[Epidemiological characteristics of human respiratory syncytial virus (HRSV) among acute respiratory infection (ARI) cases in 16 provinces of China from 2009 to 2023].

Objective: To understand the epidemiological characteristics of human respiratory syncytial virus (HRSV) among acute respiratory infection (ARI) cases in 16 provinces of China from 2009 to 2023. Methods: The data of this study were collected from the ARI surveillance data from 16 provinces in China from 2009 to 2023, with a total of 28 278 ARI cases included in the study. The clinical specimens from ARI cases were screened for HRSV nucleic acid from 2009 to 2023, and differences in virus detection rates among cases of different age groups, regions, and months were analyzed. Results: A total of 28 278 ARI cases were enrolled from January 2009 to September 2023. The age of the cases ranged from<1 month to 112 years, and the age M (Q1, Q3) was 3 years (1 year, 9 years). Among them, 3 062 cases were positive for HRSV nucleic acid, with a total detection rate of 10.83%. From 2009 to 2019, the detection rate of HRSV was 9.33%, and the virus was mainly prevalent in winter and spring. During the Corona Virus Disease 2019 (COVID-19) pandemic, the detection rate of HRSV fluctuated between 6.32% and 18.67%. There was no traditional winter epidemic peak of HRSV from the end of 2022 to the beginning of 2023, and an anti-seasonal epidemic of HRSV occurred from April to May 2023. About 87.95% (2 693/3 062) of positive cases were children under 5 years old, and the difference in the detection rate of HRSV among different age groups was statistically significant (P<0.001), showing a decreasing trend of HRSV detection rate with the increase of age (P<0.001). Among them, the HRSV detection rate (25.69%) was highest in children under 6 months. Compared with 2009-2019, the ranking of HRSV detection rates in different age groups changed from high to low between 2020 and 2023, with the age M (Q1, Q3) of HRSV positive cases increasing from 1 year (6 months, 3 years) to 2 years (11 months, 3 years). Conclusion: Through 15 years of continuous HRSV surveillance analysis, children under 5 years old, especially infants under 6 months old, are the main high-risk population for HRSV infection. During the COVID-19 pandemic, the prevalence and patterns of HRSV in China have changed.

[Effect of interferon-γ on airway inflammation following respiratory syncytial virus reinfection in mice].

Objective: To identify the role of interferon (IFN)-γ during respiratory syncytial virus (RSV) re-infection in mice. Method: Female wild type C57BL/6 mice and IFN-γ knockout mice (IFN-γ(-/-) mice) at the age of 6 to 8 weeks were randomly divided into two groups: control group and RSV group, according to random number table.Each group was further divided into primary infection group and re-infection group.There were 8 groups.Mice were sacrificed on days 5, 7, 14 to collect samples.There were 5-8 mice in each group at each time point.And experiment was repeated twice. Leukocytes in bronchoalveolar lavage fluid (BALF) were counted, left lung tissues were stained with HE and histopathological scoring (HPS) was performed.The concentrations of IFN-γ, IL-5, IL-13 were determined with ELISA.T test or single factor analysis of variance was used to compare between groups. Result: (1) Mice infected or reinfected with RSV showed pale hair, weight loss, decreased activity and anorexia.(2) IFN-γ levels significantly increased on days 5 and 7 following RSV primary infection and reinfection as compared to control groups in wild type mice ((192±44) vs.(36±8) and (531±161) vs.(23±4) pg/ml on day 5, (100±23) vs.(36±8) and (862±186) vs.(23±4) pg/ml on day 7, t=2.654, 2.513, 2.654, 3.968, all P<0.05). (3) Compared to the RSV-reinfected IFN-γ(-/-) mice, RSV-reinfected wild type mice had less body weight loss ((13.6±2.6)% vs.(22.7±2.9)% on day 5, (18.0±3.1)% vs.(26.5±1.8)% on day 7, t=2.314, 2.308, both P<0.05), lower lung tissue histopathological score ((1.50±0.09) vs.(2.07±0.11) on day 5, (1.53±0.11) vs.(2.08±0.09) on day 7, (1.10±0.06) vs.(1.59±0.08) on day 14, t=3.916, 3.890, 4.837, all P<0.01), less BALF inflammatory cells count ((11.6±2.0) vs.(44.2±10.6)×10(5)/ml on day 5, (18.2±3.9) vs.(38.3±2.2)×10(5)/ml on day 7, t=2.818, 4.786, both P<0.05), and lower levels of IL-5 and IL-13 ((24±3) vs.(148±23), (23±4) vs.(169±26) pg/ml on day 5, (30±8) vs.(233±44), (20±5) vs.(182±19) pg/ml on day 7, (91±6) vs.(129±19), (62±8) vs.(132±5) pg/ml on day 14, t=5.252, 5.445, 4.517, 7.326, 3.816, 7.577, all P<0.01). Conclusion: IFN-γ can alleviate airway inflammation following RSV reinfection in mice.