Trends in human parainfluenza virus in Scotland before and after the peak of the COVID-19 pandemic, January 2017 to October 2023.

BackgroundHuman parainfluenza viruses (HPIV) commonly cause upper respiratory tract infections, with potential for severe lower respiratory complications. Understanding seasonal increases informs strategies to prevent HPIV spreading.AimWe examined the impact of COVID-19 on HPIV epidemiological and clinical patterns in Scotland using non-sentinel and sentinel surveillance data.MethodsInformation on HPIV swab positivity (January 2017-October 2023) and demographic data was obtained from the Electronic Communication of Surveillance in Scotland (ECOSS) non-sentinel surveillance sources (laboratory-based data from hospital and community) and the Community Acute Respiratory Infection (CARI) sentinel surveillance programme (enhanced surveillance and symptom data).ResultsIn 2020 during early COVID-19 waves, HPIV detection decreased aligning with lockdowns and preventive measures. In summer 2021, HPIV positivity increased, with HPIV-3 possibly reverting to pre-pandemic seasonality, but HPIV-1 not yet re-establishing alternate-year peaks. Most positive results from non-sentinel sources came from hospital tests. Sentinel surveillance (CARI) complemented non-sentinel data, offering community-level insights. There was no significant difference in CARI swab positivity by sex in any age group. Consistent with historical trends, children under five years exhibited highest test positivity: 9.3% (95% CI: 7.6-11.2) in females and 8.5% (95% CI 7.0-10.2) in males.ConclusionThe COVID-19 pandemic impacted HPIV detection in Scotland. The decline during the pandemic peak and subsequent partial resurgence underscores the complex interplay between viral epidemiology and public health measures. Combining diverse surveillance systems provides a comprehensive understanding of HPIV dynamics. Insights into age-specific and symptom-associated patterns contribute to understanding HPIV epidemiology and refining public health strategies.