Olfactory Dysfunction After SARS-CoV-2 Infection in the RECOVER Adult Cohort.

Key Points: Question: What are patterns of olfactory dysfunction in adults after SARS-CoV-2 infection? FINDINGS: In this cohort study, 1111 of 1393 SARS-CoV-2–infected participants who reported loss in or change of smell or taste a mean of 2 years after infection (80%) had hyposmia on formal testing, a total of 321 (23%) had severe microsmia or anosmia, and the mean age- and sex-standardized score was at the 16th percentile. Hyposmia was also present in 1031 of 1563 participants (66%) with prior infection but no self-reported change or loss (mean: 23rd percentile). Meaning: These findings suggest that occult hyposmia following infection with SARS-CoV-2 is common, and olfactory testing should be considered after infection to diagnose olfactory dysfunction and counsel patients about the risks of smell loss. This cohort study examines the presence, severity, and patterns of olfactory dysfunction in US adults with and without prior SARS-CoV-2 infection. Importance: Olfactory dysfunction is common after SARS-CoV-2 infection and has been associated with cognitive loss in other conditions. Formal testing is needed to characterize the presence, severity, and patterns of olfactory dysfunction. OBJECTIVE: To characterize long-term olfactory dysfunction after SARS-CoV-2 infection. Design, Setting, and Participants: This prospective cohort study included adults enrolled in the Researching COVID to Enhance Recovery (RECOVER)–Adult study. All those with and a random sample of those without self-reported change or loss in smell or taste were offered olfactory testing, performed at 83 sites in 35 US states and territories. Participants included 2956 enrollees with prior infection (1393 with and 1563 without self-reported change or loss) and 569 without prior infection (9 with and 560 without self-reported change or loss in taste) who underwent olfactory testing a mean (SD) of 671.6 (417.8) days after the index date. Data were collected from October 29, 2021, to June 6, 2025. Exposure: SARS-CoV-2 infection. Main Outcomes and Measures: Olfactory function, as defined by age- and sex-standardized performance on the University of Pennsylvania Smell Identification Test (UPSIT), a well-validated test comprising 40 unique odors. RESULTS: The study included 3525 participants with a mean (SD) age of 47.6 (15.2) years; of 3520 with data available, 2548 (72.4%) were female or intersex. Among 1393 infected participants with self-reported change or loss, 1111 (79.8%) had hyposmia on the UPSIT, including 321 (23.0%) with severe microsmia or anosmia. Among 1563 infected participants without self-reported change or loss, 1031 (66.0%) had hyposmia, including 128 (8.2%) with severe microsmia or anosmia. Participants with prior infection and self-reported change or loss scored at the 16th age- and sex-standardized UPSIT percentile, compared with the 23rd and 28th percentiles for those without self-reported change or loss with and without prior known infection, respectively. Younger women had scores corresponding to lower mean age- and sex-standardized percentiles. Among participants who self-reported change or loss in smell, those with abnormal UPSIT scores more often reported cognitive problems (742 of 1111 [66.8%]) than those with normal UPSIT scores (179 of 282 [63.5%]). Conclusions and Relevance: In this cohort study of RECOVER-Adult participants, self-reported change or loss in smell or taste was an accurate signal of verified hyposmia, but a high rate of hyposmia among those with no reported change or loss was also observed. Formal smell testing may be considered in those with prior SARS-CoV-2 infection to diagnose occult hyposmia and counsel patients about risks.