Lethal Legionella Pneumonia With Bacteremia Due to Serotype 3 Co-infected With Staphylococcus aureus and Haemophilus influenzae

A 66-year-old man with no relevant medical history developed pneumonia. Urine antigen tests for pneumococcus and <i>Legionella</i> serotype 1 (the most common serotype) were negative, but sputum culture was positive for methicillin-susceptible <i>Staphylococcus aureus</i> (MSSA) and β-lactamase-negative <i>Haemophilus influenzae</i> (BLNAR). The patient was treated with meropenem and azithromycin, but an aerobic blood culture became positive on day 4, and mass spectrometry analysis indicated the presence of <i>Legionella</i> species. Subculture on buNrNL charcoal yeast extract (BCYE)-α agar identified <i>Legionella pneumophila</i> serotype 3. The patient was diagnosed with pneumonia caused by MSSA and BLNAR, as well as pneumonia/bacteremia due to <i>Legionella</i> <i>pneumophila</i> serotype 3. Despite changing the antibiotics to meropenem plus lascufloxacin and adding hydrocortisone and venovenous extracorporeal membrane oxygenation (V-V ECMO), the patient died. In patients with severe pneumonia, co-infection with <i>Legionella</i> species, including rare serotypes, should be considered, and universal rapid antigen tests are necessary to ensure rapid diagnosis and appropriate treatment.