The World Health Organization (WHO) on Monday said an epidemiological week has now passed with no new Ebola cases for the first time in Sierra Leone since the beginning of the outbreak.

According to WHO, the use of rapid response teams and strong community involvement in finding the Ebola virus cases is yielding results in the country worst-affected by the disease.

The virus has infected more than 13,400 people and left almost 4,000 dead in Sierra Leone.

"This is very good news but we have to keep doing this intensive working with communities to identify potential new cases early and to rapidly stop any Ebola virus transmission," said Dr Anders Nordstrom, WHO representative in Sierra Leone.

Sierra Leone is now down to a single chain of transmission, which started in Freetown but sparked a cluster of cases in Tonkolili, in the northern region of the country.

In Tonkolili, a young man, who worked in Freetown but returned to his home village, died in a hospital where he was being treated for malaria. As is done with all deaths, to ensure no case of Ebola is missed, a swab was taken. It tested positive for Ebola. Two more people, both of them from the young man's family, developed symptoms and tested positive for Ebola.

The government, WHO and other UN and international partners sent a rapid response team into the district and worked with the village chief and village task force to identify and monitor everyone who had been in contact with the young man.

Last Friday, 595 people "graduated" from quarantine in Tonkolili. However, 43 people remain quarantined until the end of this week. Another 38 people remain in quarantine in Freetown until Aug. 29.

WHO noted the Ebola response has moved to "phase three" where all efforts would be focused on tracking each and every chain of Ebola virus transmission and closing down the remaining chains as quickly as possible.

Effectively tracking chains of transmission means finding every person who has been in contact with someone proven to be infected with Ebola, monitoring them closely for symptoms for 21 days and rapidly moving them to a treatment center if they develop symptoms of potential Ebola.