(WXIN) — Health officials are trying to figure out what is behind a listeria outbreak that left people sick across the country.

While a specific food item has not been identified as the source, the CDC is concerned that several recent illnesses have been reported. Here’s what we know about the status of the investigation, and what is being done to determine the source.

What is listeria?

Listeria monocytogenes is a bacterium that can cause the serious infection of listeriosis. It can also cause common food poisoning symptoms.

The CDC says around 1,600 people get listeriosis every year, resulting in about 260 deaths. It is most likely to sicken pregnant women and their newborns, adults 65 and older, and people with weakened immune systems.

What are the symptoms of invasive listeriosis?

Invasive listeriosis happens when the bacteria spread beyond the gut to other parts of the body. Symptoms usually start within two weeks after eating food contaminated with listeria.

Symptoms in pregnant people are usually mild. However, the CDC says infection during pregnancy usually leads to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.

Symptoms in non-pregnant people can be severe. The CDC says almost one in 20 non-pregnant people with invasive listeriosis die.

Symptoms in people who are not pregnant

• fever
• flu-like symptoms such as muscle aches and fatigue
• headache
• stiff neck
• confusion
• loss of balance
• seizures

Symptoms in people who are pregnant

• fever
• flu-like symptoms such as muscle aches and fatigue

Where have the illnesses been reported?

Illnesses connected to this outbreak are scattered across the country. Michigan has the most cases.

Of the people who have gotten sick, 10 people have been hospitalized. Sick people range in age from 47 to 88 years, with a median age of 73. 73% of those sickened are female. 

When did people get sick?

The CDC says symptoms of severe illness usually start within two weeks after eating food contaminated with listeria but can start as early as the same day or as late as 70 days after. In this outbreak, illnesses have been reported as far back as July 2018.

The CDC says recent illnesses may not be reported, as it usually takes three to four weeks to determine if a sick person is part of an outbreak. The true number of people involved in this outbreak is likely higher than the reported amount, as some people recover without medical care and are not tested.

What is the source of the infections?

Health officials are still trying to determine the exact source of the infections. To do so, state and local public health officials are interviewing people to find out what foods they ate in the month before they got sick.

The CDC says public health investigators are also using a system that manages a national database of DNA fingerprints of bacteria to identify illnesses that may be part of this outbreak. This same method was used to identify the source of the Jif peanut butter salmonella outbreak.

The investigation showed that bacteria from sick people’s samples are closely related genetically. The CDC says this means people in the outbreak likely got sick from the same food.

What is being done to prevent infections?

The investigation into the infections remains ongoing as of the time of this report. Health officials are collecting different types of data to try to pin down the source of the infections.

Until health officials learn more, the CDC is advising people at higher risk for severe listeria illness to contact their healthcare provider if they have any symptoms. Healthcare providers should report any listeriosis illnesses to their health department.

If people do get sick, the CDC says they may be contacted by local or state health officials to find out what they are in the month before getting sick. They may ask for copies of receipts, shopper card numbers, or leftover food for testing.