COVID-19: THE VALUE OF TESTING

When we're talking testing, we have to consider what we would gain by testing.  Testing isn’t a cure in itself, whatever the impression often given.  So what is testing worth?

Before that, we need to look at the various types of tests, described in more detail here.


SUMMARY OF TESTING OPTIONS

In looking at the different types of tests, and their pros and cons, we discovered there are two main classes of individual tests that can be used for people outside of hospitals:

• “Got it” tests, typically looking for the RNA of the SARS-COV-2 virus that causes COVID-19
• “Had it” tests, typically looking for IgG antibodies or other immune responses, typically at least 14 days after infection

There are also community tests, notably monitoring sewerage for viral RNA as an early warning of a local surge in infections.


‘GOT IT TESTS

Most of the ‘Got It’ tests rely on taking a sample using a swab at the back of the throat and up the nose.  These are both unpleasant and unreliable processes, resulting in a ‘false negative’ result of 30% when done professionally, higher for self-swabbing as is common.  If a negative result occurs, either infectious people are released into the community, or testing has to be repeated.  The main method has been RT-PCR, where tests take a minimum of 3 hours, but more typically over 6, with a turnaround time often of more than a day. 

Quicker, cheaper tests are being developed around the world using RT-LAMP technology, such as the testing just announced for UK hospitals and care homes.  Another initiative here in the UK is targeting a lower cost per test of £20.  Which just shows how expensive the current tests must be, especially if they have to be repeated for potentially false negatives.

Whilst there is always a clamour for “more testing”, requiring more equipment, more premises (fixed or mobile) and more trained staff, there is also a difficulty in sourcing enough reagents to increase testing.  Capacity can’t simply be turned on like a tap, even if the cost was acceptable.

The other main problem is that people are infectious before they exhibit symptoms, and symptomatic for some days before they have chance to have a test and get the results back. People can be infectious for several days before they know it, and several more days before the illness is confirmed.  That's hardly ideal!

To tackle this problem needs ‘Got It’ testing every day, ideally, with immediate results.  Even once every 5 days until (or if) someone tests positive would initially require some 11 million tests a day.  Clearly impractical and horrendously expensive using current testing technology.


We therefore need alternative ‘Got it’ tests that are:

• Simpler
• Quicker
• Cheaper
• Preferably more reliable, by not being based on swabbing
• Yet clearly identify all variants of SARS-COV-2 without counting other coronaviruses

Update 12/9/20: This is the basis of "Operation Moonshot", to avoid the staggering costs that could be incurred


RT-LAMP tests are improving most of these aspects but mankind has a very long way to go to make a national testing strategy for everyone practical and affordable, be they symptomatic or not. .


Sniffer dogs are now being trained in the hope of identifying infectious people arriving (or taking off) at airports and other ports of entry.



The Worth of Got it tests

There are several reasons for Got It tests to take place:

• In hospitals (which were the early priority), care homes and other institutions:
• For patients in hospital, as part of the initial diagnosis
• For frontline staff, both with and without symptoms, to identify an outbreak amongst staff early, and conversely allow those without symptoms to go back to work
• At ports of entry:
• To at least reduce the number of new cases arriving in the country from abroad
• In the community:
• To confirm whether someone symptomatic actually has COVID-19, and whether they, their family and contacts need to self-isolate
• Ideally catch people with COVID-19 before they display symptoms, which would make a massive difference to reducing transmission

'HAD IT' TESTS

‘Had It’ tests are typically searching for the IgG antibodies, which are specific to SARS-COV-2, and can be detectable in the body weeks after infection.

These tests can help to confirm if someone suffering from the various symptoms of LongCOVID, caused by COVID-19.  That helps to identify best treatments.

If immunity is confirmed for at least say 6 months, people who have had a positive ‘Got It’ or ‘Had it’ test will have immunity.  That would let them live more freely, and especially work more freely.

However, the latter point would likely result in people needing to catch COVID-19 to protect their livelihoods, which is not what society would want.  Hospitals could quickly become overrun.

In that context, antibody tests could be dangerous!


COMMUNITY TESTING

Testing sewerage could potentially give an indication of the level of infection in a small area, depending on where samples can be taken.

This has started on a trial basis at 44 sites in England, as well as in other countries.


TEST, TRACE AND ISOLATE

The main value of “Got it” testing is for Test, Trace and Isolate.  That deserves its own blogpost, here.