Annual Surveillance Report 2022/23

1 Main Findings (week 40, 2022 to week 20, 2023)

  • The GP flu/flu-like-illness (flu/FLI) consultation rate was above the baseline intensity level between week 49, 2022 and week 02, 2023.

  • A total of 3,695 unique episodes of influenza were identified. For RSV, there were 1,443 unique episodes identified.

  • 39 sentinel samples were positive for influenza from 190 samples submitted for testing (20.5% positivity). For RSV, two samples were positive from 125 samples submitted for testing (1.6% positivity).

  • 3,678 non-sentinel samples were positive for influenza from 76,018 samples submitted for testing (4.8% positivity). For RSV, 1,462 samples were positive from 26,572 samples submitted (5.5% positivity).

  • There were 33 respiratory outbreaks reported to the PHA Health Protection acute response duty room.

  • 1,761 community-acquired emergency influenza hospital admissions were recorded. For RSV, there were 914 admissions.

  • 2,993 respiratory associated deaths out of 11,520 all-cause deaths were reported (26.0%).

  • Excess all-cause mortality was reported for eight weeks (weeks 42-44, 48, 50-52 and 01).

2 Introduction

In Northern Ireland, surveillance of influenza and other respiratory viruses is carried out by the Respiratory Surveillance Team at the Health Protection Directorate of the Public Health Agency (PHA).

Data are collated from a number of surveillance systems to provide information on the type of influenza strains circulating in the region, the timing of influenza activity, the burden of influenza on the community and health services, and the degree of excess mortality. Surveillance systems used and methods can be found at the end of this report.

Surveillance is carried out all year, with the Influenza Surveillance Bulletin being published weekly, from week 40, 2022 (reporting commenced October 3rd 2022) to week 20, 2023 (reporting ended 21st May 2023).

Measures put in place to control the COVID-19 pandemic have affected the transmission of influenza and other respiratory viruses during the previous two seasons. Changes in healthcare-seeking patterns also affect some influenza indicators directly and indirectly. Therefore, data contained within this report should be interpreted with caution, especially when comparing with previous seasons.

3 Incidence and Prevalence of Influenza and RSV

3.1 Consultation rates for flu/FLI

Since the beginning of the COVID-19 pandemic, the offer and uptake of GP consultations has changed. As a result, consultation rates in the most recent period are unlikely to be directly comparable to pre-pandemic and pandemic years.

The GP flu/FLI consultation rate exceeded the pre-epidemic threshold (low activity) of 11.3 per 100,000 population in week 49, 2022 and reached moderate activity in week 51, 2022 (≥21.8 per 100,000 population). Rates remained at moderate activity for a further two weeks before returning to low activity in week 2, 2023, and then returning to baseline activity from week 3, 2023 and remained low until the end of the season (Figure 3.1). The highest consultation rate was reported in week 51, 2022 (35.8 per 100,000 population).

Consultation rates were highest in the 0-4 age group in week 51, 2022 (40.9 per 100,000 population), followed by the 65+ age group in week 1, 2023 (39.9 per 100,000 population).

Supplementary tables of Flu/FLI consultation rates by Local Government District (LGD) and age groups are shown at the end of this report.

Northern Ireland GP consultation rates for ‘flu/FLI’ 2019/20 – 2022/23

Figure 3.1: Northern Ireland GP consultation rates for ‘flu/FLI’ 2019/20 – 2022/23

The baseline MEM threshold for Northern Ireland is 11.3 per 100,000 population for 2022-23. Low activity is 11.3 to <21.8, moderate activity 21.8 to <57.0, high activity 57.0 to <87.1 and very high activity is ≥87.1 per 100,000 population.

3.2 Episodes of influenza

The number of new influenza episodes increased steadily from week 40, 2022, with the highest number of unique episodes being reported in week 52, 2022 (636 episodes). The number of unique episodes of influenza B surpassed influenza A from week 6, 2023 (Figure 3.2). From week 40, 2022 to week 20, 2023, 1,119 episodes were typed as Flu A(H1), 498 were Flu A(H3), 1,591 were Flu A(not subtyped) and 487 were Flu B.

Episode rates were highest in the 65+ age group in week 52, 2022 (83.5 per 100,000 population), followed by the 0-4 age group in the same week (71.7 per 100,000 population). The other age groups reported similar, but lower increases in episode rates during the same period in the influenza season (Figure 3.3).

Supplementary tables of unique episodes and weekly episode rates by age groups are shown at the end of this report.