Incubation period for monkey pox: estimates from the Netherlands

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Estimated cumulative density functions, according to different parametric distributions and empirical cumulative density function of incubation periods reported for monkey pox cases in the Netherlands, May 2022 (n = 18 cases). Credit: Eurosurveillance

During the currently developing outbreak of monkey pox cases worldwide, 31 cases have been confirmed in the Netherlands until May 31, 2022. Efforts to stop the spread of infection are focused on actively finding cases, tracing close contacts and their isolation or quarantine. Related recommendations from public health authorities on the need for active monitoring and isolation for a minimum of 21 days after the last day of exposure are based on the known monkeypox incubation period (up to 21 days).

Miura et al. analyzed data from 18 confirmed cases in the Netherlands reporting the date of onset of symptoms and the most likely date of exposure. Depending on the transmission route, the typical duration of the incubation period in front of monkeypox ranges from 9 days after complex and invasive exposure, e.g. contact with broken skin, to approximately 13 days after non-invasive exposure such as droplet transfer or contact with intact skin.

In their quick communication published in Eurosurveillance today, the authors argue that “given the specific types of exposures and differences in transmission route, the incubation period for monkeypox in current outbreaks may also have different durations.”

All 31 laboratory-confirmed cases of monkeypox discovered in the Netherlands up to the end of May 2022 were males between the ages of 23 and 64 who identified themselves as having sex with men. Miura et al. analyzed the distribution of the incubation periods based on the information on the onset of symptoms and exposure histories for monkeypox among 18 of them. They used a probability-based approach, allowing exposure to be a single point in time or a time interval.

Average incubation time estimated at 8.5 days

Of the cases analyzed in this outbreak and using this best-fit (log-normal) distribution, the mean monkeypox incubation time was estimated to be 8.5 days (95% credible intervals: 6.6-10.9 days), with the 5e percentile of 4.2 days and the 95e percentile of 17.3 days.

This mean incubation time is in line with the typical timeline for so-called complex invasive exposure and “direct contact between respective broken skin or mucous membranes during sexual activity of the reported cases could be the most likely transmission route in the Netherlands.

Based on this, Miura et al. estimate that the percentage of people with monkeypox who would not develop symptoms until after 21 days is about two percent, supporting the current use of 21 days for quarantine or other approaches to avoid infectious contacts.

The authors note that “more epidemiological information on details of potential routes of exposure is needed to establish whether the results of the current study are generalizable to other men who have sex with male cases in the current outbreak, and to what extent the incubation period differs between alternative transport routes.”

What is monkey pox? A virologist explains:

More information:
Miura Fuminari et al, Estimated incubation period for monkey pox cases confirmed in the Netherlands, May 2022, Eurosurveillance (2022). DOI: 10.2807/1560-7917.ES.2022.27.24.2200448

Provided by the European Center for Disease Prevention and Control (ECDC)

Quote: Incubation period for monkeypox: estimates from the Netherlands (2022, June 16) retrieved on June 16, 2022 from

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