The summary of DENV screening
We tested 2,254 donor samples for anti-DENV IgG and IgM by ELISA between June 2019 and October 2019 at Xishuangbanna Blood Center. Out of these samples, 598 were anti-DENV IgG and/or IgM reactive by ELISA. Table 1 shows the demographic characteristics and DENV testing results of all donors in Xishuangbanna Blood Center.
Serological prevalence of DENV
The total serological prevalence was 26.53% (598 out of 2,254), and the serological prevalence was calculated in each group. The first-time and repeat donors' prevalence was 28.72% (326 out of 1,135) and 24.30% (272 out of 1,119), respectively. According to Pearson's chi-square test, there was a significant difference in the prevalence of DENV in first-time donors and repeat donors (P=0.018, χ2= 5.635). The prevalence was higher in male donors (27.86%, 399 out of 1,432) than female donors (24.21%, 199 out of 822), with 26~35 age group having the highest prevalence. In contrast, there was no significant difference in gender (P=0.059, χ2= 3.577) and age group (P=0.053, χ2= 9.337). Further analysis revealed that there were substantial differences in the prevalence of DENV in terms of occupation (P=0.001, χ2= 25.335), education(P<0.059, χ2= 31.30) and ethnicity (P=0.026, χ2= 14.358). In particular, the prevalence was the highest among farmer donors (34.03%, 97/285), and there were significant differences in the prevalence of DENV between farmers and teachers (P=0.003, χ2= 8.622), civil servants (P<0.001, χ2= 12.233) and medical staff (P=0.004, χ2= 8.466). The prevalence in donors with below-high school (BHS), high school and associate (HSAD), bachelor, and master degrees, and others were 32.09% (302/941), 27.33% (79/289), 18.64% (52/279), 23.08% (3/13), 22.13% (162/732), respectively. There wwa a significant difference in bachelor with BHS (P<0.001, χ2= 18.916) and HSAD (P<0.014, χ2= 6.052). The prevalence is the highest in Buliang nationality (47.06%, 16/34), followed by Miao nationality (33.33%, 6/18) and Dai nationality (31.88%, 88/276); then by Han (25.44%, 302/1187), Bai (15.00%, 3/20), Hani (25.30%, 84/332) and other races (25.58%, 99/387). There were significant differences between Buliang and Bai (P=0.017, χ2=5.675), Hani (P=0.007, χ2= 7.353) and Han (P=0.005, χ2= 8.019). Table 1 displays the detailed information and serological prevalence of DENV in different groups.
DENV RNA testing by PCR and NS1 antigen testing by colloidal gold method
ELISA reactive samples
We detected 598 anti-DENV reactive donor samples using ELISA. These samples were then tested for DENV RNA by PCR. Eight out of the 598 samples were positive. There 8 PCR positive samples and 142 PCR negative samples (choosing randomly from 590 PCR negative samples) were tested for NS1 antigen by the colloidal gold method. Six out of the eight samples were NS1 positive, whereas 2 out of the 142 samples were NS1 positive, with 6 out of the 142 samples being weakly positive (Their band is weaker than the control band).
ELISA non-reactive samples
We randomly chose 340 of the 1656 samples for RNA test by PCR, 5 were RNA positive. Then these 5 RNA positive samples were tested for NS1 antigen by the colloidal gold method. Three out of 5 were NS1 positive. We then chose 50 of the 335 RNA negative samples to test the NS1 antigen using the colloidal gold method, 4 out of the 50 samples were weakly positive, only 1 out of 50 was positive.
Demographic characteristics
Table 1 displayed demographics of the entire study population. In all 2,254 donors, 1,135 out of 2,254 (50.35%) were First-Time donors, and 1,119 out of 2,254 (49.65%) were Repeat donors. There were 1,432 (63.53%) were males and 822 (36.47%) were females. The educational level of most people (941 out of 2254, 41.75%) were Below High School and more than half (1187 out of 2254, 52.66%) were Han nationality.
Table 2 showed the detailed information of donors who were both ELISA reactive and PCR and/or NS1 positive. There were 16 DENV screening reactive donor samples by ELISA, and these samples were PCR and/or NS1 positive. Of the 16 donors, 8 were females, the other 8 were males, with a range of ages between 21 and 44 years old. Ten of 16 were first-time donors. Most of their education (11 out of 16) were high school and an associate degree or below high school.
Table 3 showed the detailed information of donors who were ELISA non-reactive but PCR and/or NS1 positive. There were 10 DENV screening non-reactive donor samples by ELISA, but these samples were PCR and/or NS1 Positive. There were five female blood donors and five male blood donors. They aged from 26 to 48 years old. There 5 of 10 were first-time donors. Most of their education (8 out of 10) were high school and an associate degree or below high school.