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19th July 2021
Olfactory dysfunction has been defined as the best predictor of infection with COVID-19. Moreover, in a study of 60 patients, 59 exhibited some dysfunction during a smell identification test. The study also revealed how only 58% of those tested had anosmia indicating in imperfect relationship between olfactory dysfunction and anosmia. It is possible therefore that the use of an inexpensive, rapid and sensitive method, based on olfactory dysfunction would be of potential value in identifying those with COVID-19. Based on this assumption, a team from the Division of Otolaryngology-Head and Neck Surgery, Department of Surgery, University of California, US, sought to evaluate the prognostic value of a smell test for identifying those with COVID-19. The team enrolled healthy adults (18 years and over) from a single university campus screening site. Each of the participants were tested for olfactory dysfunction using a novel scent card (SAFER Diagnostics) and immediately followed up with a PCR test for COVID-19. The card itself contained several different scents under a scratch-off and sniff label and participants had eight options: grape, floral, blueberry, banana, mint, unsure or no scent. Using a QR code, the answers were processed electronically and an incorrect choice was labelled as olfactory dysfunction. The team collected participant demographics, medical history, any COVID-19 symptoms and a subjective smell test on a binary (yes/no) and a 10-point visual analogue scale, where 0 indicated no sense of smell and 10 was a normal sense of smell. Using regression analysis, the team assessed the association between the SAFER card and PCR test results, controlling for the presence of any other COVID-19-related symptoms such as fever, fatigue and cough.
A total of 163 participants were enrolled with a mean age of 31.6 years (56.3% male) with the majority (62.5%) of white ethnicity. There were 16 participants who tested positive for COVID-19 and 7 (4.8%) who tested negative. From the 16 who were PCR positive, 12 (75%) also failed the olfactory dysfunction test. A failed scent card screen was found to be the greatest predictor for COVID-19 positivity (odds ratio, OR = 80.24, 95% CI 14.77–435.90). The authors calculated that the smell test had a sensitivity for detecting COVID-19 of 75% and a specificity of 95.2%. When adding the presence of fatigue as an associated symptom, the sensitivity of the olfactory dysfunction test increased to 93.8% and the specificity to 89.8%. However, when either fever or cough were included, there was no increase in sensitivity. Interestingly, only 6 of the 16 who tested positive for COVID-19 presented with subjective anosmia.
In a discussion of their findings, the authors noted how their rapid olfactory dysfunction test was a valuable screening tool for COVID-19. Nevertheless, they recognised that not all patients experience olfactory dysfunction but that in the presence of fatigue, the test became more sensitive. The authors concluded by calling for future studies to include a larger participant cohort to better account for other olfactory dysfunction risk factors.
Said M et al. A Rapid Olfactory Test as a Potential Screening Tool for COVID-19. JAMA Otolaryngol Head Neck Surg.
5th October 2020
The results showed that individuals who experience loss of smell were three times more likely to have COVID-19 antibodies than those with isolated taste loss. In this newly published study, researchers from University College London, recruited individuals between April and May 2020, when anosmia was not recognised as a symptom of COVID-19. Adults registered with four primary care centres in London were sent a text message asking whether their sense of taste or smell had reduced in the last month. Those answering yes were directed to an online questionnaire which collected demographics and other information and were sent a point-of-care antibody testing kit. Participants then held a video consultation with a healthcare professional who supervision collection of a whole blood sample from a finger-prick test.
A total of 33,650 text messages were sent and 590 participants recruited, of whom 567 (96%) had an antibody test and the mean age of the sample was 39.4 years (69.1% female). Among the 567 individuals, 78% of tested positive with 93.4% reporting either a complete or partial loss of a sense of smell and 90.2% either a complete or partial loss of taste. Interestingly, 40% of those testing positive had neither a cough or fever. In regression analysis, participants with a loss of smell alone were nearly three-times more likely than those with isolated taste loss to have COVID-19 antibodies (adjusted odds ratio, OR = 2.72, 95% CI 1.37 – 6.36, p < 0.001). Moreover, those with a combined loss of smell and taste were four-times (adjusted OR = 4.11, 95% CI 2.24 – 7.08, P < 0.001) to have COVID-19 antibodies.
Commenting on their findings, the authors noted that loss of smell was a highly specific symptom for COVID-19 and that this alone should be used as a criterion for self-isolation.
Makaronidis J et al. Seroprevalence of SARS-CoV-2 antibodies in people with an acute loss in their sense of smell and/or taste in a community-based population in London, UK: An observational cohort study. PloS Med 2020;17(10): e1003358. https://doi.org/10.1371/ journal.pmed.1003358