The Bundibugyo virus outbreak in the Democratic Republic of the Congo is now the largest Ebola outbreak the country has recorded. WHO’s Disease Outbreak News of 1 August, revised on the 3rd, puts it at 3,605 confirmed cases and 1,587 deaths as of 30 July. The 2018–20 epidemic in North Kivu and Ituri, the previous largest, ended with 3,323 confirmed cases — 3,481 including probable ones. The margin is 282 cases, or 8.5%. It is not the deadliest: that outbreak killed 2,299 people.
The more revealing number is not in this notice but across the series of them. WHO has published six situation updates since early June, each giving national totals and an Ituri sub-total. Running the fatality ratio at each data cut produces a clear movement: Ituri stood at 15.2% on 6 June, 17.3% on the 10th, 22.8% on the 17th, 28.5% on 1 July, 36.3% on the 15th and 41.3% on 30 July. Its crude case fatality ratio has nearly tripled in eight weeks.
Everywhere else has barely moved. Across the four other affected provinces — North Kivu, South Kivu, Haut-Uele and Tshopo — the ratio has run between 57% and 64% throughout, ending at 64.3%. In June, when WHO first drew the comparison itself, it noted that the ratio in Ituri was 15% against 64% in North Kivu and called the difference significant. That gap has now halved, from 45.5 percentage points to 23.1, and it has closed from the wrong end.
Ituri is where the outbreak was first identified, in the single Mongbwalu health zone, and it is where the response has been concentrated for eight months. It still accounts for 88% of confirmed cases and 82.6% of deaths. A rising fatality ratio in the province with the treatment centres and the established contact tracing is a different signal from a high ratio in provinces the outbreak has reached recently, and it is the one this data actually contains.
The pace has not slowed either. WHO’s previous notice, at a 15 July data cut, carried 2,124 confirmed cases and 828 deaths; fifteen days later the count had risen by 1,481 cases and 759 deaths. One caution belongs with that: WHO footnotes its own epidemic curve to say that the large number of cases reported on 22 July reflects the completion of a data-reconciliation exercise and includes cases that occurred earlier. Part of the jump is catch-up rather than new transmission, and the claim in the notice’s own summary that the week to 26 July set a record for weekly cases should not be read as evidence of acceleration.
Contact tracing is thinning. Of roughly 17,800 contacts listed, about 4,400 are not under active follow-up — a national rate near 75%, down from 82.7% on 1 July and 80.3% on 15 July. Among cases whose outcome has been recorded the fatality share is 70.8%, 1,587 deaths against 651 recoveries, with 1,365 cases still unresolved. Health workers do markedly better: 44 of their 112 resolved cases were fatal, 39.3%.
Bundibugyo is one of four Ebola species known to cause disease in people and, before this year, the least often seen — two outbreaks in Uganda and one in the DRC in the whole recorded history of the disease. Neither licensed Ebola vaccine protects against it; both are for the Zaire species. The Fold reported on 28 July that Oxford’s ChAdOx1-based Bundibugyo candidate had gone from outbreak declaration to first injection in 67 days. Uganda declared its own Bundibugyo outbreak over on 28 July.