(CNN)Ten Americans are being flown back to the United States as the Centers for Disease Control and Prevention investigates the possibility they might have been exposed to Ebola in Sierra Leone. The number could change as the investigation continues, Tom Skinner, a spokesman for the CDC, told CNN's Elizabeth Cohen on Saturday. The news comes one day after an American health care worker who came down with Ebola while volunteering in West Africa arrived at a National Institutes of Health hospital for treatment, the NIH said. "(The) CDC and the State Department are facilitating the return of additional American citizens who had potential exposure to the index patient or exposures similar to those that resulted in the infection of the index patient," the CDC said in a written statement. The Atlanta-based CDC said none of these individuals now returning from Africa have been diagnosed as having Ebola. The heath care worker with Ebola was in serious condition Friday, the NIH said. Details about the patient's identity weren't released. The patient is the second with Ebola admitted to the NIH hospital. Nina Pham, a nurse at Texas Health Presbyterian Hospital Dallas, was admitted to NIH in October after she contracted the disease while treating Liberian national Thomas Eric Duncan. Pham recovered and was released free of disease. Duncan died. NIH is one of only four hospitals in the United States that have biocontainment units and has been practicing for years to treat a highly infectious disease such as Ebola. The CDC's Skinner said the Americans coming home will stay at hotels and other housing near the University of Nebraska Medical Center in Omaha, the National Institutes of Health, or Emory University Hospital in Atlanta. More than 10,000 people have died in a West Africa epidemic of Ebola that dates back to December 2013, according to the World Health Organization. Most of the deaths have been in Guinea, Liberia and Sierra Leone. Ebola is spread by direct contact with the bodily fluids of an infected person.