Pathogens prevalent in unpasteurized milk

NEW YORK (Reuters Health) - A survey of unpasteurized milk samples drawn from dairy farms across Wisconsin found a significant presence of Coxiella burnetii and Listeria monocytogenes, two different types of bacteria that can cause serious infection and even death in some people.

These findings have particular relevance for consumers seeking raw milk products.

The study, reported at the annual International Conference on Diseases in Nature Communicable to Man held last week in Madison, Wisconsin, was based on a random sampling of milk from 901 Wisconsin dairy farms. The farms were chosen to encompass small and large herds, producers of Grade A and B milk, and all five of the state’s geographic regions.

Approximately 76 percent of the samples had detectable C. burnetii DNA, and 5 percent of the samples harbored L. monocytogenes.

Milk from larger herds and farms producing Grade A milk appeared to have a larger risk of having detectable C. burnetii, but no clear risk factors emerged to predict which farms were more likely to have L. monocytogenes in their milk. Both bacteria were broadly distributed geographically.

Presenter Dr. Suzanne Gibbons-Burgener, from the University of Wisconsin in Madison, noted that on-farm use of raw milk is legal and common, and that the sale of unpasteurized milk is legal in 28 states, though California, for example, requires a warning label.

In some states that ban the sale of raw milk, including Wisconsin, advocates of what they call Real Milk have over the past 10 years organized “Cow-Share” programs. Under these programs, consumers who want unpasteurized dairy products circumvent such bans by buying shares in a cow or herd.

A poster presentation at the meeting by the Public Health Agency of Canada reported an outbreak of Campylobacter infection in Ontario in June that was traced to cheese made at a local farm from unpasteurized milk. About two dozen people became ill and eight sought medical help.

Gibbons-Burgener pointed out that raw milk can also harbor and promote the growth of E. coli, Listeria, Campylobacter and Coxiella, and that Listeria thrives at refrigerator temperatures.

Although Coxiella probably doesn’t survive the human digestive process, and more than 50 percent of Coxiella seroconversions in humans are asymptomatic, C. burnetii can, nonetheless, cause Q fever in humans. Dr. Gibbons-Burgener noted that in 2004, an elderly Wisconsin dairy farmer developed acute Q fever after assisting with calving.

“Both bacteria continue to pose a public health threat,” she told Reuters Health, and recommended that physicians warn their immunocompromised patients about the risks of consuming raw milk.

The greater risk for raw milk drinkers is L. monocytogenes, she told Reuters, but added that the occupational risk of Coxiella infection, especially through possible aerosolization during milking, should be noted.

Q fever is characterized by the sudden onset of one or more of the following symptoms: high fever, severe headache, general malaise, muscle soreness, confusion, sore throat, chills, sweats, non-productive cough, nausea, vomiting, diarrhea, abdominal pain, and chest pain, according to the Centers for Disease Control and Prevention in Atlanta.

The fever usually lasts for 1 to 2 weeks, and weight loss may persist for some time. Thirty to fifty percent of patients with symptomatic infection will develop pneumonia, and some will develop hepatitis. Most patients will recover to good health within several months without any treatment.

L. monocytogenes, has recently been recognized as an important public health problem in the United States. It primarily affects pregnant women, newborns, and adults with weakened immune systems.

A person with listeriosis has fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. Infected pregnant women may experience only a mild, flu-like illness; however, infections during pregnancy can lead to miscarriage or stillbirth, premature delivery, or infection of the newborn.