Lymphopenia in Bacterial Sepsis and SARS-CoV-2 Infection

<b>Background:</b> Sepsis is a life-threatening organ dysfunction that results from an exaggerated host immune response to disseminated infection. The relationship between lymphopenia and sepsis has been extensively studied, and in particular, sepsis-induced lymphopenia is gradually being recognized as an essential factor in the prognosis of sepsis. Notably, sepsis-induced lymphopenia has been associated with worse outcomes, including increased risk of secondary infections, multiple organ failure, and death. Few studies have directly compared the dynamic evolution of lymphocyte counts between different etiologies of sepsis or evaluated their prognostic value using serial measurements. This study aims to explore the temporal dynamics of lymphopenia, but also of neutrophil-to-lymphocyte (NLR) ratio in patients with severe systemic infections and to assess their relationship with in-hospital mortality. <b>Methods</b>: A prospective cohort of 95 adult patients was analyzed. Absolute lymphocyte counts (ALCs) and neutrophil-to-lymphocyte (NLR) ratio values were recorded on Days 1, 3, 5, and 7. Comparisons were made between different infectious etiologies and outcomes, and ROC analysis assessed predictive performance. <b>Results and Conclusions</b>: Patients with viral sepsis ("COVID-19") showed a significant and sustained decrease in lymphocyte counts (<i>p</i> < 0.001) and a progressive increase in NLR (<i>p</i> < 0.001), unlike patients with bacterial sepsis. In correlation with outcome, regardless of etiology, lymphocyte counts were significantly lower in non-survivors from Day 3 onward, while NLR was significantly higher on Day 7 (<i>p</i> = 0.002). Early NLR and ALC had limited predictive value, but longitudinal trends were associated with poor prognosis.