Scarlet Fever and IGAS

1 Background

Group A Streptococcus (GAS) are common bacteria. GAS can be present on or in the human body, without causing infection (colonisation), but may cause skin, soft tissue and respiratory infections, including scarlet fever. GAS infections range from mild to very severe. Invasive GAS (IGAS) occurs when the bacteria proliferate in a normally sterile body site, such as the blood, soft tissues or joints. Streptococcal toxic shock syndrome (STSS) can be a severe complication of IGAS, caused by toxins that are produced by GAS, which act on host cells or tissues.

GAS is spread by close contact between individuals, through respiratory droplets and direct skin contact. GAS can also be transmitted indirectly through contact with inanimate objects, such as towels or bedding. GAS is usually diagnosed by microbiological culture of a specimen from the affected site or by a characteristic illness, such as scarlet fever.

The reduced number of cases in 2020 and 2021 during the COVID-19 pandemic is likely in part due to reduced social contact and increased use of preventive measures, and therefore lower transmission during that period. The reduction might also partly reflect changes in healthcare seeking or access during that period.

Public and clinician awareness of GAS infections has changed over time, especially during December 2022, which may contribute to changes in trends. IGAS, being more severe, is likely more consistent over time.

Detail of case definitions and methods are at the end of this document. Data were correct at 9am on 10 July 2024.

2 Cumulative number of scarlet fever and IGAS cases, 2022-2024.

The number of cases from the start of 2022 until the report date are shown (Table 2.1).

Table 2.1: Counts of cases of IGAS and scarlet fever, 2022-2024.
  IGAS Scarlet Fever
  (N=226) (N=3057)
Confirmed 209 (92.5%) 217 (7.10%)
Probable 17 (7.52%) 2840 (92.9%)

3 Scarlet Fever