The first ebola virus patient diagnosed in theUnited Statesdied Wednesday at a Texas hospital, hospital authorities said.

"It is with profound sadness and heartfelt disappointment that we must inform you of the death of Thomas Eric Duncan this morning at 7:51 am," Texas Health Presbyterian Hospital in Dallas said in a statement. A day earlier, the hospital had listed Duncan in "critical but stable" condition.

Duncan, a Liberian national, tested positive for Ebola on Sep 30. His was the first case diagnosed in the US. He arrived in Dallas on Sep 20 to visit family and fell ill several days later.

Duncan, 42, went to the Dallas hospital on Sep 26, and was given some antibiotics. Two days later, he was rushed back to the hospital as his condition worsened. He had been kept in isolation since.

Dallasnews.com reported Wednesday that a sheriff's deputy who had visited Duncan's apartment was under preliminary screening at the same hospital for some symptoms of Ebola. The mayor of Frisco, Texas, where the officer had first visited an urgent care facility, told dallasnews.com that "the risk was minimal" that the officer had contracted Ebola.

Health officials in Dallas are now observing some 50 people who may have had contact with Duncan. Among them are 10 people who had close contact with him and are deemed to be at higher risk. So far, none of them have shown any Ebola symptoms.

Ebola symptoms can include fever, muscle pain, vomiting and bleeding and can appear as long as 21 days after exposure to the virus.

Ebola, which was discovered in 1976, has killed 3,431 people and infected 7,470 since the outbreak in West Africa in March, the World Health Organization said in its latest report.

Zhang Han, associated professor of research at theUniversity of Texas Medical School at Houston, said that the possibility of Ebola spreading is minimal because everyone who had contact with Duncan has been quarantined and put under observation.

Han advised hand-washing after being out, before eating and after using the restroom.

"It'd also help to take a small bottle of antibacterial hand sanitizer with you and clean yourself whenever you feel necessary," he said.Han said that heating and evaporating vinegar at home or drinking Chinese herb such as Banlangen won't help. But a strong immune system can help fight off infection, so being in good health is one's best ally.

May Zhou contributed to this story.