Survival Analyses of COVID-19 Patients in a Turkish Cohort: Comparison between Using Time to Death and Time to Release

Survival analyses of COVID-19 data has its own unique features, in particular, the existence of two distinct events: death and release from the hospital within a very short period of time. This multiple-event situation belongs to a type where the occurrence of the first event prevents the second event to happen, and vice versa. We carried out two cause-specific univariate Cox regression survival analyses, one for time-to-death and another for time-to-release. Each survival analysis is further split into one for onset of symptom to event time and another for hospitalization to event time. We have also carried out a case-control (death vs. release) analysis without considering the time to event information. We observed that risk factors can be detected by either case-control or survival analysis, even though the goal of the two is quite different. We also observed that the two survival analyses may not both reveal a factor being a risk factor, but only one of them does. We prefer this two rounds of Cox regressions over mixture cure model which is only focused on time-to-death events which usually are sample size limited. By utilizing time-to-release events may greatly increase the sample size needed for revealing risk factors for COVID-19.   Doi: 10.28991/SciMedJ-2021-03-SI-1 Full Text: PD

Alpha variant (B.1.1.7) of SARS-CoV-2 increases fatality-rate for patients under age of 70 years and hospitalization risk overall

The emergence of new SARS-CoV-2 variants is a challenge to the control of this pandemic. It is therefore important to collect and to analyze data related to the infection caused by different variants. We have obtained more than 3,700 COVID-19 patients between April 2020 and March 2021 from Tokat, Turkey (roughly 3,100 outpatients and close to 600 inpatients) where about 30% were infected with Alpha variant (B.1.1.7). Descriptive statistics was used to characterize different subgroups. Both logistic regression and cause-specific Cox survival analysis of competing-risk was run on inpatients, to examine the impact of Alpha variant on hospitalization, on mortality and on other factors. We observed that the Alpha variant is over-represented in inpatients than outpatients so infection by Alpha variant increases the chance for hospitalization. The impact of Alpha variant on mortality seems to depend on the patient's age. For patients under age of 70, the case-fatality-rate was 0.84% (5.3%) for patients without (with) Alpha variant (Fisher's test P-value = 2.4 x 10(-10)). For patients above age of 70, the trend is opposite: the case-fatality-rate is 31.5% (13.6%) for patients without (with) Alpha variant (Fisher's test P-value = 0.0016). The two opposite trends would cancel each other, making other analyses such as cause-specific Cox regression and logistic regression non-significant. The Alpha variant increases the risk for hospitalization, increases the case-fatality-rate for lower age group, and decreases the case-fatality-rate for the upper age group. if the increase of case-fatality-rate in not the most senior group holds true, it should provide useful information for a vaccination planning to counter the impact of Alpha variants