Severe Legionella pneumophila pneumonia identified by targeted next-generation sequencing after nondiagnostic conventional testing: A case report.

Background: Severe community-acquired pneumonia may remain etiologically unresolved when conventional microbiological investigations are negative, delayed, or not readily available. Legionella pneumophila is an important atypical pathogen, but its early recognition is difficult because clinical manifestations are nonspecific and routine culture-based methods may fail to detect it. In such situations, targeted next-generation sequencing (tNGS) of lower respiratory tract specimens can provide additional microbiological evidence to support pathogen-directed treatment decisions. Case presentation: A 79-year-old woman was admitted with fever, dyspnea, and rapidly progressive severe pneumonia. Despite broad-spectrum empirical antimicrobial therapy and intensive care support, she rapidly progressed to septic shock and severe acute respiratory distress syndrome (ARDS). Conventional microbiological investigations, including routine bronchoalveolar lavage fluid (BALF) culture, were nondiagnostic. Targeted next-generation sequencing (tNGS) of BALF subsequently identified Legionella pneumophila with high read abundance, supporting pathogen-directed anti-Legionella therapy. Conclusions: Severe Legionella pneumophila pneumonia may progress rapidly to ARDS, septic shock, and multi-organ dysfunction in elderly patients with major comorbidities. In this case, BALF tNGS provided etiological evidence after conventional microbiological testing was nondiagnostic and helped support pathogen-directed antimicrobial adjustment. Early consideration of Legionella infection and timely use of lower respiratory tract molecular testing may help shorten diagnostic uncertainty and guide antimicrobial decision-making in severe pneumonia.