Epidemiology of the COVID-19 pneumonia in a group of hospitals from Madrid-Spain during the full period of the State of Alarm HM cohort.

Introduction: To describe the epidemiology pattern of the COVID-19 pandemic during all Spanish State of Alarm.

Methods: Retrospective, observational, cohort and multicenter study. Inclusion criteria: age ≥18 years old, admitted for COVID-19 pneumonia in any of the centers of the HM Hospitals Group. Exclusion criteria: voluntary discharge, death in the emergency department, transfer to centers outside the HM group or incomplete data. State of Alarm period: 31/01/2020 to 05/07/2023. Predominant COVID-19 variant was defined when it exceeded 50% of the total isolates.

Results: During the study period, 2,992 patients were admitted due to a COVID-19 pneumonia, 295 patients (9.86%) non-survive. Survivors and non-survivors were different in age and comorbidities. However, both cohorts presented a similar net of interaction between comorbidities. Hospital admissions per week showed an evolution in "peaks" with "troughs". A total of 197 (6.48%) patients were admitted to the ICU, of whom 52 (26.39%) non-survive; this subgroup stood out for having a higher proportion of septic shock, orotracheal intubation and acute renal failure, as well as a lower proportion of pulmonary thromboembolism and delirium. Concerning the viral variants, the incidence for the original variant was 4.05 cases/day, for the alpha variant 3.82 cases/day, for the delta variant 1.16 cases/day and for the omicron variant 1.35 cases/day.

Conclusion: Almost 1 of 10 patients with COVID-19 pneumonia death, a proportion that increased to 1 of 4 in case of being admitted to the ICU. Unexpectedly, interaction between comorbidities did not differ between survivors and non-survivors patients. Predominant variants were associated with different hospital admission rates but not influence the presence of peak-troughs evolution of the pandemic.