The effect of immunosuppression on outcomes in elderly patients with community-acquired pneumonia.

Background: The effect of immunosuppression on clinical manifestations and outcomes was unclear in elderly patients with CAP.

Methods: Elderly hospitalised patients with CAP were consecutively enrolled and were divided into immunocompromised hosts (ICHs) or non-ICHs groups. Clinical manifestations, severity, and outcomes were compared. The logistic regression model was used to determine the association between immunosuppression and outcomes. The primary outcome was 30-day mortality.

Results: A total of 822 patients were enrolled, of whom 133 (16.2%) were immunocompromised. There were no differences between the two groups in vital signs, oxygenation, admission laboratory tests, need for mechanical ventilation and intensive care unit admission, except for a lower lymphocyte count in the ICH group (0.9*10^9/L, IQR 0.6-1.3*10^9/L [ICH group] vs. 1.2*10^9/L, IQR 0.8-1.7*10^9/L [non-ICH group]; p < 0.001). The 30-day mortality in ICHs was 15.8%, significantly higher than the 5.1% in non-ICHs (p < 0.001). The risk distribution of severity was similar between the two groups when assessed by CURB-65 on admission; however, the significant difference was found when assessed by PSI. Notably, in the CURB-65 low-risk group, the 30-day mortality was significantly higher in ICHs than in non-ICHs (9.7% vs. 1.1%, p < 0.001); but there was no difference between ICHs and non-ICHs in PSI low-risk group (3.7% vs. 0.6%; p > 0.05). After adjusting for age, sex, and comorbidities, immunosuppression was significantly associated with a higher risk of 30-day mortality (odds ratio 5.004, 95% CI [2.618-9.530]).

Conclusions: Immunosuppression was independently associated with an increased risk of 30-day mortality. CURB-65 may underestimate the mortality risk of ICHs.