Health officials are warning seafood lovers to think twice before eating raw oysters amid a Salmonella outbreak that has sickened people in more than 20 states.

The U.S. Centers for Disease Control and Prevention (CDC) said 64 people have been infected with a rare strain of Salmonella Telelkebir.

The investigation is being carried out with help from the U.S. Food and Drug Administration (FDA) and state health agencies.

So far, 20 people have been hospitalized, and no deaths have been reported.

Illnesses began between June 21 and Nov. 28, according to the CDC. Cases have been reported in 22 states, with the highest number (10) in Pennsylvania. New York reported seven cases, while New Jersey and Virginia each reported six.

Evidence points to raw oysters as the likely source. Of 27 people interviewed, 20 (about 74%) said they ate raw oysters shortly before getting sick. That’s a lot higher than what’s typically seen in the general population, where just 1.6% of people report eating raw oysters.

Health officials warn that the outbreak numbers are likely much higher than what's been reported, as many people recover without medical care, and recent cases may not yet appear in official counts.

Those who became sick ranged in age from 10 to 76, with a median age of 52 (meaning half were older, half were younger). About 65% were male.

Among patients who reported race and ethnicity, most identified as white (85%), followed by Black (12%) and Native Hawaiian or other Pacific Islander (2%).

Lab testing helped connect the cases. Using the CDC’s PulseNet system, scientists found the Salmonella samples were genetically similar, meaning the infections likely came from the same contaminated food source.

Testing also showed no signs of antibiotic resistance in samples from 59 patients, the CDC said.

While officials continue tracing where the oysters came from, they stressed that raw oysters can carry harmful bacteria at any time of year.

"Cook oysters before eating to reduce your risk of food poisoning," the agency advised. "Do not let raw seafood, its drippings or its juices contaminate other foods."

Anyone who develops diarrhea, fever or stomach cramps after eating raw or undercooked seafood should seek medical care and report their illness to local health officials.