September 24, 2020

Saliva tests against coronavirus may be useful, but they will have to teach us to cooperate


The fever for mass tests is one of the symptoms most widespread pandemic. Large-scale detection of infected was impossible during the first waves due to technical limitations. Months later, the development of tools based on saliva samples has rekindled the idea of analyze large percentages of the population quickly, cheaply and reliably. Some even dream of doing it from home. Is this possible? And, above all, is it recommended?

Why Madrid is proof that poorly planned mass screening is useless and depletes resources

Why Madrid is proof that poorly planned mass screening is useless and depletes resources

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“With the tests you have to be clear about what you want to do them for, and it does not make sense to analyze everyone because there is a risk of generating false positives and saturate the laboratories and tracking systems, ”epidemiologist Pedro Gullón explained to elDiario.es. “When we talk about massive tests we talk about directing them to where there is more incidence, if you expect a transmission very similar to the community one it does not make so much sense.

“[Los test masivos] they are very popular at the political level, but their usefulness must be limited to situations in which you know that the benefits can outweigh the risks ”, he clarifies. In other words, they could be recommended in places with greater transmission where the “probability” of obtaining positives is higher, or where there are very vulnerable groups.

These population screenings already take place in hospitals and residences, and could also be carried out in schools with many cases. Gullón cites the example of Lleida: “When infections occurred in agri-food companies, one of the reasons why they managed to lower the incidence was because they were screened in these places without waiting for symptoms, to isolate whoever was necessary.”

And the saliva tests arrived

At the end of June a prepublication sent a clear message: the sensitivity of the tests is secondary, the most important is the frequency [con la que se hagan] and its accessibility. Days later, a opinion piece in the New York Times defended these quick, cheap and simple tests that “anyone could use every day at home”. In August the FDA approved SalivaDirect, a protocol that does not avoid PCR but allows it to be done from saliva samples, which saves time and money.

Gullón considers himself “skeptical” with the results of the saliva tests published so far, scarce, “small”, in the form of prepublication and with little data on specificity and sensitivity available. “I still have my doubts, I distrust everything that is sold as game-changer [revolución]”.

However, saliva tests have aroused great interest in the US and, by extension, the rest of the planet. Gullón asks for caution when comparing the usefulness of these tools between countries. “In the United States they are more popular because there is inequality in access and there are those who do not have the possibility of having a PCR.” There, the possibility of having a result for a few dollars can be a “great opportunity”.

And in Spain? Gullón considers that in a centralized health system like ours, where “there is not so much inequality in access to tests”, their usefulness could be “less”. In addition, they would bring with them “uncertainties” regarding their application: “It would be necessary to see who validates them, how they are distributed, who buys them, if they would be free access or not, if the test would have to be confirmed and how the cancellations are managed and what people stay home ”.

Therefore, saliva tests should be introduced with care given the “complication” that would mean that a large number of people use them. And not only because of the “very high” risk of false positives if they are used in places with a moderate incidence that has already been observed with tests. normal in places like Madrid.

“The PCRs are done within the health system, so it is much easier to manage the discharge and the contacts. If people were to take a test at home, it would create a lot of chaos ”, says Gullón. “The trackers are already saturated, as situations in which it is vital to cut the transmission chain are mixed with a large number of possible false positives [por los test rápidos de saliva] it will be very difficult to handle ”.

The epidemiologist does see utility in using saliva test for specific cases, and always following public health criteria. “They can be very useful to follow up on a positive case, lift the quarantine after 10 days if it tests negative, and also be used in Primary Care. If they are reliable like a PCR and you save the laboratory part, they could facilitate many things, but not to the point that everyone is doing it, and less at home ”. Even so, it emphasizes the need to wait for more information on the reliability of these tools.

A cooperation problem

Proactive tests, at home or not, present a less obvious problem at first glance. “Unlike masks, they protect others, not oneself,” explained biologist Carl Bergstrom a few days ago. On twitter. The researcher from the University of Washington assured that it has “little therapeutic value” to detect that we are asymptomatic, while the individual, economic and social cost is great due to isolation. Who would want to pay for it?

The success of these mass screening initiatives could require convincing ourselves to bear these costs for the common good. “It is a problem of cooperation because your individual costs are higher than the benefits you get from something that, at the same time, benefits society,” explains CSIC sociologist Luis Miller. “And, as in these cases, it is not easy to solve.”

Miller explains that one of the solutions is to reduce these individual costs. For example, through paid leave that allows positives to remain in quarantine. “To reduce the costs for the individual is to increase those of the State, which is also a problem.” This is where another strategy comes into play: fostering cooperation per se.

“Information and education campaigns will have to be carried out, as with the masks. Explain that it is annoying, but that if we do it we all benefit, ”says Miller. “Another possibility is negative incentives, in which the stigma is created that if you do that you are ‘bad’ with society, which has effects on social approval and disapproval in your group.”

“This is, and always has been, a crisis about population risk, not individual.” It is a phrase repeated in epidemiological circles that, unfortunately, has not penetrated the collective mentality. “It’s something that may not be broadcasting well,” says Miller. “There is no conscience in society that the best we can do [contra el virus] it is not pharmacological but from social behavior ”. For mass tests to succeed, we must understand that no one is safe if we are not all safe.

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