As hundreds of sick passengers steam toward Charleston onboard the Celebrity Mercury, state health officials try to explain a spike in similar stomach flu outbreaks on land.

The S.C. Department of Health and Environmental Control has investigated 43 norovirus or norovirus-like outbreaks across the state so far this year, including five in Charleston County and one in Berkeley County, according to DHEC public information director Adam Myrick. That's twice the usual number of gastrointestinal illness clusters.

"The virus does live long on surfaces, and it lives longer when it's colder this time of year," Myrick said. "This is when we see these types of outbreaks, but not in recent years on this type of pace."

Norovirus primarily spreads in confined communities, such as cruise ships, schools and hospitals. Statewide, 23 cases came from nursing homes and 14 from schools or colleges.

At its peak Tuesday, 419 of the 1,838 passengers and 27 of the 849 crew members onboard the Mercury had fallen ill. The ship set sail Feb. 15 for an 11-day Caribbean cruise from Charleston and returns to port Friday. A Celebrity spokeswoman said Wednesday that 338 guests remained sick and that the company had not yet received results from an independent laboratory to confirm norovirus.

The local outbreaks include three long-term care facilities, one school and one large event in Charleston County and one long-term care facility in Berkeley County. DHEC officials would not release the specific locations; and The Post and Courier filed a Freedom of Information Act request.

"We've got a good relationship, we've got a good partnership with these types of facilities that are reporting these illnesses to us," Myrick said. "They're coming to us for guidance, so it's actually helping public health. And if they don't -- if they're a little bit nervous about it -- it might undermine some of the reporting and some of the surveillance that we are able to do."

One local outbreak continues affecting 60 to 70 people who live or work at The Palms of Mount Pleasant, an active retirement community on Bowman Road. Executive Director Tim Cook said his staff treats the sickness as norovirus as it awaits results from sample testing.

That means restricting visitors and barring people younger than 21 and pregnant women and limiting transportation from The Palms to prevent spreading the illness. Staff posted signs about strict hygiene and deliver meals and plenty of fluids to residents.

"It's like a ghost town around here right now when usually it's a very vibrant community," Cook said.

Norovirus symptoms include nausea, vomiting, diarrhea and stomach cramps, sometimes accompanied by a low-grade fever. The highly contagious illness usually lasts a day or two and spreads through food, water or person-to-person contact.

Personnel from the federal Centers for Disease Control and Prevention will arrive in town for the Mercury's return to port Friday. Bernadette Burden of the CDC said onboard medical staff will help prevent sick passengers from transmitting the stomach flu in Charleston.

"This is not a situation where they would let people exit the vessel arbitrarily without giving them prudent medical advice," Burden said.

A cruise ship must report to the CDC any gastrointestinal problem that affects at least 2 percent of a ship's population.

"It is not unusual and it occurs quite frequently," Burden said.

About 20 residents of James Island retirement community Bishop Gadsden sailed out with the Mercury. Kimberly Farfone, public relations director at Bishop Gadsden, said staff contacted the company that booked the residents but learned nothing about specific cases yet.

Farfone said some Bishop Gadsden employees came down with norovirus-like symptoms earlier this year but that the community has not experienced an outbreak. With the residents returning home, staff continues cleaning surfaces and installing hand sanitizer stations and warnings around the premises.

"With this and the H1N1 scare earlier this year, we've become accustomed to this," Farfone said.

Prevention tips

Tips for fighting off norovirus, especially for people planning cruises:

Carry alcohol hand sanitizer.

Wash hands often.

Don't shake hands with others.

Don't eat or drink after the ill.

Source: Dr. Cassandra Salgado, MUSC associate professor of medicine

Reach Allyson Bird at 937-5594 or abird@postandcourier.com.