Retroperitoneal infection associated with Streptococcus dysgalactiae subsp. equisimilis bacteremia and lower-extremity cellulitis: a case report.

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized β-hemolytic streptococcus causing invasive infections resembling those caused by Streptococcus pyogenes. Although SDSE bacteremia commonly arises from skin and soft tissue infections, retroperitoneal infection has rarely been described. We report SDSE bacteremia with retroperitoneal lymphatic involvement suggesting possible extension from lower-extremity cellulitis. A 70-year-old man with diabetes and alcoholic liver disease presented with fever and difficulty moving and was admitted with septic shock. Initial computed tomography showed retroperitoneal lymphadenopathy, retroperitoneal inflammatory changes, and right inguinal lymphadenopathy, without gastrointestinal perforation, pancreatitis, obstructive uropathy, or abscess. On hospital day 2, right lower-leg cellulitis became evident. Blood cultures grew SDSE expressing Lancefield group A antigen. Follow-up computed tomography on hospital day 7 showed persistent retroperitoneal inflammatory changes, dilated retroperitoneal lymphatic vessels, and a thrombus near the left venous angle. These findings were compatible with retroperitoneal lymphadenitis and lymphangitis with secondary inflammation of the surrounding retroperitoneal tissue. No persistent bacteremia, infective endocarditis, osteoarticular infection, abscess formation, or other uncontrolled metastatic focus was identified. Antimicrobial therapy was discontinued on hospital day 15 after bacteremia clearance and clinical improvement. Anticoagulation was administered for the thrombus near the left venous angle and a subsequently detected pulmonary embolism. At 3 months, the retroperitoneal lesions and thrombi had resolved, and no relapse occurred during 6 months of follow-up. This case suggests that SDSE cellulitis may rarely be associated with retroperitoneal lymphatic involvement. In the absence of abscess formation or persistent metastatic infection, prolonged antimicrobial therapy may not necessarily be required.