Introduction

In 2022, the Bavarian Ministry of Health decided to strengthen the Bavarian Influenza + Corona Sentinel (BIS+C).

Goals

For molecular surveillance of acute respiratory infections (ARIs), sentinel practices (general practitioners and paediatricians) send weekly nasopharyngeal swab samples from patients with ARIs to the LGL for diagnosis of influenza, SARS-CoV-2, and respiratory syncytial virus (RSV).

Materials and methods

The BIS+C has initially focused on the diagnosis of influenza cases, as well as RSV cases in children <5 years of age. Due to the pandemic, SARS-CoV-2 diagnostics has been included in the sentinel. Since calendar week (CW) 40/2021, all samples were additionally tested for RSV regardless of patient age. Furthermore, the ARI swab sampling period has been extended from seasonal to year-round. To achieve comprehensive coverage of BIS+C sentinel surveillance for ARI pathogens throughout Bavaria, additional BIS+C sentinel practices were recruited per county or urban municipality with respect to population density through an extensive marketing campaign.

Results

Participation in BIS+C has more than doubled, from 92 practices in 2021/2022 to 196 in 2023/2024. So far, the 2023/2024 season in Bavaria has shown an RSV epidemic according to RKI definitions since CW 45/2023, mainly affecting children <4, followed by the age group 5-14 years, and an influenza A(H1N1)pdm09 epidemic beginning in CW 51/2023, primarily impacting children and middle-aged individuals. Notably, influenza's onset was later compared to the previous season (CW 44/2022). SARS-CoV-2 viruses have predominantly affected adults and the elderly > 60 years of age.

Summary

The BIS+C sentinel network represents a molecular early warning system that monitors influenza, SARS-CoV-2, and RSV in Bavaria. Together with the Bay-VOC - and wastewater monitoring project, BIS+C is one of the three pillars of molecular surveillance of viral respiratory infections in Bavaria.