Health authorities around the world are trying to curb the spread of the new corona virus – with little success so far. Several research teams have now used models to investigate what classic measures such as fever measuring and interviewing travelers bring. The result: Even in the best case, this screening only covers around a third of the infected people, in the worst case only a tenth. The reason for this is the relatively long incubation period and the sometimes asymptomatic course of the infection. The epidemic is likely to peak.
The epidemic of the new corona virus 2019-nCoV is causing concern worldwide and is already helping to severely affect the economy of China and the world. Starting from the city of Wuhan, this virus has spread rapidly in China and beyond since December 2019. Almost 25,000 cases of 2019 nCoV infections are now known and a good 425 people have died. Outside of China, cases from 24 countries are reported. Twelve people are also ill in Germany. In response to the spread of the virus, China has almost completely shut off several major cities in Hubei Province from the outside world, events have been canceled, and many factories and shops are closed.
Escaped before quarantine
But the strict quarantine measures come too late, as confirmed by the number of cases and a new model study. According to Zhanwei Du from the University of Texas at Austin, and his team, there was at least a 50 percent chance that the virus would have spread to 128 other Chinese cities before Wuhan began quarantine on January 22. According to the study, there were already at least one, probably several, undetected corona virus cases in the cities of Beijing, Shanghai, Guangzhou and Shenzhen. “The current quarantine can certainly limit the spread of the virus from Wuhan,” said the researchers. “But when it was set up, the new type of corona virus had long spread all over China and parts of the world.” This is supported by the fact that there are now sick people in every Chinese province and region.
Health authorities worldwide are now trying to curb the further spread of the coronavirus by various measures. This includes fever measurement at airports, train stations and other places of arrival for long-distance travelers, but also surveys of passengers arriving from China. Some airlines, including Lufthansa, have also temporarily suspended direct flight connections to China. Several research groups have now investigated what screening measures against the introduction of the virus bring. The basis of the model studies is the assumption that the time from infection to the development of the first symptoms in 2019-nCoV takes an average of five to six days. However, cases are known in which the incubation period was two weeks. The proportion of infections that are almost asymptomatic is also decisive for the effectiveness of the screenings. According to current estimates, the proportion of these subclinical cases in 2019-nCoV could be very high.
Screenings only work in a few cases
Regarding the detection rate of the screenings, both model studies come to almost the same result: only a small part of the infected passengers is identified by fever measurements and surveys. Billy Quilty of the London School of Hygiene and Tropical Medicine (LSHTM) and his colleagues found that only nine out of 100 infected travelers are recognized at the entrance screening after a long-haul flight. “Incoming inspection for flights from affected areas appears to be a sensible measure to prevent the introduction of the corona virus,” said Quilty. “However, our work underlines that thermal screening cannot detect every traveler with this virus.” A second research team led by Katelyn Gostic from the University of Chicago comes to similar conclusions. “Even under the best conditions, if only an infection of 20 remains asymptomatic and all travelers go through both an exit and an entry control, only 34 percent of the cases would be recognized on average,” said the researchers. If one assumes a higher proportion of subclinical cases, the effectiveness of the screening measures would be significantly lower: only one in ten infected people would be detected.
According to the researchers, this means that in addition to the screenings, other methods of epidemic prevention are necessary. These can include, for example, that arriving passengers are asked to report any symptoms that occur later and that their contact details are recorded if necessary. This makes it easier to find the possible contact persons in the event of an illness. “Our results underscore the need for measures that enable travelers and their contacts to be tracked retrospectively in the event of illness,” said Gostic and her team. A quarantine of passengers arriving from Hubei, as last carried out with the evacuated Germans, can help to identify infected people without symptoms of illness before they unwittingly carry the virus on.
So far there are no signs that the epidemic is losing momentum. According to Zhong Nanshan from the national team of experts in China, the peak of coronavirus infections is only expected in ten days to two weeks. However, the basis of these assumptions has not been announced.
Source: Zhanwei Du (University of Texas, Austin) et al. Preprint; William Quilty (London School of Hygiene and Tropical Medicine) et al. Preprint; Katelyn Gostic (University of Chicago) et al., preprint; WHO