The popular opinion that 21 days is enough to determine if a person has contracted Ebola or not may be wrong, according to a new study by Drexel University, Pennsylvania.
According to study author Charles Haas, the current 21-day recommendation likely stems from data for the 1976 Ebola outbreak in Zaire. “In that outbreak, the latest case to convert did so at 21 days,” he said. One problem: The analysis from this outbreak included only 109 cases.
“I wouldn’t say [the analysis] has been lacking — I would say they had a small data set,” he said. “And the WHO and CDC apparently never updated their recommendations with data sets from succeeding outbreaks.”
When Haas included data from other Ebola cases — for example, the 1995 outbreak in Congo, as well as 4,010 confirmed and probable cases from the first nine months of the current outbreak in West Africa — he made a startling discovery: There’s up to a 12 percent chance that the incubation period could extend beyond the 21-day mark.
“I believe it should be greater than 21 days,” Haas told Yahoo Health; in the paper, he noted that “21 days may not be sufficiently protective to public health.” Based on data from the Congo outbreak, the necessary period could be as long as 31 days.