UCLA. US: In the past decade, the H1N1 virus and Ebola are just two of the
diseases whose spread was spurred by international airline travel.
Screening passengers at airports, therefore, could be one key method for
slowing the global spread of infectious diseases.
And although a team lead by UCLA researchers has found that airport
screening misses at least half of infected travelers, the scientists say
that rate could be improved. Their research was published in eLife, a highly regarded open-access online science journal.
The life scientists used a mathematical model to analyze screening
for six viruses: the SARS coronavirus, the Ebola virus, the Middle East
respiratory syndrome coronavirus, the Marburg virus, Influenza H1N1 and
Influenza H7N9.
“We found that for diseases with a long incubation period, such as
Marburg and Ebola, taking passengers’ temperature to test for fever is
particularly ineffective at the start of an epidemic but does pick up
more cases as the epidemic stabilizes,” said Katelyn Gostic, a lead
author of the study and a UCLA doctoral student in the laboratory of
Professor James Lloyd-Smith. “With diseases such as swine flu, which
take a shorter time to incubate, fever screening is the most effective
method throughout an epidemic.”
Depending on the circumstances, airport workers conduct screenings
before passengers board their flights, when they land at their
destinations, or both. The researchers write that although fever
screening on arrival has been criticized for being ineffective, it can
catch cases that are missed before passengers’ flights depart. Screeners
often use infrared non-contact thermometers to help identify sick
passengers, but previous studies have shown that the devices identify
fevers no more than 70 percent of the time, so the “double-check” of
arriving passengers can help catch people who were missed before their
departures.
Currently, traveler questionnaires are one of the tools screeners use
— asking passengers, for example, whether they have been in contact
with an infected individual (in the case of Ebola) or have handled live
poultry (for viruses like avian influenza). The researchers write that
screeners could more effectively identify sick passengers if those who
create those questionnaires understand the risk factors for each
disease, which would help them to better tailor the surveys.
The researchers found that no more than 25 percent of passengers
answered honestly about whether they had been exposed to influenza
during the 2009 pandemic, and that some may have hidden their symptoms
by taking medication.
“Anyone who reports honestly puts himself or herself at risk of delay
or detainment; this is a terrible incentive for truthful reporting,”
Gostic said. “A high number of people use over-the-counter drugs like
acetaminophen that conceal fevers and can make their symptoms
undetectable, which is likely an overlooked problem.”
Lloyd-Smith, a UCLA associate professor of ecology and evolutionary
biology and senior author of the research, said current screening
programs can reduce the rate of importing infections, but nowhere close
to zero.
“Even under the best-case scenarios we considered, arrival screening
missed at least half of infected travelers for all pathogens,” he said.
“Traveler screening by these methods is inherently leaky.”
The researchers identified ways to make current screening as effective as possible and highlighted how it can be improved.
“An important gap is that we have little direct data on the efficacy
of departure screening,” Lloyd-Smith said. “This is needed to weigh the
benefits of different screening policies and areas for investment. For
example, in the current Ebola outbreak, how many potential travelers
were turned away before boarding airplanes to depart West Africa? Of
these, how many were actually Ebola cases? There is broad agreement that
departure screening is probably more efficient than arrival screening,
but we don’t actually have any examples where we know how well it worked
in practice.”
In the paper, the researchers recommend cost-effectiveness studies
that allow policy makers to assess the social and economic impact of
screening policies at departure and arrival, but note that these studies
will require more extensive data on the efficacy of current screening
practices. They also recommend studies to quantify how many travelers
are using fever-suppressing drugs, and evaluating the possible use of
incentives to encourage honest reporting.
Adam Kucharski from the London School of Tropical Hygiene and
Medicine was the study’s other co-author. The research was supported by
the National Institutes of Health, the National Science Foundation and
the Medical Research Council in the U.K.