3.1 Baseline Characteristics
A total of 15543 patients with ARIs were collected in this study, including 9725 males (62.57% of total) and 5818 females (37.43% of total), with an average age 49.33±19.31 years, the ages of the eligible patients from 21 days to 87 years old. The subjects included 5701 (36.68%) upper respiratory infection (URTIs) and 9842 (63.32%) LRTIs, the baseline characteristics are shown in Table 1.
3.2 Overall detection rate of eight common pathogens
As shown in Table 2, among the 15543 samples, 5597 specimens carried at least one virus or atypical pathogen, with a positive detection rate of 36.01%, of which 4178 (74.65%) were single infection and 1419 (25.35%) were mixed infection. The most predominant pathogen was MP, with a detection rate of 18.12% (2816/15543), followed by Flu B (11.65%, 1811/15543), CP (7.00%, 1088/15543), RSV (4.18%, 649/15543), PIV (2.83%, 440/15543), Flu A (1.69%, 26/15543), LP (1.00%, 156/15543) and ADV (0.70%,109/15543).
3.3 Detection rate of virus and atypical pathogen from different gender groups
As shown in Table 3 , there was no significant difference in total positive detection rate between different genders (χ2 =1.15, P=0.284). However, the detection rate of Flu A, MP and ADV was significantly higher in male (Flu A: χ2=6.90, P =0.009; MP: χ2=15.70, P <0.001; ADV: χ2=7.51, P =0.006), the positive detection rate of PIV and mixed infection was higher in female (PIV: χ2=22.34, P <0.001; Mixed infection: χ2=26.73, P <0.001).
3.4 Detection rate of viral and atypical pathogen from different age groups
All of the ARIs patients are divided into four age groups, representing ages of <18, 18-45, 46-69 and >69. As shown in Table 4, the predominant pathogen among different age groups varied. In age <18 years, Flu B (17.54 %, 759/4327) was the most prevalent virus, followed by MP (10.98%, 475/4327) and RSV (8.20%, 355/4327). In Age 18-45, MP (33.76%, 1018/3014) had the highest incidence, followed by CP (7.53%, 227/3014) and Flu B (4.28%, 129/3014). In the groups of 46-69 and >69, MP (middle-aged:19.27%,726/3767; elderly:13.46%,597/4435) was the most predominant pathogens. The positive detection rates of Flu A, Flu B, PIV, RSV and MP were significantly different in different age groups (Flu A: χ2=9.07, P =0.028，Flu B: χ2=9.72, P =0.021, PIV: χ2=22.83, P <0.001, RSV: χ2=86.8, P <0.001, MP: χ2=134.45, P <0.001), and all of them, except MP, were infected frequently in patients under 18 years old, and MP was most common in patients aged 18-45 years. In addition, the mixed infection rate (11.05%) of Age <18 years was significantly higher than that of other age groups
3.5 Detection rate of virus and atypical pathogen from different season groups
According to the meteorological division method, all the patients were divided into four groups: Spring (March, April and May), Summer (June, July and August), Autumn (September, October and November) and Winter (January, February and December). The results showed that the common respiratory infection in the northwest China was seasonal, with higher detection rates in Autumn (39.65%, 1287/3246) followed by Winter (37.37%, 1727/4622), Summer (36.21%, 1439/3974) and Spring (30.91%,1144/3701), with significant differences in pathogen detection rates in different seasons (χ2=64.17, P <0.001). Flu A, Flu B, ADV and MP mainly detected in winter, PIV mostly occurred in spring, CP, LP and RSV were more infected in autumn, mixed infections were common in autumn and spring (Table5, Figure 1). The detection rate of all pathogens in different seasons was statistically significant (P <0.001).