Estimated Incubation Period of COVID-19
- The median incubation period from infection with SARS-CoV-2 to onset of symptoms is approximately 5 days.
- 97.5% of people infected with SARS-CoV-2 will exhibit symptoms by 11.5 days.
- Monitoring people exposed to SARS-CoV-2 for 14 days for development of symptoms should be sufficient to identify 99% of cases or more.
What is the incubation period between exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus and symptom onset?
Authors searched news and public health reports of coronavirus disease 2019 (COVID-19) cases from areas without community transmission in both the English and Chinese literature. Time of possible exposure to SARS-CoV-2 and onset of any symptom, onset of fever, and time of case detection were recorded and, where not reported, conservatively estimated. The authors fit a log-normal distribution to incubation time, but also tested several alternative models. They also computed the expected number of undetected symptomatic cases from their incubation period estimates that might occur during an active monitoring period, ranging from 7-28 days, with varying risks of infection after exposure.
Overall, 181 cases from outside Hubei province occurring before February 24, 2020, were analyzed. The majority of cases were from outside of mainland China (n = 108). Most had history of travel to Wuhan or contact with travelers from the region. The authors estimated the median incubation period to be 5.1 days (95% confidence interval, 4.5-5.8 days); 97.5% of people who were infected exhibited symptoms by 11.5 days (95% confidence interval, 8.2-15.6 days). Similar results were obtained in analysis looking only at fever onset.
The authors then computed that if risk of exposure is low (1 in 10,000 exposed people) or medium (1 in 1,000 exposed people), 7 days of monitoring would be sufficient to identify >99% of symptomatic cases. However, if monitoring definitely infected people, monitoring durations >14 days could be required to capture >99% of symptomatic cases.
The incubation period between infection and onset of symptoms for SARS-CoV-2 is approximately 5 days. Monitoring or quarantine for 14 days will identify approximately 99% or greater of symptomatic infections among patients exposed.
This study provides quantitative estimates of the incubation period between exposure to SARS-CoV-2 and development of symptomatic infection. They support a duration of 14 days for active monitoring and quarantine for exposed or infected persons to develop symptoms. There are a few important limitations to consider. These data were developed from cases which were recognized as overt COVID-19. Other studies have suggested that a large number of SARS-CoV-2 infected patients may only experience mild symptoms, perhaps insufficient to prompt those infected to seek medical care. Furthermore, it is also possible that some individuals never develop symptoms. The implications of both of these to quarantine or active monitoring durations for exposed individuals are complex and not fully understood.
Clinical Topics: Prevention
Keywords: Coronavirus, Coronavirus Infections, Fever, Infectious Disease Incubation Period, Primary Prevention, Public Health, Quarantine, Risk, SARS Virus, severe acute respiratory syndrome coronavirus 2
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