Invasive group A streptococcal infection

Invasive group A streptococcal infection is a serious invasive disease caused by Group A Streptococcus (Streptococcus pyogenes), a gram-positive coccus growing in chains that shows beta-hemolysis on blood agar and belongs to Lancefield group A ^[2]. The organism possesses an array of virulence factors that underpin its capacity to invade tissue and cause severe disease ^[1].

In roughly 10% of cases, bacterial superantigen toxins stimulate a large proportion of T cells and lead to streptococcal toxic shock syndrome ^[1]. Pregnant individuals with symptomatic infection often present with flu-like illness including high fever, upper respiratory or gastrointestinal symptoms, early shock, and infection-induced strong uterine contractions suggestive of placental abruption ^[4]. The disease can progress rapidly and severely, with high maternal and infant mortality reported in pregnancy-associated cases ^[4].

Invasive group A streptococcal infections are uncommon but serious, with high case fatality rates ^[1]. Periodic resurgences in industrialized countries have been reported since the 1980s, with current incidence estimated at about 3–4 per 100,000 population ^[1]. During the late COVID-19 pandemic, several high-income countries experienced a surge with notable paediatric morbidity and mortality ^[3].

Group A Streptococcus most often spreads directly from person to person through respiratory droplets ^[2]. It can also be transmitted by contact with infected saliva, wound drainage, or nasal secretions, and rare foodborne or possible fomite-based environmental spread may occur, though pets are not known to transmit the bacteria ^[2].

Prevention focuses on limiting exposure and person-to-person spread, prompt treatment of group A streptococcal infections, and application of infection-control precautions ^[2]. Preventive antibiotics may be used when appropriate, but no vaccine is currently available ^[2].

1. 1 Steer AC et al. Invasive group a streptococcal disease: epidemiology, pathogenesis and management. Drugs. 2012 Jun 18. PMID: 22686614. doi: 10.2165/11634180-000000000-00000. PubMed: https://pubmed.ncbi.nlm.nih.gov/22686614/
2. 2 US Centers for Disease Control and Prevention. Clinical Considerations for Group A Streptococcus | Group A Strep | CDC [Internet]. cited 23 Oct 2026. Available from: https://www.cdc.gov/group-a-strep/hcp/clinical-guidance/index.html
3. 3 Flamant A et al. Invasive group A streptococcal infections: lessons learned from the 2022-23 upsurge. Lancet Infect Dis. 2026 Feb. PMID: 40651487. doi: 10.1016/S1473-3099(25)00343-3. PubMed: https://pubmed.ncbi.nlm.nih.gov/40651487/
4. 4 Yamada T et al. Invasive group A streptococcal infection in pregnancy. J Infect. 2010 Jun. PMID: 20359498. doi: 10.1016/j.jinf.2010.03.011. PubMed: https://pubmed.ncbi.nlm.nih.gov/20359498/