Tests on packages of sprouts, seeds, wash water and processing surfaces at an Idaho sprout-growing operation did not turn up evidence of Salmonella that federal and state regulators have attributed to an outbreak that sickened at least 25 people in five states.

The U.S. Food and Drug Administration confirmed those test results, which were first reported Wednesday by the Spokesman-Review newspaper in Spokane.

Stephanie Yao, spokeswoman for the FDA, explained that negative test results do not rule out sprouts from Evergreen Fresh Produce as the source of the outbreak. She said the investigation is ongoing.

Twice on Wednesday the FDA acknowledged there was no microbiologic evidence linking implicated products or a producer to an outbreak. In an unrelated case, the FDA said tests at a South Carolina raw milk dairy, named as the likely source of Campylobacter infections, detected no traces of the outbreak strain of bacteria.

In the sprouts case, epidemiologic investigations in June by local, state and federal public health agencies concluded that alfalfa sprouts and spicy sprouts (a mix of alfalfa, clover and radish sprouts) grown by Evergreen Produce in Moyie, Idaho, were the likely cause of a cluster of Salmonella infections, primarily in the midland Northwest.

Nine people in Washington state, seven people in Montana, three in Idaho, and one in both North Dakota and New Jersey were stricken with the identical strain of Salmonella Enteritidis, according to the Centers for Disease Control and Prevention.

In the search for a common source, the initial exposure information from the first 13 confirmed case patients showed that nine (69 percent) had reported eating alfalfa sprouts during the week before the onset of their symptoms, according to the FDA. The background rate of sprout consumption in the U.S. population is 4.4 percent, so the 69 percent exposure rate was significant epidemiologic evidence, and raw sprouts are a known vehicle for pathogenic bacteria. Traceback information indicated the sprouts the case patients had eaten were grown by Evergreen Produce.

At that point, FDA issued a consumer advisory warning people not to eat Evergreen Produce brand alfalfa sprouts and spicy sprouts, the suspect varieties.

Nadine Scharf, owner of the Idaho sprouts growing operation, initially refused to recall her spouts without “concrete proof” that they had caused the illnesses, but later complied with public health authorities’ request to withdraw the sprouts from the market.

Scharf told the Spokesman Review she has had to lay off 10 of her 14 workers and sell three vehicles to raise cash to pay her bills. She continues to produce small amounts of mung bean, clover and broccoli sprouts, she told the newspaper.