BROWNSVILLE, Texas - In fewer than 36 hours last spring, three children were born without brains at Valley Regional Medical Center here.
Two of the babies were stillborn. The third hung on for three days, doomed by a gruesome, fatal defect that leaves infants with an open skull and only the rudiments of a brain.
The deaths from the rare defect, anencephaly, puzzled Margaret Diaz, an occupational health specialist. She thought the three cases could have been a statistical fluke. Then she had a chance conversation with a radiologist.
He had recently performed ultrasound examinations on seven pregnant women. Each, he said, was carrying a child without a brain.
Doctors soon learned of at least 10 more cases, most of them clustered in this city of 98,000 along the Rio Grande. The outbreak here and in surrounding Cameron County may be the largest ever in the United States.
Across the river in Matamoros, Mexican health officials are worried, too. Two anencephalic children were delivered at the general hospital there in 1990, but 10 were born last year.
Diaz's alarm has prompted full-blown investigations by the U.S. Centers for Disease Control, three Texas agencies and a local group of lawyers, doctors and chemists. So far, they have few answers.
But some here have their suspicions. Long uneasy about the heavy pollution in their sister city of Matamoros, Brownsville residents now fear an environmental time bomb has gone off.
Like other Mexican border towns, Matamoros is struggling under the residue left by years of unchecked industrial growth.
It is dominated by U.S.-owned companies that came south over the past three decades for cheaper labor, favorable trade rules and lax enforcement of environmental laws. Today, Matamoros is an ugly sprawl of industrial plants and shacks housing Mexican workers. Its open sewers contain toxic wastes and human refuse. Its factories spew fumes and chemicals.
While CDC experts are considering environmental factors in their investigation, they say the inquiry is in its early stages and that they have no evidence linking the strange deaths to Matamoros' chemical stew.
"It would be a tremendous medical breakthrough if we could find what caused just half of those Texas cases," said Dr. Gregg Sylvester, an epidemiologist. "I suspect that the causes of anencephaly may involve a multitude of factors and that we won't find a single cause."
Investigators in the Texas outbreak are theorizing that exposure to some chemical or other environmental or genetic factor prevented the Brownsville mothers from having sufficient folic acid in the crucial first weeks of pregnancy, said Dr. James E. Cheek, a CDC epidemiologist.