Discussion
Many kinds of viruses can cause ARTI with various clinical symptoms. Early detection of virus is not only beneficial for the recovery from infection,12 but also conducive to the control of virus outbreaks so as to avoid wider spread. Besides, it also strongly helps epidemiological investigation.13
The present study is the first one in the past decade to investigate the epidemiology of respiratory viruses in west China. We found that the total number of children with ARTI in the second year was more than that in the first year. In both years, there were more boys than girls with similar boy: girl ratios. The majority of children with ARTI were young boys, indicating that boys were more vulnerable to ARTI than girls.14 The average age of the population was only 2.2 ~ 2.3 years old, and nearly 50% of the children were less than 1 year old. The heavier burden of viral respiratory infections in children less than 1 year might be a result of an immature immune system and waning of maternal antibodies after 6 months old. Then, children are able to develop antibodies by themselves between the age of 2.5 to 3.5 years old to prevent viral infections.15
Previous epidemiological data showed that RSV was the most predominant respiratory virus in children.16 However, our data revealed that Flu A was the most common virus in our region. It could be caused by the usage of more sensitive detection methods or the seasonal variations nature of virus distributions. Our results are aligned with a study in which Flu A was found to be the most predominant virus among Chinese young children, followed by RSV.17 In our study, RSV was predominantly detected in children less than 5 years old, while Flu A and B were mainly in 5 ~ 10 years old, suggesting that RSV is likely to be infected in the family or community, while Flu A and B might mainly be infected in school.
The characteristics of geographical areas could significantly affect the observed burden of each respiratory virus.9 The weather in west China belongs to subtropical monsoon humid climate. The monthly positive rates of the two years were mostly similar, indicating the positive rate of viruses remains almost unchanged in the same region unless there were a large number of imported cases. The monthly trend has been consistent until January. The highest burden of viral infection in the first year was recorded in January, while in comparison the positive number in January 2020 decreased significantly, mainly due to measures against SARS-CoV-2 such as strict home isolation and long-term wearing of masks, which could effectively block the spread of the viruses. The sharp decrease in the number of infection was consistent with the data provided by the China National Influenza Center on 5 June 202018, proving that measures taken by our country against SARS-CoV-2 were completely effective.19Compared with other viruses, the positive rates of Flu A and RSV were higher throughout the study period. We knew that Flu A and RSV have obvious seasonality. The positive number increased when the weather got colder (autumn and winter) and decreased when the weather was warmer (spring and summer). The total number of positive samples increased from October in the past two years. Therefore, it’s reasonable to infer that the infection rate of respiratory virus in 2020 may gradually increase from October if less strict isolation measures would be taken because of the blockage of SARS-CoV-2 in China.
Due to the timely adoption of various isolation measures, SARS-CoV-2, which broke out in late 2019, did not break out widely in our region. Besides, few cases have been observed in children and adolescents because they have a more favorable clinical course than adult.20 From the outbreak to 3 June 2020, our hospital has tested all presumed cases for SARS-CoV-2 nucleic acid, as well as SARS-CoV-2 antibody tests for 21241 hospitalized patients and their families, but none of the test results were positive. Therefore, the possible influence of SARS-CoV-2 on the positive rate of the seven respiratory viruses in children could be excluded.