Pyogenic spondylitis and bilateral psoas abscess caused by Streptococcus agalactiae sequence type 283: A case...

Streptococcus agalactiae sequence type (ST) 283 is an emerging, hypervirulent lineage predominantly identified in Southeast Asia and strongly associated with foodborne transmission linked to raw freshwater fish consumption. While ST283 was responsible for the 2015 outbreak in Singapore, no human infections have been reported in Japan to date. We describe a travel-associated case of invasive ST283 disease in a Japanese man residing in Vietnam in 2010, representing the earliest documented S. agalactiae ST283 infection in a Japanese individual. A 67-year-old previously healthy man developed progressive lower back pain and fever while living in Vietnam and presented to our institution nine days after symptom onset. Computed tomography and magnetic resonance imaging revealed L2-L3 pyogenic spondylitis with bilateral psoas abscesses. Blood cultures grew S. agalactiae susceptible to β-lactams, and targeted intravenous penicillin followed by ampicillin resulted in complete clinical and radiological resolution after six weeks of therapy. Whole-genome sequencing of the bloodstream isolate demonstrated serotype III-ST283 harboring tetM, pilus islands 1 and 2a, AlphaC, and Srr1. Phylogenetic comparison with a publicly available regional dataset showed close relatedness to isolates recovered in Vietnam during 2015-2016, supporting local acquisition in Vietnam in 2010, predating the 2015 Singapore outbreak. This case highlights that ST283 infections may occur outside recognized endemic settings and may be imported into non-prevalent countries through international travel. Clinicians should consider ST283 in invasive S. agalactiae infections with meningoencephalitis, septic arthritis, and/or spinal infections among travelers returning from Southeast Asia and obtain relevant exposure histories, including consumption of raw/undercooked freshwater fish.