COVID-19 research briefs: Case fatality ratio due to COVID-19 appears to be declining

Reference

Horwitz LI, Jones SA, Cerfolio RJ, et al. Trends in COVID-19 risk-adjusted mortality rates. J Hosp Med. Published online October 21, 2020. doi: 10.12788/jhm.3552.

Synopsis

Research Brief #71: Case fatality ratios appear to be declining from what they were in March and April, 2020. However, it isn't clear whether this is due to more testing, a demographic shift toward younger patients, or better treatment. These authors at New York University Langone Health gathered data on admissions of adults hospitalized with laboratory-confirmed SARS-CoV-2 infection between March 1 and August 31, 2020, with mortality data available through October 8, 2020. They developed a multivariate model for mortality that included age, sex, race, tobacco use, the presence of each of 9 comorbidities, and admission oxygen saturation, D-dimer, serum ferritin, and C-reactive protein levels. They used this model to calculate the expected number of deaths given the patient mix for each month, compared that with the actual number of deaths to calculate standardized mortality ratios (SMRs), and applied the SMR to the overall mortality to calculate adjusted mortality rates for each month. They used a second approach that calculates the average marginal effects in a model that included the month, and determined the percent difference in mortality between March and the months that followed. The authors found that the SMR decreased from 1.26 in March to 0.38 in August, and the adjusted mortality rate decreased from 25.6% in March to only 7.6% in August. The calculation using the average marginal effect had similar results. Thus, after adjusting for patient factors and severity of illness on admission, it appears that improvements in treatment may be related, probably due to a combination of factors such as the use of corticosteroids and anticoagulants, less aggressive use of mechanical ventilation and proning during ventilation, a lower burden on the critical care system, and (possibly) the use of remdesivir and convalescent plasma.