Assessing the impact of Delta and Omicron in German intensive care units: a retrospective multistate analysis based on nationwide inpatient billing data

Abstract

Abstract Background The spread of several severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) variants of concern (VOC) repeatedly led to increasing numbers of coronavirus disease 2019 (COVID-19) patients in German intensive care units (ICUs), resulting in capacity shortages and even transfers of COVID-19 intensive care patients between federal states in late 2021. In this respect, there is limited evidence on the impact of predominant VOC in German ICUs on the population level. Methods A retrospective cohort study was conducted from July 01, 2021, to May 31, 2022, using nationwide inpatient billing data from German hospitals on COVID-19 intensive care patients and SARS-COV-2 sequence data from Germany. A multivariable Poisson regression analysis was performed to estimate incidence rate ratios (IRRs) of transfer (to another hospital during inpatient care), discharge and death of COVID-19 intensive care patients associated with Delta or Omicron, adjusted for age group and sex. Furthermore, a multistate model was used for the clinical trajectories of COVID-19 intensive care patients to estimate their competing risk of transfer, discharge or death associated with Delta or Omicron, while further addressing patient age. Results Poisson regression analysis comparing Omicron versus Delta infection yielded an estimated adjusted IRR of 1.23 (95% CI 1.16–1.30) for transfers, 2.27 (95% CI 2.20–2.34) for discharges and 0.98 (95% CI 0.94–1.02) for deaths. For ICU deaths in particular, the estimated adjusted IRR increased from 0.14 (95% CI 0.08–0.22) for the 0–9 age group to 4.09 (95% CI 3.74–4.47) for those aged 90 and older compared to the reference group of 60-69-year olds. Multistate analysis showed that Omicron infection was associated with a higher estimated risk of discharge for COVID-19 intensive care patients across all ages, while Delta infection was associated with a higher estimated risk transfer and death. Conclusions Retrospective, nationwide comparison of transfers, discharges and deaths of COVID-19 intensive care patients during Delta- and Omicron-dominated periods in Germany suggested overall less severe clinical trajectories with Omicron. Age confirmed as an important determinant for fatal clinical outcomes in COVID-19 intensive care patients, necessitating close therapeutic care for the elderly and appropriate public health control measures.