As of January 25, 2020, up to 75,800 individuals in Wuhan, Hubei province, China — the epicenter of the outbreak of the 2019-nCoV coronavirus — may have been infected with the novel virus, according to new modeling research from the University of Hong Kong.
2019-nCoV coronavirus. Image credit: University of Hong Kong.
“Not everyone who is infected with 2019-nCoV would require or seek medical attention,” said University of Hong Kong’s Professor Gabriel Leung, co-author of the study.
“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.”
“The apparent discrepancy between our modeled estimates of 2019-nCoV infections and the actual number of confirmed cases in Wuhan could also be due to several other factors. These include that there is a time lag between infection and symptom onset, delays in infected persons coming to medical attention, and time taken to confirm cases by laboratory testing, which could all affect overall recording and reporting.”
The new estimates also suggest that multiple major Chinese cities might have already imported dozens of cases of 2019-nCoV infection from Wuhan, in numbers sufficient to initiate local epidemics.
The early estimates underscore that it will likely take rapid and immediate scale-up of substantial public health control measures to prevent large epidemics in areas outside Wuhan.
Further analyses suggest that if transmissibility of 2019-nCoV could be reduced, both the growth rate and size of local epidemics in all cities across China could be reduced.
“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 University of Hong Kong’s Professor Joseph Wu, corresponding author of the study.
“Large cities overseas with close transport links to China could potentially also become outbreak epicenters because of substantial spread of pre-symptomatic cases unless substantial public health interventions at both the population and personal levels are implemented immediately.”
“Based on our estimates, we would strongly urge authorities worldwide that preparedness plans and mitigation interventions should be readied for quick deployment, including securing supplies of test reagents, drugs, personal protective equipment, hospital supplies, and above all human resources, especially in cities with close ties with Wuhan and other major Chinese cities,” Professor Leung said.
In the study, Professor Leung, Professor Wu and their colleagues used mathematical modeling to estimate the size of the epidemic based on officially reported 2019-nCoV case data and domestic and international travel data.
The researchers assumed that the serial interval estimate — the time it takes for infected individuals to infect other people — for 2019-nCoV was the same as for SARS.
They also modeled potential future spread of 2019-nCoV in China and internationally, accounting for the potential impact of various public health interventions that were implemented in January 2020 including use of face masks and increased personal hygiene, and the quarantine measures introduced in Wuhan on January 23.
They estimate that in the early stages of the Wuhan outbreak (from December 1, 2019 to January 25, 2020) each person infected with 2019-nCoV could have infected up to 2-3 other individuals on average, and that the epidemic doubled in size every 6.4 days. During this period, up to 75,815 individuals could have been infected in Wuhan.
Additionally, estimates suggest that 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). Together these cities account for over half of all outbound international air travel from China.
While the estimates suggest that the quarantine in Wuhan may not have the intended effect of completely halting the epidemic, further analyses suggest that if transmissibility of 2019-nCoV could be reduced by 25% in all cities nationally with expanded control efforts, both the growth rate and size of local epidemics could be substantially reduced.
Moreover, a 50% reduction in transmissibility could shift the current 2019-nCoV epidemic from one that is expanding rapidly, to one that is slowly growing.
“It might be possible to reduce local transmissibility and contain local epidemics if substantial, even draconian, measures that limit population mobility in all affected areas are immediately considered,” said University of Hong Kong’s Dr. Kathy Leung, co-author of the study.
“Precisely what and how much should be done is highly contextually specific and there is no one-size-fits-all set of prescriptive interventions that would be appropriate across all settings.”
“On top of that, strategies to drastically reduce within-population contact by canceling mass gatherings, school closures, and introducing work-from-home arrangements could contain the spread of infection so that the first imported cases, or even early local transmission, does not result in large epidemics outside Wuhan.”
The study was published today in The Lancet.
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Joseph T. Wu et al. Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study. The Lancet, published online January 31, 2020; doi: 10.1016/S0140-6736(20)30260-9
