The 2007-08 outbreak involved mostly children in 34 states; one-third of all patients had to be hospitalized. In many cases, parents didn't know that turtles can carry salmonella.
Despite a 1975 ban on selling small turtles as pets, they continue to be sold illegally.
The American Veterinary Medical Association estimates that the number of pet turtles nationwide doubled from 950,000 in 1996 to almost 2 million in 2006.
"It's very easy to think of turtles as being a very gentle and nice pet," but many carry salmonella, without showing any signs, said Julie Harris, a scientist at the federal Centers for Disease Control and Prevention and the report's lead author.
Salmonella in turtle feces can end up on their shells and body, and can spread to people who handle them.
An infected turtle can spread the same strain of salmonella to others during shipping, which may be how the outbreak occurred. Turtles involved were bought at pet shops, flea markets, from street vendors and online. The Food and Drug Administration contacted retailers involved and their investigation is ongoing, the report said.
"Continued, collective efforts are needed, both on state and federal levels, to enforce the ban and protect public health," the report said. It appears in October's Pediatrics, released Monday.
Authorities began investigating in September 2007 after a Union County, N.C., teen swam in her backyard pool with two pet turtles and a friend from South Carolina. Both girls developed bloody diarrhea, vomiting, fever and stomach cramps; one developed kidney failure and spent eight days in the hospital.
Salmonella bacteria traced to those turtles matched salmonella later found in three other North Carolina children. Other cases turned up elsewhere, many involving direct contact with turtles, including children kissing turtles or putting them in their mouths, Harris said.
Indirect contact likely also occurred, she said. For example, children playing with turtles at school may have brought the germs home and spread them to family members, Harris said.
Illnesses from the same kind of salmonella turned up coast to coast through January 2008, including 12 people in California, 10 each in Pennsylvania and Texas, and nine in Illinois.
No one died in the outbreak but many required several days of hospital treatment, Harris said.
"Everyone from pediatricians to other public health professionals needs to really stress that reptiles and especially turtles are a source of salmonella infections," she said.
The ban only affects turtles less than about 4 inches in diameter because of reports that young children had gotten sick after putting the small reptiles in their mouths.
David Bergmire-Sweat, a North Carolina epidemiologist who investigated the Union County case, said he's heard of families letting turtles walk on kitchen surfaces where food is prepared, and babies being bathed in sinks where turtle cages are washed.
Because the federal ban was enacted more than 30 years ago, "many people just don't remember," he said.
Recent efforts to overturn the ban, backed by turtle farmers, have failed.
Veterinarian Mark Mitchell, a University of Illinois zoological medicine professor, has been working with Louisiana turtle farmers in research aimed at raising salmonella-free turtles. Initial efforts involved cleansing turtle eggs with antibiotics, but that led to strains of antibiotic-resistant bacteria.
Mitchell said now he's focusing on washing eggs in disinfectants similar to chlorine. He says the industry has been unfairly saddled with harsher restrictions than producers of human foods also blamed for recent salmonella outbreaks.
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