Epidemiological study on respiratory syncytial virus-caused respiratory infection in children and preliminary analysis of changes in immune function
Objective 
To analyze the epidemiological characteristics of respiratory syncytial virus (RSV)-caused respiratory diseases in children in Hebei Province and the changes in peripheral blood lymphocyte subsets and inflammatory indexes. 
 
 
Methods 
A total of 9 491 sputum specimens and 9 491 paired peripheral blood specimens were collected from children admitted to Hebei Children′s Hospital for respiratory infection in 2018. RSV-positive sputum specimens were screened by multiple detection reagents for 13 kinds of respiratory pathogens. Flow cytometry was uses to detect T and B lymphocytes and NK cells in peripheral blood samples of randomly screened RSV-positive children. Procalcitonin (PCT) was measured by Roche E411 luminescence analyzer. Hypersensitive C-reactive protein (hs-CRP) was detected by Roche Cobas 8000 C701 biochemical analyzer. White blood cells (WBC) were measured by Sysmex XN-BN3 hematometer. 
 
 
Results 
The positive rate of RSV in children with respiratory diseases was 13.08% in Hebei Province in 2018. There were significant differences in RSV-positive rates among different age groups (χ2=479.297 6, P<0.000 1). The positive rate of RSV decreased gradually with age (χ2=-20.282 7, P<0.000 1) and was higher in male than in female (χ2=34.552 7, P<0.000 1). The incidence of co-infection of RSV with other respiratory pathogens was 29.49% (366/1 241), mainly caused by human rhinovirus (HRV, 150/1 241) and adenovirus (ADV, 40/1 241). The main epidemic seasons of RSV infection were winter and spring. The epidemic trends of simple RSV infection and co-infection were consistent. There were significant differences in inflammatory indexes, WBC (P<0.01), CD4+ (P=0.015) and CD4+ /CD8+ cells (P=0.016) between simple RSV infection and co-infection groups. 
 
 
Conclusions 
RSV was a common pathogen causing respiratory diseases in children in Hebei Province. The younger the children were, the more likely they were to be infected with RSV. RSV infection was easily complicated by HRV or ADV infection. The epidemic seasons of RSV infection in Hebei were winter and spring. Both simple infection and co-infection of RSV might result in immune dysfunction. 
 
 
Key words: 
Respiratory syncytial virus; Lymphocyte subsets; Molecular epidemiology; Immunity