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The outbreak in the Southwest is still under investigation, but "it's very plausible epidemiologically" that the newly recognized hantavirus is the cause of the outbreak, said the CDC's Arnold Kaufmann, a director of the investigation.

The cases represent the first outbreak of hantavirus infection in the United States. Hantaviruses have been found in common rats in U.S. cities and in other wild American rodents, but until now they had not been known to make the leap to humans, Mr. Kaufmann said.

"Now Navajos are finding themselves shunned in public places and business establishments. . . . Navajos have been made to feel like plague-bearers and lepers," he said.