Ebola in Texas
A worker in a hazardous material suit looks out from the apartment unit where a man diagnosed with the Ebola virus was staying in Dallas, Texas, October 5, 2014.Reuters

The first person diagnosed with Ebola in the United States, Liberian national Thomas Eric Duncan, died on Wednesday morning at a Dallas hospital, a hospital spokesman 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," hospital spokesman Wendell Watson said in an emailed statement.

Duncan became ill after arriving in the Texas city from Liberia on Sept. 20 to visit family, heightening concerns the world's worst Ebola outbreak on record could spread outside of the three worst-hit West African countries. About 48 people with whom Duncan had been in contact are being monitored.

Ebola has killed more than 3,400 people in Liberia, Sierra Leone and Guinea since the outbreak began in March, nearly half of all those infected, according to the World Health Organization. While several American patients have been flown to the United States from West Africa for treatment, Duncan was the first person to start showing symptoms of the disease on U.S. soil.

A Spanish nurse who treated a priest who worked in the region is also infected.

Duncan was able to fly to the United States from Liberia's capital Monrovia, which is at the epicenter of the Ebola outbreak, because he did not have a fever when screened at the airport and filled out a questionnaire saying he had not been in contact with anyone infected with Ebola.

Liberian officials have since said that he lied on the questionnaire and had been in contact with a pregnant woman who later died of the disease. Ebola can take as long as three weeks before its victims show symptoms, at which point the disease becomes contagious. Ebola, which can cause fever, vomiting and diarrhea, spreads through contact with bodily fluids such as blood or saliva.

Duncan began feeling ill shortly after his arrival in Texas. He went to Texas Health Presbyterian Hospital in Dallas on Sept. 25, but was initially sent home with antibiotics. His condition worsened, he returned Sept. 28 by ambulance and was diagnosed with the disease.

"The past week has been an enormous test of our health system, but for one family it has been far more personal. Today they lost a dear member of their family. They have our sincere condolences, and we are keeping them in our thoughts," David Lakey, commissioner of the Texas Department of State Health Services said in a statement.

Officials have said as many as 48 people may have been exposed to the disease by Duncan, and that the 10 people at highest risk are cooperating with public health authorities by staying in quarantine voluntarily. The other 38 people who may have been exposed are being checked routinely for fever.

U.S. Centers for Disease Control and Prevention (CDC) Director Dr. Thomas Frieden said he was confident the disease would not spread widely within the United States. U.S. officials are also expanding their response in West Africa.