PHOENIX (AP) -- Tests show a wildlife biologist at Grand Canyon National Park most likely died of plague.

The death of 37-year-old Eric York triggered a health scare and led to about 30 people being given antibiotics as a precaution.

An official who has been briefed on the test results confirmed that they were positive for plague, although the test isn't absolutely conclusive. The official didn't want to be named because an official announcement hasn't yet been made.

The National Park Service plans a midday press briefing to formally announce the test results. York died last week, and officials suspected plague or hantavirus because of his work and hobbies.

Both diseases, while rare, are endemic to the Southwest. Plague is transmitted primarily by fleas and direct contact with infected animals.

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