What is the true incidence of Coronavirus? An empirical model using evacuees from Wuhan

Many people think that the official estimates of total infections from nCov-2019 are lower than the true incidence because of failure to count mild infections, or even worse, for some this is due to a cover-up by the Chinese government trying to hide the real entitity of the epidemic. I came up with the idea of using infection counts from evacuees (people repatriated by other countries) to have the most reliable data.

Using estimates of pathogen prevalence following phylodynamic methods ( which measure how quickly observed genomes share ancestry to estimate the rate of exponential growth) Trevord Bedford estimates a median total incidence on 8 Feb of 55,800 total infections since start of epidemic with a 95% uncertainty interval of between 17,500 and 194,400 total infections. This approach estimates an infection-to-case reporting rate of between 18% and 100%.

MRC’s Neil Ferguson was estimating that official figures were underreporting by a factor of 10x the real number of total infections.

I adopted a rather straightforward approach to this, by using data on evacuees from Wuhan to other countries. These are groups of non Chinese citizens living in Wuhan that were repatriated to their home countries during the last few weeks following the coronavirus outbreak. Most countries placed these individuals in strict quarantine and monitored them for flu-like symptoms. The suspicious cases were tested for coronavirus.

An advantage of using infection data from evacuees is that all the individuals were screened for the virus, at least at a symptomatological level, and the individuals showing symptoms were tested in the lab for the virus. This will result in a complete report of infections, which includes also mild cases. Moreover, fears of a cover-up by China are dissipated because the tests are carried out in other countries.

The official number of infected individuals in Wuhan was obtained from the CSSE interactive map, on the day the evacuees were boarded on the flight back to their home countries. Dividing the number of infected individuals by the Wuhan population (11 millions) gives the incidence of the virus. This figure was compared to the incidence among the evacuees (N. infected/number of people evacuated) for each country. Dividing the incidence among the evacuees by the estimated incidence in Wuhan gives the extent of the reporting rate (or underestimation factor). The reporting rate is estimated at 17.3%, or an “underestimation factor” of 5.78x, lower than Neil Ferguson’s estimate but closer to the lower bound (18%) of Trevor Bedford’s prediction.

Today’s confirmed cases according to CSSE is 43,126. I estimate the true total infections to be 250,000 as of February 11th.

Table 1. Infections among Wuhan evacuees.

	Japan	Italy	Germany	France	USA	S.Korea	France 2	USA 2	Taiwan	Canada
Infected	5	1	2	0	1	2	1	1	1	0
Total	206	54	124	179	195	700	254	600	247	174
Date	Jan 29	Feb 3	Feb 1	Jan 31	Jan 29	Jan 31	Feb 2	Feb 5	Feb 3	Feb 7
Wuhan official infected	6930	17730	12870	10800	6930	10800	15480	24660	17730	30600
Wuhan total pop	11100000	11100000	11100000	11100000	11100000	11100000	11100000	11100000	11100000	11100000
Wuhan official infected rate	0.0006243243243	0.001597297297	0.001159459459	0.000972972973	0.0006243243243	0.000972972973	0.001394594595	0.002221621622	0.001597297297	0.002756756757
Repatriates infected rate	0.02427184466	0.01851851852	0.01612903226	0	0.005128205128	0.002857142857	0.003937007874	0.001666666667	0.004048582996	0
Underestimation coefficient	38.87698062	11.59365796	13.91082036	0	8.214008214	2.936507937	2.823048282	0.7502027575	2.534645869	0

The updated infections among Wuhan evacuees from different countries can be seen here.