Despite a small drop in new cases, transmission remains "widespread" in Sierra Leone, according to the World Health Organisation. Reuters

Sierra Leone will confine around 2.5 million people to their homes across the capital and in the north in a three-day shutdown aimed at stemming the Ebola epidemic, it revealed on 19 March.

"The lockdown will be conducted from March 27 to March 29 and will be like the one we conducted in September last year," said Palo Conteh, head of the country's National Ebola Response Centre.

Sierra Leone has just 0.01 doctors per thousand people. A scarcity of ambulances and health centres has complicated the Ebola response measures.

Meanwhile, health officials say two more American aid workers arrived in the United States on to be monitored for Ebola.

The two bring to 17 the number of Americans flown back from West Africa's Sierra Leone since Friday for monitoring. None have tested positive.

All are connected to an unidentified American who returned to the U.S. last week after he came down with Ebola. He is in critical condition at a government hospital in Bethesda, Maryland.

The other aid workers are staying near hospitals with special isolation units in Bethesda, Maryland, Atlanta, and Omaha, Nebraska, if they get sick.

However, a Centers for Disease Control and Prevention spokeswoman said two are now considered to be at low risk. They will go home for the 21-day monitoring period.

The epidemic has claimed almost 10,000 lives out of 20,747 known cases worldwide over the past year. Overall, 838 health workers have been infected, killing 495 of them, said WHO.

The West African nations of Sierra Leone, Liberia and Guinea have been hardest hit in the yearlong Ebola outbreak.