Interventions for the prevention of persistent post‐COVID‐19 olfactory dysfunction

Background Loss of olfactory function is well recognised as a cardinal symptom of COVID‐19 infection, and the ongoing pandemic has resulted in a large number of affected individuals with abnormalities in their sense of smell. For many, the condition is temporary and resolves within two to four weeks. However, in a significant minority the symptoms persist. At present, it is not known whether early intervention with any form of treatment (such as medication or olfactory training) can promote recovery and prevent persisting olfactory disturbance. Objectives To assess the effects (benefits and harms) of interventions that have been used, or proposed, to prevent persisting olfactory dysfunction due to COVID‐19 infection. A secondary objective is to keep the evidence up‐to‐date, using a living systematic review approach. Search methods The Cochrane ENT Information Specialist searched the Cochrane COVID‐19 Study Register; Cochrane ENT Register; CENTRAL; Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished studies. The date of the search was 16 December 2020. Selection criteria Randomised controlled trials including participants who had symptoms of olfactory disturbance following COVID‐19 infection. Individuals who had symptoms for less than four weeks were included in this review. Studies compared any intervention with no treatment or placebo. Data collection and analysis We used standard Cochrane methodological procedures. Our primary outcomes were the presence of normal olfactory function, serious adverse effects and change in sense of smell. Secondary outcomes were the prevalence of parosmia, change in sense of taste, disease‐related quality of life and other adverse effects (including nosebleeds/bloody discharge). We used GRADE to assess the certainty of the evidence for each outcome. Main results We included one study of 100 participants, which compared an intranasal steroid spray to no intervention. Participants in both groups were also advised to undertake olfactory training for the duration of the trial. Data were identified for only two of the prespecified outcomes for this review, and no data were available for the primary outcome of serious adverse effects. Intranasal corticosteroids compared to no intervention (all using olfactory training) Presence of normal olfactory function after three weeks of treatment was self‐assessed by the participants, using a visual analogue scale (r