Epidemiology

Following a prolonged decline in the prevalence of scarlet fever since the late 19th century, outbreaks have re-emerged from around 2011 in mainland China, Hong Kong, South Korea, Taiwan, Singapore, and Vietnam, and from around 2014 in the UK and other European countries.[8][9]​ In England, the incidence of scarlet fever tripled in 2014 compared with 2013.[5] The median age of cases in 2014 was 4 years old and outbreaks were common in nurseries and schools. Over 19,000 cases were reported in England in 2016.[5]

These outbreaks have been associated with low mortality, unlike in previously documented epidemics in the 19th and early 20th centuries.[9] However, it is unclear whether this difference in outcome is due to Streptococcus pyogenes (group A streptococcus [GAS]) strain variation, modern diagnosis and patient care, better sanitation, widespread use of antibiotics, or other factors.[9] Although the mortality rate is low, a resurgence in scarlet fever outbreaks has resulted in increased hospital admissions.[5][9]

Scarlet fever can occur at any age but mainly affects children aged 1 to 10 years, and it is most common in children aged 3 to 6 years. Scarlet fever is uncommon in children <1 year old and in adults.[5][6][7]​ GAS infection is responsible for about 15% to 30% of pharyngitis episodes in children; and for around 5% to 15% of pharyngitis infections in adults.[2] It is estimated that scarlet fever develops in about 10% of patients with GAS pharyngitis.

According to the UK Health Security Agency, notifications of scarlet fever and invasive GAS (iGAS) disease in England were higher than expected from September 2022 to February 2023, with the peak observed in December 2022.[10]​ The notifications have significantly reduced since then and are now in line with the expected number for the time of year.[11] Unusual increases in pulmonary presentations of iGAS infection in children, particularly empyema, have been reported over this period.[12]

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