Coronavirus: Epidemic's scale may be far greater with two-third cases escaping detection globally, says report
Scientists say it's not clear if there's community transmission going on because many countries are not doing diagnostic testing on anyone except for returning travelers or their close contacts
Over two-thirds of coronavirus disease or COVID-19 cases may have gone undetected globally, scientists from Imperial College London estimate in a new report.
They suggest that the scale of the epidemic might be far greater than thought. Undetected cases, they add, could make it harder for experts to trace human-to-human transmission.
"We are starting to see more cases reported from countries and regions outside mainland China with no known travel history or link to Wuhan City," Natsuko Imai, one of the authors on the new report, told New Atlas.
According to reports, coronavirus has killed at least 2,619 people worldwide. The number of infections globally has surged past 79,000. Though most of the confirmed cases are concentrated in mainland China, the virus has spread to 29 other countries or regions. There are 27 reported deaths and 1,800 infections outside mainland China.
To stem the tide of the outbreak, the report suggests that countries need to ramp up their surveillance. In this report, the team tested the accuracy of surveillance in various countries by looking at the average volume of travelers flying out of China's Wuhan — the epicenter of the outbreak.
"We compared the average monthly number of passengers traveling from Wuhan to major international destinations with the number of COVID-19 cases that have been detected overseas," Sangeeta Bhatia, an author of the report, told New Atlas.
Following this, the team estimated the number of COVID-19 cases exported from mainland China that have remained undetected. The team believes that unreported coronavirus cases might hover between 60-70%, globally, which is approximately two-thirds of the cases.
Despite having received a large number of passengers from Wuhan, some countries may have detected significantly fewer cases than expected, the report says.
The disease spread outside mainland China
"The number of cases in the rest of the world is very small compared to what we have in China, but that may not stay the same for long," World Health Organization Director-General Tedros Adhanom Ghebreyesus told reporters at the organization's headquarters in Geneva on February 20.
Since then, COVID-19 cases have been reported in large numbers in Iran, Italy and South Korea. This has sparked international concerns over how the virus is spreading.
Health experts have not been successful in tracing the source of infections among communities that have no links to China. Some scientists suspect that poor surveillance could have resulted in community transmission of the outbreak. Reports suggest that surveillance based on symptoms alone is not effective.
"We don't really know if there is community transmission going on in other parts of the world because, for the most part, countries are not doing diagnostic testing on anyone but returning travelers or their close contacts," Tom Inglesby, director of the Center for Health Security of the Johns Hopkins Bloomberg School of Public Health, told Vox.