This study aims to emulate a hypothetical target pragmatic multi-center, non-blinded trial of adult inpatients in the PINC AITM dataset with B-lactam treated culture confirmed monomicrobial invasive Group A streptococcus (GAS) between the years 2015-2021

Inclusion Criteria:

• Adult inpatients patients (=> 18 y of age)
• Monomicrobial Group A streptococcus invasive infection
• Primary therapy with a B-lactam agent (initiated before or on same day as adjunctive anti-toxin therapy)

Exclusion Criteria:

• Patients with a polymicrobial GAS culture (non-GAS organisms identified on eligibility GAS culture)
• Patients who received linezolid but have a documented linezolid resistant isolate
• Patients with GAS infections of non-sterile non-invasive sites (i.e sites which do not meet above mentioned inclusion criteria) which include but not limited to the lower urinary tract, upper respiratory tract
• Patient with concomitant MSSA/MRSA invasive infection (+/- seven days of index GAS eligibility culture)
• Patients who receive both anti-toxin agents (violation of protocol)
• Patient who do not complete at least 3 days of B-lactam (violation of protocol)

Adult inpatients with culture confirmed proven or probable invasive monomicrobial GAS in the PINC AI (TM) Database admitted between 2015-2021 who receive a β-lactam therapy for a minimum of 3 days within 3 days of culture will be eligible for inclusion in the emulated trial. Patient will be included if they then receive an anti-toxin therapy within 3 days of culture being drawn, as long as B-lactam therapy has been initiated prior or on the same day as antitoxin therapy.