Overall activity

The number of iGAS cases reported in quarter 2 2024 (105 cases) reduced by 15.3% when compared to quarter 2 2023 (124 cases) and is within the range reported in quarter 2 from 2017-2023 (16 to 124 cases).

With the exception of 2017, 2022 and 2024, iGAS activity was highest in the first quarter of each year.

As expected with seasonal patterns of iGAS activity, quarter 2 2024 iGAS case numbers were higher than reported in quarter 3 (72 cases) and quarter 4 2023 (74 cases) but similar to quarter 1 2024 (104 cases, see Figure 1).

Age

Historically, iGAS cases are more commonly reported in older adults with case numbers increasing with age.

In quarter 2 2024, most cases were reported in those aged 45-64 years (32.4%, 34 out of 105) and 65 years and older (31.4%, 33 out of 105).

When compared with quarter 2 2023, there were reductions in case numbers reported from all age groups except those aged 45-64 years and the largest proportions were in adults aged 65 years and older (33.1%, 41 out of 124) followed by 45-64 years (23.4%, 29 out of 124) and 15-44 years (22.6%, 28 out of 124) (Figure 2). 

NHS board activity

In Quarter 2 2024, all NHS boards – except NHS Orkney and NHS Western Isles – reported iGAS cases with larger NHS boards reporting most cases (Figure 3):

• NHS Lothian – 24.8% (26 out of 105 cases)
• NHS Greater Glasgow and Clyde – 15.2% (16 out of 105 cases)
• NHS Tayside – 12.4% (13 out of 105 cases)

iGAS mortality

The were 10 deaths among the 105 iGAS cases reported in Quarter 2 2024 with a case fatality rate (CFR) of 9.5%. This is within the range reported annually since 2018 (Table 1).

Most of the deaths (60.0% or 6 out of 10 cases) and the highest CFR (18.2% or 6 out of 33 cases) occurred in adults aged 65 years and above suggesting that older people are more susceptible to iGAS and its complications.

iGAS emm type

In Quarter 2 2024, emm typing was available for 76.2% of cases and 32 different emm types were identified.

Historically, emm type 1 has been the most commonly identified emm type in Scotland.

However, in Quarter 2 2024 the most common was emm type 3.93 (20 cases, 25.0%) followed by:

• emm type 89.0 – 10 cases (12.5%)
• emm type 28.0 – 6 cases (7.5%)

Between quarter 1 and quarter 2, the proportion of emm type 1.0 cases has reduced further to account for only 6.3% of the cases in quarter 2 compared to 12.2% in quarter 1. Similarly, the proportion of cases with emm type 76.0 has decreased from 8.1% in Q1 2024 to 2.55 in quarter 2 2024. By contrast, the proportion of emm type 89.0 cases has increased from 1.4% in quarter 1 2024 to 12.5% in quarter 2 2024.

The changing distribution of iGAS emm types and any potential impact on transmissibility and disease severity are not yet fully understood.