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Nasal swab test may not be enough as a diagnosis for Covid-19, says study

Prashasti Awasthi Mumbai | Updated on August 14, 2020

Researchers of a study published in the journal Lancet found the presence of SARS-CoV-2 in the endothelial cells of seven patients who tested negative for the virus when the nasal swab testing was conducted on them.

Researchers also suspected that the Covid-19 infection has caused increased C-reactive protein (248 mg/L) — substance produced by the liver in response to inflammation — and decreased lymphocyte count (7·7 per cent) — a kind of white blood cells in the blood samples.

High C-reactive protein levels can also indicate that there's inflammation in the arteries of the heart, which can mean a higher risk of a heart attack. While lymphocyte count can put patients at greater risk of catching an infection.

The Lancet study also highlights the shortcomings of currently available testing methods for SARS-CoV-2 infection.

Although the sensitivity and specificity of currently available PCR and serology tests are high, swab samples that are taken incorrectly are known drivers of the relatively large number of false-negative tests for SARS-CoV-2, the study said.

Serology is a diagnostic examination of blood serum, especially with regard to the response of the immune system to pathogens.

The authors said: “Our finding that the patient's serology remained negative is compatible with the hypothesis that some patients with Covid-19 might not establish humoral immunity; an observation that has also been made for other coronaviruses.”

In summary, this case emphasises the use of SARS-CoV-2 PCR testing of skin biopsy samples — a process of taking skin samples from the surface of the body to examine patient’s medical condition — as an additional diagnostic tool, can help shed light on the actual prevalence of Covid-19 in the general population.

The authors believe that further studies are needed to understand to what extent and at what point during their disease course, patients with Covid-19 actually develop immunity, especially with regard to the current ongoing efforts to develop a vaccine to SARS-CoV-2, and the concept of herd immunity generation.

Published on August 14, 2020

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