Q&A: What is the actual minimum incubation period for Ebola virus?
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Key takeaways:
- The minimum incubation period was established as 2 days in 1976 during the first described outbreak of Zaire ebolavirus.
- The actual minimum incubation period for Ebola virus is most likely 4 days.
The minimum incubation period for Ebola virus may not actually be 2 days, researchers wrote in The Lancet Infectious Diseases.
Aaron D. Kofman, MD, and colleagues wrote in a commentary that the minimum incubation period — or the time from infection with the virus to the development of first symptoms — of Ebola virus was thought to be 2 days, an assumption based on reports following the first Ebola investigation in 1976.
In their ne commentary Kofman and colleagues wrote that “concluding that the minimum incubation period for Ebola virus diseases is 2 days based on these reports is flawed for several reasons.”
Healio spoke further with Kofman, an Epidemic Intelligence Service officer in the CDC’s Viral Special Pathogens Branch, about those reasons, what the actual incubation period is and what impact this could have on outbreaks.
Healio: What prompted this paper and has the assumed minimum 2-day incubation period influenced how we have responded to Ebola outbreaks, including how we conduct contact tracing?
Kofman: Our motivations to address this topic stemmed from both the practical challenges of Ebola outbreak response and a desire to better understand Ebola pathogenesis. The minimum incubation period was established as 2 days in 1976 during the first described outbreak of Zaire ebolavirus. However, there has been scant evidence since then, either in the literature or during outbreak responses, to clearly support this timeframe.
And while this issue may at first seem academic, there are real-world consequences to continuing to use a minimum incubation period that is not biologically plausible. For example, linking two confirmed cases of Ebola using a two-day incubation period can obscure the identification of the true source patient. Because the true source patient is never identified, their contacts are never identified and followed, which can then lead to undetected chains of disease transmission and prolongation of the outbreak.
Healio: How about the maximum incubation period, which is 21 days? That’s how we determine when Ebola outbreaks are over. How did things settle on 21 days, and is that correct?
Kofman: We did not evaluate the maximum incubation period as part of this work. This may be an area worthy of investigation in the future.
Healio: What is the actual minimum incubation period, if it’s not 2 days, and what might that mean to future outbreak responses?
Kofman: Our research concluded that the actual minimum incubation period is likely to be 4 days. Using a more accurate minimum incubation period will allow epidemiologists to construct more accurate chains of disease transmission, which may in turn reduce missed chains of disease transmission and hasten outbreak control.
Healio: What is the clinical take-home message?
Kofman: The clinical take home message is that the minimum incubation period for Ebola virus is not 2 days and is most likely 4 days. Ill patients who last had contact with a source patient less than 4 days ago are unlikely to have acquired Ebola from that source patient and should receive a prompt work-up for other diseases that may mimic Ebola at its early stages, such as malaria, typhoid fever and others.
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