Altitude and case fatality rate from COVID-19 during the pandemic in Peru, 2020-2022

Objectives: To evaluate the functional form of the association between the district altitude of residence and the case fatality rate of COVID-19 cases in Peru during the 2020-2022 period. Materials and methods: A retrospective cohort study was conducted using secondary data from the Ministry of Health of Peru on COVID-19 cases and deaths. District altitude of residence was categorized into four groups (0-500; 501-2,000; 2,001-3,500; and ≥3,501 masl). The outcome was death from COVID-19 according to the official death registry. Poisson regression was used to estimate adjusted relative risks for individual and contextual variables, using robust variance clustered by district. The analyses were repeated according to the five epidemic waves that occurred between March 2020 and December 2022. Results: A non-linear association was observed between the altitude of residence and death from COVID-19, consistent with a "U-shaped" pattern, characterized by a lower risk of death in cases residing between 2,001 and 3,500 masl compared to those residing between 0 and 500 masl. This pattern remained consistent in the analyses stratified by epidemic wave. Conclusions: In Peru, during the 2020-2022 period, the data do not support a monotonic decrease in the risk of death from COVID-19 with increasing altitude of residence. On the contrary, the results suggest a non-linear relationship, with lower lethality at intermediate altitudes (2,001-3,500 masl).