Summary of DENV screening
Table 1 shows the demographic characteristics and DENV testing results of all donors in Xishuangbanna Blood Center over the study period. Screening ELISA for anti-DENV IgG and IgM was completed 2,254 donor samples. Of these samples, 598 (26.5%) were anti-DENV IgG and/or IgM reactive.
Serological prevalence of DENV
As noted above, total serological prevalence was 26.5%. Serological prevalence was then calculated in various donor subgroups. Of the 2,254 donors assessed, 1,135 (50.35%) were first-time donors, and 1,119 (49.65%) were repeat donors. Prevalence in first-time donors was 28.72% (326 out of 1,135) and, in second time donors, 24.30% (272 out of 1,119). Pearson's chi-square testing suggested a significant difference in the prevalence of DENV in first-time donors and repeat donors (P=0.018, χ2= 5.635).
Numerically, prevalence was greater in male donors (27.86%, 399/1432) than females (24.21%, 199/822) and among those 26-35 years old than in other age groups. However, these differences were not statistically significant (males vs females, P=0.059, χ2= 3.577; by age group, P=0.053, χ2= 9.337).
Further analysis revealed substantial differences in the prevalence of DENV by occupation (P=0.001, χ2= 25.335), educational level (P<0.0059, χ2= 31.30) and ethnicity (P=0.026, χ2= 14.358). In particular, prevalence was 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 educational level of the largest proportion of donors (941 out of 2254, 41.75%) were Below High School (BHS), and this group also had the highest prevalence of DENV ELISA reactivity, 32.09% (302/941). Prevalence then decreased with increasing levels of education: high school and associate (HSAD), 27.33% (79/289); bachelor, 18.64% (52/279); master degrees, and others, 23.08% (3/13). Significant differences in prevalence were noted between those with BHS and bachelors’ degrees (P<0.001, χ2= 18.916) and BHS and HSAD (P<0.014, χ2= 6.052).
Among the various ethnic groups identified, prevalence was highest among those identifying as Buliang (47.06%, 16/34), Miao (33.33%, 6/18), and Dai (31.88%, 88/276); then Han (25.44%, 302/1187), Bai (15.00%, 3/20), Hani (25.30%, 84/332) and others (25.58%, 99/387). Significant differences were noted in prevalence among Buliang and Bai (P=0.017, χ2=5.675), Hani (P=0.007, χ2= 7.353) and Han (P=0.005, χ2= 8.019).
DENV RNA testing by PCR and NS1 antigen testing by colloidal gold method
ELISA reactive samples
Antibody-reactive donor samples were then tested for DENV RNA by PCR. Eight of the 598 samples were positive. These 8 PCR positive samples and 142 PCR negative samples (chosen randomly from 590 PCR-negative samples) were tested for NS1 antigen by the colloidal gold method. Six out of the eight PCR positive samples were NS1 positive, whereas two of the 142 PCR negative samples were NS1 positive, with six of the 142 samples being weakly positive. (That is, bands were seen with these samples but were weaker than the control band.)
ELISA non-reactive samples
We randomly chose 340 of the 1656 samples for RNA test by PCR. Five of these were RNA positive. Then these 5 RNA positive samples were tested for NS1 antigen by the colloidal gold method. Three out of the five were NS1 positive. We then chose 50 of the 335 RNA negative samples to test the NS1 antigen using the colloidal gold method. Four of the 50 samples were weakly positive; only one of the 50 was positive.
Demographic characteristics
Table 2 provides detailed information on donors who were both ELISA reactive and PCR and/or NS1 positive. All 16 DENV screening ELISA reactive samples were PCR and/or NS1 positive. Of these eight female and eight male donors, ages ranged 21 to 44 years; ten were first-time donors. Educational levels for most (11 of16) were BHS or HSAD.
Table 3 provides detailed information on the 10 donors, five female, five male, who were ELISA non-reactive but PCR and/or NS1 positive. Ages ranged 26 to 48 years old. Five were first-time donors. Most (8 of 10) were in the lowest two educational groups.