Maryland has the second-highest number of cases in an outbreak of listeria, a bacterial infection that can cause flulike symptoms, the Centers for Disease Control and Prevention reported Friday.

Two people have died of the infection, one in Illinois and one in New Jersey. All of the 28 people who became ill were hospitalized. One was a pregnant woman who recovered, and the child was not affected. The CDC said the outbreak may involve many more people whose symptoms were mild and were never tested.

The cause of the outbreak has not been identified, but the CDC reported some of the 28 people in 12 states where the bacterial infection has been found said they had eaten meats sliced at deli counters, particularly turkey and liverwurst at a variety of grocery stores.

The agency is advising people to avoid eating meats sliced at a deli unless they are heated before eaten.

A CDC map of the outbreak shows states in the Northeast, along with several in the South and Midwest, with Maryland having five or six cases and New York reporting seven or eight. The people got sick from May 29 to July 5, but it can take weeks to identify the bacteria in a sick person and report it.

The symptoms usually start within two weeks of eating food contaminated with listeria.

The symptoms — for those who aren’t pregnant — include headache, stiff neck, fever, loss of balance and confusion. Nearly one in six people infected with listeria dies. People over 65, those with weakened immune systems and pregnant women are most at risk.

Pregnant women suffer less severe symptoms, but the infection usually leads to miscarriage, stillbirth or premature birth, according to the CDC.

This summer, some local ice cream had to be recalled because listeria was detected at Totally Cool, an Owings Mills ice cream manufacturer that helped produce a local brand. Listeria has also been identified in soft cheeses, enoki mushrooms and leafy greens.