Nonpharmaceutical Interventions Affected Characteristics, Seasonality of RSV

Nonpharmaceutical interventions (NPIs) were found to have an effect on the characteristics and seasonality of respiratory syncytial virus (RSV) in the wake of the COVID-19 pandemic, according to a study published by Viruses. Further studies on this relationship are warranted, according to the authors.

RSV is a widespread respiratory pathogen that affects all age groups, but especially older adults and young children. The virus can cause lower respiratory tract infections, including obstructive bronchiolitis. NPIs, including nationwide lockdowns and closings of schools, were implemented during the first months of the COVID-19 pandemic, which led to reduced RSV activity in the winter of 2020 and 2021.

The study aimed to characterize the local epidemiology of infections of RSV and the age distribution during the 2017-2018, 2018-2019, and 2019-2020 seasons before the pandemic and the 2021-2022 season after the pandemic.

Respiratory samples were collected between October 2017 and September 2022 from both pediatric and adult inpatients and outpatients at the University Hospital of Leipzig, Germany. Re-testing was done within 6 weeks and defined as a single case; all data about underlying conditions from the day of RSV infection were retrieved retrospectively. Patients were considered immunocompromised if they were receiving chemotherapy, had severe chronic neutropenia, were receiving steroids or other immunomodulatory medicines, had aplasia of the thymus gland, or had an infection of HIV.

If respiratory symptoms were not present at the time of admission and occurred 72 hours after admission, the RSV infection was classified as nosocomial. PCR tests were used to assess COVID-19 infection. The RSV seasons before the start of the COVID-19 pandemic were defined as October 1 through September 30 of the following year; the RSV season after the COVID-19 pandemic was the spring of 2021 after the alleviations of NPIs through the following year.

There were a total of 908 samples originating from 803 unique cases that had the presence of RSV. Most cases were observed in calendar week 41 of 2017 and week 22 of 2018 during the 2017-2018 season. Similarly, the 2018-2019 season found the most cases between week 47 of 2018 and week 22 of 2019, whereas the 2019-2010 season found the most cases between week 45 of 2019 and week 14 of 2020. The peak of RSV detections occurred in February in all 3 seasons prior to the pandemic. The 2021-2022 season found that the most cases were observed between week 27 of 2021 and week 9 of 2022.

The lowest temperatures of the year were found to coincide with RSV detection, with peak RSV detections in adults coming in March and peak pediatric cases coming in February in the 2017-2018 season; the adult and pediatric patients had their RSV detection peaks at the same time in the other seasons.

Overall RSV positivity rates in the main detection intervals had a range of 4.0% in the 2019-2020 season to 11.5% in the 2021-2022 season, with the 2017-2018 season and the 2018-2019 season having 6.4% positivity and 8.3% positivity respectively. These numbers differed when looking at the cohorts separately, with the adult cohort having peak positivity rates of 3.8%, 6.8%, 3.8%, and 9.4% for the 2017-2018, 2018-2019, 2019-2020, and 2021-2022 seasons respectively; the pediatric patients had 25.6%, 30.7%, 27.7%, and 48.9% for the same seasons, respectively, indicating significantly more pediatric cases in the post-pandemic season.

A higher percentage of siblings were found to contract RSV in the 2021-2022 season and a higher percentage of outpatients was also found. A lower frequency of fever, pneumonia, and usage of budesonide inhalations were associated with RSV infections in 2021-2022. However, co-infections were higher in pre-pandemic seasons and had different compositions of pathogen types. The adult cohort had a significantly younger mean age in the 2021-2022 season compared with the pre-pandemic seasons (47 vs 64 years). Arterial hypertension and cardiovascular diseases were less frequent in the 2021-2022 seasons.

Genotyping for RSV infection could have led to biases, and asthma could have been underestimated in the pediatric cohort. Proof of causality could also not be shown due to the retrospective design of the study. Severe cases could have been favored due to sampling in a hospital. The age spectrum also could have been an underrepresentation of patients who weren’t in high-risk groups. There was also a limited number of adult RSV cases to assess.

The researchers concluded that these results indicated that pre-existing immunity and adherence to contact restrictions measures likely influenced the the resurgence of RSV in pediatric and adult populations.

"Additional epidemiologic studies or population-based surveillance programs are warranted," the authors wrote, "as behavioral changes are likely to have an influence on the circulation of respiratory pathogens for the near future."

Reference

Honemann M, Thiem S, Bergs S, et al. In-dept analysis of the re-emergence of respiratory syncytial virus at a tertiary care hospital in Germany in the summer of 2021 after the alleviation of non-pharmaceutical interventions due to the SARS-CoV-2 pandemic. Viruses. 2023;15:877. doi:10.3390/v15040877