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Covid: the salivary test that discovers it in advance

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INTERCEPT Sars-CoV-2 RNA 1.5 to 4.5 days before viral load reaches the detection range of the nasal swab. Caltech has created an early test directly from saliva: a non-invasive method, but it seems highly effective for a quick diagnosis. Fundamental to reduce the asymptomatic and presymptomatic spread of Covid-19 and its variants, as well as to maximize the effectiveness of therapeutic treatments.

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Researchers from the California Institute of Technology announced the discovery on medRxiv- The preprintĀ server for health sciences. “We monitored family contacts of people recently diagnosed with Sars-CoV-2 infection with self-collected nasal and saliva samples twice daily with an inactivating and stabilizing guanidine-based swab, which preserves the ‘Viral Rna. Then we quantified the viral loads of Rna with a high-sensitivity PCR test, to see if they too had been infected. ā€In all cases in which the disease has been developed, even in an asymptomatic form, the Rna of the new coronavirus appeared earlier in saliva than in mucus.

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“Our tests detected the virus in saliva 1.5 to 4.5 days before the viral load in the samples exceeded the detection limit of low-sensitivity nasal swabs,” explains the research team, coordinated by the biomedical engineer. Rustem Ismagilov. In a man under 40, with significant symptoms starting from the ninth day, the nasal swab was positive three days after the infection while the salivary test from Caltech gave the same result a day and a half earlier. Another man under 60, with fever already on the day of the infection and other important symptoms starting from the eighth, tested positive for the swab on the sixth day while his saliva was already positive on the third. The best result was obtained in an elementary school girl who had no symptoms until the ninth day but tested positive for the nasal swab with the first sampling on the seventh day while the early salivary sample gave the same result from the afternoon of the second day. “It was possible to observe a high viral load in saliva samples when the nasal swab was still negative or had too low a load to be detected by traditional tests,” add the researchers.

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The study was financed by the Bill & Melinda Gates Foundation, which last year made an extra $ 250 million available to support research, development and fair distribution of all life-saving tools against Covid-19. ā€œThe results indicate that both the sampling site and the sensitivity of the test are critical to ensure early diagnosis. In any case, our study must be interpreted in the context of its limitations, starting with the fact that all samples were self-collected. We trained our participants and always monitored the quality of the draws, but our results do not establish whether the samples collected by healthcare professionals would have provided the same results. Second, most of the samples were provided upon waking or just before bed, with strict guidance on not eating, drinking, or brushing your teeth prior to sample collection. So it can be difficult to get samples with this level of control during screening and routine testing, ā€they add.

Early detection of infection allows people to self-isolate earlier, reducing transmission within families and communities. “Diagnostics capable of reliably detecting even the early stages of Sars-CoV-2 infection is essential to protect vulnerable populations, including individuals hospitalized for reasons not related to Covid and all those suffering from chronic diseases”.

Although vaccination is reducing the severe outcomes of Covid-19, much of the world will never be immunized just like those under the age of 16, an age group currently not eligible for vaccination. Therefore testing remains an important tool for preventing epidemics. “Now – the researchers conclude – a larger study with individuals from different genetic backgrounds, medical conditions and Covid lineages would be ideal to provide a more nuanced and representative understanding of viral dynamics in saliva and nasal swab samples.”

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