Africa CDC says Congo's Ebola outbreak may be three times the official count

Africa's public health agency said this week that the Ebola epidemic in the Democratic Republic of the Congo may be three times larger than the official register. Through 25 August, Congo had recorded 5,713 confirmed infections and 2,744 deaths. A threefold undercount would imply about 17,100 infections. The confirmed case-fatality ratio has risen to 48 percent from 27 percent two months earlier.

The virus is Bundibugyo, not Zaire ebolavirus. That species usually produces a somewhat milder and less typical illness, which Africa CDC officials say may keep some infected people away from clinics. The outbreak was declared on 15 May. Scientists who have reviewed the early cases think transmission in the mining town of Mongbwalu, in Ituri, may have begun as early as February.

Ituri still accounts for about 85 percent of cases and 79 percent of deaths. The epidemic has now reached 54 health zones in six provinces: Ituri, North Kivu, South Kivu, Haut-Uélé, Tshopo and Bas-Uélé. Bas-Uélé recorded a confirmed case in Buta with travel history to Haut-Uélé and symptom onset on 4 August. Uganda has reported a small number of cases in Kampala tied to travel from Congo, and single imported cases have been treated in France and Germany.

Contact tracing is the number that most worries the epidemiologists. Over the three weeks to 25 August, authorities identified only about one fifth of the contacts Africa CDC would have expected from the confirmed cases. Yap Boum II, who leads emergency preparedness at the agency, has said fewer than 10 percent of newly detected cases are coming from known contact lists. In a controlled outbreak that share is usually 90 to 95 percent. Kyeng Mercy, who heads epidemic intelligence, told a briefing that detection may be capturing only 30 to 40 percent of infections, which would put the true burden above 10,000 and possibly near 15,000.

WHO figures from mid-August already showed a daily average of about 90 confirmed cases in the first three months, faster than the same window in West Africa in 2014-16 or in North Kivu in 2018-20. The current outbreak passed 1,000 confirmed cases in about 40 days. The 2018 Congo outbreak took roughly 235 days to reach that mark. It has already exceeded the 3,317 cases of 2018-20, which had been Congo's largest Ebola event. About 60 percent of recent weekly deaths have occurred outside treatment centres.

Armed conflict and population movement in the east make the usual tools harder to use. Lists of contacts go stale when people flee a clash or a mining shift. Health workers cannot follow every name on a roster if a road is closed. Treatment-centre beds have run near capacity in earlier phases of this wave. Calls for more money have come from WHO, Africa CDC and officials who worked the 2014 response.

The United States CDC raised its own Ebola response to Level One in June, its highest internal setting. That decision reflected speed and geographic spread, not a new virus. Bundibugyo still has no widely deployed vaccine equivalent to the Zaire shots used in previous Congo campaigns. Therapeutics and monoclonal antibodies are in use where supply and cold chain allow. The practical limit remains finding the people who are ill before they infect the next household.

An effective reproduction number a little above 1, which Africa CDC currently estimates at national level, means the outbreak is still growing, though not exploding in every zone. That average hides local spikes. If the undercount is close to the agency's range, the world is looking at the second-largest Ebola outbreak on record by official numbers and, on the modelled figures, an event that could challenge the West African total. The next few weeks of contact tracing will show which description is closer.