Background

An outbreak of Ebola was confirmed by health officials on May 15. According to the World Health Organization (WHO), the outbreak has led to nearly 400 confirmed cases and almost 80 deaths across the DRC, Uganda, and South Sudan.

Initially, WHO had estimated there were more than 900 suspected Ebola cases but updated that number to 116 last week after lab testing and epidemiological investigations ruled out hundreds of illnesses initially thought to be Ebola.

On May 16, WHO declared a public health emergency of international concern, noting there are several signs of "a much larger outbreak than what is currently being detected and reported, with significant local and regional risk of spread."

The current outbreak is being driven by a species of orthoebolavirus called Bundibugyo, which health officials have less experience dealing with as there have only been two documented Bundibugyo outbreaks in the past and there are no licensed vaccines or therapeutics for this species of virus.

WHO officials have warned the epidemic is outrunning response efforts. On June 5, WHO Director General Tedros Adhanom Ghebreyesus announced a $518 million six-month emergency plan to combat the outbreak.

"The outbreak is moving fast, and we are still playing catch-up," Tedros said. "Containing Ebola requires political commitment, sustained finances, and trust in engaging the communities."

CDC says Ebola outbreak could be record-breaking

In its report, CDC built models on three different numbers of cumulative deaths as reported by May 24 to account for the uncertainty around the number of deaths caused by the Bundibugyo virus: 50, 100, and 200.

Four scenarios were then evaluated for each death total, with each using different percentages of symptomatic infected persons detected, isolated, and treated. The isolation scenarios were 20%, 50%, 70%, and 95%.

"If large-scale and sustained public health interventions are not rapidly implemented to reduce disease transmission, this outbreak could become as large as the 2014-2016 West Africa Ebola virus disease outbreak, which resulted in more than 28,000 cases and more than 11,000 deaths," CDC said in the report.

CDC officials noted the projections for the outbreak are not forecasts but instead planning scenarios aimed at showing how the outbreak could evolve under different conditions to help governments and aid organizations prepare for a range of outcomes and direct resources where needed.

Officials also emphasized that the current risk to the United States remains low. "For Americans going about their daily lives, including those with travel plans that do not involve the affected countries, there's no recommended change in behavior at this time," said Satish Pillai, the CDC official overseeing the agency's Ebola response.

However, health officials and experts have noted that while the risk to the United States remains low, allowing the outbreak to grow would increase the chances of cases appearing elsewhere.

Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health, said CDC's analysis "affirms what we have worried about since the beginning: This outbreak is following a dangerous trajectory and will get a lot worse unless we do more to stop it at its source."

However, while the projections "correctly point to the potentially explosive nature of the outbreak and the importance of contact tracing and isolation in containing it," things don't always need to be so pessimistic, said Justin Lessler, an epidemiologist with the University of North Carolina.

Lessler said that local efforts to contain the outbreak could make a difference. Even so, "a lot depends on where the virus gets to as it spreads across east Africa, which is home to large cities and densely populated areas, and outbreaks in the size range they project are completely possible."