Misc 13/11/2020

Doubts about the real decrease in infections in Madrid

The decline has coincided with the replacement of PCRs with faster but less sensitive antigen tests

Ot Serra
3 min
Dos veïns del barri madrileny de de Vallecas aquest dissabte passejant pel carrer

MadridA few weeks ago, Madrid was the epicentre of coronavirus infections in Europe, with a cumulative incidence of up to 700 cases per 100,000 inhabitants in 14 days (CI) and an increasing hospital pressure, but the figures have been falling since the end of September. Yesterday the Ministry of Health recorded an CI of 328.9. This is a drastic decrease compared to the figures registered a month and a half ago. As for mortality rates, which are reported with more delays and give specific information about older people, not enough decrease is noticed in order to determine a trend. But is the apparent improvement in infection transmission numbers and hospital pressure real, considering that the measures to restrict mobility that have been implemented in Madrid have been less forceful than everywhere else in the State?

Less restrictive measures

In the Spanish capital the curfew starts at midnight, and bars and restaurants only have capacity limitations, but they have not been ordered to close as it has happened in Catalonia. The Community of Madrid maintains that its strategy of confining certain health areas has worked because it has allowed the virus to be "cornered". They began by closing areas that reported more than 1,000 cases, then 750, then 500, and every Friday the Community raises or applies perimeter confinements of the areas depending on the evolution of the situation. Another key measure of the supposed success, according to sources at the Madrid Regional Ministry of Health, is the use of antigen tests in primary care and emergency medicine, which have gradually replaced PCR tests. The main advantage of this diagnostic method is that, in addition to being cheaper, it gives results in 15 minutes; therefore, it allows transmission to be cut off quickly by locating the close contacts of the person who has tested positive.

"Madrid is doing well. It has implemented a strategy of massive testing and it is giving results, without having to close down the economy", said yesterday the infectious disease expert Oriol Mitjà in declarations to Planta baixa. This is, however, an opinion that is not shared by all the experts consulted by ARA, some of whom point towards the opposite direction. "The tests are being applied as a screening to people who are not even close contacts", said epidemiologist and doctor in public health Pilar Serrano to ARA. The secretary of the Madrid Association of Epidemiologists reminds us that the sensitivity of antigen tests is lower than that of PCR tests - 75% in asymptomatic people -, which means that testing people who are not suspected of being infected is not effective because it can lead to false negatives that would not occur if they were given PCR tests. "By changing the test you may stop detecting cases. Patients with a lower viral load may not be detected by the antigen test," agrees epidemiologist Joan Caylà, a member of the Spanish Society of Epidemiologists.

Madrid bought five million antigen testing units in September and allocated a portion of them to the aforementioned massive neighborhood tests. The Community summoned chosen citizens by SMS, who could then voluntarily take the test. Sources from the regional government say that more than a thousand positive people have been detected without symptoms, who, if this initiative had not been carried out, would have not been detected. Antigen testing is also a simpler technique, unlike PCRs, which requires more infrastructures and are not feasible for mass screening, says CSIC systems biology expert Saúl Ares. "Half a loaf is better than none," he says, and admits that, although false negatives can result from this practice, they are not very contagious at the time. After a few weeks their viral load may increase and they become more contagious, but the same thing can happen with PCR tests, he points out.

It is necessary to analyze the figures from Madrid with caution, which is what sources close to the Minister of Health, Salvador Illa, expressed yesterday in Congress. "Madrid is stabilizing but the situation is still fragile and unstable," they said. "We should verify the data, ensure that the evolution is positive, which could be, and determine what has been relevant for the improvement", said Caylà, who also recalled that Madrid has been one of the communities that have had more delays in case notifications.

Figures are still high

In recent days, the technical director of Health, Fernando Simón, said that the measures implemented in the Spanish capital were bearing fruit, but warned that the situation is still worrying. In this sense, the researcher of the research group BIOCOM-SC of the Universitat Politècnica de Catalunya, Daniel López, assures that a tolerable CI would be around 100 cases per 100,000 inhabitants, and that the important issue is to reduce the speed of propagation. Therefore, he emphasizes that the most effective measure is to reduce mobility and to make the population aware of it. Madrid survives with few restrictions, an improvement in hospitals, and an apparent decrease in contagion that generates suspicion.