The University of Louisville Journal of Respiratory Infections


The author(s) received no specific funding for this work


Introduction: The period from exposure to a potential pathogen to the manifestation of symptoms, i.e.  the incubation period, is time the virus spends replicating in the host. An estimation of this period and subsequent quarantine of the host can limit potential spread, particularly in asymptomatic carriers. Effective contact tracing, length of self-quarantine, repeat testing, and understanding of disease transmission are all contingent on a true estimation of this incubation period.

Methods: Articles in English published since December 1st, 2019, on Google scholar, PubMed, and Research Gate, along with bulletins from the World Health Organization and the Centers for Disease Control and Prevention, were identified using the keywords, “SARS-CoV-2,” “COVID-19,” “median incubation period,” “mean incubation period,” “symptom onset,” “quarantine,” and “exposure interval” and reviewed independently by two authors to establish consensus. Travel to Wuhan, or in absence of travel, the earliest possible exposure, were used to calculate mean or median incubation period. Correspondingly, we reviewed the advised lengths of quarantine period.

Results: Five studies with a combined sample size of 505 patients were reviewed for mean/median incubation period. Four studies recommended periods for self-quarantine, ranging from 2 to 14 days. Linton et al. reported the shortest estimate of median incubation period at 4.3 days (95% confidence interval [CI] 4.5–5.6), whereas the longest was by Backer et al. at 6.4 days (95% CI 4.5–5.8). Similarly, the shortest estimation of mean incubation period was by Liu et al. (n=16) at 4.8 days (95% CI 2.2–7.4) days while the longest at 5.5 days (95% CI 4.5–5.8) was by Lauer et al. (n=181). Although the range for quarantine in these four studies was 12.5–14 days, all four recommended 14 days as the optimum for self-quarantine.

Conclusion: An estimate of incubation period is instrumental in outlining an effective quarantine measure. Calculation of the incubation period using mathematical models has established an accurate measure, albeit with uncertainty increasing towards the tail of each distribution. Based on a thorough review of these studies, a quarantine period of 14 days can be recommended, allowing 97.5% of the infected people to show symptoms. These symptomatic patients would be further evaluated based on their respective state health guidelines so that they may be effectively isolated and treated.



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