AUTLAN, Mexico – Inspectors are collecting soil, water and produce samples, reviewing export logs and combing packing plants in three major tomato-growing states in Mexico.

But the U.S. Food and Drug Administration appears no closer to finding the source of a mysterious salmonella outbreak that has sickened more than 900 people nationwide. It's not even 100 percent sure that tomatoes are the cause.

A team of three FDA inspectors has gone through five farms in the western states of Jalisco and Sinaloa in the past two weeks, looking at all aspects of tomato production: the greenhouses where they are grown, the packing plants where they are shut into boxes, the shipping methods for the trip north to the U.S.

They also plan to visit the northern state of Coahuila to finish up their study.

The results can't come too soon for the three Mexican states that were targeted by the FDA, along with farms in Texas and Florida.

Bonanza 2001 farm in Autlan, Jalisco, which normally exports about 12,000 tons of tomatoes a year to the U.S., has hundreds of tons sitting in a warehouse near the Texas-Mexico border as demand has plummeted, said spokesman Luis Almejo.

They may rot.

Sinaloa growers also face big losses.

“We're demanding that they release those results as soon as possible so that Sinaloa can be cleared of any suspicion,” said Manuel Tarriba, president of Sinaloa's Tomato Growers Association. Tarriba said he expects to get results by the end of next week.

The outbreak, which began in April in the U.S., has affected 943 people so far in 40 U.S. states, more of a third of them in Texas, according to the Centers for Disease Control and Prevention. There have been 225 cases reported since June 1 – evidence that the source likely has not been contained.

The U.S. tomato industry has taken a US$100 million hit as restaurants temporarily dropped tomatoes from their menus, and farmers have had to plow under their fields or leave crops to rot in packinghouses.

Mexico has not calculated its losses. But growers here worry they still may be under a shadow of suspicion as late as November, when greenhouses harvest their summer tomatoes.

Last week, the U.S. government said it is looking at other vegetables but insisted that tomatoes remain the main suspect in the outbreak.

Salmonella can be transmitted to humans when fecal material from animals or humans contaminates food. Fever, diarrhea and abdominal cramps typically start eight to 48 hours after infection and can last a week. Many people recover without treatment. But severe infection and death are possible. At least 130 people have been hospitalized in this outbreak, the CDC says.

FDA inspectors wouldn't speak to an Associated Press reporter at the Bonanza 2001 farm, one of 15 in Jalisco state that export to the U.S.

As they reviewed the packing plant, workers in aprons, hairnets and plastic gloves cleaned and packed the last tomato harvest to be shipped to the company's warehouse in Pharr, Texas.

Bonanza has about 150 acres of greenhouse tomatoes in a lush valley near Jalisco's south coast, an area shared by several U.S.-owned tomato growing companies, including San Antonio-based Desert Glory, North America's largest grower of greenhouse tomatoes.

Jalisco state agriculture official Martin Figueroa said the FDA inspectors visited only Bonanza but left open the possibility of returning.

In Sinaloa, which grows about 40 percent of all tomatoes sent to the U.S., they checked full operations – including irrigation methods – at four farms, Tarriba said.

Sinaloa state wrapped up its winter harvest in June. Farmers now are cleaning their greenhouses and waiting for U.S. clearance before planting more tomatoes. They also are asking Mexican and U.S. authorities to come up with a binational certification program that would establish the same sanitation standards at every agricultural producer in Mexico, Tarriba said.

Currently, private U.S. certification companies check sanitation standards in Mexico.

He said once Sinaloa is cleared, the state will launch a damage-control ad campaign in the United States.

“We have to gain back the consumers' trust,” Tarriba said.