Assessing reporting delays and the effective reproduction number: The Ebola epidemic in DRC, May 2018-January 2019

On August 1, 2018, the Democratic Republic of Congo declared its 10th and largest outbreak of Ebola inflicting North Khivu and Ituri provinces. The spread of Ebola to Congolese urban centers along with deliberate attacks on the health care workers has hindered epidemiological surveillance activities, leading to substantial reporting delays. Reporting delays distort the epidemic incidence pattern misrepresenting estimates of epidemic potential and the outbreak trajectory. To assess the impact of reporting delays, we conducted a real-time analysis of the dynamics of the ongoing Ebola outbreak in the DRC using epidemiological data retrieved from the World Health Organization Situation Reports and Disease Outbreak News. We analyzed temporal trends in reporting delays, epidemic curves of crude and reporting-delay adjusted incidences and changes in the effective reproduction number, R_t. As of January 15, 2019, 663 Ebola cases have been reported in the Democratic Republic of Congo. The average reporting delay exhibited 81.1% decline from a mean of 17.4 weeks (95% CI 13-24.1) in May, 2018 to 3.3 weeks (95% CI 2.7-4.2) in September, 2018 (F-test statistic = 44.9, p = 0.0067). The Ebola epidemic has shown a two-wave pattern with the first surge in cases occurring between July 30 and August 13, 2018 and the second on September 24, 2018. During the last 4 generation intervals, the trend in the mean R_t has exhibited a slight decline (rho = -0.37, p < 0.001), fluctuating around 0.9 (range: 0-1.8). Our most recent estimate of R is at 0.9 (95% CI: 0.4, 1.1) during the last generation interval. Our most recent analysis of the Ebola outbreak in DRC indicates that the Ebola virus still active although transmission is characterized by a low fluctuating reproduction number. Yet, this pattern does not imply that the epidemic can be easily controlled particularly in the context of unstable epidemiological surveillance efforts hindered by unpredictable local violence.