A New York City hospital is testing a patient who traveled to a West African nation where Ebola has been reported, according to local media reports.
Mount Sinai Hospital on Manhattan's Upper East Side said the male patient, who had a high fever and gastrointestinal symptoms, had been placed in strict isolation and was being screened to determine the cause of his symptoms, according to reports.
The World Health Organisation has said the death toll from the world's worst Ebola outbreak had risen to 887 by 1 August.
The total number of cases in the four west African countries affected stood at 1,603 on the same date, the WHO said.
Nigeria, the latest country to register the disease, has had up to four cases, of which three are classed as "probable" Ebola and one as "suspected", the Geneva-based agency said.
Meanwhile, a second US aid worker who contracted Ebola while helping to fight the disease in west Africa is expected to arrive in Atlanta tomorrow.
Missionary Nancy Writebol, 59, will fly on a medical aircraft from Liberia to Atlanta to be treated by infectious disease specialists in a special isolation ward at Emory University Hospital, according to Christian mission group SIM USA.
The specialists on Saturday began treating 33-year-old US doctor Kent Brantly, who also returned home after being stricken with Ebola during the emergency response to the worst outbreak on record of the virus.
Ms Writebol and Dr Brantly, who served on a joint team run by Christian aid groups SIM USA and Samaritan's Purse, are believed to be the first Ebola patients ever treated in the United States.
They are returning separately because the plane equipped to transport them can carry only one patient at a time.
Ms Writebol is in serious condition, SIM USA said.