA is known to cause healthcare-related infections. S. aureus is a common type of bacteria found on the skin and upper respiratory tract, and does not cause disease in healthy people and animals. However, it may cause infections in areas such as damaged skin or surgical wounds.

As the most common antimicrobials are ineffective on MRSA bacteria, its treatment is difficult. A person or animal with asymptomatic MRSA carriage, may occassionally get an MRSA infection.

Is MRSA found in animals or meat in Finland?

In Finland, MRSA has been detected in animal production in pigs, dairy cattle and horses. Numerous MRSA findings in pigs have been made at pig farms. In dairy cattle, MRSA findings are uncommon. MRSA is also rarely found in dogs and cats.

In 2015, Evira examined a total of 303 samples from fresh pork meat for MRSA strains. The incidence of MRSA is fresh pork was relatively low. MRSA was found in nine (3 %) of the samples. Of these, seven were of domestic origin. Most of the pork samples studied were of domestic origin; a total of 11 samples were from imported meat products. All MRSA strains were of type CC398. MRSA does not usually cause disease in pigs. Year 2017 altogether 220 samples from fresh pork meat were analysed. Most of these were of domestic origin. MRSA was found in 6 % of the samples. In this survey, all MRSA strains were also of type CC398.

The prevalence of MRSA in pigs has been studied in Finland on four occasions. Environmental dust samples were taken from more than 200 Finnish pig farms as part of an EU-wide survey in 2008. MRSA bacteria were found in the environmental samples of one farm. The prevalence of MRSA in slaughter pigs was studied in 2009–2010 by analysing samples from 59 slaughter batches, of which 22 % tested positive for MRSA. All 68 special-level pig breeding farms were screened for MRSA in 2011–2012, and none of them had the MRSA bacterium.

Samples were recollected from slaughter pigs between 2016–2017. Of the analysed slaughter batches, altogether 77 % contained MRSA.

The prevalence of MRSA had therefore increased in slaughter pigs. However, any findings of MRSA in slaughter pigs in the survey are not a reflection of the MRSA situation on the primary production farms, as the pigs may have contracted MRSA during transport or in slaughterhouse pens.

How is MRSA transmitted between people and animals?

MRSA bacteria can be transmitted between people and animals. Due to this, the incidence of MRSA in pig farms, for example, may cause a risk of infection to people working in close contact with MRSA carrying animals. The use of antibiotics at animal production farms increases the prevalence of resistant bacterial strains and may help sustain the source of infection. Due to this, antibiotics should only be used on justified grounds. In households, MRSA can be transmitted from people to pets and vice versa, and it is often difficult to determine the original carrier. Good hygiene both in homes and on the farms, including hand hygiene, is the best way to prevent infection.

Is food safe from MRSA?

According to latest studies, MRSA is not contracted by eating foods that contain MRSA bacteria. The risk of getting MRSA infection through handling of meat is also low. MRSA transmission in kitchens can be prevented with good food preparation practices and hand hygiene. Common hygienic methods are effective against foodborne bacteria, including sufficient heating, proper handling of raw materials, and good hand hygiene while preparing food.

At what temperature is MRSA destroyed?

MRSA infections, like those from other unwanted foodborne bacteria, can be prevented with good food preparation practices and hand hygiene. MRSA is destroyed from food through heating.

Keep these in mind when preparing food:

  • sufficient heating (meat should be heated to at least 75° C),
  • proper handling of raw materials (for example preventing cross-contamination from raw meat to cooked food or fresh ingredients such as salads),
  • carefully wash and dry dishes and utensils (when washing by hand, wash utensils used to handle raw meat last in as hot water as is tolerable; in machine wash, temperature should be 60° C. In both methods, it is important that dishes are dried completely before their next use), and
  • always wash hands before preparing food and between work stages (at home, thorough washing with soap and warm water is usually enough; use hand sanitiser if there is flu or stomach flu in your household, and remember that preparing food for others when sick is not advised).