Aim
To alert clinicians to contact risk and prophylaxis for infections due to Group A streptococcus.
Background
Group A streptococcus (GAS) also known as Strep A, beta-haemolytic strep or Streptococcus pyogenes, causes a spectrum of infections including tonsillitis, impetigo and scarlet fever.
There has been an increased incidence of hospitalisations due to invasive GAS (iGAS) infections, generating a number of Victorian Chief Health Officer alerts. ‘Invasive’ disease is defined by the isolation of the bacteria from a sterile site, including blood stream, lungs, cerebrospinal fluid and/or deep muscle layers. iGAS is now a nationally notifiable condition, and in Victoria an urgent notification for medical practitioners and pathology services in Victoria ("Changes to invasive group A streptococcal disease notification", 2024).
Contacts
Individuals at greatest risk of secondary infection following exposure to a case with iGAS include mother-neonate pairs and household or household-like contacts (Communicable Diseases Network Australia, 2024). This risk period is within 30 days of exposure of the index case diagnosed with iGAS. Identification of secondary cases outside of this period is rare.
There should be a lower threshold for those contacts who may be deemed at higher risk due to underlying medical conditions, older or younger age, and/or recent illness.
Definitions of contacts
- Birthing mother-baby pairs
- Household or household-like contacts
- Those who have spent more than 24 hours in the same house as the index case in the week prior to onset of symptoms
- Those who have had sex or had other intimate contact with a case during the case’s infectious period (Communicable Diseases Network Australia, 2024):
Contact prophylaxis with antibiotics
Those at greatest risk of iGAS are those who are at the extremes of age, pregnant women, First Nations people and those with chronic medical comorbidities (Communicable Diseases Network Australia, 2024). Recommendations may involve a risk-benefit assessment for each individual.
It is important that regardless of whether antibiotics are prescribed, relevant contacts should be warned of signs and symptoms which warrant medical attention. Throat swabs are not recommended to determine whether antibiotics are required.
Guidelines for contact prophylaxis vary between jurisdictions (locally in Australia and internationally).
Assuming 100% effectiveness of antibiotic prophylaxis, the number needed to treat (NNT) to prevent a single secondary case of iGAS is comparable to that for invasive meningococcal disease, 271-1022 vs 200 (Hung et al., 2024).
Antibiotic choice for prophylaxis
When giving antibiotics, it should ideally be given within 48 hours of exposure to the index case (but no later than 10 days). Suitable antibiotics in the community include oral cephalexin for ten days, alternatively azithromycin or clindamycin in case of allergy, as outlined in the RCH Clinical Practice Guidelines (RCH Clinical Practice Guidelines, 2024).
References
Changes to invasive group A streptococcal disease notification (2024). https://www.health.vic.gov.au/health-advisories/changes-to-invasive-group-a-streptococcal-disease-notification. Accessed: 23 May 2024.
Hung, T.Y., Phuong, L.K., Grobler, A., Tong, S.Y., Freeth, P., Pelenda, A., Gibney, K.B. and Steer, A.C. (2024). Antibiotics to eradicate Streptococcus pyogenes pharyngeal carriage in asymptomatic children and adults: a systematic review. Journal of Infection, 88(3), p.106104.
Invasive Group A Streptococcal (iGAS) Disease – CDNA National Guidelines for Public Health Units (2024). Version 2.0. Accessed: 23 May 2024.
RCH Clinical Practice Guidelines. Invasive group A streptococcal infections: management of household contacts. https://www.rch.org.au/clinicalguide/guideline_index/Invasive_group_A_streptococcal_infections__management_of_household_contacts/. Accessed: 11 May 2024.
Bibliography
ACT Government. Invasive Group A streptococcal disease (iGAS). https://www.act.gov.au/health/topics/diseases/invasive-group-a-streptococcal-disease-igas Accessed: 11 May 2024.
Department of Health - Victoria (2024). Invasive Group A streptococcal disease (iGAS). https://www.health.vic.gov.au/infectious-diseases/invasive-group-a-streptococcal-disease-igas. Accessed: 11 May 2024.
Government of South Australia. Invasive Group A streptococcal disease (iGAS). https://www.sahealth.sa.gov.au/wps/wcm/connect/public+content/sa+health+internet/conditions/infectious+diseases/igas. Accessed: 11 May 2024.
Government of Western Australia - Department of Health (2023). Invasive Group A streptococcal disease (iGAS). https://www.health.wa.gov.au/Articles/F_I/Invasive-group-A-streptococcal-disease. Accessed: 11 May 2024.
Northern Territory Government (2022). Invasive Group A streptococcal (iGAS). https://health.nt.gov.au/public-health-notifiable-diseases/invasive-group-a-streptococcal-igas. Accessed: 11 May 2024.
NSW Department of Health (2023). Invasive Group A Streptococcal control guideline. https://www.health.nsw.gov.au/Infectious/controlguideline/Pages/invasive-group-a-strep.aspx. Accessed: 11 May 2024.
Queensland Government (2024). Invasive Group A streptococcal (iGAS) disease. https://www.qld.gov.au/health/condition/infections-and-parasites/bacterial-infections/invasive-group-a-streptococcal-disease. Accessed: 11 May 2024.
Tasmanian Government - Department of Health (2023). Invasive Group A Streptococcus (iGAS). https://www.health.tas.gov.au/publications/invasive-group-streptococcus-igas. Accessed: 11 May 2024.