HOUSTON — As word spread today that the first U.S. death from the swine flu outbreak was a Mexican toddler being treated in a Houston children's hospital, the baffling illness began bleeding over into the fevered national debate over illegal immigration.

Groups favoring a crackdown on illegal immigration cited the death as proof of their long-standing contention that uncontrolled borders pose a public health danger to U.S. citizens.

Conservative talk-radio hosts invoked Typhoid Mary-like scenarios directly blaming "illegal aliens" from Mexico for introducing the illness into the United States.

And a Houston city councilwoman suggested that city officials were endangering the lives of local citizens by allowing foreigners to be treated in the city's hospitals.

"Who are we infecting by even bringing people into our hospitals?" asked the councilwoman, Toni Lawrence. "Until we know more, we have to make some tough decisions. We need to look out for Houstonians first."

Local and federal health officials sought to tamp down the emerging anti-foreigner backlash. They noted that Children's Hospital of Houston, where the boy from Mexico City had been under treatment since being airlifted from the border city of Brownsville, Texas, on April 14, had taken the same precautions to isolate the child as it does with any patient suffering from a contagious disease.

The 23-month-old boy, whom officials declined to identify, died Monday. No other patients or medical personnel at the hospital have shown any signs of swine flu, officials said.

"Houston hospitals deal with infectious diseases every day. There's nothing special here," said Kathy Barton, spokeswoman for the city's health department, who said she had begun to hear Houston residents blaming Mexicans for the swine flu crisis.

"This case did not represent any threat to Houston," Barton added. "We hope our community will remain compassionate."

The mayor of Brownsville, Pat Ahumada, said he worried that a national panic over swine flu "will become one more excuse they are using to discriminate against Mexicans and call for closing the borders."

Ahumada, a staunch opponent of the fence U.S. officials are constructing along the border with Mexico, said he had detected no signs of alarm in his city, where American and Mexican citizens routinely intermingle every day.

For their part, groups favoring immigration reform emphasized that many of the U.S. cases of swine flu reported so far, such as the cluster at a school in New York City, resulted from American citizens falling ill after traveling to Mexico and had nothing to do with Mexicans crossing into the U.S.

"The whole issue of 'these people bring diseases' has been part of the anti-immigration rhetoric in America for as long as we've had a country," said Douglas Rivlin, spokesman for the National Immigration Forum, a pro-immigrant advocacy group. "Yet so far the story has been mostly about folks who have traveled to Mexico and came back sick, and that is a very different issue than how we reform our immigration system."

But anti-immigration groups were not persuaded.

"The swine flu issue raises a variety of other questions which will invariably affect the prism through which immigration policy is debated," said Dan Stein, president of the Federation for American Immigration Reform, which favors a crackdown on illegal immigration. "It illustrates how any country that doesn't properly control its borders leaves itself wide open to the importation of a major health crisis."

Michael Savage, a nationally syndicated radio talk-show host, was one of several conservative commentators sounding similar themes, according to Media Matters for America, a liberal media-monitoring group.

"Make no mistake about it: Illegal aliens are the carriers of the new strain of human-swine avian flu from Mexico," Savage said.

"What better way to sneak a virus into this country than give it to Mexicans?" asked Neal Boortz, another radio host whose broadcast was monitored by Media Matters.