Decline in mortality among hospitalised covid-19 patients in Sweden: a nationwide observational study

Abstract

OBJECTIVE It is important to know if mortality among hospitalised covid-19 patients has changed as the pandemic has progressed. The aim of this study was to describe the dynamics of mortality among patients hospitalised for covid-19 in a nationwide study. DESIGN Nationwide observational cohort study of all patients hospitalised in Sweden 1 March to 30 June 2020 with SARS-CoV-2 RNA positivity 14 days before to 5 days after admission, and a discharge code for covid-19. SETTING All hospitals in Sweden. PARTICIPANTS 15 761 hospitalised patients with covid-19, with data compiled by the Swedish National Board of Health and Welfare. MAIN OUTCOME MEASURES Outcome was 60-day all-cause mortality. Patients were stratified according to month of hospital admission. Poisson regression was used to estimate the relative risk of death by month of admission, adjusting for pre-existing conditions, age, sex, care dependency, and severity of illness (Simplified Acute Physiology, version 3), for patients in intensive care units (ICU). RESULTS The overall 60-day mortality was 17.8% (95% confidence interval (CI), 17.2% to 18.4%), and it decreased from 24.7% (95% CI, 23.0% to 26.5%) in March to 13.3% (95% CI, 12.1% to 14.7%) in June. Adjusted relative risk (RR) of death was 0.56 (95% CI, 0.51 to 0.63) for June, using March as reference. Corresponding RR for patients not admitted to ICU and those admitted to ICU were 0.60 (95% CI, 0.53 to 0.67) and 0.61 (95% CI, 0.48 to 0.79), 3 respectively. The proportion of patients admitted to ICU decreased from 19.5% (95% CI, 17.9% to 21.0%) in the March cohort to 11.0% (95% CI, 9.9% to 12.2%) in the June cohort. CONCLUSIONS There was a gradual decline in mortality from March to June 2020 in Swedish hospitalised covid-19 patients, which was independent of pre-existing conditions, age, and sex. Future research is needed to explain the reasons for this decline. The changing covid-19 mortality should be taken into account when management and results of studies from the first pandemic wave are evaluated.

Second wave mortality among patients hospitalised for COVID-19 in Sweden: a nationwide observational cohort study

“…Figure 2B shows that the crude 60-day mortality decreased from 24•7% (95% CI, 23•0%-26•5%) for March to 10•4% (95% CI, 8•9%-12•1%) for July-September (as reported previously [1]), but later increased to 19 As can be seen in figure 4, the overall adjusted RR for death within 60 days for December was higher than RRs for June, July-September, October, and November, and was similar to the RR for May. The pattern was similar for non-ICU-treated and ICU-treated patients.…”

“…During the first pandemic wave, management and care of patients with COVID-19 changed considerably [1], and most likely these improvements were partly the reason for the decline in mortality during the first wave. However, during the second half of 2020 no essential changes were made in the national recommendations of standard-of-care for hospitalised COVID-19 patients in Sweden [13], but even so mortality increased.…”

“…To this end, patients were categorised according to month of admission. Data on comorbidity (including Charlson Comorbidity Index; CCI), care dependency prior to admission, and ICU data were extracted as described previously [1]. Briefly, to classify comorbidities we used ICD-10 codes registered as in-and outpatient diagnoses during the last five years in the National Patient Register, and prescribed drugs filled out during the year preceding diagnosis, according to the National Prescribed Drug register.…”

“…During the first pandemic wave, a substantial decline in mortality was noted among patients hospitalised for COVID-19 in many countries, including Sweden [1][2][3][4][5][6], but not in all countries [7]. The decline in mortality was believed to be due to a combination of factors, including improved patient triage, decreased patient load, improvements in care and standard medication, and possibly changes in virus virulence [1][2][3][4]. Since the relative importance of these factors were unknown, no one could foresee how mortality would change during forthcoming waves.…”

“…The study population was derived from cross-linked national population-based registers, using the same design and statistical methods described previously [1].…”