Pre-departure airport testing could lead to more than 100 million travelers being falsely identified as having Covid, according to an IATA expert.
Speaking at CAPA Live event, Thomas Pellegrin, Senior Principal, IATA consulting, said, “False positives and false negatives carry serious implications for air travel. When a false positive happens, we incorrectly inform a healthy traveller they may be infected which is stressful at best, but will also require a re-test to confirm diagnosis at additional cost and time. It also means they may have to delay and cancel plans.
“When a false negative happens, this incorrectly lets an infected passenger through and risk infection importation at the destination and undermine the trust of the governments.”
A quirk of maths means that for a disease with low prevalence, such as Covid-19, the rate of false positives can be unexpectedly high.
Pellegrin outlined a scenario in which 100 travellers were tested on departure. He used values for sensitivity (the true positive rate) and specificity (the true negative rate) similar to those achieved in the field using the most commonly used PCR tests – 70 per cent and 95 per cent respectively – and a virus prevalence of 4 per cent in a random population.
Pellegrin said, “The likelihood that a traveller who tested negative is actually uninfected is high – 99 per cent. That is really good. But surprisingly and counterintuitively, the likelihood that a traveller who tested positive is actually infected is low, only 37 per cent. If we tested half of last year’s travellers – 2.2 billion – that would return 106 million false positives in one year, the equivalent of the number of passengers handled by the world’s busiest airport, Atlanta.”
The roll-out of widespread testing has a number of technical and operational challenges on top of this.
He said, “The challenge of screening non-symptomatic travellers is that they do not present symptoms and governments are hesitant to lift travel quarantines. Testing restores that trust and enables full border reopening but states need to agree on one or more standards and that depends on several technical and operational challenges.”
Pellegrin said that because the crisis had cost the aviation sector billions already, it must not add another economic burden to airlines and airports. Any testing regime should also not divert qualified medical personnel needed by public health authorities. There are also logistical challenges in getting equipment and supplies in sufficient quantities to the points at which they are required.
He added, “Eventually vaccines will replace the need for testing, but the long lead times and uncertainties linked to vaccine research, development, trials, approvals, manufacturing, shipping and inoculating at scale are such that testing is expected to remain necessary for the foreseeable future.”
