OTAY MESA, Calif. -- A nonstop line of trucks coming from Mexico enters the portals of the giant cargo facility here, and a small stream of them are siphoned off onto the U.S. Customs and Border Protection inspection docks.

	John Beale, Post-Gazette Trucks line up for inspection at the border crossing from Mexico at Otay Mesa, Calif., one of the major checkpoints where green onions may have entered the U.S. that eventually sickened and killed people in Beaver County. Click photo for larger image. More on the hepatitis A outbreak Mexico closes 4 green onion exporters

There, the drivers idle by their trucks waiting for customs inspectors, Food and Drug Administration officials and other inspectors to clear their paperwork and their cargo.

The shipments of green onions that U.S. government officials say sickened and killed people in Beaver County passed through this port between San Diego and Tijuana, Mexico, or one of the other major crossings in southern California or Arizona.

About 3,000 trucks pass through this facility each day. The drivers are directed to one of the 105 bays where a gang of inspectors from the Otay Mesa Cargo Facility go over trucks 12 hours a day with an array of tools from laser range finders to drug-sniffing dogs.

Sometimes inspectors just look at a sample of the load, sometimes they ask for a partial off-load, sometimes a full off-load. The process can take from 45 minutes to all day.

Yesterday, Apolonio Munoz waited by his truck, which was carrying tomatoes, basil, cucumbers and zucchini.

Agricultural Inspector Kevin Schonborn dumped a bag of basil on a stainless steel table and picked through it with gloved hands. In short order he had a vial with three tiny eggs of a moth floating in alcohol. Finding no larvae, he allowed the truck to pass through.

	John Beale, Post-Gazette Kevin Schonborn, a U.S. Customs and Border Protection agriculture inspector, looks through produce in Otay Mesa. Behind Schonborn is truck driver Apolonio Munoz of Tijuana, Mexico. Click photo for larger image.

Munoz is a "commercial crosser." Many of the drivers coming from Baja California don't have documents to cross the border.

"So the truck starts with a driver from the southern part of the state, then he comes up to Tijuana, jumps out, and a commercial crosser gets in and just goes across the border," said Ramses Stevens, who runs an Arizona-based firm that manages import-export logistics for large firms. U.S. Customs requires drivers that come through to be registered; the process includes a criminal background check.

After Munoz clears customs, he will drive his refrigerated truck, or "reefer," to San Diego, where another driver will take it to a large market in Los Angeles.

The reefers are parked together along one side of the facility, with fish on the corner where the prevailing wind would carry it away from the inspectors. Along another side are the "informals," vans and small pickups owned by individuals, rather than small companies.

The inspectors' equipment and expertise uncover drugs, bug-infested plants, improperly licensed drivers, missing documentation and some food-borne illnesses. Trucks with violations can be turned back, detained for further analysis, or have their loads destroyed (at the owners' expense).

Even empties can turn out to be full.

	Reforma Archivo via AP Border inspectors use sophicticated technology, such as mobile X-ray scanning technology, to "see" into hidden compartments, which may contain drugs or, as shown in this image, a human cargo. Click photo for larger image.

Luis Diaz, the supervisor of customs inspectors at Otay Mesa, is an expert on that. His inspectors X-ray trucks, use the range finder to determine whether the truck is the same size inside as out -- a 40-footer that's a 38-footer inside is a good candidate for a hidden compartment -- and check out tires and trailer walls with the "buster," a density checker that can tell inspectors that a tire might have more than air inside.

The customs inspectors work alongside FDA officials, Fish and Wildlife inspectors and state and county inspectors at the huge facility, which sits across the border in the Mexican state of Baja California.

"Customs has a huge responsibility," said Stevens. "They are the first and really only line of defense."

The inspectors know how to ferret out problems.

"You have these immaculately clean stainless steel tables where they're checking things, they might run the dog around, run the truck through the X-ray, ask the driver, 'When was the last time you had the gas tank worked on?' or 'Why is there dirt all over this onion?' "

If anything doesn't add up, "they can get on the horn, call the FDA, the Mexican officials, find out if this company has had problems in the past," Stevens said.

	John Beale, Post-Gazette Agricultural inspectors check nearly every shipment of produce that is brought into the U.S. from Mexico. Click photo for larger image.

"You can spend gadzillions of dollars on equipment, but our most important asset is the eye, ears and other senses of the inspectors."

Still, with 3,000 trucks a day crossing the border at Otay Mesa, they can only do detailed inspections of a small portion of the 18-wheelers coming through.

And they can't detect hepatitis A.

Joseph Tracey, an inspector for the Food & Drug Administration, said that hepatitis A is particularly difficult to detect. The vegetable shows no visible signs of the virus, and since the incubation period is long, the problem won't be apparent until weeks after the truck crossed the border.

"It doesn't lend itself to analysis, like eColi," said Tracey. There is no way to test vegetables for the virus, and even if there were a test, even testing a sample of a load wouldn't mean that the virus couldn't be lodged in the remaining product, he said.

	John Beale, Post-Gazette An inspector examines a vial containing moth eggs. No larvae were found in the produce that contained the eggs, so the shipment was allowed to pass into the U.S. Click photo for larger image.

That's why the FDA is simply detaining shipments from the companies that shipped green onions to Beaver County and places in the South where there were outbreaks of hepatitis A this fall. The Otay Mesa facility has not handled any of those shipments.

Looking for the source is more a matter of guilt by association than the kind of laboratory proof possible in the case of other food-borne illnesses.

The manifests and other documentation required to cross the border contain identification numbers that show where the load came from and where it is headed. Those allow officials to "back-trace" shipments. Government investigators go to the farms and look for unsanitary conditions or other types of contamination that indicate there might be systemic problems. "It's sort of a roundabout way of finding the source of contamination," he said.