Evidence before this study

A once common cause of childhood death, the incidence and severity of scarlet fever dropped substantially over the course of the 19th and 20th centuries. The reasons for the decline, predating the advent of effective treatments, remain unexplained. Historical epidemiological patterns described in Europe and North America are similar to those seen in modern times, with highest incidence observed in children but with adults also susceptible to disease. Periodicity in disease incidence was well described with epidemic years occurring every 4–6 years.

Subsequent to a prolonged period of low incidence, a sharp increase in scarlet fever incidence was seen in England during the spring of 2014, triggering a number of investigations to assess the effect on individuals, health-care services, settings affected by outbreaks, and identify potential drivers. We searched PubMed for studies published between January, 2000, and July, 2017, with the keywords “scarlet fever” and either “epidemiology” or “surveillance” to identify data from other countries describing recent trends. We also searched ProMED for posts mentioning “scarlet fever” without date restriction. This identified sequential reports from Vietnam, South Korea, Hong Kong, and China describing the sudden and widespread increase of scarlet fever incidence from 2008 onwards. England is the first European country to note such a change.

Added value of this study

Our study is the first to describe the impact of a modern-day resurgence in scarlet fever in Europe. We describe the sudden increase in incidence in 2014 with notifications made for one in 500 children under 10 years of age. Incremental rises were seen in each of the subsequent 2 years, with incidence reaching 33 cases per 100 000 in England and Wales in 2016. Against a historical time series, this places 2016 as the year with the most scarlet fever cases since 1967. Increased incidence was seen across the country and, although incidence varied, no discernible geographical gradient was evident. Outbreaks in schools and nurseries were common. A rise in hospital admission for scarlet fever was seen with one in 40 patients admitted for management of the condition or potential complications. Whole-genome sequencing of clinical isolates identified no novel lineage or associated genetic element and we identified a range of emm types. Comparison with historical UK data showed that the magnitude of the recent upsurge in scarlet fever was unique, suggesting the current phenomenon is not explained by the usual cyclical patterns in disease incidence.

Implications of all the available evidence

To our knowledge, England is the first western hemisphere country to describe an upsurge in scarlet fever incidence after reports in several countries in east Asia. Microbial explanations have been largely excluded, suggesting that other forces are affecting our population's susceptibility to this infection or its capacity to spread. Although most cases of scarlet fever are not severe, the rate of hospital admission during this upsurge is high and the impact on public health has been substantial, particularly with regards to the management of outbreaks. As such, uncovering the drivers behind this rise in scarlet fever outbreaks remains a priority.