CHICAGO — Add the MRSA "superbug" to the list of concerns you bring to the beach nowadays, a research doctor said today.

It's still safe to go in the water, especially if you shower thoroughly before and after swimming, but antibiotic-resistant Staphylococcus aureus, a strain of bacteria that can cause staph infections that are difficult to treat with traditional anti-infection drugs such as methicillin, can be caught when you take a dip in ocean water, said Dr. Lisa Plano of the University of Miami's Miller School of Medicine.

MRSA stands for methicillin-resistant Staphylococcus aureus, or multiple-resistant Staphylococcus aureus. It has become a deadly and growing problem in hospitals in recent years.

"MRSA is in the water and potentially in the sand," Plano told a group of reporters today at the annual meeting of the American Association for the Advancement of Science. "This constitutes a risk to anyone who goes to the beach and uses the water … Most of us won't get infected but it only takes one infected person to spread [MRSA to others]."

So-called staph or Staphylococcus aureus, the kind that responds to antibiotics, is not a big deal typically out in the general public. About a third of us has it living in the nose or on the skin all the time, and we don't get sick from the bug. But for babies, the elderly and other people with compromised immune systems, staph can lead to an infection that can be deadly.

And in any population, when people catch the antibiotic-resistant strain (MRSA), doctors struggle to find a way to kill the infection.

Both the staph that responds to antibiotics and MRSA (which does not) have long been problems in hospitals, but the bugs have cropped up in locker rooms full of healthy people more recently, including some rumored infections among NFL and NBA players. Staph and MRSA can also occur in daycare settings.

A 'complicated bug'

Scientists already knew staph could spread in water. Now the research led by Plano shows that MRSA is also found at the beach — in the sea water and potentially in the sand.

To pin this down, Plano and her colleagues recently studied 1,300 adult bathers at a South Florida beach, half of whom took a dip in the water and brought back a sample of water for later lab analysis, and the other half of whom sat on the beach for 15 minutes.

Some 37 percent of the ocean water samples had Staphylococcus aureus in them, and 3 percent of those were the antibiotic-resistant strain of the bug, Plano said, even though the beach is located nowhere near a sewage source.

In other words, the "call was coming from inside the house" — probably, the bathers.

The staph was relatively mild strain, Plano said, but the strain of MRSA was particularly virulent, she said. One weird thing she found was that a later genetic analysis of the bugs in the water samples indicated a very low presence of markers for genes that cause the skin infections associated with staph.

"Staph is a really complicated bug," Plano told LiveScience in a phone interview earlier in the day. "S. aureus has an excess of 40 different virulence factors that it could potentially have and use to establish different types of infections, and not all staph will have all of them. Basically, most staph will have some of them, and what I looked at and what I compared these to are ones we knew to be associated with skin-infecting bugs."

In the sand too

Municipal pools and most private pools are safe from S. aureus if chlorine levels are appropriate, Plano said.

But there is some evidence that staph is spread in beach sand, she said. In one study, several quarts of staph-free sea water was poured over 14 previously staph-free toddlers in diapers who had played for 10 minutes in beach sand. The water that flowed off the kids was collected and analyzed — some of it was found to have S. aureus in it.

"If they had MRSA on their skin, they would've had MRSA in the sand," Plano said. It's unclear if staph and MRSA incubate in ocean water, she said. "We know that MRSA can be isolated from marine mammals such as dolphins and seals, which suggests MRSA is still in the water," she said, but more research needs to be done to find out how long organisms can survive in the water.

Recommendations: shower

Still, there is no reason to shun the beach, Plano said, but people should shower before and after going in the water. And, it is wise to avoid the beach if you have an open wound.

Plano just wants people to be aware of the potential risks of S. aureus and MRSA at the beach.

"This is a very complicated issue," she said. "There is a tremendous amount of work that still needs to be done for us to understand the risk of person at beach being exposed to Staph aureus. You shouldn't fear the beach. You go to the beach. You should have fun. You should embrace it."

The research was funded by the National Science Foundation, the Florida Department of Health and Environmental Protection, the Centers for Disease Control and Prevention, and the Environmental Protection Agency.