Imperial College London researchers estimate there may be over 4,000 cases of the novel coronavirus outbreak, in a new report.

This article was updated on 29 January 2019

Its authors are from the MRC Centre for Global Infectious Disease Analysis, and J-IDEA, the Abdul Latif Jameel Institute for Disease and Emergency Analytics.

The report states most cases have been epidemiologically linked to exposure at a seafood market in Wuhan, which has been closed since 1 January 2020 in efforts to contain the outbreak.

Using the number of cases detected outside China, the report finds it is possible to infer the number of clinically comparable cases within Wuhan City that may have occurred thus far.

Calculations 

The report estimates that a total of 4,000 cases of 2019-nCoV in Wuhan City had onset of symptoms by 18 January 2020 (the last reported onset date of any case before the report's publication).

This estimate is based on the following assumptions:

• Wuhan International Airport has a catchment population of 19 million individuals.
• There is a mean 10-day delay between infection and detection, comprising a 5-6 day incubation period and a 4-5 day delay from symptom onset to detection/hospitalisation of a case (the cases detected in Thailand and Japan were hospitalised 3 and 7 days after onset, respectively).
• Total volume of international travel from Wuhan over the last two months has been 3,301 passengers per day. This estimate is derived from the 3,418 foreign passengers per day in the top 20 country destinations based on 2018 IATA data, and uses 2016 IATA data held by Imperial College to correct for the travel surge at Chinese New Year present in the latter data (which has not happened yet this year) and for travel to countries outside the top 20 destination list.

The report concludes it is likely that the Wuhan outbreak of coronavirus has caused substantially more cases of moderate or severe respiratory illness than currently reported.

Following the initial report, published on 17 January, the researchers have updated their estimates to reflect the growing numbers of confirmed cases of coronavirus, with a second report published on 22 January.

The authors write: "Our estimates of the size of the outbreak in Wuhan have more than doubled since our first report. This is a result of the number of cases detected outside mainland China having increased." 

They add: " Given this evidence for human-to-human transmission, enhancing rapid case detection will be essential if the outbreak is to be controlled."

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Read the full Coronavirus report.

Guidance from the World Health Organization on the coronavirus outbreak is available here.

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