An unidentified patient was being tested on Wednesday at a Philadelphia Hospital for possibly having been exposed to the deadly Ebola virus, a hospital official said.

“Preliminary testing indicates that the patient has another condition, which is likely the cause of their illness,” the Hospital of the University of Pennsylvania Chief Medical Officer, Patrick Brennan, said in an emailed statement.

The tests have not yet shown Ebola, he said.

The hospital stressed that it was conducting the tests “in an abundance of caution” because the patient met the screening criteria for Ebola. The patient will remain isolated under ‚Äúproper protocols and precautions” until the tests are concluded, it said.

A hospital spokesperson declined to elaborate on the statement.

The World Health Organization said a person infected with Ebola can take anywhere from two to 21 days to develop symptoms, which often start with fever, fatigue, muscle pain, headache and sore throat before advancing to vomiting, haemorrhagic fever and diarrhoea.

On average, the Ebola virus kills half of those infected with it, the WHO said. Humans are not infectious until they develop symptoms, it said.

The virus, which was first discovered in 1976, had its largest and most complex outbreak in West Africa in 2014 through 2016, the organization said.