Two dead in listeria outbreak linked to deli meat. Here’s what to know.

Here’s what to know about the bacteria and the latest outbreak.

The CDC is aware of 28 people infected with the strain of listeria in the outbreak, from a dozen states: New York (7 cases); Maryland (6); Virginia (2); New Jersey (2); Massachusetts (2); Georgia (2); Missouri (2); Illinois (1); Pennsylvania (1); North Carolina (1); Wisconsin (1); Minnesota (1). They had a median age of 75.

It added that the outbreak “may not be limited to the states with known illnesses.” Samples from those infected were collected between May 29 and July 5, and “recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak,” the agency said.

Of the two known deaths, one was in Illinois and the other in New Jersey.

Many people affected by the outbreak reported to the CDC that they had eaten meat they had sliced at deli counters, at a range of supermarkets and delis.

Investigators are still working to determine the specific products that may be contaminated, the agency said Friday. It noted that the most commonly consumed meats were turkey, liverwurst and ham but that there was not enough information to say which deli meats were behind the outbreak.

It said there was no evidence to date that people were getting sick from prepackaged deli meats.

Listeria is the infection usually caused by eating food contaminated with the Listeria monocytogenes bacterium. While the bacteria are common — living in moist environments, soil, water, decaying vegetation and animals — the infection is rare. It most often occurs in humans through food contamination. People who are pregnant, adults 65 and older, newborns and those with weakened immune systems are most at risk of falling seriously ill from a listeria infection.

Foods that are more likely to be contaminated include soft cheeses; premade deli salads; unheated deli meat, cold cuts, hot dogs and fermented or dry sausages; refrigerated pate or meat spreads; cold-smoked fish; raw milk products; sprouts and melons.

The first and most common symptoms of listeria infection are diarrhea and vomiting. Those typically begin within 24 hours of eating food contaminated with listeria and usually last one to three days. While unpleasant, these symptoms are not usually considered life-threatening.

In serious cases, the bacteria spreads beyond the intestines and is classified as an invasive illness. These symptoms usually start within two weeks. They include fever, flu-like symptoms such as muscle aches and fatigue, headache, stiff neck, confusion, loss of balance and seizures.

About 1 in 6 people with invasive listeriosis who are not pregnant die, according to the CDC. It is the third-leading cause of death from foodborne illness in the United States.

Although not typically fatal, invasive illness during pregnancy usually leads to miscarriage, stillbirth, premature delivery or a life-threatening infection for the newborn.

Anyone experiencing listeria symptoms should contact a health-care provider.

For those at higher risk, the CDC recommends not eating meat that has been sliced at a deli counter unless it is reheated to an internal temperature of 165 degrees Fahrenheit or until steaming hot just before serving.

Listeria can also grow on foods kept in the refrigerator and is killed by heating food to a high enough temperature. Recommended practices include cleaning refrigerators, containers and surfaces that may have touched sliced deli meat.

Delicatessens should follow Agriculture Department guidelines on controlling listeria.