Probable Longer Incubation Period for Elderly COVID-19 Cases: Analysis of 180 Contact Tracing Data in Hubei Province, China

Abstract

Background

Factors associated with the incubation period of COVID-19 are not fully known. The aim of this study was to estimate the incubation period of COVID-19 using epidemiological contact tracing data, and to explore whether there were different incubation periods among different age gr1oups.

Methods

We collected contact tracing data in a municipality in Hubei province during the full outbreak period of COVID-19. The exposure periods were inferred from the history of travel in Wuhan and/or history of exposure to confirmed cases. The incubation periods were estimated using parametric accelerated failure time models accounting for interval censoring of exposures.

Results

The incubation period of COVID-19 follows a Weibull distribution and has a median of 5.8 days with a bootstrap 95% CI: 5.4–6.7 days. Of the symptomatic cases, 95% showed symptoms by 14.3 days (95% CI: 13.0–15.7), and 99% showed symptoms by 18.7 days (95% CI: 16.7–20.9). The incubation periods were not found significantly different between male and female. Elderly cases had significant longer incubation periods than young age cases (HR 1.49 with 95% CI: 1.09–2.05). The median incubation period was estimated at 4.0 days (95% CI: 3.5–4.4) for cases aged under 30, 5.8 days (95% CI: 5.6–6.0) for cases aged between 30 and 59, and 7.7 days (95% CI: 6.9–8.4) for cases aged greater than or equal to 60.

Conclusion

The current practice of a 14-day quarantine period in many regions is reasonable for any age. Older people infected with SARS-CoV2 have longer incubation period than that of younger people. Thus, more attention should be paid to asymptomatic elderly people who had a history of exposure.

Keywords:

• infectious disease
• coronavirus
• incubation period
• epidemiology

Acknowledgments

We thank all the staffs and health workers who did the contact tracing and collected the data. This work was supported by the Special Emergency Research Project on COVID-19 at Hubei University of Medicine (Grant No. 2020XGFYZR06), and Shiyan Emergency Scientific Research Project of COVID-19 Prevention and Control Technology (Grant No. 20Y02).

Disclosure

The authors report no conflicts of interest in this work.