Background: COVID-19 has disproportionately affected older adults. Yet, healthcare trajectories experienced by older persons hospitalized for COVID-19 have not been investigated. This study aimed at estimating the probabilities of transitions between severity states in older adults admitted in COVID-19 acute wards and at identifying the factors associated with such dynamics.

Methods: COVID-19 patients aged ≥60 years hospitalized between March and December 2020 were involved in the multicentre GeroCovid project-acute wards substudy. Sociodemographic and health data were obtained from medical records. Clinical states during hospitalization were categorized on a seven-category scale, ranging from hospital discharge to death. Based on the transitions between these states, first, we defined patients' clinical course as positive (only improvements), negative (only worsening), or fluctuating (both improvements and worsening). Second, we focused on the single transitions between clinical states and estimated their probability (through multistage Markov modeling) and associated factors (with proportional intensity models).

Results: Of the 1024 included patients (mean age 78.1 years, 51.1% women), 637 (62.2%) had a positive, 66 (6.4%) had a fluctuating, and 321 (31.3%) had a negative clinical course. Patients with a fluctuating clinical course were younger, had better mobility and cognitive levels, fewer diseases, but a higher prevalence of cardiovascular disease and obesity. Considering the single transitions, the probability that older COVID-19 patients experienced clinical changes was higher within a 10-day timeframe, especially for milder clinical states. Older age, male sex, lower mobility level, multimorbidity, and hospitalization during the COVID-19 first wave (compared with the second one) were associated with an increased probability of progressing towards worse clinical states or with a lower recovery.

Conclusion: COVID-19 in older inpatients has a complex and dynamic clinical course. Identifying individuals more likely to experience a fluctuating clinical course and sudden worsening may help organize healthcare resources and clinical management across settings at different care intensity levels.