Washing your hands with hydroalcoholic gel, smelling it and using a QR code to answer a short questionnaire. These very simple actions make up the world's first patented mass screening system for COVID cases.Citrus fruits and apples are two of the first aromas that people with the SARS-CoV-2 virus stop detecting.
"Citrus" -- I don't remember seeing this at all, so I looked further into the report: "Based on the literature and habits of our Mediterranean study population, it was determined that the most suitable odoriferous substance was lemon." via Institute for Research in Fundamental Sciences in Iran and R DOty at U Penn: Moein, S. T. et al. Smell dysfunction: A biomarker for COVID-19. Int. Forum Allergy Rhinol. 10, 944–950 (2020). https://pubmed.ncbi.nlm.nih.gov/32301284/ -- This study used the University of Pennsylvania Smell Identification Test (UPSIT) which has 40 odorants; I can't read the paper because paywall, but I guess "citrus" or "lemon" is one of those odors. The paper wasn't meant to find the most prevalent non-detectable odor, but I guess it was just sitting there in the data?
"The antigen tests on the market have an average sensitivity of 80%, which means that the number of false negatives is 20%. What we have developed is not a diagnostic test, but a screening system that aims to detect the maximum possible number of positives and prevent false negatives," explained the researchers.
They studied antibody levels in people infected during the early days of the pandemic—in all, they studied blood samples of 306 people who had donated blood for study after recovering from a COVID-19 infection. In comparing the antibody levels with other data provided by the donors and their doctors, the researchers determined that those people who had higher antibody levels tended to be the same people who had reported losing their sense of smell or taste. They found that such patients were twice as likely to lose one or the other sense as those who did not have higher-than-average levels of antibodies in their blood.
The reason some people fail to recover their sense of smell after COVID-19 is linked to an ongoing immune assault on olfactory nerve cells and an associated decline in the number of those cells, a team of scientists led by Duke Health report.