The usefulness of a quantitative olfactory test for the detection of COVID-19

Abstract

AbstractBackgroundDuring 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 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.MethodsOutpatients had their forehead temperature checked with an infrared non-contact thermometer (temperature guns). 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 if the patients were positive or negative for COVID-19 infection. We considered the number of ‘hits’ (correct answers) ≤ 5 as positive for loss of smell (LOS) in the olfactory test; ≥ 6 hits was considered negative for LOS (i.e. normal olfactory function). All data were analyzed using Excel and Matlab software.ResultsIn the present study, 165 patients were eligible for the olfactory test and nasopharyngeal swab collection RT-PCR. Five patients were excluded because of inconclusive PCR results (n=2) and 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 PCR+ patients scored significantly worse in the olfactory test (5.5±3.5) compared to RT-PCR-patients (8.2±1.8, p<0.001). 0/44 PCR+ patients presented with a fever (≥37.8°C). In contrast an olfactory SIT had a specificity of 94.8% (95% CI, 89.1 – 98.1), sensitivity of 47.7% (95% CI, 32.7 – 63.3), accuracy of 0.82 (95% CI, 0.75 – 0.87), positive predictive value of 77.8% (95% CI, 59.6 – 88.8), negative predictive value of 82.7% (85% CI, 78.7 – 86.7), and odds ratio of 16.7.ConclusionOur results suggest that temperature checking failed to detect COVID-19 infection, while an olfactory test may be useful to help identify COVID-19 infection in symptomatic patients.