May 23, 2001 -- Most people are familiar with bacteria such as salmonella causing food poisoning -- the painful cramping, diarrhea, and vomiting that follow a meal that was undercooked or improperly stored or handled. But CDC scientists in Atlanta are reporting a far more serious outbreak of salmonella -- one that doesn't come from food, but was passed from person to person and didn't respond to the antibiotic used most often to treat the infection.
The first recorded outbreak of infection with this resistant type of salmonella occurred in nursing homes in Oregon; it is described in the May 24 issue of The New England Journal of Medicine. But CDC epidemiologist Frederick J. Angulo, DVM, PhD, tells WebMD that another outbreak has since hit a Florida hospital and nursing home.
What is particularly troubling about these outbreaks is the evidence that infection was spread by patient-to-patient contact, which suggests this type of salmonella is much more infectious than the previously recognized strains.
"Usually it takes a lot of salmonella, a very high dose, to infect someone," says Glenn Morris, MD, chairman of the department of epidemiology at the University of Maryland School of Medicine in Baltimore. Morris, a nationally recognized expert on salmonella, was not involved in the study.
The fact that such a high dose is usually needed is why "we don't see outbreaks of salmonella in day care centers," says Angulo. But with this specific type of salmonella bacteria, he says, it only takes about 10 of the organisms to infect another person. That means careful hand washing by patients must be ensured and other strenuous infection control measures be implemented and strictly enforced, he says.
This type of salmonella infection hasn't been seen in the U.S. since the 1960s. Before then, it was common for patients in hospitals to pass a variety of bacteria -- including salmonella -- to other patients.
"But then we instituted infection-control measures, and [this type of] infections became rare," Angulo says. "In developing countries, salmonella outbreaks [in hospitals] are still very common."
What's most concerning about this new strain of salmonella is that it is difficult to treat. Almost all salmonella infections are easily treated with antibiotics such as Cipro, but this new strain is the exception.
This super-salmonella strain was brought to the U.S. by a patient who suffered a stroke while traveling in the Philippines in 1995. Angulo says the patient was probably infected during his three-month treatment at the hospital in the Philippines. The patient was then sent to a nursing home in Oregon and while there infected eight other patients. One of those patients was briefly transferred from the nursing home to a hospital, and while hospitalized infected another elderly patient.
The most likely scenario is that both patients were bathed in the same tub, a tub that wasn't adequately cleaned between baths, Angulo says. The patient infected in the hospital was subsequently discharged to a different nursing home, where the infection spread to a roommate.
In all, 11 people, two nursing homes, and two hospitals were involved in an outbreak that continued over a four-year period, says Angulo.
"Salmonella in a nursing home is an absolute disaster," says Morris. Although healthy adults can weather a salmonella infection with a few days of discomfort, among the very young and the very old -- who have poorer immune systems to fight infections -- the bacteria can be a killer because the infection can spread to the blood, causing a life-threatening condition know as bacteremia. The patients in the Oregon outbreak were aged 64 to 90.
And salmonella is a pesky and persistent bacteria that many people excrete in their stool for up to two years after the acute illness is passed, says Morris. This process can be disastrous as the infection continues to be passed to more and more patients.
"You keep repeating this cycle of transmission," he says. "It can be very difficult to break this without draconian measures, such as isolating patients, and no nursing home is going to do that."
Scientists think that in the future, hospitals and nursing homes are likely to see more rather than less of this super salmonella. Hope for warding it off involves following good infection-control measures, including use of antibacterial cleaning solutions that can kill salmonella on surfaces like doorknobs and telephones, along with good old-fashioned -- but often-neglected -- hand washing.