By Keith Coffman
DENVER (Reuters) - Two people in Colorado have died in the last month in a listeria outbreak following a puzzling surge in cases of gastrointestinal infection caused by the food-borne bacteria, state public health officials said.
Alicia Cronquist, a state epidemiologist, said nine people in Colorado were hospitalized with the infection in August, including the two who died, with seven cases tallied in just the last week.
Colorado typically sees 10 cases of listeria per year, Cronquist said. Between 2000 and 2010, the state averaged just two cases in the month of August.
"It's very concerning, and our goal is to learn if there is a product that is contaminated," Cronquist told Reuters of the latest outbreak.
The majority of the recently infected patients were elderly women, she added.
The elderly, pregnant women and others with compromised immune systems are most likely to be sickened by the bacteria, according to the Colorado Department of Public Health and Environment.
Those vulnerable groups should avoid certain foods such as hot dogs and deli meats unless they have been heated to 165 degrees Fahrenheit, the department said in a news release.
Unpasteurized soft cheeses, refrigerated smoked seafood, cold cuts and meat spreads also can be sources of the bacteria, which normally does not sicken healthy people.
Cronquist said tracing the source of the outbreak involves interviewing infected patients to see if there is a common element in the foods they ate, then using DNA testing to identify the strain of the bacteria.
A recent multi-state recall of smoked salmon from Illinois-based Vita Food Products due to the potential for listeria contamination has not been ruled in or out as the source, Cronquist said.
Symptoms of the illness include nausea, diarrhea, stiff neck and confusion. In extreme cases, a patient can suffer convulsions, and the infection can cause miscarriages and stillbirths in pregnant women.
Antibiotics can knock down the infection in most but not all cases.
(Editing by Steve Gorman and Cynthia Johnston)