Microbiological spectrum, clinical outcomes, and risk factors for bloodstream infections during immune checkpoint inhibitor therapy: a nested case-control study.

[BACKGROUND] Immune checkpoint inhibitors (ICIs) modulate host immunity and may increase infection risk. The pathogen profile, outcomes, and predictors of bloodstream infections (BSIs) in ICI recipients are not well defined; we aimed to characterise these features and identify independent risk factors.

[METHODS] We performed a retrospective nested case-control study within a cohort of 2,584 adult cancer patients who received ICIs at a tertiary centre from January 2018 to December 2023. We identified 185 BSI cases occurring during or within 90 days after the last ICI dose and matched each case 1:2 to infection-free controls by cancer type, ICI agent, and time at risk. Demographics, comorbidities, cancer and treatment details, laboratory values, concomitant medications, and outcomes were extracted and analysed using conditional logistic regression.

[RESULTS] Cases (median age 62 years; 65.4% male) had predominance of gram-positive organisms (54.1%), led by Staphylococcus aureus (18.4%) and Enterococcus spp. (12.4%); gram-negatives comprised 37.8% with Escherichia coli being the most frequent (15.1%), and opportunistic pathogens (Listeria, Candida) made up 8.1%. Multivariable analysis identified prior corticosteroid use ≥14 days (prednisone equivalent ≥10 mg/day for ≥14 days; adjusted odds ratio [aOR], 4.12; 95% CI, 2.58-6.59;  < 0.001), proton pump inhibitor use (aOR 2.05; 95% CI 1.31-3.22), and baseline absolute lymphocyte count <1.0 × 10^9/L (aOR 2.33; 95% CI 1.48-3.68) as independent predictors. All-cause 30-day mortality among cases was 24.9%.

[CONCLUSION] BSIs in ICI-treated patients involve a broad pathogen spectrum, including opportunists and are associated with substantial mortality; corticosteroid exposure, PPI use, and lymphopenia identify high-risk patients who may benefit from targeted surveillance and preventive strategies.