7e - Strengthening molecular surveillance of ARIs in the federal state of Bavaria, Germany: Expansion of the Bavarian Influenza Sentinel (BIS+C)

Background : In 2022, the Bavarian Ministry of Health decided to strengthen the Bavarian Influenza Sentinel (BIS+C). In BIS+C, primary care practices collect weekly nasopharyngeal swabs from patients with acute respiratory infections (ARIs) for virological diagnostics, resulting in molecular surveillance of ARIs.

Methods : Since 2009, the BIS+C sentinel has focused on Influenza and Respiratory Synzytial Virus (RSV) diagnosis in children aged <5 years. Due to the pandemic, it has been extended to SARS-CoV-2 and RSV diagnostics in specimens from all age groups. Not only the sampling period was elongated from seasonal to year-round, but also the number of swabs taken per practice and week was increased. To achieve comprehensive coverage throughout Bavaria, additional practices were recruited per municipality through an extensive marketing campaign.

Results : Sentinel participation has more than doubled, from 92 practices (2021/2022) to 197 (2023/2024) resulting in over 10.000 specimens since CW 40/2023. According to RKI definitions, the 2023/2024 season revealed an RSV epidemic caused mainly by the subtype RSV A (CW 45/2023 to 09/2024) in children <4 years. In addition, an Influenza A(H1N1)pdm09 epidemic was defined (CW 51/2023 to 13/2024), that primarily impacted children and middle-aged individuals. Notably, its onset was delayed compared to the previous Influenza A(H3N2) epidemic (CW 44/2022). In both seasons, Influenza B cases (Victoria lineage) occurred since the fiscal year’s change1. SARS-CoV-2 affected mostly adults and the elderly > 60 years and peaked in CW 50/2023 (positivity rate of 33.8%).

Conclusions The BIS+C sentinel network serves as a perfect means for monitoring ARI trends in the Bavarian primary health care sector. It thus constitutes a far-sighted molecular early warning system, enabling a rapid response to potential health threats.