With a high incidence, group tests are not useful

In the middle of the school, with omicron multiplying, the health centers and the saturated hospital emergencies, the concept 'pool testing' or group test is

With a high incidence, group tests are not useful

In the middle of the school, with omicron multiplying, the health centers and the saturated hospital emergencies, the concept 'pool testing' or group test is rescued as a possible formula to test the population and detect positives massively and at the same time profitable. Next, some issues that will bring you a little more to the reality of this test whose philosophy is to do more with less to save resources.

It is about forming groups of 10, 15, 20 people or more, from which samples are extracted that are mixed in one to make a PCR. If it is negative, it is understood that the whole group is free from Covid-19. If, on the contrary, "was positive, the next step would be to do the test individually," explains Rafael Cantón Moreno, head of the microbiology service at the Ramón and Cajal University Hospital of Madrid.

First, it saves resources. Fewer tests are used, less plastic material, tubes, etc. It is simple, in a single PCR several people tested. Fundamentally, it saves time and money. A data: With a prevalence of 0.5% of infection in a given city, group tests allow to examine seven million people in less than two months.

In the words of Canton, it is "a very interesting strategy in situations in which the proportion of positivity is low". However, with the positivity we have now, around 40% in primary school, the 'Pool Testing' "is not cost-effective [...] begins to be in an epidemiological situation below 5% or 3%" . And he adds: "You have to use tests with rationality. Of course, at the epidemiological moment we have in Spain, it would not be an adequate strategy because, given the current incidence, it would be necessary to study everyone individually."

A document of the Government of Chile is also witnessed, where group tests have also been used: "The convenience of applying 'pool testing' will depend on prevalence (the probability that a person has the virus). If the prevalence is low. , since in this case, group samples will be more likely to give negative and, therefore, it is not necessary to test individually. " On the other hand, "if the prevalence is high -Mayor to 30% - then it is not convenient."

The idea comes from World War II. It is when it was used for the first time with the aim of detecting syphilis. Later, in the 1980s, it served for HIV. As the microbiologist of Ramón and Cajal Hospital points out, "we have also used it to dimension what is the circulation of the hepatitis virus, for example" and of course, with Covid, but in other contexts of lower incidence.

In Israel, Ghana, Singapore, China, Chile ... in the United States, the FDA authorized a laboratory so that it could execute emergency group test and in Spain, has worked with the 'Pool Testing' the Vigo Hospital, for example . "It's something that was done at a moment when it lowered the incidence. In fact, there are publications of Spanish groups that have validated it, but in other contexts of lower incidence."

According to Cantón Moreno, it is possible, but already associated with concrete projects. That is, when the incidence is lowered and the cases are mostly asymptomatic (such as a more respiratory virus), "will not be very interested as a method for screening or as a specific diagnosis, but it can be very interesting to do an epidemiological study in a population concrete to dimension a specific situation ".

Updated Date: 10 January 2022, 20:18

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