While Dantes can't say for sure what is behind the decline, he suspects better infection-control practices have helped, such as isolating patients who have MRSA in a hospital or other health-care facilities, as well as better barrier precautions such as doctors wearing sterile gowns.
"The next step in trying to reduce invasive MRSA infections is actually looking at folks outside the health-care setting," Dantes said.
The second study, on swine-related infection, may provide some clues. Researchers from Johns Hopkins Bloomberg School of Public Health evaluated more than 5,700 patients with MRSA or skin and soft tissue infections, comparing them to nearly 3,000 healthy patients.
The investigators zeroed in on 200 samples taken from those with and without infection, then used Google Earth to find the home addresses of those with MRSA and those without. About 11 percent of the infections may be related to the exposure to livestock operations, they found.
Many antibiotics used in the United States are used for growth enhancement of livestock, and most of these are excreted in manure, the researchers noted. Many of the antibiotics are from the same drug families used to treat human infections, so extensive use can result in drug-resistant bacteria that can spread to humans, either by animal contact or in the food chain, by eating the meat.
Researchers in the Netherlands already have recognized the potential link with livestock exposure, publishing findings as recently as 2012, said Dr. Edward Septimus, a professor of internal medicine at Texas A&M Health Science Center and a member of the antimicrobial resistance committee for the Infectious Diseases Society of America. He reviewed the new studies.
The report of declining infections, he said, is welcome but not surprising news. The new report "confirms the trends we have seen in the last three or four years," Septimus added.
"The good news is, we are making progress," he pointed out. "It doesn't mean Staphylococcus aureus is no longer an important pathogen, because it is."
He also credits better infection-control practices for the decline, along with more awareness.
To minimize risk of invasive MRSA, Dantes and Septimus suggested following good hygiene at home, washing hands regularly and keeping any open area on the skin clean. Loved ones of hospitalized patients should make sure that those who care for the patients follow good hygiene practices, such as washing their hands before exams.