Irene Hartmann
06/16/2020 - 7:01
- Clarín.com
- Society
Almost three months after the mandatory quarantine, the expansion of the coronavirus in Argentina has been concentrated in the Capital and the Buenos Aires suburbs. As for the more than 500 new daily patients on the Buenos Aires side, one could stay swimming in a comparative ocean of confusing numbers ( 500 is a lot or a little? And with respect to what? ) Or, instead, attend to another indicator, one that says something more about the spread of the virus and the control strategy of the health authorities: the positivity index, that is, the confirmed diagnoses on a number of tests. Nationally it is 15.7%, but in the City of Buenos Aires it is close to 45% .
Before sizing those figures, a couple of clarifications. What is positivity and why does it matter? It is simple. This is a complex pandemic, among other things because most of those infected do not have symptoms or are very mild, and yet they infect others, who in turn have no symptoms or are very mild, and they infect others, which gives rise to an indomitable vicious circle that takes the lives of the most vulnerable . The main international health organizations (including the WHO) recommend testing. Testing a lot. The more possible.
Because the more swabs (PCR tests) are done, the more quickly the "Trojan horses", these light carriers, will be found, in order to isolate them and stop the chain of infections. Now, how much is "testing a lot"? Can we test the entire population? No. Can we at least test the 3 million porteños, where the epidemic now seems to focus? Neither. Argentina does not have similar resources.
DetectAr operation in the La Boca neighborhood. Photo: Luciano Thieberger.
Damián Zopatti, clinical doctor and director of Statistics at the Hospital de Clínicas, explained it: “Germany and South Korea followed the hypothesis that the more tests are done, the better. But this is possible in a favorable economic situation, with almost unlimited reagents. For them it was effective. You passed a corner and they tested you. If you were positive, then they called you and isolated you. We are at the other extreme. As we do not have the economic possibility or the quantity of reagents, this long quarantine was decided. We assume that we are all positive and we stay inside . ”
Between the comings and goings of announcements of a quarantine that is becoming more flexible in droppers ( barbijo yes, hairdressers no; running yes, children yes, businesses in certain blocks no ... ), the city of Buenos Aires seems to be implementing its own strategy , translated in the neighborhood operation "DetectAr" .
The last available number of tests carried out in Buenos Aires is 1,254 PCRs in one day , of which 44.8% were "positive" . Its alot?
After the World Health Organization determined that Covid-19 had taken on the dimension of a pandemic, its Director of Emergencies, Mike Ryan, said at a press conference that countries that had conducted extensive PCR tests had obtained between a 3% and 12% of positive diagnoses . And he explained: "If you get to a point where there is a small percentage of positive evidence, it may seem reassuring, but the danger is that you are looking in the wrong place. "
Ryan thus spoke of a numerical balance : "... it may vary, but we would certainly like to see countries test at the level of 10 negative tests for 1 positive as a general benchmark of a system that is doing enough testing (...) if 80% or 90% of the people you evaluate are positive, you are missing out on many cases ”.
The elements of the Covid-19 swab with which the famous PCR test is performed. / Getty Images / AFP
On several occasions, the national health authorities took as a reference that “10% positivity recommended by the WHO”. So why not test more in the City of Buenos Aires?
Own path
From the Buenos Aires Health portfolio they offered an explanation: “It would be a technical error to think that due to the positivity index, little is being tested. We have clusters in the DetectAr plan. The positivity index increases because you are going to look for people and they are people that you know are close and close contacts of the positives , which causes positivity to rise ”.
“Although the positivity is higher at the beginning, you have to see how the curve ends . For example, Balvanera has a positivity rate of 56%, but we went looking for them and this does not include testing all the residents of the neighborhood, so it is a biased number. You have to be careful with those indices, if you are changing the parameters of the strategy, ”they pointed out.
What the City does is reduce the sample , a concept that Zopatti clarified: “If we had the possibility of testing ourselves, we would do it, but we cannot. So we decided to test only those who go to the health system. It is a particular branch of infected and ends up giving another index of positivity. For example, at Hospital de Clínicas we get our own positivity index. From April 26 to March 1 it gave us that 19% of those who arrived were positive. The figure was high because it was a small or selective population . "
A man has his temperature checked before entering El Cruce hospital, in Florencio Varela, Buenos Aires province, Argentina, on May 14, 2020, amid the new coronavirus pandemic. (Photo by RONALDO SCHEMIDT / AFP)
We will have to see if the Buenos Aires strategy is working. For now, on May 30 Clarín published that CABA had the highest positivity rate in the country, with 39% . And that percentage - in tune with Covid's expansion - is on the rise. Wouldn't it be reasonable to test more?
Taking figures from Our World in Data as of June 3, Argentina had performed less than 7 tests for each positive diagnosis it obtained. Greece, 234. Italy, 135. Uruguay, 103.
From City Health they explained that the decision not to test anymore " does not go through a lack of reagents . Everything indicated in the protocol is tested." And more too. Because the DetectAr device is swabbing close contacts of Covid patients, even when they have not manifested symptoms , a criterion that, it should be clarified, is not currently included in the "suspicious case" protocol of the National Ministry of Health.
For Zopatti, the economic cost cannot be avoided: “It must be borne in mind that the kit for one reagent ranges from 3,500 pesos , not counting labor. It is priceless in Latin America. In other words, each country has to adapt this to its reality ”.
According to the mathematician Guillermo Durán (principal investigator of the Conicet and director of the Institute of Calculation of the Faculty of Exact and Natural Sciences of the UBA), what would make sense at this point is to refine and accelerate the so-called " contact tracing ", that is, searching for close contacts.
"The ideal is to test as much as possible, symptomatic and asymptomatic, but when the positivity index is so high and you lack tests (reactive), it is best to assume 'covid' in all suspected cases and use the test for your close contacts " This is what Durán defined as an “intelligent” use of resources.
What is Coronavirus? How is it spread and what are its symptoms?
Watch the specialIn other words, “ testing more, but not 'tun-tún' . In other words, it is essential to isolate suspects, monitor contacts closely and test them. And follow the chain: before new positive contacts, go to the contacts of the contacts.
According to the expert, “Great Britain reported having 25,000 people doing that task. Here, the Province and Capital do it, but those forces would have to be multiplied. It takes a lot of trained people, on the street and in call centers. It is urgent to speed up contact tracing. If not, you don't stop the spread anymore. ”
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