The Medicine Cabinet: Ask the Harvard Experts
By Howard LeWine, M.D.
Q: I have been taking care of my brother’s dog while he was hospitalized to treat an infection in his leg. I just found out it was MRSA. What is MRSA? Could the dog be infected and pass it to me?
A: MRSA is short for methicillin resistant Staphylococcus aureus. Originally, all strains of staph aureus bacteria were killed by good old penicillin. But then, many years ago, a strain of staph became resistant to penicillin. A new antibiotic, methicillin, was developed as the “cure” for penicillin-resistant staph.
Methicillin and similar drugs remained effective against almost all staph infections for some time, but of course that didn’t last. Now there are multiple strains of staph that are resistant to penicillin, methicillin and a host of other antibiotics.
Staph aureus bacteria, including MRSA, are all around us and reside on our skin and inside our nose. Just having staph bacteria sit on our skin, but not underneath our skin or inside our body, does not mean there is an infection. Doctors call it colonization. Colonization does not require antibiotics.
Now back to your brother’s dog. Dogs, as well as cats, can carry staph aureus. But these pets are more likely to carry a different, less dangerous staph species called Staphylococcus pseudintermedius.
In fact, this Staphylococcus pseudintermedius can be considered “normal” in a dog. Most healthy dogs carry these bacteria in their bodies without ever getting sick. And this type of staph bacteria is very rarely transmitted to humans.
It’s unlikely but possible that this particular dog’s mouth is colonized with MRSA. So a dog bite could potentially lead to a MRSA skin. But if you just played, petted and even were licked by the dog, then there really is no danger to you.
If you washed your hands after being with the dog, then there is an excellent chance that there is no MRSA on your skin. Washing your hands or cleaning them with an alcohol-based gel is the best way to wash away all bacteria and viruses and avoid spreading them to other parts of your body and to others.
(Howard LeWine, M.D. is an internist at Brigham and Women’s Hospital in Boston and assistant professor of medicine at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)