New study estimates more than 75,000 people in Wuhan infected with coronavirus

Since its emergence in December 2019, the 2019-nCoV coronavirus epidemic has infected just over 9,500 people in China, including around 6,000 people in Hubei province, according to official reports. However, a new study estimates that the cases of people infected in Wuhan could actually amount to more than 75,000. A number which, if confirmed, means that the previously announced death rate would be much lower than expected.

"We estimate that 75,815 people were infected in Wuhan as of January 25, 2020," reports a team led by Gabriel Leung of the University of Hong Kong in the journal The Lancet . As of January 31, the Chinese government has declared that the number of confirmed cases has exceeded 9,700 for the whole of China, including 213 deaths.

For Hubei province - including Wuhan, a city of 11 million people in central China - the official figure was nearly 6,000 confirmed cases and just over 200 deaths. The World Health Organization (WHO) said on Thursday that the epidemic was a global health emergency, but said it did not recommend restrictions on international trade or travel.

An increase in cases due to incubation and screening times

"The apparent discrepancy between our modeled estimates of infections at 2019-nCoV and the actual number of confirmed cases in Wuhan could be due to several factors," says Leung. A time lag between infection and onset of symptoms, delays in medical treatment of infected people, and the time it takes to confirm cases with laboratory tests "could all affect the recording and listing of cases".

A) Cumulative number of confirmed cases infected with the new coronavirus 2019 as of January 28, 2020 in Wuhan, in mainland China and outside mainland China. (B) The main outgoing air and rail transport routes from Wuhan during chunyun 2019. The darker and thicker edges represent a larger number of passengers. Outbound international air travel (in yellow) accounted for 13.5% of all outbound air travel, and the top 40 domestic air routes (in red) accounted for 81%. The islands of the South China Sea are not shown. Credits: Joseph T Wu et al. 2020

The study found that each person who contracted the virus, which emerged in December, could have infected an average of two to three people, and that the epidemic had doubled in size every 6.4 days. If the virus spreads so quickly nationwide, "it is possible that epidemics are already developing in several major Chinese cities, with a lag of one to two weeks behind Wuhan" says Joseph Wu, professor at the University from Hong Kong.

A potentially lower mortality rate than previously estimated

If the new case estimate is correct, it would mean that the 2019-nCoV virus death rate is significantly lower than the preliminary figures suggested, with far less than one percent of cases found to be fatal.

But a low death rate can still lead to a large number of deaths if the virus spreads widely. Seasonal flu, for example, kills between 290,000 and 650,000 people a year, according to the World Health Organization (WHO).

In the United States, the death rate among people infected with the flu is 0.13%, according to the Centers for Disease Control (CDC). The 2002/03 SARS (severe acute respiratory syndrome) epidemic started in Guangdong province and killed 774 people out of a total of 8096 infected people.

The 2012 MERS (Middle East Respiratory Syndrome) epidemic killed 858 of the 2,494 people infected. The respective mortality rates of patients with SARS and MERS were 9.5 and 34.5%, much higher than for the new coronavirus.


Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study

Prof Joseph T Wu, Kathy Leung, Prof Gabriel M Leung, 

Published:January 31, 2020


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