Testing times in Covid-19 response

The message from the World Health Organisation’s director general could not have been more unequivocal when he declared Covid-19 ‘the defining global health crisis of our time’.

During a briefing given on March 16, 2020 Dr Tedros Adhanom Ghebreyesus said, “We cannot stop this pandemic if we don’t know who is infected. We have a simple message for all countries: test, test, test.”

Public Health England has developed what it describes as a highly sensitive test to detect the virus, with results retuned in 24 hours. The need for more tests that produce quicker results is, however, a matter of global urgency to halt the inexorable spread of Covid-19.

The government knows this and on March 6, Bedfordshire-based Mologic said it had been awarded around £1m from a £46m fund made available to finance efforts aimed at controlling Covid-19.

On announcing the award, Mologic’s medical director, Dr Joe Fitchett, said rapid detection of the virus is important to stop its spread and to this end the company will develop a point-of-need diagnostic test device.

Dan Haworth, head of diagnostics and partner at Cambridge Design Partnership, told The Engineer that diagnostic device developers typically design systems that consist of a consumable part, and a reusable reader that controls the test process, provides the user interface, stores the results and connects to hospital/lab networks to provide real time epidemiological monitoring.

“The consumable needs to carry out complex processing of the sample and reagents. For example, sample introduction, sample preparation, nucleic acid amplification and detection,” he said. “The amplification process generates billions of copies of ‘amplicon’ [amplified DNA strands] so the whole process must be sealed, otherwise leakage could cause false positives for a prolonged period of time.”

Dominic Lloyd-Lucas, head of engineering technology at 42 Technology, a product development and engineering consultancy based in St. Ives, Cambridgeshire, explained that the Covid-19 virus comprises a protein and the genome sequence is known from data released by Chinese scientists.

“The key in developing a rapid, handheld diagnostic device is being able to detect small quantities in samples of saliva or sweat as the assay needs to be both sensitive and specific to this target,” he said. “PCR [polymerase chain reaction] is slow as the amplification stage takes time, and although direct detection offers a potential shortcut there will be issues in getting a representative sample into the device: biosamples can be hugely variable and with small samples the risk of contamination or another artefact may be higher.”

Indeed, sample preparation is a complex process that includes breaking open the virus to extract the RNA (Ribonucleic acid), washing away inhibitors, concentrating the RNA and mixing it with freeze dried reagents to initiate amplification. According to Haworth, key technical challenges involve implementing these complex functions in an easy-to-use device.

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“The reader system needs to provide valving, timing and actuation of fluids and reagents to control the test process – but making this reliable and low cost is a challenge,” he said. Also, special attention needs to be given to ensure the device architecture is suitable for high volume manufacture, such as multi-cavity injection moulding and test performance is robust to manufacturing and assembly tolerances, he added.

“There are a lot of technical risks and challenges to consider when designing these systems,” he said.

Diagnostic device developers and drug makers are being aided by regulatory bodies such as the US Food and Drug Administration (FDA), which is fast-tacking device deployment under ‘emergency use’ conditions, a scenario applicable to Roche which has been authorised ‘emergency use’ to run a Covid-19 test on Cobas 6800 and 8800 lab analysers.

“In a pandemic situation, the regulators will be under intense pressure to permit fast development,” said Lloyd-Lucas. “But this has to be balanced against the possible negative outcomes if the assay fails to detect infection and gives the all-clear wrongly, meaning that an infected person goes back into the community and unwittingly infects others.

“Conversely, if the assay is too easily triggered, for example, by a sample artefact, then healthcare providers could be overwhelmed with disproportionate numbers of those who do not need treatment. Sufficient evidence of specificity and sensitivity needs to be demonstrated and the relevant clinical scientist teams will have to make a judgement of this, and to persuade the regulators accordingly.”