Disease threats from crayfish, frogs described at IDSA

Oct 22, 2010 (CIDRAP News) – Reports presented at the Infectious Diseases Society of America's (IDSA's) annual conference today revealed that contaminated crayfish can cause severe illness and looked at the risk of contracting Salmonella infections from pet frogs, among other findings.

A press conference on foodborne disease included a report on four illnesses, two of them severe, caused by Vibrio mimicus infections in people who had eaten cooked crayfish. The presentation also included a report on 113 cases of salmonellosis, mostly in children, linked to pet frogs, which was described as the first multistate Salmonella outbreak linked to amphibians.

In another study, researchers from the Centers for Disease Control and Prevention (CDC) found that black children were about twice as likely as white children to contract salmonellosis, including severe cases. The IDSA's 48th annual meeting is being held in Vancouver, B.C.

Crayfish-linked illnesses
Emily J.Cartwright, MD, of the CDC reported on the investigation that ensued when Spokane, Wash., health officials were notified of two people hospitalized with V mimicus infections in June of this year. The pathogen, rare in the United States, can cause a severely dehydrating diarrheal illness resembling cholera, she said.

The probe led to a cohort study of 22 people who had attended a "crayfish boil" on Jun 19, 2010, or had eaten leftover crayfish the next day. Four of eight people who ate the leftover crayfish got sick, whereas none of those who ate only the freshly cooked crayfish fell ill. No other food items or environmental exposures were linked to the illnesses.

Cartwright said an interview with the cook at the event revealed that the crayfish had been boiled for 20 minutes but then were placed in the same container where the raw crayfish had been stored. Afterward the leftovers were refrigerated for 20 hours. "We believe that it became contaminated in that container and exposed to juices from the raw crayfish," she said.

She added that the contamination in the container wasn't enough to sicken people who ate the crayfish when still hot, but the cold-tolerant pathogen became more of a threat after the leftovers were refrigerated for hours. She said the crayfish were ordered from an online seafood company, but the original source was not traced.

Two of the four ill patients required intensive care for severe dehydration and kidney failure, but they fully recovered with treatment. The other two patients had only a mild diarrheal illness and recovered without treatment, Cartwright said.

"People should be aware that improperly handled crayfish can be a source of Vibrio mimicus infection and it's important to wash hands after handling raw crayfish," she said.

Salmonella from pet frogs
Shauna L. Mettee, MSN, MPH, of the CDC reported on the salmonellosis outbreak traced to pet frogs. Although reptiles and amphibians are known Salmonella carriers, no multistate outbreak linked to amphibians had been reported previously, says the abstract of her report. (The outbreak was detailed in a Morbidity and Mortality Weekly Report article earlier this year.)

Investigation of the outbreak began in the fall of 2009. The CDC found 113 cases of Salmonella Typhimurium from 31 states with illness onset between Apr 1, 2009, and Mar 31, 2010, including 18 cases that required hospitalization. The median age of patients was 5 years, and 77% were younger than 10.

A CDC case-control study showed that cases were significantly associated with exposure to frogs. Only 21 case-patients knew what type of frog they'd been exposed to, and most said it was the African dwarf frog, which is sold in pet stores and marketed toward children, Mettee said. Environmental samples from aquariums in patients' homes yielded Salmonella isolates matching the outbreak strain.

A traceback investigation led to one frog breeder in California, and the outbreak strain was found at the breeder's facility, Mettee reported. There is no federal regulation of aquatic frog sales, she said, but officials advised the breeder on various steps to reduce Salmonella loads and improve monitoring and surveillance, she said. She commented that the outbreak may still be continuing.

The CDC recommends that families who have children under age 5 or elderly or immunocompromised members should not keep pet frogs, Mettee said. Also, those who have pet frogs should wash their hands thoroughly after any contact with them and should consider their habitat and water to be contaminated.

Racial disparities in infant salmonellosis
Patricia M. Griffin, MD, a CDC expert on enteric disease epidemiology, reported that an analysis of 12 years worth of data from the CDC's FoodNet surveillance system showed a higher rate of salmonellosis in black infants than in white or Asian infants. The FoodNet surveillance system covers 10 states with about 15% of the US population.

Griffin said infants in general are about 10 times as likely as older people to have salmonellosis and are also much more likely to have severe illness.

"What we found was that black infants were about twice as likely as white infants to have Salmonella infections and to have severe Salmonella infections," she said.

The analysis included 6,179 salmonellosis cases in babies less than a year old, about 61% of whom were white, 30% black, 6% Asian, and 4% other. The CDC used census figures to calculate average annual incidence per 100,000 population and came up with 163 for black infants, 114 for Asians, and 84 for whites, according to the report abstract.

Black infants also were more likely than white infants to have invasive disease: 9% versus 4% of cases, the report says.

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