Temperature screening at airports 'ineffective, Hiqa warns

Temperature screening at airports 'ineffective, Hiqa warns
Hiqa determined that temperature screening for Covid-19 at airports is ineffective.

Mass thermal screening at airports to identify Covid-19 is ineffective, the State health services watchdog has found.

The Health Information and Quality Authority (Hiqa) looked at the “best available evidence” on whether non-contact thermal screening could be used to effectively identify cases of the novel coronavirus.

Detection rates were "consistently low" across the studies, the authority said.

It examined 11 primary studies, three rapid reviews and one systematic review relating to Covid-19 and other respiratory virus pandemics.

“Current evidence is insufficient to support the use of mass thermal screening at airports to effectively identify cases and limit the spread of Covid-19,” Hiqa concluded.

All studies were conducted at points of entry, such as airports, so their relevance to other community settings, like schools, is uncertain.

Currently, people must fill in the Covid-19 passenger locator form before they arrive in Ireland and give it to an officer when they enter the State.

The form must include the person's address or the address of where they are staying while in the country as well as a contact number. 

The European Union Aviation Safety Agency has previously stated that it should be recognised that thermal screening has many limitations and there was “little evidence” for its effectiveness in detecting Covid-19 cases.

Hiqa’s deputy chief executive and director of health technology assessment, Dr Máirin Ryan, said thermal screening was used in other respiratory outbreaks, such as the 2009 H1N1 Influenza pandemic in Asia and Australia, to improve detection and reduce the time taken to isolate infected individuals.

She explained that the screening usually involved a combination of fever screening, such as temperature testing, alongside self-reporting of exposure risk or symptoms.

“However, the evidence clearly shows that this type of test is likely to be ineffective in limiting the spread of Covid-19,” she said.

Thermal screening was not going to pick up people who were asymptomatic or pre-symptomatic and it was known that pre-symptomatic cases were responsible for up to 50% of onward transmission of the virus.

About 25% of symptomatic cases never develop a fever and the duration of infectivity is still uncertain.

“The fever tends to wax and wane. And we know that even after a fever an individual will remain infectious for a number of days," said Dr Ryan.

Thermal screening is noted to be high cost and resource-intensive. Detection rates are very low due to a large proportion of cases that have no symptoms, are infectious before showing any symptoms or who do not present with fever. 

The technology only picks up a small number of cases and sometimes returns false negatives so it can give a false sense of safety.

Two modelling studies estimated that about half of infected cases would be identified using airport fever screening.

While advances in technology may help overcome some of the problems associated with thermal screening, detecting infected people who do not present with fever remains an issue.

An updated evidence summary on the immune response to Covid-19 by the authority states that it is still unclear whether long-term immunity to the SARS-CoV-2, the virus that causes Covid-19, is possible.

The “adequacy or long-term duration” of the immune response is not yet known, it concludes.

“The vast majority of patients do mount an immune response. So they do demonstrate antibodies that are targeted to be protective against SARS-CoV-2 and those antibodies do seem to persist up to at least three months. But we are not certain about the long term immunity to SARS-CoV-2.” 

Over 90% of patients developed a neutralising antibody response that protected them against the virus but a "handful" of new studies suggested that it might be possible to be reinfected.

Hiqa’s evidence summary notes that many studies have reported the re-detection of the virus following recovery.

“While most patients were asymptomatic on re-detection, cases of new symptom onset and serology suggestive of reinfection have been reported, suggesting reinfection may be possible,” it concluded.

No study was found to show whether individuals re-detected with the virus or other human coronaviruses were infectious to others.

The evidence summaries were developed by Hiqa following requests from the National Public Health Emergency Team’s clinical expert advisory group.

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