An individual who arrived to the U.S. from Mali tested negative for the Ebola virus at Bellevue Hospital Center in Manhatttan, health officials said on Thursday.

The patient remains in isolation, health officials said. Because preliminary Ebola tests may be negative, the patient will receive further tests for the virus.

Dr. Craig Spencer, a physician with the only confirmed case of Ebola in New York, was released from Bellevue on Nov. 11 after he was cleared of the virus following 19 days of treatment.

Spencer had traveled to Guinea to work with Doctors Without Borders.

Approximately 5,500 people have died from Ebola, according to Reuters, with the outbreak centered around West African countries. Six people have died in Mali from Ebola, and public health workers have raised concerns that more cases of the infection could arise because the country shares a border with Guinea where the outbreak is more severe.