Federal health officials are investigating a recent listeria outbreak after multiple people were sickened in four states.
In a notice detailing its probe, the U.S. Centers for Disease Control and Prevention (CDC) wrote that the bacterial infections are likely traced back to Hispanic-style fresh and soft cheese, though a particular brand or type of cheese responsible for the illnesses has yet to be identified.
It noted that while illnesses started last October, the number of those infected with listeria monocytogenes infections is likely higher than reported and may not be linked to the states in which cases were confirmed.
“The true number of sick people in an outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because some people recover without medical care and are not tested for Listeria,” the CDC said. “In addition, recent illnesses may not yet be reported as it usually takes 2 to 4 weeks to determine if a sick person is part of an outbreak.”
No deaths have been reported.
Of the four people public health officials spoke to, three reported eating at least one type of Hispanic-style fresh and soft cheese, and all said they had eaten queso fresco.
The CDC noted that investigators were using the CDC PulseNet database — essentially a catalog of DNA fingerprints of bacteria that cause foodborne sickness — to identify illnesses that could be a part of the outbreak.
The CDC and FDA have yet to identify a specific brand or type of Hispanic-style fresh and soft cheese responsible for the outbreak.
The DNA fingerprinting found that bacteria from samples of the infection were closely related, meaning those infected were sickened by the same food.
State officials have begun testing samples of Hispanic-style fresh and soft cheeses from stores in response to their findings.
Both the CDC and FDA are advising that those at higher risk for listeria illness do not eat any Hispanic-style fresh and soft cheeses until a specific type or brand is identified as the culprit.
“You are at higher risk for severe Listeria illness if you are pregnant, aged 65 or older, or have a weakened immune system due to certain medical conditions or treatments. If you are not in these groups, you are unlikely to get very sick from Listeria,” the FDA said.
For pregnant individuals, symptoms may include only fever, muscle aches, and fatigue. Listeria infection during pregnancy may lead to a life-threatening infection of the newborn, premature delivery, stillbirth or miscarriage.
For those who are not pregnant, possible symptoms include headache, confusion, loss of balance, stiff neck, convulsions, muscle aches and fever.
The agencies also advise that cheese-eaters check the labels of Hispanic-style fresh and soft cheeses to make sure they have been “made with pasteurized milk,” though they warn that Hispanic-style soft cheeses made from pasteurized milk have caused listeria outbreaks in the past.
Soft cheeses made with unpasteurized milk are approximately 50 to 160 times more likely to cause listeria infection than when they are made with pasteurized milk.
“Although pasteurization of milk kills Listeria, products made from pasteurized milk can still become contaminated if they are produced in facilities with unsanitary conditions,” the CDC wrote in a Food Safety Alert.
Listeria infections can cause severe illness when the bacteria spread beyond the gut. While symptoms of that illness typically start one week to a month after eating contaminated food, symptoms may start as soon as the same day or as late as 70 days after.
Listeria can cause common food poisoning symptoms as well, and those who experience them usually recover without treatment.
The CDC and FDA instruct those who have these symptoms after eating Hispanic-style fresh and soft cheeses to call their health care provider immediately.