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20th July 2021
The use of mitigation strategies for COVID-19 such as social distancing and the wearing of face-masks have helped to minimise the spread of the virus. In addition, the use of an effective Test-Trace-Isolate (TTI) strategy, involving the testing of symptomatic cases and tracing their contacts, is crucial for the detection of the virus. The current gold standard test is the polymerase chain reaction (PCR) although this testing modality can only be undertaken within a hospital laboratory and is therefore expensive for population-wide testing. While the testing process itself takes several hours, there are additional time constraints and which slow the overall process, e.g., transporting of samples to the laboratory testing site, presence of a sufficient number of trained staff and high sample volumes. An alternative is the use of lateral flow tests and these have been recognised as being able to increase testing capacity.
Lateral flow tests are are much cheaper than PCR tests and can be produced in large quantities and deliver results on site and within 15 to 30 minutes. Whereas PCR tests involve amplification of the nucleic acid sample, lateral flow tests rely on the detection of a viral antigen in the patient’s sample and are therefore deemed to be of lower sensitivity. However, there have been no comparative studies of outcomes associated with the use of PCR and antigen testing in the same patient cohort and this led a team from the Centre for Primary Care, Wolfson Institute of Population Health, Queen Mary University, London, to assess the diagnostic accuracy of both methods in the same patients. The study was undertaken among a network of general practitioners in Austria and included patients who self-reported mild to moderate flu-like illness (e.g., cough, fever, runny nose etc). Such individuals received a same-day appointment and given an antigen test and also given a PCR test.
Based on lateral flow tests for 2562 patients, 1027 who tested positive, were also given a PCR test and of whom, 826 (79.7%) tested positive. From this cohort of 826, 788 had also tested positive on the antigen test. The authors then calculated that overall sensitivity of the lateral flow tests to be 95.4%, with a specificity of 89.1%. In addition, positive lateral flow and PCR tests were correlated (r = 0.968).
The authors discussed how these findings indicated that using antigen tests for patients with mild to moderate symptoms, allows for a reliable and accurate detection of COVID-19 and which is comparable to PCR. They concluded that implementation of lateral flow tests should be accompanied by standardised training for operators, quality assurance of testing and a coordinated approach to services.
Leber W et al. Comparing the diagnostic accuracy of point-of-care lateral flow antigen testing for SARS-CoV-2 with RT-PCR in primary care (REAP-2). EClinicalMedicine 2021
2nd November 2020
Current COVID-19 diagnostics rely on a PCR test, which can only be undertaken via laboratory analysis and, in some cases, the result is not available for a few days. Now researchers from the UK and Germany have reported their preliminary findings on the use of a device that analyses a breath sample to identify infected patients within 10 minutes. The study makes use of exhaled volatile organic compounds (VOCs) in breath which are subjected to gas chromatography and either mass spectrometry (GC-MS) or ion mobility spectrometry. The researchers based their study on the fact that there are distinct breath biochemistry derangements in respiratory illness and that this could be utilised for the detection of those infected with COVID-19 compared to other viral illnesses. The study recruited participants who presented with respiratory symptoms consistent with COVID-19 and this was confirmed with a PCR test. Participants then exhaled through a disposable tube and a sample of breath withdrawn and placed in the GC-MS.
A total of 98 patients were recruited of whom 79% had confirmed COVID-19. Differentiation of COVID-19 from other conditions was possible in 81.5% of patients. Exhaled breath compounds were attributed to a combination ketosis, impaired gastrointestinal function and inflammatory responses. A distinct panel of compounds including ethanal, octanal, acetone, butanone, methanol, heptanal and one unidentified compound, provided the basis to rule in COVID-19.
The authors reported that the instrument can be easily used in emergency departments for a quick assessment of whether a patient has COVID-19 and that the sampling technique does not pose a risk for clinicians performing the task. They called for further and larger studies to validate these preliminary findings.
Ruszkiewicz DM et al. Diagnosis of COVID-19 by analysis of breath with gas chromatography-ion mobility spectrometry – a feasibility study. EClinical Medicine 2020; https://doi.org/10.1016/j.eclinm.2020.100609