Pneumococcal Infectious Aortic Aneurysm: A Caution for a Life-Threatening Vascular Complication Caused by Non-Vaccine-covered Serotypes

The 23-valent pneumococcal polysaccharide vaccine (PPSV23) has contributed to reducing pneumonia caused by Streptococcus pneumoniae. However, in Japan, invasive pneumococcal diseases caused by non-vaccine-covered serotypes have increased over the years. A 73-year-old man with a history of PPSV23 was referred to our hospital due to persistent fever and back pain following pneumococcal pneumonia. Contrast-enhanced computed tomography revealed an infectious aneurysm (IAA) at the distal part of the aortic arch. The patient was surgically treated with in situ aortic reconstruction and administered antibiotics. On pathogenic examination of the resected IAA, atherosclerotic changed aortic wall, neutrophil infiltration, and abscesses were observed. Although multiple blood culture tests were negative, tissue culture tests and 16S ribosomal RNA gene-based polymerase chain reaction identified S. pneumoniae. According to capsular polysaccharide synthesis B gene-based serotyping, the serotype was identified as 23A, which is not covered with PPSV23. Serotype 23 is among the most frequently identified serotypes in recent years and associated with in-hospital mortality. Although several pneumococcal serotypes are responsible for lethal infections, the association between these serotypes and disease is uncertain. Further studies on the association between pneumococcal serotypes and IAA, and the development of a broader-covered vaccine are required.Learning objective:•To be able to make a differential diagnosis of invasive pneumococcal pneumonia in patients with persistent fever and newly emerging back pain following pneumococcal infection.•To understand the importance of combining culture tests and molecular analysis to diagnose invasive pneumococcal diseases accurately.•To understand the threat of non-vaccine-covered serotypes even in patients with vaccination histories because the vaccine is limited to only one-fourth of all pneumococcal serotypes.