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Scientists: Listeria strain in SD milk not harmful

PIERRE (AP) — Experts say the listeria strain found in a sample of raw milk sold in South Dakota is not the one that often makes people sick, and raw milk proponents say attention brought to the case by state officials created undue negative attention.

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The state Agriculture Department on Jan. 21 announced that a sampling of bottled raw milk from Brookings-based Jerseydale Farms tested positive for listeria. The agency cautioned the public that unpasteurized milk bought from the operation might contain harmful bacteria.

However, scientists told the Capital Journal that the listeria strain found in the milk — listeria innocua —is not the one that poses health threats. A different strain, listeria monocytogenes, is responsible for "99.9 percent" of listeria infections in people, said Russ Daly, a state public health veterinarian at South Dakota State University.

Data from the federal Centers for Disease Control and Prevention indicate that listeria has been discovered in 37 different outbreaks in the U.S. since 1998, and that the listeria monocytogenes strain has been found in every case.

"Listeria innocua is not on the radar for public health," said Barbara Mahon, a CDC medical epidemiologist.

The state Agriculture Department said it was obligated to inform the public about a possible health threat, even though tests of the listeria strain hadn't been completed at the time of the announcement.

"We are obligated to notify the public of pathogenic bacteria," communications officer Jamie Crew said. "We have informed the public of listeria in the specific sample and the species type is available to the public if requested."

Vikram Mistry, a professor in SDSU's Dairy Science Department, said the presence of listeria serves as a warning to officials.

"Listeria monocytogenes and listeria innocua can live in the same environment, suggesting that the presence of innocua could imply the presence of monocytogenes," Vikram said. "Thus the presence of listeria in general raises cautionary flags and has to be investigated."

Jerseydale Farms owner Trever Gilkerson said the Agriculture Department's announcement "made a big fuss for nothing at all."

Jerseydale Farms was permitted to sell its milk again on Jan. 27 after a second sample of raw milk tested negative for listeria.

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