Invasive group A streptococcal disease (iGAS)

• Group A streptococci causes a wide range of illnesses from non-invasive disease such as pharyngitis to more severe invasive infections such as necrotising fasciitis
  
  
• invasive group A streptococcal disease (iGAS) is defined as an infection associated with the isolation of group A streptococci (GAS) from a normally sterile body site
  • three clinical syndromes are described:
    • (i) group A streptococcal toxic shock syndrome differentiated from other types of iGAS infections by shock and multi-organ system failure early in the course of infection
    • (ii) necrotising fasciitis characterised by extensive local necrosis of subcutaneous soft tissues and skin, and
    • (iii) infections characterised by the isolation of GAS from a normally sterile site in patients not meeting the criteria for streptococcal toxic shock syndrome or necrotising fasciitis
      • included in this group are bacteraemia with no identified focus and focal infections such as meningitis, pneumonia, peritonitis, puerperal sepsis, osteomyelitis, septic arthritis, myositis, and surgical wound infections
        
        
• epidemiology of iGAS
  • epidemiology of iGAS is complex
  • more than 120 different M protein serotypes and/or emm sequence types of S. pyogenes exist and numerous distinct streptococcal pyrogenic exotoxins (spes) have been described
  • incidence in 2022 of invasive group A strep in children was reported as (2):
    • 2.3 cases per 100,000 children aged 1 to 4 compared to an average of 0.5 in the pre-pandemic seasons (2017 to 2019)
    • 1.1 cases per 100,000 children aged 5 to 9 compared to the pre-pandemic average of 0.3 (2017 to 2019)
  • deaths within 7 days of an iGAS diagnosis in children under 10 in England
    • 4 deaths in children under 10 during the high season for Group A Strep infection (2017 to 2018)
      
      
• carriage and transmission
  • asymptomatic pharyngeal carriage of GAS is common, with prevalence ranging from 5% to 30% of the general population
  • person-to-person spread of GAS within families or other closed communities has been widely reported with linked cases of invasive and noninvasive infections
  • remains uncertainty about the risk of invasive disease among close contacts of an index case of invasive disease and whether this risk warrants antibiotic prophylaxis
    • a 19-200 fold increased risk among household contacts has been reported in the literature. Recommendations for antibiotic prophylaxis regimens vary by country
      
      
  • people at increased risk for sporadic iGAS include those aged over 65 years of age; those who have recently been infected with varicella virus; those with HIV infection, diabetes, heart disease or cancer; and those using high-dose steroids or intravenous drugs
    
    
• treatment of invasive Group A streptococcus (3)
  • maintain a low threshold for considering pulmonary complications of GAS, especially if presenting with an illness compatible with bacterial pneumonia, and concurrent or recent scarlet fever, or GAS infection or the patient was recently in contact with a case of scarlet fever/GAS infection. Prompt initiation of appropriate antibiotics remains key
  • take a throat swab, blood cultures and other appropriate samples including respiratory culture, tissue and fluid samples
  • in the case of culture-negative fluid specimens, consider the use molecular diagnostics such as GAS-specific PCR or 16S rDNA PCR, as guided by microbiology specialists. Send all positive isolates (or DNA extract if molecular diagnosis only) to UKHSA reference lab for further typing and investigation
  • treatment of suspected or confirmed iGAS should be as directed by local trust guidelines or contact local microbiology for advice
    
    
• chemoprophylaxis
  • oral Penicillin V (250-500mgs QID for 10 days) is the drug of first choice where chemoprophylaxis is indicated.
    • azithromycin (12mgs/kg/day for 5 days) is a suitable choice for those who are allergic to penicillin. In the unlikely event of an allergy to penicillin and azithromycin then contact the local Consultant Microbiologist to discuss a suitable alternative
      
      
• management of contacts of GAS (3)
  • contacts will be identified by HPTs (Health Protection Teams)
    • HPTs will advise on who requires prophylaxis. For information, the following individuals who are close contacts of cases are recommended for antibiotic prophylaxis due to higher risk of severe outcomes:
      • pregnant women from >= 37 weeks gestation
      • neonates and women within the first 28 days of delivery
      • older household contacts (>=75 years)
      • individuals who develop chickenpox with active lesions either seven days prior to onset in the iGAS case or within 48 hours after the iGAS case commences antibiotics, if exposure is ongoing
    • close contact is defined as:
      • prolonged contact with the case in a household-type setting during the 7 days before onset of symptoms and up to 24 hours after initiation of appropriate antimicrobial therapy in the index case

Reference:

• Health Protection Agency, Group A Streptococcus Working Group (December 2004). Interim UK guidelines for management of close community contacts of invasive group A streptococcal disease
• UK Health Security Agency (UKHSA) (December 2nd 2022). UKHSA update on scarlet fever and invasive Group A strep.
• NHS England. Group A streptococcus communications to clinicians (December 2022).