Opportunistic Invasive Infection by Group A Streptococcus During Anti-Interleukin-6 Immunotherapy.

Invasive group A Streptococcus (GAS) in immunocompetent individuals is largely linked to hypervirulent strains. Congenital immunodeficiencies and those acquired from chronic disease or immunosuppressant drugs also increase risk of severe illness. We recovered GAS from the blood of a patient receiving a biologic inhibitor of IL-6. Growth of this serotype M4 isolate in human blood or a murine bacteremia model was promoted by IL-1 or IL-6 inhibition. Hyperinvasive M1T1 GAS was unaffected by IL-6 in both models. These findings based on a natural experiment introduce IL-6 signaling deficiencies as a risk factor for invasive GAS.