Many of the victims were children; six were hospitalized for vomiting, fever and severe diarrhea. Some passed the illness to others. The germ they had was resistant to five drugs spanning several classes of antibiotics.

"This is likely an underrepresentation of how large the problem is," because others who were sick may not have gone to doctors and not all labs do the kind of tests that would detect this germ, said Dr. Chris Braden, an epidemiologist at the Centers for Disease Control and Prevention.

Salmonella infections are common from reptiles, especially small turtles called red- eared sliders that are banned but have made an illegal comeback in several states in recent years. The 2003 monkeypox outbreak that originated in imported African rats and spread to U.S. prairie dogs showed the risks of owning exotic pets.

But cuddly little pocket pets like hamsters were not thought to pose much of a problem.

Gerbils, guinea pigs, ferrets and rabbits could also carry the germ, the CDC said.

"This outbreak highlights the fact that there is no perfectly safe pet. Parents and children should wash their hands thoroughly after contact with any pet" -- even the family dog, said Dr. Stephen J. Swanson, a CDC epidemiologist working in the Minnesota Department of Health.

CDC started investigating last summer after Minnesota officials found the unusual infection in a 5-year-old boy sickened after playing with and kissing a pet mouse that had severe diarrhea and later died.

Tests showed that both had a drug-resistant strain of salmonella, a relative of the germ that causes typhoid fever. The same strain was found in a 4-year-old boy hospitalized in South Carolina and in his pet hamster, which also died.

Officials then checked PulseNet, a national germ reporting database designed to detect unusual trends, and found 28 other cases from December 2003 to October 2004.

Of the 22 people they have been able to interview, 13 had contact with rodents bought from pet stores and two caught salmonella from others who were ill. Seven had no known contact with rodents; investigations are continuing on the rest.

Cases have been confirmed in Illinois, Kentucky, Missouri, Pennsylvania, South Carolina, Georgia, Michigan, Minnesota, New Jersey and North Carolina.

Diarrhea is common in rodents, and many animal dealers routinely use antibiotics to prevent this. Such use may have spurred this multidrug-resistant strain to emerge, health officials speculate.

But not all of the animals in this outbreak were sick, so people should not think healthy ones don't carry the bacteria, Swanson said.

"We only looked for this particular strain. There may be other salmonellas that may be linked to pocket pets," Braden added.

Dr. Robert Tauxe, chief of foodborne illness at CDC, said detecting an outbreak like this would not have been possible before PulseNet, a system he helped start in 1996. It was expanded nationwide in 2001.

"With great luck, a case of illness in Minnesota might have been linked to one hamster and that would have been the end of it," Tauxe said. "We would never have been able to identify it as a nationwide problem."

In light of the outbreak, CDC recommends:

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