Age-Related Asymptomatic Rhinovirus Infections Contribute to the Sustained Prevalence in Adults and Are Not Mitigated by Nonpharmaceutical Interventions.

BACKGROUND

Rhinovirus (RV) is a common respiratory virus, but asymptomatic RV infections in adults still require further investigation. Nonpharmaceutical interventions (NPIs) for COVID-19 markedly reduced other respiratory viruses, yet RV circulation appeared to persist. We describe the epidemiology of asymptomatic and symptomatic adult RV infections in Shanghai across periods with and without strict NPIs.

METHODS

We performed a retrospective, hospital-based repeated cross-sectional study at a large hospital in Shanghai over two epidemic cycles (March 2021 to February 2022 and June 2023 to May 2024). Adults undergoing routine SARS-CoV-2 screening (asymptomatic group) and hospitalized adults with respiratory symptoms (symptomatic group) were systematically sampled. Nasopharyngeal swabs were tested by RT-PCR, and RV-positive samples underwent genotyping and quantitative viral load assessment. Clinical characteristics, co-/secondary infections, and age-specific patterns were compared using χ2 tests and nonparametric tests, and associations between RV prevalence and climate variables were evaluated using correlation analysis.

RESULTS

Among 89,571 adults, 865 RV infections were identified. Asymptomatic RV detection remained low and similar during and after strict NPIs (0.68% vs. 0.56%). Adults aged 18-59 years had higher asymptomatic infection rates than those ≥ 60 years (0.68% vs. 0.55%, p = 0.022). RV-A predominated, while RV-C was associated with higher viral loads and more frequent symptoms. Total monthly rainfall showed the strongest negative correlation with asymptomatic RV prevalence (r = -0.418, p = 0.042). Symptomatic cases had higher co-infection rates.

CONCLUSIONS

Persistent asymptomatic RV infections in young and middle-aged adults were unaffected by NPIs. Older adults were more often symptomatic and experienced more frequent co-infections.