With the UK government stockpiling tests and Operation Moonshot gearing up for mass testing there is an acceptance that testing for Covid-19 is an important part in the effort to control the current pandemic. The lateral flow tests that are being proposed are a move away from the accepted “gold standard” PCR test for detecting viruses but are they the best answer?
Lateral flow tests are certainly much cheaper than PCR meaning that they are an affordable option for mass and repeated screening. In addition, the relative ease of use means that can be easily rolled out to large populations- in Slovakia half the population (3.6m people) were tested in October.
The limitation comes in the accuracy of the tests. Oxford University and the government’s Porton Down facility found that the sensitivity of the lateral flow tests was 76.8% at high viral loads (Ct values of 25) and fell to 56% when tested in a community setting. This means that even in the best setting 1 in 4 carriers of the virus would be missed. In Slovakia, even with this level of inaccuracy, mass testing has been shown to reduce the spread of the virus reducing the number of new cases from 3,363/day to 2,579 cases/day. However, this is not the same as asymptomatic screening for N. Sea workers where viral loads are likely to be low and the hope is that testing prior to mobilisation will prevent infections developing over the next 2 -3 weeks period. Based on current testing figures 80,000 individuals have been tested for Covid-19 prior to mobilisation approx. 700 have tested positive and been excluded from the workplace. As a result, there have been only 7 cases detected offshore. This is with PCR testing in which the sensitivity of the testing process is in excess of 90%. In contrast, if the lateral flow test was used it is likely that 175 – 322 cases would have been missed -even of only 20% of these individuals developed symptoms 35-64 CMED evacuations would have been required and each would have had the potential to lead to widespread infection offshore.
Amongst US university students repeat testing with lateral flow tests every 2 days appears to be effective in reducing spread on the campus whilst accepting that students will be students, similarly the proposed testing in Liverpool will not eradicate the disease from the city it will however effect a reduction in spread.
The whole debate about testing has been hampered by a blinkered approach to the problem and one solution does not fit all. Repeat tests with lateral flow kits maybe the answer to reducing infection in Slovakia, they might limit the effects on American university campus life and may even be the answer in Liverpool but they are not the best test to prevent infection getting to North Sea oil facilities. The answer to the question posed is pick the right test at the right time and you will get the right result of any particular situation.Leave a reply