Invasive pneumococcal disease caused by CO₂-dependent Streptococcus pneumoniae serotype 24F sequence type 162: A case...

We report the case of a man in his 70s who developed invasive pneumococcal disease (IPD) caused by CO₂-dependent Streptococcus pneumoniae. He was admitted with suspected pneumonia based on chest X-ray and computed tomography imaging findings. Ceftriaxone treatment was initiated following the collection of sputum samples and two sets of blood cultures. The antimicrobial treatment was then changed to sulbactam/ampicillin (SBT/ABPC) because urine pneumococcal antigen testing performed on admission was positive. The following day, CO₂-dependent S. pneumoniae was isolated from the blood cultures and sputum sample, leading to a diagnosis of IPD. The patient continued SBT/ABPC treatment (6 g/day) but remained febrile and died 4 days after admission. Serotyping and whole-genome sequence analysis of the isolate revealed that it was serotype 24F and sequence type (ST) 162. A c.536C > T mutation was identified in murF of the isolate compared with S. pneumoniae Spain9V-3. The isolation of CO₂-dependent S. pneumoniae serotype 24F ST162 from pediatric patients in Japan was recently reported. However, to the best of our knowledge, this is the first reported IPD case in an elderly patient caused by CO₂-dependent S. pneumoniae serotype 24F ST162. Thus, even in adults with IPD, caution should be exercised going forward.