3.1 Trends

Scarlet fever notifications in Northern Ireland have remained relatively low in recent weeks. (Figure 3.1; incident cases are shown by date of recording by PHA). January had the highest number of notifications recorded by PHA in 2023, likely attributable to delays in the statutory notification process over the Christmas and New Year holiday period due to cases being reported by date recorded, not date of symptom onset. (Figure 3.2). Notifications have since steadily declined. Supplementary Table 7.1 shows counts of probable and confirmed scarlet fever notifications recorded by week.

Figure 3.1: Incidence of scarlet fever notifications, by week of notification, all ages, 2022 - 2024.

Please note: in the figure above the most recent week is incomplete

Figure 3.2: Incidence of scarlet fever notifications, by month of notification, all ages, 2016 - 2024.

Please note: in the figure above the most recent month is incomplete

4.1 Trends

IGAS reports typically follow a seasonal pattern, with cases typically highest in spring. NI experienced unusually high levels in December 2022 and January 2023. (Figure 4.1). The number of monthly cases reported recently is comparable to previous years.

Figure 4.1: Incidence of IGAS reports, by month of report, all ages, 2016 - 2024.

Please note: in the figure above the most recent month is incomplete

5.1 Four Nations Rapid Review of IGAS

On 4th March 2024 a rapid review into IGAS deaths in children that occurred at the end of 2022 and early 2023 was published in collaboration with PHA, Public Health Wales (PHW), UK Health Security Agency (UKHSA), Public Health Scotland and the National Child Mortality database. This review, Four Nations Rapid Review of iGAS Deaths in Children can be accessed by visiting https://phw.nhs.wales/fournationsigasreport.

6.1 Scarlet Fever Case Definitions

Confirmed case: Clinical diagnosis of scarlet fever by a health professional and GAS detected on a throat swab

Probable case: Clinical diagnosis of scarlet fever by a health professional

6.2 IGAS Case Definitions

Confirmed case: An individual who has an IGAS infection, which is defined as the isolation of group A Streptococcus (GAS) from a normally sterile body site, such as blood, cerebrospinal fluid, joint aspirate, pericardial/peritoneal/pleural fluids, bone, endometrium, deep tissue or deep abscess at operation or post-mortem. It also includes severe GAS infections, where GAS has been isolated from a normally non-sterile site such as throat, sputum, vagina or wound in combination with a severe clinical presentation, such as streptococcal toxic shock syndrome (STSS), necrotising fasciitis, pneumonia, septic arthritis, meningitis, peritonitis, osteomyelitis, myositis or puerperal sepsis, and cellulitis accompanied by a systemic presentation necessitating hospitalisation.

Probable case: An individual who has a severe clinical presentation consistent with IGAS infection, such as STSS, necrotising fasciitis, myositis, puerperal sepsis, and cellulitis accompanied by a systemic presentation necessitating hospitalisation, in the absence of microbiological confirmation of GAS AND either:

1. the clinician considers that GAS is the most likely cause

2. there is an epidemiological link to a confirmed case.