October 21, 2020

Experts agree that doing PCR at airports is useless

This July, tourists have already begun to arrive in Spain, from countries in the Schengen Area and also from other continents, to which the European Commission has given the green light. Travelers – foreigners and Spaniards – who set foot in our country’s airports this summer will pass three controls to screen imported cases of COVID-19: a documentary one, with a digital questionnaire about their state of health and habits; a visual one, in case they had noticeable symptoms; and one of temperature, which considers a person above 37.5 degrees suspicious. Neither in Barajas, nor in El Prat, nor in any airport will there be diagnostic tests, or PCR or rapid tests. “There is no capacity,” said Fernando Carreras, deputy director of Foreign Health, the body that oversees the entire operation. And neither do experts or agencies advise it.

The European Center for Disease Prevention and Control (ECDC), It does not even contemplate in its guide for safe flights to carry out tests at destination airports: His recommendation is that the local national, regional and local health authorities ensure that, once the person is there, they are accessible to him, but not at the same border control. There are many reasons. The first is given by José Martínez Olmos, Alberto Infante and Daniel López-Acuña, public health specialists: “There is no justification, nor material and logistical capacity, to carry out PCR tests on the hundreds of thousands of people who enter the country through international airports.” Neither in Spain, nor in any country, do many others agree.

The second is that the PCR only gives a “still” image of the moment, continues Pedro Gullón, from the Spanish Society of Epidemiology (SEE). “The PCRs offer us an exclusive image of the moment”, and nobody can assure that a negative today is not a positive tomorrow and that can be “problematic” for the monitoring of tourists and for their own self-control. From the Spanish Society of Preventive Medicine, Public Health and Hygiene (SEMPSPH), they point it out the same: “30 seconds after a negative in PCR you have been able to catch it.” They provide a third reason: Although PCR is one of the most reliable tests, “its profitability in asymptomatic patients is unknown. The false negative rate is too high to trust everything to it.”

Professor Philip Nolan, rector of the National University of Ireland, made a calculation the other day to demonstrate all this: taking into account the sensitivity and specificity of these tests – even though they were high, 85% and 98% -, at an airport at If 50,000 travelers arrived and 50 of them had COVID-19, 30 would be detected, 20 would be lost, and 1,000 false positives would be generated.

A second option, which the Popular Party has requested of Pedro Sánchez, is the PCR at origin, that is, that the person who is going to fly must be tested beforehand. The ECDC does open up more to that, although with many doubts. Among them, the dangerous window period of up to 72 hours that can occur between having the result and traveling, again due to false positives and negatives, and due to the legal problems it could entail. In the SEMPSPH they believe that “in any case”, that could be the policy to be implemented, but they also do not see it clearly for the same reasons as the destination PCR: “In the presymptomatic period many false negatives are taking place. It does not solve anything.” Furthermore, it would require even more intense international coordination. Gullón shares the arguments: “More or less the same thing happens. You can do it 48 or 72 hours before traveling and test negative, but perhaps be an active infection at the time of flight.”

Some experts suggest that both source and destination PCRs are selective. “It would have been desirable not to ignore the epidemiological differences. If this had been the case, it should have meant that those countries that are above the threshold set for third countries, which is the European average of the cumulative incidence in the last 14 days, in At this time, Portugal, the United Kingdom and Sweden should submit their travelers to perform a randomized PCR, at the point of embarkation and at the point of arrival, in order to increase the probability of detecting asymptomatic patients “, synthesize Martínez Olmos , Infante and López Acuña. Gullón also talks about this: the possibility of “false positives” increases as the prevalence of origin decreases, that is, a PCR is more reliable the greater the possibility of carrying the disease, for example, if you have symptoms or come from those countries. At the moment this is not being negotiated in Europe.

Rapid tests and serological passports, discarded

An apparent third way would be rapid tests, which detect the presence of antibodies to the disease in the body in about 15 minutes. The specialists unanimously discard them: the logistics and capacity are equally complicated and, above all, they only serve for screening. They give too many wrong results, even if they differentiate between IgG (long-term antibodies) and IgM (antibodies that are generated with the infection still active). “If it is positive, you don’t know for sure if it is a current or past infection, what do you do with the traveler?”, They ask at SEMPSPH.

The idea is related to another one that was heard a lot at the beginning of the pandemic: the serological passport, a document that reflects the level of antibodies and allows travel. Almost everyone also rejects it already. “The percentage of the population with antibodies is too low. More than 90% of the population in many countries would not be able to travel, it would be a restriction on freedom of movement based on health, it would not solve anything. And also, knowing that the Antibodies only last for a short period of time. ” The ECDC guide also does not endorse immunity passports, so little is known about it.

Negative PCR cannot be understood that way either, like a passport that exempts you from being a danger: “You can get it immediately afterwards. When you go with a vaccination card to a country that requires it, you are certifying that you cannot transmit the disease. The PCR doesn’t tell you that, “they explain at SEMPSPH.

“There is no good solution”

Mar Faraco, a Foreign Health doctor who is working these days in airports as some 650 colleagues, maintains that these procedures are not viable. “You have to think that thousands and thousands of travelers are entering a day. The infrastructure and the cost is impossible. It cannot be implemented by any country, Hong Kong has tried it and the assemblies were incredible at an unthinkable cost.” At airports, what Foreign Health detects are “suspects”, which are derived from tests managed by the autonomous communities. The spokesman for the Ministry of Health, Fernando Simón, also recognized it: it would be “crazy” to think that all imported cases that can arrive in Barajas or El Prat can be detained. What is attempted is to minimize risks.

“The problem is that there is no good solution”, they settle in the SEMPSPH, “the EU’s has been good within the possibilities, cheap, simple and in accordance with current legislation. The health questionnaire will be useful, although it may not seem so : there you know the onset of symptoms and who may be exposed. If it works well, it will help the tracking a lot. “


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