Length of stay distributions of hospitalized COVID-19 cases during a mixed Omicron-Delta epidemic in Australia

By Pooja Toshniwal PahariaReviewed by Danielle Ellis, B.Sc.Mar 22 2022

In a recent study posted to the medRxiv* preprint server, researchers determined the hospital stay lengths for coronavirus disease 2019 (COVID-19) patients infected by the Omicron and Delta variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Additionally, they compared the hospital stays during the mixed Delta-Omicron wave to that in Delta-only infections.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

Background

COVID-19 continues to cause considerable morbidity across the entire globe, owing to the emergence of several SARS-CoV-2 variants that cause variable COVID-19 incidence and severity. The duration of COVID-19 hospital stays in intensive care units (ICU), and wards due to the Omicron and Delta infections is an essential factor in assessing the variant-specific disease severity and changes in the COVID-19 burden on healthcare systems.

About the study

In the present study, researchers comparatively evaluated the length of hospital stay of SARS-CoV-2-positive patients infected during the mixed Omicron-Delta wave and Delta-only wave in residents of New South Wales (NSW), Australia.

The hospital stay lengths were assessed during two periods – the Delta-Omicron wave between December 15, 2021, and February 7, 2022, and the Delta wave between July 1, 2021, and December 14, 2022. The team also evaluated the hospital stay lengths for patients residing in the Omicron-dominant NSW’s Hunter New England Local Health District (HNE LHD).

Data were obtained from NSW’s admitted patient data collection (APDC) and NSW health ministry. Every datum comprised the date and time of hospitalization and discharge of COVID-19-patients. These data, along with patient age and date of symptomatic onset, were applied to an age-stratified competing-risk survival model for determining the multi-state clinical progression of COVID-19.

In the case of multiple ward transfers, data were linked to single stay information, wherein individuals were assumed to be hospitalized from the earliest episode until their most recent hospital discharge. Patients with two consecutive episodes more than 48 hours apart, symptomatic onset post-hospitalization, or hospital stay lengths exceeding 120 days were removed from the study. Additionally, a sensitivity analysis was performed.

Results

Data were obtained from 19,574 patients, of which 2,146 patients with hospital episodes separated by more than 48 hours (n = 85, 619, and 1,442 for Omicron HNE, Delta, and mixed Delta-Omicron waves, respectively) were excluded. Additionally, 2,314 patients with symptomatic onset post-admission (n = 107, 589 and1,618 for HNE, Delta, and Delta-Omicron periods, respectively) were excluded. Nine patients with Delta-induced hospital stay exceeding 120 days were also excluded. About 86%, 80%, and 82% of the Delta, Delta-Omicron, and HNE Omicron patients were included in the final analysis. The sensitivity analysis indicated that the average hospital occupancy period accurately corresponded to the filtered data.

The average length of hospital stay for Delta-Omicron infections was half of that for Delta infections. The average hospital occupancy period was lower across all ages among the HNE LHD patients. The average ward occupancy period was directly proportional to patient age for both the infection periods.

The likelihood of ward discharge across ages was higher for the mixed Omicron-Delta and Omicron infections than the Delta infections. Contrastingly, the likelihood of ICU admissions from wards was significantly lower for all ages for Omicron-Delta and Omicron infections than the Delta infections. However, the probabilities of ward admission post ICU admission were similar for all ages. Regarding the ward-to-discharge parameter, significant differences were only observed in patients aged above 70 years infected by the Delta variant.

The mean ward occupancy period for the Delta-Omicron infections for age groups 0-39, 40-69, and above 70 years were 2.2, 3.9, and 7.6 days, respectively. In contrast, the corresponding mean ICU occupancy periods were 3.6, 5.8, and 12.3 days for Delta infections, respectively. The mean ward-to-discharge durations for HNE LHD patients with Omicron infections were 2.1, 2.9, and six days for the corresponding age groups, respectively.

Conclusion

Although the average ward occupancy periods were significantly higher for the Delta-Omicron infections, the mean ICU occupancy periods were greater for the Delta infections. This indicates that although the Omicron variant is highly transmissible, it causes less severe infection compared to the Delta variant. Thus, despite a significant rise in COVID-19 incidence with the emergence of the Omicron variant, there is a decrease in the COVID-19 burden for healthcare systems.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources