Testing People For COVID-19

The ongoing COVID-19 pandemic highlights the importance of a quick and reliable way of detecting this infection to reduce its spread. There are multiple testing methods available. They differ in their time and material requirements and their ability to correctly identify those with the virus and those without it (i.e., their sensitivity and specificity). Some tests are designed to detect the virus directly, others – in particular antibody tests – do not detect the virus itself but rather the established response to COVID-19 infection¹. Moreover, with modern technology, there are also some unconventional ways to detect this disease.

Direct detection

Direct testing detects either the viral nucleic acid or other parts of the virus, most often from a nasopharyngeal swab, although the virus can be found also in other sources. The recommended test for diagnosis of SARS-CoV-2 infection is the detection of viral RNA by nucleic acid amplification, mainly by PCR². It is a very sensitive method; however, it can also detect trace amounts of the virus in the final, non-infectious stage of the disease. Moreover, it requires special temperature conditions, is time demanding and expensive, and thus not suitable for mass screening.

On the other hand, antigen tests that detect viral particles are rapid and cheap. They are also easy to use and interpret – many are similar to common home pregnancy tests. These attributes predestine them for use in mass testing. However, they are only able to detect a substantial viral load – those that are likely the most infectious – and are less specific than PCR tests.

Nevertheless, it seems that the authorities are preparing to use antigen testing in large. One country – Slovakia – has already attempted to test its whole population for SARS-CoV-2³. They were able to test more than 3.6 million people (two-thirds of the population) in just two days, of whom about 1.06% were found to be positive⁴. With tens of thousands of people in quarantine, they hope to curb the spread of the virus and relieve the burden on hospitals.

Indirect testing

The presence of SARS-CoV-2 can be uncovered also by monitoring the immune response of the organism to the virus. Rapid serological tests have been developed for the detection of SARS-CoV-2 antibodies (IgG and IgM), which require only finger-prick testing and can be evaluated at home. However, antibody tests detect the immune response to the virus, which varies greatly, and are not effective at the earliest phase of infection. Thus, their utility for public health management is questionable⁵. 

COVID-19 and scent detection dogs

There are also some unorthodox approaches trying to curb the spread of the virus. Volatile organic compounds produced during respiratory infections can cause specific scent imprints that can be detected by trained dogs. A pilot study training dogs for COVID-19 detection showed that just with a week-long training, dogs were able to distinguish between COVID-19-positive and negative people really well, with an average sensitivity of 82.63% and specificity of 96.35%⁶. While the numbers look promising, it is far from ready for testing in the field.

AI diagnostics

A modern time pandemic calls for innovative approaches. One such example is the MIT Open Voice model⁷. Its AI speech processing framework leverages acoustic biomarker feature extractors to pre-screen for COVID-19 from cough recordings. When compared with official tests, the model achieves a sensitivity of 98.5% and specificity of 94%, and it is even more impressive for asymptomatic subjects, where the sensitivity reaches 100% with a specificity of 94.2%. This method has the potential of a free, non-invasive, readily available, and scalable COVID-19 screening tool, particularly for the asymptomatic people, to support the ongoing approaches to contain the spread of COVID-19.

There are many different approaches to COVID-19 testing, each with its advantages as well as limitations. Nonetheless, what the situation calls for is likely not the identification of the single best method, but a well-thought-through plan employing various ways to detect the infected people. After all, our future might depend on it.

References

1. La Marca, M. Capuzzo, T. Paglia, L. Roli, T. Trenti, and S. M. Nelson, “Testing for SARS-CoV-2 (COVID-19): a systematic review and clinical guide to molecular and serological in-vitro diagnostic assays,” Reproductive BioMedicine Online, vol. 41, no. 3. Elsevier Ltd, pp. 483–499, 01-Sep-2020.
2. https://www.who.int/news-room/commentaries/detail/advice-on-the-use-of-point-of-care-immunodiagnostic-tests-for-covid-19
3. Holt, “Slovakia to test all adults for SARS-CoV-2,” Lancet, vol. 396, no. 10260, pp. 1386–1387, Oct. 2020.
4. https://www.theguardian.com/world/2020/nov/02/slovakia-carries-out-covid-mass-testing-of-two-thirds-of-population
5. J. Deeks et al., “Antibody tests for identification of current and past infection with SARS-CoV-2,” Cochrane Database of Systematic Reviews, vol. 2020, no. 6. John Wiley and Sons Ltd, 25-Jun-2020.
6. Jendrny et al., “Scent dog identification of samples from COVID-19 patients - A pilot study,” BMC Infect. Dis., vol. 20, no. 1, p. 536, Jul. 2020.
7. Laguarta, F. Hueto, and B. Subirana, “COVID-19 Artificial Intelligence Diagnosis using only Cough Recordings,” IEEE Open J. Eng. Med. Biol., pp. 1–1, Sep. 2020.