9,900 Catalans to be tested over two weeks: the low-down on the survey that will reveal the spread of COVID-19 among the population

On Monday the Catalan authorities began to contact the subjects selected for testing, but none have been tested yet

After a two-week delay, the seroprevalence survey that aims to provide a picture of the spread of COVID-19 among Spain’s general population by testing up to 36,000 households across the country has finally kicked off this week. However, it has been an uneven start. In Catalonia up to 9,900 people living in 3,409 households have been contacted by phone, but no immunity tests have been administered yet. Although Spain’s Health Ministry had initially announced that they would be conducting the survey on their own, eventually they decided to divide up the task among the various regional administrations, some of which are running into logistics issues due to the organisational demands posed by testing on such a massive scale. Catalonia’s Health Minister, Alba Vergés, explained on Monday that they had begun giving out appointments by phone in up to 146 primary care centres.

What will the tests be like? When will the results be known? Why do the Spanish authorities believe that the survey is so important? What follows is the low-down on the first batch of massive testing ever done on the general population, regardless of whether they were ill or not.

When will we know the results?

The plan is for the survey to be carried in three phases. That is, the same subjects will be tested three times over a six-week period, with a two-week break in between tests. The macro survey will be coordinated by Raquel Yotti, the director of Instituto de Salud Carlos III, in partnership with Spain’s Instituto Nacional de Estadística (INE) —the government body tasked with selecting which households are to be tested. On Monday Ms Yotti stated that they expect the tests’ preliminary results to keep coming in and that they should provide a diagnostic within just one week, once the first half of the testing has been completed. The first full picture will emerge in two weeks’ time, but the whole survey will not be concluded until the end of the first week in June. This calendar is different from the initial timeline provided, which didn’t anticipate getting any results until the very end, after an eight-week period.

Why are these tests important?

The Spanish government places a great deal of importance on these tests and they claim that Spain is the first European country to launch an effort of this magnitude. They also keep mentioning that, according to the OECD, Spain is one of the countries that have administered the most CRP tests. Nevertheless, at a press conference on Tuesday PM Pedro Sánchez is expected to roll out his plan to ease the lockdown without having any data from the survey.

During an online Q&A with media in Madrid’s La Moncloa palace, Ms Yotti remarked that it is important “to ascertain the magnitude of the epidemic on different levels: national, regional and local”. “The data we obtain will allow us to make better-informed decisions”, she added, and she went on to say that it is equally vital to find out the extent of the spread by age group and demographic cohort.

What will the tests be like?

The idea is to test each subject a total of three times. Ms Yotti asked the general public to cooperate, even though testing is voluntary and people may opt out. So far they have been phoning up the households selected by the INE. Every individual will need to fill in a form and will receive an appointment for a test at home and another at a medical centre, to avoid any risk of infection. The initial antibody test will involve taking a small sample of blood from a prick on the finger, as if testing for glucose level, and the results will be available in ten minutes. The second blood test will be done at a health centre in order to analyse the results more in depth. It should be pointed out that the antibody tests that the Spanish authorities are distributing aren’t always reliable. Some subjects who test negative go on to test positive on a CRP test. These tests reveal whether an individual has been infected with the coronavirus at some point.

How many tests have been administered in Spain so far?

This survey is not a form of mass-testing the population, as the total sample of potential participants is only 90,000 (about three people per household, which on average includes 2.5 members in Spain). The initial tests will check for antibodies and so far the Spanish authorities have distributed 2.8 million such kits. Furthermore, in a statement released on Monday the Spanish Health Ministry announced that they have administered 310,038 antibody tests and over one million CRPs (1,035,522 to be precise) so far. The ministry claims that the OECD published a report on Monday stating that Spain is the eight member state to have carried out the most tests: 28.6 for every 1,000 people.

Is the information valid for Catalonia?

Last week Catalonia’s Health Minister pointed out that the survey was insufficient for Catalonia because it was organised by province rather than health care region. The latter would have painted a clearer picture with a view to easing the lockdown restrictions. Still, she added that they would carry it out in such a way that it might be supplemented with data provided by the Catalan administration. However, on Monday she only mentioned that the phone calls had begun and gave no further details.

What are the other immunity tests saying so far?

They suggest the exact opposite of what was initially thought: not many people have become infected but remain asymptomatic. “The preliminary results of some surveys suggests that only a relatively small percentage of the population, even in the worst hit areas, might have become infected. No more than 2 or 3 per cent”. That is what WHO’s secretary general Tedros Adhanom said last week when he spoke about the scientific studies that aim to detect coronavirus antibodies in healthy individuals in order to estimate how many people might have caught the disease without developing any symptoms.

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