CDC warns Ebola outbreak could exceed 20,000 cases

A fast-growing Ebola outbreak in the Democratic Republic of the Congo and Uganda could top 20,000 cases within three months unless isolation and other public health measures expand quickly, the U.S. Centers for Disease Control and Prevention warned in new analyses released Friday.

The outbreak is caused by Bundibugyo, a rare type of Ebola for which no vaccines or treatments are currently available. The World Health Organization has reported 397 confirmed cases and 65 deaths, according to NBC News. The WHO has declared the outbreak an international health emergency, NPR reported.

CDC models based on data through May 24 laid out several possible paths for the outbreak. In a worst-case scenario, assuming only 20% of Ebola patients isolate and access to vaccines and treatments remains limited, the outbreak could cause more than 20,000 cases. NBC News reported that the scenario could involve more than 2,000 deaths, while NPR reported the CDC projections showed at least 4,000 deaths within the next three months alone.

“If only 20% of cases enter isolation within two days of symptom onset, more than 20,000 cases are projected in two out of three of our scenarios,” Jason Asher of the CDC’s Center for Forecasting and Outbreak Analytics said at a briefing.

CDC officials emphasized that the numbers are not predictions. “Our models today are built on current data and our understanding of current conditions,” Asher said. “They’re designed to support action, not to generate alarm.” He said the modeling “is not a forecast; it is a planning tool.”

Even under a more optimistic scenario, the CDC found risks remain. NBC News reported that if about 70% of cases isolate, there is still about a 1 in 5 chance the outbreak could exceed 10,000 cases within three months. NPR reported Asher said that if 70% of cases start isolating within two days of symptom onset, there is a 94% probability of keeping the outbreak below 10,000 cases over that period.

The 2014-2016 West Africa Ebola outbreak remains the largest on record, with more than 28,000 cases and more than 11,000 deaths.

Public health experts said the projections underscore the urgency of the response. Dr. Krutika Kuppalli, an infectious diseases physician at UT Southwestern Medical Center and former World Health Organization medical officer, called the projections “concerning.”

“Under certain scenarios, the current Bundibugyo Ebola outbreak could grow into one of the largest Ebola outbreaks ever recorded,” she wrote in an email to NBC News. Still, she said, “one of the most important takeaways from this CDC analysis is that the future of this outbreak is still very much within our control.”

Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health, told NPR, “The 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.”

The response has faced major obstacles. Standard Ebola tests initially did not detect the Bundibugyo strain, and the outbreak’s epicenter, Ituri province in Congo, is a conflict zone. CDC officials also said questions remain about how many cases are being missed, how many people are isolating and how widely the outbreak could spread.

Dr. Satish Pillai, who is leading the CDC’s Ebola response, said the situation remains “fluid” and that the percentage of cases being detected and isolated appears to be on the lower end. “This is a dynamic situation,” he said.

A separate CDC report released Friday found the risk to the general U.S. population remains low. No Ebola cases linked to the outbreak have been reported in the United States. “The domestic risk remains low for the general US population,” Pillai said, adding that there is no reason for people to change their behavior or worry about international travel except to Congo or Uganda.

“We’ve responded to Ebola outbreaks before,” Pillai said. “We know how to end this. Our goal is control, containment and ending the outbreaks in DRC and Uganda. And we are working every day towards that goal.”