Coronavirus | Building a persuasive, data-backed case for consistent PCR testing

Virus trail: Stepping up PCR testing helps increase detection of COVID-19, authors of the study said.   | Photo Credit: Shiv Kumar Pushpakar

A paper scheduled to be published in the peer-reviewed U.S. journal Health Affairs has shown a strong corelation between testing intensity and reduced transmission of COVID-19.

The study, by Ravindra Prasan Rannan-Eliya and co-authors from the Institute for Health Policy in Colombo, Sri Lanka, explicitly quantifies testing for COVID-19 at a global scale, accounting for interventions and ecological factors. “The robustness of the relationship between testing and transmissibility is consistent with a known mechanism,” Dr. Ravindra explains, on a call.


According to the authors, around half or more of COVID-19 transmissions is caused by people who are asymptomatic or who have only minor symptoms, so only increasing PCR (polymerase chain reaction) testing make it possible to increase detection and isolation of infectious cases, and then to increase the numbers of their potentially infectious contacts who are isolated. This remains the only known approach that blocks person-to-person transmission sufficiently to stop the epidemic.

“The basic thing was to try and evaluate how much impact PCR testing has on COVID-19 spread. WHO (World Health Organisation) guidelines refer to PCR testing intensity. It became clear that the more testing that the countries did, they did better with reference to COVID-19 cases,” Dr. Ravindra says. On top of their table is Vietnam, which has a high test-to-case ratio. Today, they haven’t got a case of COVID-19. The paper lays that at the footstool of very aggressive testing.

The paper also advances the theory that freezing mobility, as in lockdowns, had very little impact on the transmission of the virus itself. “We looked at mobility related factors — mobile phone related, and from Google and Facebook data. If you look at phone data, globally, it is very hard to show a benefit. There was a marginal impact in Europe, not large,” Dr. Ravindra explains. India, which had a national lockdown, and in countries such as Bolivia, Peru and Chile, there was hardly any benefit from the measure.

A PCR evangelist, Dr. Ravindra advances a strong case for continuing with a high level of PCR tests, even as vaccines are rolled out. He does think, however, in resource strapped settings, where the health system has failed to build testing capacity, using antigen tests might be the way out. With the good kits, and there are a lot of bad kits out there, the specificity is nearly as good as a PCR, maybe. However, high sensitivity is only good in symptomatic people. And given that over 50% of people have no symptoms or minor ones, this instrument is indeed blunted, he says.

Will the entry of several vaccine candidates change the testing dynamics some? Dr. Ravindra explains: “None of the vaccines candidate we have so far are good enough to eliminate the virus. The vaccine will be much more effective if you have other control measures. The obvious thing is to do the testing….We do know that governments, such as in China and Melbourne, that aggressively tried to kill it [the virus], managed to do so with 6-8 weeks. You just have to throw everything at it.” Funds will have to be dedicated to testing, just as they have to be used to treat people with the infection, and nations that do so, will see substantial benefits, he adds.

An earlier version of this article mentioned the name of the journal incorrectly. The error is regretted.

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Printable version | Jan 21, 2021 2:21:43 PM |

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