Usefulness of a Quantitative Olfactory Test for the Detection of COVID-19

Author(s): Marcos A Lessa1, Stella M Cotta-Pereira, Frederico R Ferreira, Therezinha M Castiñeiras, Rafael M Galliez, Débora S. Faffe, Isabela de C Leitão, Diana Mariani, Erica R Nascimento, Flávia S Lessa, Isabella B Succi, and Carlos A Pedreira

Background: During the COVID-19 pandemic, olfactory dysfunction (anosmia or hyposmia) has been reported by many patients and recognized as a prevalent and early symptom of infection. This finding has been associated with viral-induced olfactory neuron dysfunction rather than the nasal congestion typically found in cold- or flu-like states. In the literature, the prevalence of anosmia varies from 15% to 85%, and the studies, in general, were based on the subjective evaluation of patients’ self-reports of loss of smell (yes or no question). In the present study, we quantitatively evaluated olfactory dysfunction and the prevalence of fever in symptomatic patients suspected of having COVID-19 using a scratch-and-sniff olfactory test and infrared temperature testing with RT?PCR as the gold-standard comparator method to diagnose COVID?19 infection. Methods: The forehead temperature of outpatients was checked with an infrared noncontact thermometer (temperature gun). After that, they received two olfactory smell identification test (SIT) cards (u-Smell-it™; CT, USA) that each had 5 scent windows and were asked to scratch with a pencil and sniff each of the 10 small circles containing the microencapsulated fragrances and mark the best option on a response card. Nasopharyngeal swabs were then collected for reverse transcriptase?polymerase chain reaction (RT?PCR) to determine whether the patients were positive or negative for COVID?19. We considered the number of hits (correct answers) ? 5 as positive for loss of smell (LOS) in the olfactory test; ? 6 hits were considered negative for LOS (i.e., normal olfactory function). All the data were analyzed using Excel and MATLAB software. Results: One hundred sixty-five patients who were eligible for the olfactory test and nasopharyngeal swab collection RT?PCR were included. Five patients were excluded because of inconclusive PCR results (n=2) or missing data (n=3). A total of 160 patients completed all the protocols. The RT?PCR positivity rate for COVID-19 was 27.5% (n=44), and compared with RT?PCR-negative patients, RT?PCR-positive patients scored significantly worse on the olfactory test (5.5±3.5) (8.2±1.8, p<0.001). None of the PCR-positive patients presented with fever (?37.8°C). In contrast, an olfactory SIT had a specificity of 94.8% (95% CI, 89.1–98.1), a sensitivity of 47.7% (95% CI, 32.7–63.3), an accuracy of 0.82% (95% CI, 0.75–0.87), a positive predictive value of 77.8% (95% CI, 59.6–88.8), a negative predictive value of 82.7% (85% CI, 78.7–86.7), and an odds ratio of 16.7. Conclusion: Our results suggest that temperature monitoring failed to detect COVID-19 infection, while an olfactory test may be useful for identifying COVID-19 infection in symptomatic patients.