Characteristics and Outcomes of Immunocompromised Patients With COVID-19 Infection Admitted to an Intensive Care Unit: A Retrospective Cohort Study

Background Several studies have reported that the course of illness is different in immunocompromised and non-immunocompromised patients with COVID-19 infection. The impact of COVID-19 on immunocompromised patients is not clear due to conflicting evidence from different observational studies. Aim This study aimed to compare the characteristics and outcomes of immunocompromised and non-immunocompromised patients with COVID-19 infection admitted to an intensive care unit and to evaluate whether the immunocompromised status is associated with increased mortality. Methods We conducted this retrospective cohort study using an electronic database in St. George Hospital, a tertiary ICU in Sydney. We included all adult patients (age >16 years) admitted to the ICU with COVID-19 infection over a 33-month period (March 1, 2020, to November 30, 2022). We collected the data on demographics, comorbidities, clinical characteristics, interventions, and outcomes for all patients. We used logistic regression and multivariate adaptive regression splines (MARS) to determine the predictors of mortality. We used propensity score analyses to check whether immunocompromised patients had higher hospital mortality compared to non-immunocompromised patients. Results A total of 258 patients (mean age 61 ± 16 years, males 65%, mean APACHE II score 14 ± 5, unvaccinated 58%, and immunocompromised 17%) were studied. The immunocompromised patients were older, had higher APACHE II and III scores, and had a higher vaccination rate. The hospital mortality was higher in immunocompromised patients (39.5% vs. 14.4%, p < 0.001). On multivariate logistic regression, age (OR 1.05, 95% CI 1.01-1.1, p = 0.02), APACHE III (OR 1.05, 95% CI 1.02-1.09, p < 0.001), vasopressor use (OR 6.7, 95% CI 2.6-17.2, p < 0.001), and single-dose vaccination (OR 3.76, 95% CI 1.19-11.9, p = 0.02) were independent predictors of mortality. APACHE III (score > 70) was the only variable of importance using the MARS model. The "covariate balancing propensity score" analysis did not reveal increased mortality in immunocompromised patients (OR 2.02, 95% CI 0.78-5.23, p = 0.14). Conclusion In this small, single-center study, an immunocompromised state was not an independent predictor of hospital mortality. The prediction models for risk of death indicated a trend towards increased mortality.