PORTLAND – Growing numbers of Mainers are contracting a staph infection that is resistant to commonly used antibiotics.

The infection, methicillin-resistant Staphylococcus aureus (MRSA), strikes an estimated 1.2 million people nationwide each year, resulting in death for tens of the thousands of the most vulnerable, according to a new study from the Association for Professionals in Infection Control & Epidemiology.

In Maine, hundreds of people are infected with the bacterium. The actual number of cases is hard to pin down because hospitals aren’t required to report staph infections to the state.

But one indicator comes from NorDx, which provides laboratory testing services in southern Maine. NorDx found that 822 people contracted MRSA last year, up from about 535 in 2000.

Don Piper, chief medical technologist for NorDx, said some of the rise is because of NorDx’s increasing volume of work. Still, the numbers are significant and worrisome because front line antibiotics don’t work on the bacterium, he said.

“The treatment requires antibiotics that are less effective and may have more side effects,” Piper said.

MRSA, which has been called a “superbug,” accounted for about 2 percent of all staph infections in the 1970s, according to the Association for Professionals in Infection Control & Epidemiology. It now accounts for more than 60 percent, the association said.

While MRSA is harmless when on the skin or inside the nose, a break in the skin can allow the germs to enter and multiply. The result can range from a painful boil to a bloodstream infection; it can also lead to pneumonia.

Hospitals in Maine say they are seeing more MRSA cases, which they attribute to a rise in a new strain of the bacteria found in community settings. People are spreading MRSA by sharing equipment and personal items such as towels and gear at homeless shelters, fitness centers and schools.

The Cumberland County Jail and the Maine State Prison had outbreaks two years ago affecting nearly a dozen inmates. Bowdoin College had three cases over the past school year and at one point closed down several athletic facilities after a football team member was infected.

Years ago, most cases were of elderly people who underwent many hospital procedures and often were under a long-term care, said Kim Ware, infection control coordinator at MaineGeneral Hospital in Augusta, which treated 38 cases of community MRSA last year, up from 14 in 2005.

“What we’re seeing now are young people who have not had any exposure to the hospital or to long-term care,” she said.

Darcie Tocco, a 24-year-old restaurant cook in Portland, recently noticed a small bump on her thigh that started out looking like a little pimple but grew to the size of a penny and got so hard that it felt like a pebble was lodged under her skin.

When she went to the emergency room at Maine Medical Center a couple of weeks ago, she discovered that she had contracted MRSA.

She has since learned that the best way for people to reduce the risk of staph infection is to keep their hands clean, keep cuts and scrapes clean and covered until healed, avoid contact with other people’s wounds or bandages, and avoiding sharing personal items such as towels or razors.

“The only thing you can really do is have really good hygiene,” Tocco said.