Cats and MRSA: don't blame Tigger!

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that causes infections in different parts of the body. It's tougher to treat than most strains of staphylococcus aureus -- or staph -- because it's resistant to some commonly used antibiotics. Though most MRSA infections aren't serious, some can be life-threatening. Staph can usually be treated with antibiotics. But over the decades, some strains of staph -- like MRSA -- have become resistant to antibiotics that once destroyed it. MRSA was first discovered in 1961. It's now resistant to methicillin, amoxicillin, penicillin, oxacillin, and many other antibiotics.

MRSA is spread by contact. So you could get MRSA by touching another person who has it on the skin. Or you could get it by touching objects that have the bacteria on them. MRSA is carried, or "colonized," by about 1% of the population, although most of them aren't infected.

MRSA infections are most common among people who have weak immune systems and are living in hospitals, nursing homes, and other heath care centers. Infections can appear around surgical wounds or invasive devices, like catheters or implanted feeding tubes. Rates of infection in hospitals, especially intensive care units, are rising throughout the world. In U.S. hospitals, MRSA causes more than 60% of staph infections.

MRSA is also showing up in healthy people who have not been living in the hospital. This type of MRSA is called community-associated MRSA, or CA-MRSA. The CDC reports that in 2007, 14% of people with MRSA infections had CA-MRSA, and the rates of infection are growing fast, especially in young people. In a study of Minnesotans published in The Journal of the American Medical Association, the average age of people with MRSA in a hospital or healthcare facility was 68. But the average age of a person with CA-MRSA was only 23.

MRSA has been identified not only in people, but in dogs and cats as well. MRSA from people can cause infections in pets, and pets can be a source of MRSA for people. An investigation into the prevalence of MRSA in people and their pets, published in the Journal of the American Veterinary Medical Association entitled “An investigation of methicillin-resistant Staphylococcus aureus colonization in people and pets in the same household with an infected person or infected pet” revealed that in households in which one or more persons had experienced MRSA infection, both humans and pets, including cats, were found to be infected. The isolates from humans were the same as those isolated from pets. This proved that cross-species infection can indeed occur, but it can be difficult to tell whether the infection was from human to pet, or from pet to human. The authors of the article speculate that the humans were the source of infection for the pet, and not the other way around, because the isolates were community-associated MRSA strains. Affected pets weren’t in contact with other animals, so they likely got the infection from their owners.

I once received an e-mail from a worried cat owner who was considering putting her cat to sleep because she acquired an MRSA infection, and was blaming the cat for it. I think this study sheds a bit more light on the topic, namely that cats and people can both be infected with MRSA, but you cannot blame your cat for being the source of infection, and in fact, it is more likely that the pet owner is the source of infection for the cat, and not the other way around.