An interesting article in Science Advances published by Larremore and others in January 2021 looks at this important subject.

Because SARS-CoV-2 can spread from individuals with presymptomatic, symptomatic, and asymptomatic infections, the reopening of societies and the control of virus spread will be facilitated by robust population screening.  Within this, virus testing is central. 

After infection, individuals undergo a period of incubation during which viral titres are too low to detect.  This is then followed by exponential viral growth, leading to peak viral load and infectiousness and ending with declining titres and clearance.  

Given the pattern of viral load kinetics, this study modelled the effectiveness of repeated population screening considering test sensitivities, frequency, and sample-to-answer reporting time.  

Their results demonstrated that effective screening depended largely on the frequency of testing and speed of reporting and was only marginally improved by high test sensitivity.  

The study therefore concluded that screening should prioritise accessibility, frequency and sample-to-answer time and that analytical limits of detection should be secondary.

They showed that repeated population screening of asymptomatic individuals could be used to limit the spread of SARS-CoV-2 and that the impact of this repeated population screening was expressed as a reduction of the reproductive number R.

The London General Practice, the leading London doctors’ clinic in Harley Street provides a full testing service for SARS-CoV-2 infection.  

It under takes rapid lateral flow tests, fit to fly PCR swabs and all government regulated travel swabs and a fast track service for PCR.

Dr Paul Ettlinger
BM, DRCOG, FRCGP, FRIPH, DOccMed

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