(Reuters Health) - People with certain conditions, including leukemia, other cancers and pregnancy, are at the greatest risk of getting sick from the food-borne bacterium Listeria, French researchers report in a new study.
Doctors and public health officials have known that these conditions make people more vulnerable to listeriosis, but this study is the first to rank the size of the risk for people with each condition.
The results "will help focus risk communication for the medical community," said Ramon Guevara, an epidemiologist for the County of Los Angeles Department of Public Health, who was not involved in the study.
"If you do have an outbreak you want to say who are the high-risk people," he added.
Earlier this year, 30 people died in the Unites States in an outbreak of listeriosis, spread by contaminated cantaloupe.
Deli meat, raw cheese, produce and smoked seafood are also thought to potentially harbor Listeria, but it's uncommon that people actually get sick from it.
The study looked at nearly 2,000 cases of listeriosis in France -- affecting 39 out of every 10 million people -- from 2001 to 2008.
Despite its rarity, listeriosis is still considered an important public health concern because it's relatively deadly compared to other food-borne illnesses, lead author Dr. Véronique Goulet at the Institut de Veille Sanitaire in Saint-Maurice wrote in an email to Reuters Health.
More than 400 of the 2,000 people who developed listeriosis died.
None of the cases involved an outbreak.
About one in six of the listeriosis cases in France affected pregnant women.
Among the remaining cases, 65 percent of the people involved had an underlying health condition, and 41 percent were undergoing treatment that suppressed their immune systems.
Goulet and her team determined that people with chronic lymphocytic leukemia were at the greatest risk of developing listeriosis -- more than 1,000 times higher than the general French population.
Fifty-five out of every 100,000 people with this leukemia developed listeriosis.
People with other cancers, such as myeloma, lymphoma, and esophageal and liver cancers, were also at a much higher risk of getting sick from Listeria, as were people undergoing dialysis.
Anywhere from 13 to 17 out of every 100,000 people with one of these conditions fell ill with listeriosis, according to findings published in Clinical Infectious Diseases.
Goulet pointed out that even though diabetics and the elderly also have a greater chance of developing listeriosis than the general population, the number of cases among these groups is very small.
"I would like to target recommendations for prevention to persons with hematological malignancy (blood, bone marrow and lymph cancers), especially those undergoing immunosuppressive treatment," Goulet said.
The Centers for Disease Control and Prevention advise people to wash produce before eating, including scrubbing the outside of firm fruits and vegetables such as melons and cucumbers.
In addition, keep the refrigerator colder than 40 degrees Fahrenheit, thoroughly cook meat and toss freshly-sliced deli meats after three to five days.
Depending on the level of risk, Goulet said, some people should avoid eating certain foods, but it's not necessary for everyone.
"For example, as the incidence is very low in the elderly population with no concomitant underlying disease, it is perhaps not advisable to make general recommendations such as to avoid eating deli-meat or cheeses such as feta or camembert, or smoked fish," Goulet wrote.
The cantaloupe outbreak earlier this year, which was one of the most deadly food-borne outbreaks in the United States, was traced back to unsanitary conditions at a packing plant in Colorado.
ReferencesClinical Infectious Diseases, online December 9, 2011.
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