Results
A total of 11813 samples were collected in two years, and the socio-demographic variables of all the samples were outlined in Table 1. In the first year (March 3rd, 2018 to March 3nd, 2019), 82.8% (4294/5184) patients were less than 5 years old. The mean age of the children was 2.2 (2.5) years old, with more than half (58.1%) of the patients being less than 1 year old. In the second year (March 4th, 2019 to March 3rd, 2020), 81.7% (5414/6629) of patients were less than 5 years. The mean age of the children was 2.3 (2.5) years old, with 45.4% of the patients being less than 1 year old. There was no significant difference either in the mean age (P=0.085) or in the constituent ratio of age (P=0.102) between the two years. The total number of samples from boys were higher than that from girls (P<0.01). The ratio of boy: girl was 1.36 and 1.37 in two respective years, without statistical difference (P=0.85).
The overall positive detection rates of the all the samples were 44.8% in the first year and 42.3% in the second year, without significant difference (P=0.09). The two predominant viruses were Flu A and RSV in both years, with Flu A accounting for 47.3%, 47.5% and RSV accounting for 32.7%, 24.7% of the positive samples in the two respective years. The third predominant virus was Flu B and the positive rates of the other four viruses were low. Though there was no significant difference in the overall positive rates between the two years, especially the positive rates of Flu A (P=0.93), the positive rate of RSV in the first year was significantly higher than that in the second year (P<0.001).
35.1% of children with positive viruses were below 5 years old in the first year. In this age group, Flu A and RSV were significantly more common (P<0.01). The proportion of RSV decreased to 1.6% (P<0.01) while that of the Flu A increased significantly to 77.2% (P<0.01) in the 5-10 years group. In the second year, 31.9% of children with positive viruses were below 5 years old. Flu A and RSV, accounting for 40.7% and 31.7% of the total positive viruses, were significantly more common (P<0.01). However, Flu B was more common than RSV (20.7% vs. 10.6%, P<0.01) in the 5–10 years old age groups. In both years, the virus positive detection rates of children in <5 years group (>30%) was significantly higher than those in the high age group (around 10%).
Among the children who came to our hospital because of ARTI, the number of boys was significantly higher than that of girls. From all the positive samples, 25.8% were boys and 19.0% were girls in the first year, 25.0% were boys and 17.3% were girls in the second year. The constituent ratio of boy: girl has no statistical significance between the two years (P=0.34). The positive detection rates in boys were of no significant difference with those in girls (44.9% vs. 44.7%, P=0.96 and 43.2% vs. 41.1%, P=0.27 in two respective years), and differences between gender were not statistically significant for the seven viruses (P>0.05).
The overall distribution of samples in both years was shown in Figure 1. The seasonal distributions of each respiratory virus in the first and second year were shown in Figure 2 and Figure 3, respectively. Flu A and RSV demonstrated pronounced seasonality, with peak infection occurred in autumn and winter (from October to December), and lowest activity in early of the year (from April to August). Flu B had a small peak in January and March, but the number of positive cases in other months was small. Because of the higher total number of children in the second year, the monthly positive number in the second year was always higher than that in the first year except in January. There were 586 positive samples in January 2019, while in comparison the positive number in January 2020 decreased significantly to 354. In order to eliminate the influence of the difference in the total number of children tested, we converted the number of infections to the positive rate of each month. The number of other viruses was too small to detect any seasonality, so we only made analysis on the positive rates of Flu A and RSV. As shown in Figure 4, the monthly positive rates of Flu A and RSV were consistent in two years with obvious seasonality.