Ebola is spreading faster than responders can track it in eastern Congo, where health workers managed to follow up with barely one in five identified contacts in a single day.

Authorities in the Democratic Republic of Congo (DRC) reported 83 confirmed infections, 746 suspected cases and 1,603 identified contacts as of May 21, according to the health ministry.

Yet health workers were able to follow up with only 342 contacts that day – about 21 per cent of the total under monitoring – according to ministry data released on Friday.

The figures suggest the response is falling behind the outbreak itself, even as governments and international agencies ramp up emergency measures after the World Health Organization (WHO) declared the epidemic a public health emergency of international concern on May 17.

The outbreak has now spread across three provinces including South Kivu, where officials confirmed a case this week near Bukavu, a major city near Congo’s border with Rwanda.