Olfactory Performance in Post Mild-to-Moderate Acute Covid-19 across 2 Years

ABSTRACT

Background: Previous longitudinal studies (n=6) of objective olfaction performance post-acute COVID-19 have a maximum follow-up of 6-month and do not often test biomarkers. Although olfactory dysfunction appears to improve within two months of symptom onset, 4/6 longitudinal studies show persistent olfactory impairment. Method(s) PCR-confirmed COVID-19 patients in the prospective ADAPT cohort (Sydney, Australia) were assessed across 18 acute symptoms and hospitalization status 40% mild, 50% moderate, 10% severe/hospitalised - none deceased). Blood samples were taken 2 (N=179), 4 (N=148) and 12-month (N=118) post-diagnosis. The NIH Odor Identification Test (OIT) and the Cogstate brief cognitive battery were performed. 58 also had an olfaction test at 24-month. The OIT raw data were transformed into demographically-corrected T-scores. OIT's attrition was completely random and only initial age (40+/-15 versus 47+/-15) differed between patients lost to follow-up and those in the study at 24-month. We tested peripheral neurobiomarkers (NFL, GFAP, S100B, GM-CSF) and immune markers (Interleukin-IL panel 1-beta, 1Ralpha, 4, 5, 6, 8, 10, 12p40, 12p70, 13, and MCP-1, TNF-alpha and INF-gamma), analyzed as Log transformed and elevated/normal range using published references. Our previous analyses had shown no relationship with the kynurenine pathway, but an association of impaired olfaction and impaired cognition at 2-month only. Linear mixed effect regressions with time effect (months) tested olfaction trajectories (random subject effect) and their association with the biomarkers (main and time interaction). Result(s) At 2 months post-diagnosis 30% had impaired olfaction and those who had acute severe disease were more likely to be impaired (54% versus 26%, p=.009). 21%, 31% and 37% had impaired olfaction at 4, 12 and 24-months. Olfactory performance declined over time (p< .0001), which was dependent on the initial performance (Fig 1). Neurobiomarkers were within the normal range. IFN-gamma, IL-1Ralpha, IL-13 and TNF-alpha increased across time, p< .03-p< .0005. TNF-alpha and IFN-gamma showed a time covariance with poorer olfaction performance. Conclusion(s) Post-acute mild to moderate COVID-19 is associated with a declining olfactory performance up to 2-yr post-diagnosis, especially when initially impaired with the provisio of attrition although random. Olfactory performance decline may be mediated by upregulated immune parameters which are distinct from those driving cognitive changes. (Figure Presented).