Age dependence of the natural history of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): an analysis of Diamond Princess data

BACKGROUND: Following an outbreak of coronavirus disease 2019 (COVID-19) on the cruise ship Diamond Princess, passengers and crew were followed-up to determine prognosis. This study examined the epidemiological determinants of COVID-19 natural history using these follow-up data. METHODS: Infection status, diagnosis, clinical symptoms and prognosis were analysed for all passengers and crew members on the Diamond Princess. In addition, the risk of infection associated with exposure within cabin rooms, as well as the risks of various clinical manifestations of disease, along with their epidemiological determinants, were analysed. RESULTS: The adjusted odds ratio (aOR) of infection for individuals tested by polymerase chain reaction on or after 12 February 2020 compared with individuals tested before this date was 0.53 [95% confidence interval (CI) 0.39–0.72], reflecting decreased transmission during onboard quarantine. Among infected individuals, older age was associated with elevated odds of symptomatic illness (aOR 1.01, 95% CI 1.00–1.02), severe disease (aOR 1.08, 95% CI 1.05–1.12) and death (aOR 1.12, 95% CI 1.05–1.21). CONCLUSIONS: Severe COVID-19 disease, death and symptomatic illness were more frequent among older individuals on the Diamond Princess. Older elderly cases (age ≥80 years) had the highest risks of severe disease and death. Inter-room transmission was prevented successfully by the onboard quarantine.