Group A streptococcus (GAS) is responsible for mild to very severe disease. The epidemiology of an upsurge in invasive GAS (iGAS) infections in Ireland, 2012–2015 was investigated.

Epidemiological typing of iGAS (n = 473) isolates was performed and compared to non-invasive (n = 517) isolates. Clinical data of notified iGAS was obtained from the national infectious disease information system.

Annual incidences of iGAS cases (n = 561) were 2.33–3.66 per 100,000 population. Bacteraemia was the most common clinical presentation (75%) followed by focus without bacteraemia (19%) and necrotizing faciitis (7%). Streptococcal toxic shock syndrome occurred in 19% of presentations. The main invasive emm types in rank order were emm1, emm3, emm28, emm12 and emm89 whereas emm4, emm28, emm3, emm12, emm89 and emm1 predominated in non-invasive infections. Invasive emm1 and emm3 showed annual fluctuations (15–48% and 4–37%, respectively) and predominated in most clinical presentations of iGAS. Superantigens speA, speG, speJ was associated with iGAS disease and, speC, speI and ssa with non-invasive infections. There was 4.3% erythromycin and 5.6% tetracycline resistance. The main resistant types were emm11, emm28 and emm77.

Cyclic increases in emm1 and emm3 occurred during the iGAS upsurge. Continued surveillance of GAS is therefore essential given the epidemiological changes that occur in a short time period.