gms | German Medical Science

Background: Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infection. During the COVID-19 pandemic and with non-pharmaceutical interventions (NPIs) e.g contact restrictions substantial changes to RSV seasonality and epidemiology occurred. We aim to describe serological indicators and contact frequency within a German cohort (MuSPAD) and explore the effect of contact patterns and household composition on serological indicators for RSV reinfection in adults from 2020 to 2023.

Methods: MuSPAD participants contributed serum samples and completed contact surveys across three rounds. RSV post-F-protein titers were quantified via multiplex immunoassays, with potential cutoffs explored for presumed reinfection. Contact frequencies within and outside households were described. To assess the effect of contact behavior and household composition on serological indicators using a directed acyclic graph, logistic regression models, and tested interaction.

Results: Geometric mean ratios of post-F-protein titers were 0.94 (CI-95: 0.93, 0.96) from 2020/21 to 2022 and 1.05 (CI-95: 1.03, 1.08) from 2022 to 2023. A titer increased cutoff of >=1.2 identified 7% as “reinfected” in the 2021/22 and 16% in 2022/23. The bootstrapped mean (CI-95) of contacts reported per participant within 24 hours was 8.27 (7.94, 8.55) between January - August 2021, 16.54 (15.81, 17.25) between June-July 2022 and 9.0 (8.35, 9.59) between April-June 2023. Contact patterns varied by age and gender, with women more inclined towards non-household contacts (29% vs. 22/21% for men) and men showing higher propensity for household-only contacts (14-20% vs. 16-26%). Participants aged up to 49 and those 80+ tended towards non-household-only contacts in 2020/21, while those between 50 and 79 engaged in contacts in both settings. In 2022, all age-groups exhibited a predominant trend of contacts in both settings, except for those above 80 favoring household-only contacts, consistent with observations in 2023.

There is no evidence that the number of non-household contacts of participants effected their increase of titer in post-F-protein. However, every additional household contact in 2020/21 appears to increase the odds for an increased titer in 2022 (OR: 1.2, CI-95: 0.98, 1.44, adjusted OR: 1.73, CI-95: 1.19, 2.6, with interaction term: OR: 5.27, CI-95: 1.21, 24.1), but not in 2023 (OR: 0.94, CI-95: 0.82, 1.05, adjusted OR: 1, CI-95: 0.89, 1.11). We noted interaction of contacts within household and household composition in the first period (for living with adults (OR: 0.08, CI-95: 0, 0.65) and living with kids (OR: 0.25, CI-95: 0-05, 1.09).

Conclusion: Combining serological indicators of reinfection with a novel multiplex assay and longitudinal contact assessments, we propose ratios of >=1.2 and >=1.25 in post-F-protein titers between two years as plausible cutoffs for presumed reinfection. Dynamics of reinfection with RSV varied across age-groups between 2021 and 2022, with a higher proportion of participants showing indications of reinfection in the 30-39 age group in 2021 but not in 2022. Female participants and those aged 30 to 39 increased their contacts notably after the lifting of restrictions. No effect of contact frequency on serological indicators for reinfection outside the household was found, although household contacts in 2020/21 may have elevated the likelihood of presumed reinfection.

The authors declare that they have no competing interests.

The authors declare that a positive ethics committee vote has been obtained.