Patterns of case fatality and hospitalization duration among nearly 1 million hospitalized COVID-19 patients covered by Iran Health Insurance Organization (IHIO) over two years of pandemic: An analysis of associated factors
Authors: Mehrizi Reza , Golestani Ali , Malekpour Mohammad-Reza , Karami Hossein , Nasehi Mohammad Mahdi , Effatpanah Mohammad , Rezaee Mehdi , Shahali Zahra , Akbari Sari Ali , Daroudi Rajabali 
Published: February 2024

Background
Different populations and areas of the world experienced diverse COVID-19 hospitalization and mortality rates. Claims data is a systematically recorded source of hospitalized patients’ information that could be used to evaluate the disease management course and outcomes. We aimed to investigate the hospitalization and mortality patterns and associated factors in a huge sample of hospitalized patients.

Methods
In this retrospective registry-based study, we utilized claim data from the Iran Health Insurance Organization (IHIO) consisting of approximately one million hospitalized patients across various hospitals in Iran over a 26-month period. All records in the hospitalization dataset with ICD-10 codes U07.1/U07.2 for clinically/laboratory confirmed COVID-19 were included. In this study, a case referred to one instance of a patient being hospitalized. If a patient experienced multiple hospitalizations within 30 days, those were aggregated into a single case. However, if hospitalizations had longer intervals, they were considered independent cases. The primary outcomes of study were general and intensive care unit (ICU) hospitalization periods and case fatality rate (CFR) at the hospital. Besides, various demographic and hospitalization-associated factors were analyzed to derive the associations with study outcomes using accelerated failure time (AFT) and logistic regression models.

Results
A total number of 1 113 678 admissions with COVID-19 diagnosis were recorded by IHIO during the study period, defined as 917 198 cases, including 51.9% females and 48.1% males. The 61–70 age group had the highest number of cases for both sexes. Among defined cases, CFR was 10.36% (95% CI: 10.29–10.42). The >80 age group had the highest CFR (26.01% [95% CI: 25.75–26.27]). The median of overall hospitalization and ICU days were 4 (IQR: 3–7) and 5 (IQR: 2–8), respectively. Male patients had a significantly higher risk for mortality both generally (odds ratio (OR) = 1.36 [1.34–1.37]) and among ICU admitted patients (1.12 [1.09–1.12]). Among various insurance funds, Foreign Citizens had the highest risk of death both generally (adjusted OR = 2.06 [1.91–2.22]) and in ICU (aOR = 1.71 [1.51–1.92]). Increasing age groups was a risk of longer hospitalization, and the >80 age group had the highest risk for overall hospitalization period (median ratio = 1.52 [1.51–1.54]) and at ICU (median ratio = 1.17 [1.16–1.18]). Considering Tehran as the reference province, Sistan and Balcuchestan (aOR = 1.4 [1.32–1.48]), Alborz (aOR = 1.28 [1.22–1.35]), and Khorasan Razavi (aOR = 1.24 [1.20–1.28]) were the provinces with the highest risk of mortality in hospitalized patients.

Conclusion
Hospitalization data unveiled mortality and duration associations with variables, highlighting provincial outcome disparities in Iran. Using enhanced registry systems in conjunction with other studies, empowers policymakers with evidence for optimizing resource allocation and fortifying healthcare system resilience against future health challenges.