Researchers, using computer modelling, have calculated that up to 75,800 individuals may have contracted the novel coronavirus in the Chinese city of Wuhan as of January 25, a number that is far greater than the official estimate of 1,300 infected people.
According to the study, published in the journal The Lancet, given the lack of a robust and detailed records of suspected, probable, and confirmed cases of the novel coronavirus infection (2019-nCoV), the true size of the epidemic, and its pandemic potential remain unclear.
"Not everyone who is infected with 2019-nCoV would require or seek medical attention. During the urgent demands of a rapidly expanding epidemic of a completely new virus, especially when system capacity is getting overwhelmed, some of those infected may be undercounted in the official register," explained study senior author Gabriel Leung from the University of Hong Kong.
The discrepancy between the model's estimates of the coronavirus infections, and the actual number of confirmed cases in Wuhan may be due to several factors such as the time lag between infection and symptom onset, delays in infected persons coming to medical attention, and time taken to confirm cases by laboratory testing, the researchers said.
According to the new estimate, multiple major Chinese cities might have already imported dozens of cases of 2019-nCoV infection from Wuhan, in numbers sufficient to initiate local epidemics.
"If the transmissibility of 2019-nCoV is similar nationally and over time, it is possible that epidemics could be already growing in multiple major Chinese cities, with a time lag of one to two weeks behind the Wuhan outbreak," said study lead author Joseph Wu from the University of Hong Kong.
"Large cities overseas with close transport links to China could potentially also become outbreak epicentres because of substantial spread of pre-symptomatic cases unless substantial public health interventions at both the population and personal levels are implemented immediately," Wu added.
In the study, the scientists used mathematical modelling to calculate the size of the epidemic based on officially reported 2019-nCoV case data, and domestic as well as international travel data.
They assumed that the time it takes for infected individuals to infect other people for 2019-nCoV was the same as for severe acute respiratory syndrome (SARS) -- also caused by a pathogen in the coronavirus family. In their estimate, the researchers also modelled potential future spread of 2019-nCoV in China and internationally, accounting for the potential impact of various public health interventions implemented in January 2020.
These interventions included the use of face masks, and increased personal hygiene, and the quarantine measures introduced in Wuhan on January 23.
Based on these calculations, the researchers said that in the early stages of the Wuhan outbreak -- from December 1, 2019 to January 25, 2020 -- each person infected with could have spread the virus to 2-3 other individuals on average.
They added that the epidemic doubled in size every 6.4 days, likely infecting 75,815 individuals in Wuhan during this period. According to the study, cases of 2019-nCoV infection may have spread from Wuhan to multiple other major Chinese cities as of January 25, including Guangzhou (111 cases), Beijing (113), Shanghai (98), and Shenzhen (80).
The scientists said taken together these cities account for more than half of all outbound international air travel from China. With their analysis, the researchers believe that the quarantine in Wuhan may not have the intended effect of halting the epidemic.
If transmissibility of the virus could be reduced by a fourth in all Chinese cities with expanded control efforts, both the growth rate and size of local epidemics could be substantially reduced, they added. A 50 per cent reduction in transmissibility, the team said, may shift the current 2019-nCoV epidemic from one that is expanding rapidly, to one that is slowly growing.
The researchers urged authorities worldwide to ready preparedness plans and mitigation interventions for quick deployment, including securing supplies of test reagents, drugs, personal protective equipment, hospital supplies, and human resources.