Figure 1.

Chronology for all Ebola virus disease (EVD) outbreaks. The primary case results from zoonotic spillover and leads to a period of undetected transmission. It is typically determined retrospectively with epidemiological investigations. The index case is the first case to be recognized and marks the official beginning of an outbreak. The final case includes the 42-day observation period. Colours around numbers indicate the following groupings of outbreaks by spillover date: 1976–2012, west Africa (2013), 2014–2018, and ongoing DRC (2018). Locations in parentheses are reported outbreak spillover locations. *For the 1977 DRC (Bonduni) outbreak, the primary case, index case, and final case are the same.