Significantly longer Covid-19 incubation times for the elderly, from a case study of 136 patients throughout China

Jiang, Ally Bi-zhu; Lieu, Richard; Quenby, Siobhan

Objective: To infer Covid19 incubation time distribution from a large sample. Method: Based on individual case data published online by 21 cities of China, we investigated a total of 136 COVID19 patients who traveled to Hubei from 21 cities of China between January 5 and January 31, 2020, remained there for 48 hours or less, and returned to these cities with onset of symptoms between January 10 and February 6, 2020. Among these patients, 110 were found to be aged 15 to 64, 22 aged 65 to 86, and 4 aged under 15. Findings: The differential incubation time histogram of the two age groups 15 to 64 and 65 to 86 are adequately fitted by the log normal model. For the 15 to 64 age group, the median incubation time of 7.00+1.10 - 0.9 days (uncertainties are 95 % CL) is broadly consistent with previous literature. For the 65-86 age group, the median is 10.9+2.7 - 2.0 days is statistically significantly longer. Moreover, for this group, the 95 % confidence contour indicates the data cannot constrain the upper bound of the log normal parameters μ, σ by failing to close there; this is because the sample has a maximum incubation time of 17 days, beyond which we ran out of data even though the histogram has not yet peaked. Thus there is the potential of a much longer incubation time for the 65 to 86 age group than 10 to 14 days. Only a much larger sample can settle this.