Overwhelming post-splenectomy infection caused by Streptococcus agalactiae, sequence type 10 with capsular serotype Ib encapsulating ST10/1b occurring 30 years after splenectomy: a case report.

Overwhelming post-splenectomy infection (OPSI) is a rapidly progressive and potentially fatal condition that affects individuals without a spleen. Encapsulated bacteria are among the most common pathogenic microorganisms of OPSI. Streptococcus agalactiae (group B streptococci; GBS) is an encapsulated Gram-positive pathogen. Although it causes various invasive infections in adults, including bacteremia, septic shock, and toxic shock syndrome, it has rarely been associated with OPSI. We describe a case of GBS-associated OPSI in a 72-year-old man who developed septic shock 30 years after undergoing splenectomy for gastric cancer. The patient exhibited acute systemic illness and severe musculoskeletal pain without an identifiable infectious focus. S. agalactiae was identified in his blood cultures and whole-genome sequencing identified the isolate as sequence type 10 with capsular serotype Ib. The patient recovered after prompt hemodynamic support and β-lactam therapy. Subsequently, appropriate post-splenectomy vaccinations and standby antibiotics were administered. This was an unusual case of OPSI caused by GBS and associated with fulminant systemic inflammatory response. Our case highlights the lifelong vulnerability of individuals with asplenia, even decades after splenectomy. This is also the first report of genetically characterized GBS-associated OPSI, providing the capsular serotype of GBS-associated OPSI and novel molecular epidemiological insights into this rare clinical entity.