(CNN) -- A healthcare worker at Texas Health Presbyterian Hospital has tested positive for Ebola after a preliminary test, the state's health agency said.
Confirmatory testing will be conducted by the Centers for Disease Control and Prevention in Atlanta.
The employee helped care for Thomas Eric Duncan, the first person ever diagnosed with Ebola in the United States. Duncan died on Wednesday.
"We knew a second case could be a reality, and we've been preparing for this possibility," Dr. David Lakey, commissioner of the Texas Department of State Health Services, said in a statement Sunday morning.
"We are broadening our team in Dallas and working with extreme diligence to prevent further spread."
If confirmed by the CDC, the healthcare worker's case would mark the first known transmission of Ebola in the United States and the second-ever diagnosis in the country.
David Sanders, associate professor at biological sciences at Purdue University, said he thinks the CDC testing will likely support the preliminary results.
"It sounds likely that it's positive, and it's going to stay positive."
Globally, the disease has wrought catastrophic consequences.
The World Health Organization estimates more than 8,300 have contracted Ebola during the current outbreak. Of those, more than 4,000 people have died.
Three countries -- Sierra Leone, Guinea and Liberia -- have been hardest hit. And many of those who care for the ill have also come down with the disease.
More than 100 healthcare workers have died of Ebola in Liberia, according to WHO. Other healthcare workers in the country are threatening to strike if their work conditions don't improve.
And the first infection outside of Africa was a nurse's aide in Spain, Teresa Romero Ramos.
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