Table 2.

Key time-to-event intervals for laboratory-confirmed COVID-19 cases by epidemic period, as of Feb 17, 2020

	All	Period 1 (Dec 24 to Jan 27)	Period 2 (Jan 28 to Feb 8)*	Difference†(95% CI), p value
Time from symptom onset to first health-care consultation, days‡	2·5 (0·0–10·0), n=2888	3·0 (0·0–11·1), n=1836	1·6 (0·0–7·0), n=1052	1·4 (1·2–1·6), p<0·0001
Time from symptom onset to hospital admission, days‡	3·8 (0·0–12·0), n=2001	4·4 (0·0–14·0), n=1310	2·6 (0·0–9·0), n=691	1·8 (1·5–2·1), p<0·0001
Time from first health-care consultation to hospital admission, days‡	1·5 (0·0–9·0), n=1725§	1·4 (0·0–9·0); n=850	1·4 (0·0–9·0), n=353	0·0 (0·2–0·4), p=0·6551
Time from symptom onset to official reporting, days‡	7·4 (1·0–18·0), n=5024§	8·9 (2·0–19·8), n=2727	5·4 (1·0–12·0), n=2079	3·5 (3·3–3·7), p<0·0001

Data are mean (95% CI), n, unless otherwise specified.

^*To account for reporting delays, we excluded the last 9 days of data (ie, data after Feb 8, 2020).

^†Difference between periods 1 and 2; Welch two-sample t test was used to calculate the p value.

^‡Estimated from empirical data through complete-case analysis; the estimates obtained by fitting gamma, Weibull, and lognormal distributions are reported in the appendix (pp 15–17).

^§Sample size may be different from the sum of the two periods because it also includes cases without recorded date of symptom onset, which was used for classification of cases into temporal periods.