Strep A infection. Conceptual coloured scanning electron micrograph (SEM) of Strep A infection. Strep A infection is usually a mild illness that can be easily treated with antibiotics. But in rare circumstances, it can get into the bloodstream and cause a serious illness, called invasive Group A strep. A recent increase in invasive group A strep (iGAS) infections among children has occurred in 2022-2023. iGAS infections include necrotizing fasciitis and streptococcal toxic shock syndrome. This images shows red blood cells and strep A bacteria (purple). Magnification: x 5000 when printed at 10 centimetres across.