(UPDATED COVERAGE, 12:10 P.M., MAY 8) The Food and Drug Administration is trying to get to the bottom of three different foodborne illness outbreaks related to alfalfa sprouts since February.

In early May, Caudill Seed Co., Louisville, Ky., withdrew from the market certain batches of its seeds after FDA investigations of two separate Salmonella Saintpaul outbreaks led back to the seed distributor. Several days later, Eloy, Ariz.-based Arizona Hydroponic Farming recalled its already expired alfalfa sprout products because of a different strain of salmonella found during routine testing at a produce market in Los Angeles.

Arizona Hydroponic supplied sprouts to Los Angeles Calco, a distributor, on April 9. Los Angeles Calco recalled its products April 23.

Also in April, Bridgeport, Conn.-based Amalgamated Produce Inc. recalled its sprouts listeria showed up in routine testing at a retailer.

Omaha, Neb.-based SunSprout Enterprises Inc. recalled its alfalfa sprouts early March after the initial outbreak of Salmonella Saintpaul occurred in the Midwest. Tests at the company’s facility and on products resulted in no positive finds.

Caudill Seed’s withdrawal included all batches of alfalfa sprouts with six-digit lot numbers that begin with 032. All the seeds involved are packaged in 50-pound white bags marked with a white or yellow label with the seed distributor’s name. Caudill Seed imported the seeds from Italy, said Lyle Orwig, spokesperson.

Although the FDA has identified seeds with these specific lot numbers, none of the administration’s testing in Caudill’s facility has come back positive for salmonella.

“The evidence is largely epidemiological, but not entirely,” said Sebastian Cianci, spokesperson for the FDA. “A positive sample from spent irrigation water matches the (Pulsed-Field Gel Electrophoresis, bacteria’s fingerprint) pattern of the ill persons involved in this outbreak.”

Cianci did not say where the positive sample was found. As of May 7, the Centers for Disease Control and Prevention reported that 35 Salmonella Saintpaul illnesses since March had been linked with this investigation, as well as 186 during the outbreak in February and early March. The two outbreaks happened in different parts of the country, supporting a link to seeds and not a specific grower.

“The two strains are indistinguishable,” said Lola Russell, media relations for CDC.

The FDA and Centers for Disease Control and Prevention issued a consumer advisory, which recommended not eating the product altogether, April 26.

“I’ve had nothing to sell for two and a half weeks,” said Ting Hsiao, manager and operator of Arizona Hydroponic. “Not after the FDA made that announcement.”

There is no evidence incriminating alfalfa seeds from other lots, according to the FDA, but the consumer advisory remains in place.

The recent contaminations with sprouts caused groups like the FDA and United Fresh Produce Association to remind growers to follow specific guidance for the sprout industry developed in 1999.

“If they adhere to the FDA guidance, that’ll go a long way to help prevent any similar events in the future,” Orwig said.

The FDA’s guidelines include treating seeds prior to sprouting to reduce the likelihood of pathogens, as well as testing spent irrigation water after the second day of the four-day sprout growing process.

“It is not realistic to believe that illness will be completely eliminated, but we believe that these recommendations, when consistently and appropriately followed, can significantly enhance the safety of sprouts,” Cianci said. “However, there are a number of factors in the seed disinfection process and especially in the sampling and analyses of spent irrigation water, that if done incorrectly can undermine the effectiveness of these food safety steps.”

Cianci said in the past, failures in how samples were collected, analyses were done or test results were interpreted likely contributed to contaminated product reaching the market.