Case Report: Community-acquired pneumonia due to coinfection with Streptococcus pneumoniae and Legionella pneumophila

Streptococcus pneumoniae is the most common bacterial cause of CAP, whereas Legionella pneumophila is an important atypical pathogen frequently associated with severe disease and an increased risk of complications. Coinfection with these two microorganisms is less frequently reported and may pose significant diagnostic and therapeutic challenges. We present the case of a 62-year-old non-smoking man with multiple comorbidities, including type 2 diabetes mellitus, coronary artery disease, left bundle branch block, arterial hypertension, and hypercholesterolemia, who presented with a 4-day history of fever, malaise, headache, progressive dyspnea, chest pain, productive cough, and purulent sputum. Chest imaging revealed bilateral bronchopneumonia with pleural effusion. Microbiological investigations confirmed coinfection with Legionella pneumophila serogroup 1 by urinary antigen testing and Streptococcus pneumoniae by real-time PCR (BioFire) from sputum, with a bacterial load of 10⁷, consistent with acute infection. The patient received combined antimicrobial therapy targeted at the identified etiological pathogens, together with comprehensive supportive and symptomatic treatment to address the multiple complications that occurred during the course of hospitalization. This therapeutic approach resulted in gradual clinical improvement and complete recovery. This case highlights the importance of considering bacterial coinfection in severe community-acquired pneumonia with multiorgan involvement and the value of combining urinary antigen testing with molecular diagnostics for early etiological diagnosis and timely targeted treatment.