Contaminated water is one of the likeliest suspects as U.S. and Mexican inspectors yesterday began searching Baja California fields for the source of a deadly hepatitis A outbreak in the United States, a U.S. Food and Drug Administration official said.
Joe Baca, the agency's food safety compliance director, said the binational team will focus on water used to irrigate the fields, wash the onions and make the ice used to keep them fresh during the long journey to the U.S. East Coast.
"The quality of water in the fields and the packing houses is a concern," he said.
The binational group will spend about two weeks visiting eight locations in Baja California and Sonora owned by four growers, Baca said. The operations have been linked to green onions served in restaurants in Tennessee, Georgia, North Carolina and Pennsylvannia. More than 900 people were sickened in the four states, and three people died in Pennsylvania.
Since the illnesses broke out over only a couple of months, they probably were caused by a small number of onions, said Dean Cliver, a professor of food safety at the University of California Davis.
"That suggests something went wrong briefly," Cliver said. "That suggests there's not a long-term problem in Mexico."
The greatest chance of finding the hepatitis A source is if the virus still is lingering in the water the companies use for cleaning or packing, he said.
"Water is probably the strongest suspect. There are ways to test for hepatitis in water," Cliver said.
The inspectors will also examine the health and health care of the onion workers and the sanitary practices in the fields, Baca said.
Hepatitis A, a liver disease caused by a virus spread by fecal matter, is common in Mexico. But most people become infected before the age of five and are immune from further outbreaks the remainder of their lives.
"A big concern is children working in the fields. They're the ones most likely to be sick," Baca said.
But Cliver said that by the time children are old enough to work in the fields, they've already been infected with hepatitis and are no longer transmiting the virus.
Based on the epidemiological data gathered so far, Baca said, "there's a good indication" that all four of the targeted firms were involved in the spread of the disease.
Nevertheless, he said, it's possible that only one is the source and that onions from the others were contaminated when shipments were mixed together when they arrived at their destination.
Mexican federal agents have closed the four growers whose farms are being inspected and U.S. border inspectors have been told to turn back their produce. But Mexico's 22 other green onion growers are still allowed to ship onions to the United States.
Although Baja California agents are cooperating in the investigation, Agriculture Secretary Juan Pablo Hernández Díaz criticized U.S. officials for blaming area growers without proof the disease originated in the state.
He said they have "insinuated that (the Mexican product) is the prime suspect, generating distrust in consumption of the produce, which is causing great economic losses."
Staff writer Sandra Dibble contributed to this report.