Diagnosed and subjectively perceived long-term effects of COVID-19 infection on olfactory function assessed by supervised machine learning (preprint)

Background Loss of olfactory function appears to be a typical COVID-19 symptom, at least in early variants of SARS-CoV2. The time that has elapsed since the emergence of COVID-19 now allows us to assess the long-term prognosis of its olfactory impact.Methods Participants (n = 722 of whom n = 464 reported having had COVID-19 dating back with a mode of 174 days) were approached and tested in a museum as a relatively unbiased environment. Olfactory function was diagnosed by assessing odor threshold and odor identification performance. Subjects also rated their actual olfactory function on a 100-mm visual analog scale and provided analogous retrospective estimates of their smelling ability before the COVID-19 infection and immediately after it.Results Diagnosed olfactory function did not differ in former COVID-19 patients from controls. Olfactory diagnoses included 20% decreased olfactory function in former patients and 18.7% in controls, which was not significant. Of former patients, 145 (31.2%) retrospectively reported temporarily reduced olfactory function. Only nine 9 patients (2.2%) reported ongoing reduction of their olfactory function. Overall, former patients rated their current olfactory function significantly better than controls. Supervised machine learning was able to detect past COVID-19 infection from self-assessment of current olfactory function, but not from diagnosed current olfactory function, better than by guessing, although accuracy was intermediate, not suggesting utility as a clinical test.Conclusions While retrospectively about one-third of former CVID-19 patients recalled olfactory symptoms associated with prior infection, the present results suggest a positive long-term prognosis for COVID-19-associated olfactory loss.

Olfactory and Gustatory Dysfunction as An Early Identifier of COVID-19 in Adults and Children: An International Multicenter Study (preprint)

Abstract Objective: Evaluate the prevalence and characteristics of olfactory or gustatory dysfunction in COVID-19 patients Study Design: Multicenter Case Series Setting: 5 tertiary care hospitals (3 in China, 1 in France, 1 in Germany) Subjects and Methods: 394 PCR confirmed COVID-19 positive patients were screened, and those with olfactory or gustatory dysfunction were included. Data including demographics, COVID-19 severity, patient outcome, and the incidence and degree of olfactory and/or gustatory dysfunction were collected and analyzed. The Questionnaire of Olfactory Disorders (QOD) and Visual Analogue Scale (VAS) were used to quantify olfactory and gustatory dysfunction respectively. All subjects at one hospital (Shanghai) without subjective olfactory complaints underwent objective testing. Results: Of 394 screened subjects, 161 (41%) reported olfactory and/or gustatory dysfunction and were included. Incidence of olfactory and/or gustatory disorders in Chinese (n=239), German (n=39) and French (n=116) cohorts were 32%, 69%, and 49% 138 respectively. The median age of included subjects was 39 years old, 92/161 (57%) were male, and 10/161 (6%) were children. Of included subjects, 10% had only olfactory or gustatory symptoms, and 19% had olfactory and/or gustatory complaints prior to any other COVID-19 symptom. Of subjects with objective olfactory testing, 10/90 demonstrated abnormal chemosensory function despite reporting normal subjective olfaction. 43% (44/102) of subjects with follow-up showed symptomatic improvement in olfaction or gustation. Conclusions: Olfactory and/or gustatory disorders may represent early or isolated symptoms of SARS-CoV-2 infection. They may serve as a useful additional screening criterion, particularly for the identification of patients in the early stages of infection.

Predictive value of sudden olfactory loss in the diagnosis of COVID-19 (preprint)

Introduction: Recent reports suggest that sudden smell loss might be a symptom of SARS-CoV-2 infection. The aim of this study was to investigate the frequency of olfactory loss in an out-patient population who presented to a coronavirus testing center during a 2-week period and to evaluate the diagnostic value of the symptom sudden smell loss for screening procedures. Methods: In this cross-sectional controlled cohort study, 500 patients who presented with symptoms of a common cold to a corona testing center and fulfilled corona testing criteria, completed a standardized diagnostic questionnaire which included the patients main symptoms, time course and an additional self-assessment of the patients current smell, taste function and nasal breathing compared to the level before onset of symptoms. Results: Out of the 500 patients, 69 presented with olfactory loss. Twenty-two of them subsequently tested positive for SARS-CoV-2. Only twelve out of the patients without olfactory loss tested positive, resulting in a frequency of 64.7% for the symptom sudden smell loss in COVID-19 patients. Compared to COVID-19 patients without smell loss, they were significantly younger and less severely affected. Changes in nasal airflow were significantly more pronounced in SARS-CoV-2 negative patients with olfactory complaints compared to the patients with smell loss who were tested positive for SARS-CoV-2. By excluding patients with a blocked nose, the symptom sudden smell loss can be attested a high specificity (97%) and a sensitivity of 65% with a PPV of 63% and NPV of 97% for COVID-19. Conclusion: Considering the high frequency of smell loss in non-hospitalized COVID-19 patients, acute olfactory impairment should be included in the WHO symptoms list and should be recognized as an early symptom of the disease. In contrast to other acute viral smell impairment, COVID-19 associated smell loss seems to be only rarely accompanied by a severely blocked nose.