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HEALTH-VIRUS-SCREENING
Coronavirus screening ‘missing more than half of cases’: study
PARIS, Feb 26, 2020 (bss/AFP) – Global screening efforts to prevent the
rapid spread of coronavirus are likely to fail, according to new research
warning that even best-case screenings of air travellers will miss more than
half of infected people.
The novel coronavirus has infected more than 80,000 people worldwide
since its emergence in central China last month.
Traveller screening using temperature monitors and questionnaires is a
key response measure, yet the World Health Organization (WHO) on Wednesday
said for the first time the number of new cases outside mainland China
exceeded those within it.
Researchers in the United States and Britain in a study published in the
journal eLife used computer models to predict the impact of screening, based
on the latest data of how the coronavirus behaves and how long it takes for
patients to show symptoms.
Building on similar work in 2015, they found that many cases would
inevitably be missed and called for a re-think in how nations screen
passengers.
“If someone doesn’t realise they have been exposed, and doesn’t yet show
symptoms, then they are fundamentally undetectable,” Katelyn Gostic, a
postdoctoral scholar at the University of Chicago and lead author told AFP.
“We estimate that on average, screening will miss about two thirds of
infected travellers.”
Gostic stressed that these misses were not the result of human error,
but rather an inevitable by-product of how the virus behaves.
The WHO says that the typical incubation period — that is the time
between a patient contracting the virus and symptoms showing — is around 10-
14 days.
This means that patients could be contagious without even knowing it,
rendering temperature tests searching for a tell-tale fever and even self-
reporting of exposure largely useless.
Upon screening, travellers fall into one of four categories: symptomatic
but unaware of exposure; aware but asymptomatic; symptomatic and aware; and
neither symptomatic nor aware.
Gostic and the team found that the final category were completely
undetectable by traditional screening methods, and travellers in the third
category could only be caught if they were willing to self report.
– ‘Tipping point’ –
Even assuming a best-case scenario where only one in 20 passengers were
“subclinical” — that is, infected but not showing symptoms — the models
predicted that 53 percent of cases would be missed.
“Substantial fractions of the people who have tested positive in
quarantine… did not show any detectable symptoms at the time of diagnosis,”
said Gostic.
“Some of these people may be true subclinical cases. Others will
probably develop symptoms in a few days time. Either way, these stories
illustrate the difficulty of screening, where the goal is to detect cases as
early as possible, but where people simply don’t show detectable symptoms
early in the course of infection.”
Gostic warned that the world may be at a “tipping point” where screening
and even the kind of quarantine measures seen in the outbreak’s epicentre
Wuhan are no longer effective.
“Governments should be thinking about pandemic mitigation,” she said.
“But we should recognise the hard work and immense value that on-the-
ground containment efforts have brought up until this point-providing time
for healthcare workers and policy makers to prepare.”
BSS/AFP/BZC/1930HRS