Overall activity

When compared to Quarter 1 (January to March 2023, weeks 1 to 13), iGAS activity in Quarters 2 to 4 has decreased.

This would be expected according to the pattern of iGAS observed in previous seasons.

Apart from years 2017 and 2022, iGAS activity was highest in the first quarter of each year. In 2017, iGAS activity was highest in the second quarter but was highest in Quarter 4 of 2022, coinciding with high number of cases seen during the 2022/2023 season.

Age

For years 2018, 2019, 2020, 2021 and 2023, iGAS activity was highest in the first quarter (January to March).

During years 2018, 2019, 2021 and 2023, activity was lowest in the third quarter (July to September).

In relation to age, most iGAS cases were in the older age groups with those aged 45 years and over accounting for 52.7% of the cases in the fourth quarter of 2023 and 70.8% of all the cases in quarter 3 2023.

The 15 to 44 years age groups accounted for 13.9% and 28.4% of all iGAS cases in the third and fourth quarters of 2023, respectively.

NHS board activity

In 2023, all health boards reported at least one case of iGAS.

Activity was highest in Greater Glasgow and Clyde (GGC) with 22.8% (106 out of 465) of the cases and Lothian with 17.2% (80 out of 465) of the cases.

In Quarter 4 2023, GGC and Lothian accounted for 23% of the cases each (17 out of 74).

In 2023, Orkney (three cases), Shetland (three cases) and Western Isles (one case) reported less than five cases each.

It is important to note that these boards have lower populations compared to the other health boards.

iGAS mortality

Meanwhile, the number of iGAS cases and proportion of death were highest in 2023 (465 cases with 55 deaths – a CFR of 11.8%).

The second highest number of cases (381) and CFR (8.9%) was observed in 2019.

During the period 2017 to 2023, the CFR ranged from 2.8 to 11.8%, although historical recording of iGAS cases and related deaths may be incomplete.

iGAS emm type

There were 44 different emm types reported in 2023 among the 71.6% of the cases that were typed.

As observed in previous years, emm type 1.0 with 55.6% of the typed cases was the most common.

The second most common emm type, 12.0, only had 22 cases (6.6%), while 17 emm types had one case reported each.

Conclusion

In summary, iGAS case reports decreased by 63.1% between Quarter 1 2023 and Quarter 3 2023.

This pattern, with activity at a peak in Quarter 1 and lowest in Quarter 3, was observed in five out of the seven-year study period between 2017 and 2023.

In 2023, most of the iGAS (52.7%) cases were in those aged 45 years and above.

There were 55 iGAS deaths reported among the cases in 2023 with a CFR of 11.8%.

Most of the iGAS samples in 2023 were typed (71.6%, 333/465) and emm type 1.0 was the most common type accounting for 55.6% (185/333) of those that were typed.