The double threat: bacterial and fungal co-/superinfection in viral pneumonia

INTRODUCTION: Respiratory viral pneumonias are a leading cause of severe respiratory failure and intensive care unit (ICU) admission worldwide. Although viral infection itself drives significant morbidity and mortality, secondary bacterial and fungal superinfections represent a critical 'double threat' in critically ill adults, exacerbating lung injury, prolonging organ dysfunction, and complicating antimicrobial management. Experience from the Influenza A (H1N1) pdm09 and SARS-CoV-2 pandemics highlights a persistent mismatch between low documented bacterial co-infection rates and widespread empiric antibiotic exposure, underscoring diagnostic uncertainty and antimicrobial stewardship challenges in the ICU. AREAS COVERED: This review examines the epidemiology, immunopathogenesis, and diagnostic approaches to bacterial and fungal superinfection in adult ICU patients with severe viral pneumonia. Evidence is synthesized from large ICU cohorts, pandemic data, and established consensus definitions for influenza- and COVID-19-associated pulmonary aspergillosis (IAPA, CAPA). The review discusses advances in molecular diagnostics, lower respiratory tract sampling, bronchoalveolar lavage - based mycology, and biomarker-guided strategies, with a focused literature search of ICU-specific studies. EXPERT OPINION: Bacterial and fungal superinfections, while infrequent, carry substantial clinical impact in severe viral pneumonia. A multimodal, ICU-adapted diagnostic strategy integrating pathogen detection with host-response assessment is essential to support timely therapy, enable antimicrobial de-escalation, and align superinfection management with stewardship principles.