Severe Legionella pneumophila pneumonia complicated by rhabdomyolysis and myocarditis: a case report

Legionella pneumophila is an important cause of severe community-acquired pneumonia and may be accompanied by extrapulmonary abnormalities. Hyponatremia and hepatic biochemical abnormalities are recognized clinical clues, whereas rhabdomyolysis and myocarditis are uncommon complications. In severe community-acquired pneumonia, guideline-recommended rapid and targeted microbiological tests should be prioritized before broad metagenomic sequencing. We report a 57-year-old previously healthy man who presented with high fever, cough with scant sputum, shortness of breath, diffuse myalgia, weakness, headache, mild disorientation, and dark-colored urine. Laboratory tests showed marked systemic inflammation, rhabdomyolysis, hyponatremia, hepatic injury, and elevated cardiac biomarkers. Chest computed tomography revealed multilobar pulmonary infiltrates predominantly involving the left lung. Before mNGS, pharyngeal-swab respiratory pathogen RNA testing performed by the infectious diseases service was negative, although the assay did not include a Legionella target, and routine culture of bronchoalveolar lavage fluid (BALF) yielded no growth. Blood cultures obtained during the diagnostic evaluation also remained negative. Legionella urinary antigen testing was not available at our institution at the time of admission, and targeted lower-respiratory Legionella nucleic acid testing was not performed. BALF mNGS was subsequently undertaken and detected 800 sequence reads of Legionella pneumophila, whereas simultaneous whole-blood sequencing yielded only a low-level concordant signal of 14 reads that was not interpreted as evidence of bacteremia or systemic dissemination. Cardiac magnetic resonance imaging showed subepicardial late gadolinium enhancement compatible with myocarditis. Initial empirical omadacycline was subsequently changed to levofloxacin because of suspected adverse reactions, after which fever and systemic abnormalities gradually resolved. This case illustrates severe Legionella pneumophila pneumonia complicated by rhabdomyolysis and myocarditis and underscores the importance of diagnostic and antimicrobial stewardship. In severe community-acquired pneumonia, Legionella urinary antigen testing and targeted lower-respiratory culture or nucleic acid testing should be prioritized when locally available. Where urinary antigen testing is unavailable, targeted lower-respiratory Legionella testing or referral testing should be considered where feasible before broad metagenomic sequencing. Metagenomic sequencing should be regarded as a complementary or rescue approach when recommended conventional and targeted tests are unavailable or unrevealing, rather than as routine first-line testing.