Why don't people pay it up front

Fighting pandemics: Keeping track of contacts backwards to move forward

A video conference with Hitoshi Oshitani from the Japanese Subcommittee on Novel Coronavirus Disease Control opened his eyes, says US infectious disease specialist KJ Seung. It had become clear to him why what had been done so far in the USA to find and isolate the contacts of Covid 19 patients had so little success, explains Seung. As a member of the non-profit organization "Partners In Health" he helps implement the contact tracing program in Massachusetts, USA.

While most states warn contact persons, i.e. people to whom infected people may have passed the virus on, Japan does it the other way around. And with great success, as Seung has to admit. Since then, he has also implemented this method in the US state of Massachusetts. »With retrospective contact tracking, we can find clusters in a much more targeted manner; we can identify more cases and in a much more efficient way. "

This article is featured in Spectrum - The Week, 48/2020

The strategy is based on the knowledge that it is mainly »super spreaders« that are driving the pandemic. From a purely statistical point of view, there is a high probability that whoever infected the infected person passed the virus on to a number of other people. A so-called cluster, a group of infected people, forms around it. "We're trying to find the source of the infection because there has to be a cluster somewhere," explains Oshitani.

On the hunt for the clusters

In June, researchers at the London School of Hygiene and Tropical Medicine estimated that around 80 percent of transmissions come from around ten percent of those infected. "With the classic, forward-looking method, you have to identify a lot more confirmed cases to find a cluster." If, on the other hand, someone from the ten percent pool is found, their contacts are followed up again in a classic, forward-looking manner - after all, they probably have more infected.

"With retrospective contact tracking, we can find clusters much more purposefully" (KJ Seung)

With "retrospective contact follow-up" one therefore looks for those contacts that a patient had before he was infected. This is how you try to find the source of your contagion. This approach is based on the knowledge that most people infected with Covid-19 do not infect anyone, while only a few pass the virus on to others. This finding is not new, but its importance for fighting the pandemic has so far been underestimated by those responsible in Europe and the USA, explains technology sociologist Zeynep Tüfekçi: “Countries that overlook this characteristic of the virus are risking the worst of two worlds: tough restrictions that barely help stop the virus from spreading. "

The theory is easy to explain, says Tüfekçi in a webinar by the Berkman Klein Center for Internet and Society at Harvard University, to which KJ Seung and his Japanese colleague Hitoshi Oshitani, who is considered one of the pioneers behind the Japanese approach, are invited . This approach, which focuses on the discovery of clusters by means of retrospective contact tracing, among other things, has resulted in relatively low numbers in Japan - without sophisticated surveillance technology, without a strict lockdown, despite fewer tests and despite a densely populated population.