Following a health warning earlier this week from California officials about fresh oysters from Mexico, the U.S. Centers for Disease Control and Protection issued its own public alert today.

The CDC is working with officials in Mexico and in several U.S. states on an investigation of a multistate outbreak traced to raw oysters. Various pathogens, including Vibrio, Shigella, E.coli, Campylobacter and norovirus, have sickened people in at least five states, according to the warning posted today by the CDC.

All of the federal and state health agencies in the United States have had standing warnings for years advising the public to not eat raw oysters because of the dangers of viruses, parasites and bacterial contamination. The danger increases in warmer months because water temperatures become more comfortable growth mediums for the pathogens. 

Illnesses (in the current outbreak are) linked to raw oysters harvested from Estero El Cardon estuary in Baja California Sur, Mexico. On May 6, DiCarlo Seafood Wilmington of California recalled some oysters harvested from Estero El Cardon, posted a limited recall. On May 7, Estero El Cardon was closed to further oyster harvesting pending investigation.

Yesterday the Food and Drug Administration posted a public warning about contaminated oysters from SOL AZUL, S.A. DE C.V. that were shipped to California.

“Mexico implemented a precautionary closure of the growing area on May 7, 2019, as a result of Vibrio parahaemolyticus and other gastrointestinal illness concerns,” according to the FDA’s warning. “On May 8, Mexico was informed a Shigella outbreak was /confirm/ied. The growing area implicated remains closed while authorities investigate the cause and the extent of the outbreak, to ensure implicated shellfish is removed from the food supply.”

From Dec. 16, 2018, through April 4 this year, 16 people in the United States have been confirmed with infections as part of the outbreak. Of the 15 patients with the information available, two were so sick they had to be admitted to hospitals. Patients range in age from 26 to 80 years old. Sixty-seven percent are male.

Additional patients are expected to be identified through whole genome sequencing and other laboratory methods, which can match pathogen strains from food samples to those identified in samples from sick people. Also, it can take several weeks from the onset of symptoms for patients to be logged by the CDC because of the lag time between initial laboratory testing and the federal agency receiving confirmed reports from state and local health officials.

“Laboratory testing on samples from patients identified multiple pathogens causing infections. Some people were infected with more than one pathogen,” the CDC reported today. “(Some of the) ill people reported eating raw oysters sold by restaurants in California and Nevada.” Illnesses have also been confirmed in Illinois, New Hampshire and Alaska.

Patient counts by pathogen or illness as reported by the CDC are:

Three cases of Shigella flexneri infection;

Three cases of Vibrio parahaemolyticus infection;

One case of Vibrio parahaemolyticus and Shiga toxin-producing E.coli (STEC) non-O157 co-infection;

One case of Vibrio parahaemolyticus and Shigella flexneri co-infection;

One case of Shigella flexneri and Campylobacter lari co-infection;

One case of Vibrio albensis infection;

One case of norovirus genogroup 1 infection;

One case of infection with Vibrio of unknown species; and

Four cases of illness without a pathogen identified.

Don’t ignore illnesses
The CDC, FDA, and state and local health officials urge people to seek medical attention if they become ill after eating raw oysters. Any illness should also be reported to the local health department. E. coli and Vibrio infections are particularly dangerous because they stand a better chance of producing serious complications such as kidney failure, brain damage, amputations and death.

Some tips to remember include:

Avoid eating raw and undercooked shellfish, including oysters, to reduce the risk of illness.

If you do eat shellfish, cook it until it reaches an internal temperature of at least 145 degrees F. A quick steaming isn’t sufficient to kill the pathogens that cause illnesses in humans.