Overall seroprevalence and GMT of EV-D68
In total, 515 participants aged between 5 months and 83 years (male to female ratio was 0.98:1) were tested for nAb against EV-D68. Groups of participants aged < 1, 1-3, 4-6, 7-19, 20-39, 40-59 and ≥ 60 years, included 45, 67, 96, 86, 67, 86 and 68 samples, respectively. The overall seroprevalence of EV-D68 was high, with 422 (81.9%; 95% CI:78.4-85.0) seropositive samples among 515 participants, and the overall GMT in seropositive samples was 248.0 (95% CI: 215.3-285.7).
The seroprevalence and GMT of EV-D68 in age groups
The analysis of the different age group indicated that EV-D68 seroprevalence trended to increase with age (z = 131.2, P < 0.0001), ranging from 42.2% (95% CI: 29.0-56.7) in infants to 49.3% (95% CI: 37.7–60.9) in toddlers to 71.9% (95% CI: 62.2–79.9) in preschoolers, and reached over 90% in groups of participants aged ≥ 7 years, especially as high as 100% in the 40–59 and ≥ 60 age groups (Fig. 1). Highly statistically significant differences in seroprevalence were observed among the 1–3, 4–6 and 7–19 age groups (χ2 = 39.2, P < 0.0001). Moreover, the GMT of nAb against EV-D68 showed an increased trend with age, except for a small dip at the 20–39 age group (Fig. 1). Children under 1 year of age presented the lowest GMT value (39.8, 95% CI: 21.2–74.8), and the elderly older than 60 years of age had the highest one (405.0, 95% CI: 323.8-506.6). A significant increase in GMT was observed between the 4–6 age group (133.2, 95% CI: 97.5-182.2) and the 7–19 age group (283.7, 95% CI: 203.5-395.6) (t = 3.262, P = 0.0014). To further analyze the immune responses, four nAb antibody titer ranges were defined: no (< 1:16), low (1:16 − 1:1:32), moderate (1:64 − 1:256) and high (1:512-1:2048). The analysis indicated that most participants aged ≥ 7 years presented with moderate and high nAb titer levels, whereas children aged ≤ 6 years with low and moderate ones (Fig. 2).
The seroprevalence and GMT of EV-D68 in gender and district groups.
The overall seroprevalence against EV-D68 were 82.8% (95% CI:77.64–86.9) and 81.2% (95% CI:76.0-85.4) in males and females, respectively. As shown in Table 1, EV-D68 seroprevalence trended to increase with age, from 45–100% of males and from 40–100% of females, but no significant gender-specific difference in seroprevalence of EV-D68 was observed (χ2 = 0.2203, P = 0.6388). In addition, the overall GMT in seropositive samples was 206.8 (95% CI:171.0-250.1) and 234.3 (95% CI:195.0-281.5) in males and females, respectively, and gender also didn’t show significant impact on GMT value (t = 0.9309, P = 0.3524). Moreover, serum samples were collected from 6 districts of Xiamen City (Table 2). There was no significant difference in seroprevalence of neutralizing antibody against EV-D68 between downtown and suburbs (χ2 = 2.727, P = 0.099), although slightly lower GMT value for EV-D68 was found in the city center when compared to the suburb group (t = 2.715, P = 0.0069). These data indicated that gender and geographic area are not the main factors affecting the EV-D68 epidemic trend in Xiamen City.
Table 1
Seroprevalence and GMT of nAb against EV-D68 by gender
Age groups (year) |
Gender | < 1 | 1–3 | 4–6 | 7–19 | 20–39 | 40–59 | ≥ 60 |
Seroprevalence%(95%CI) |
Male | 45.0 (25.8–65.8) | 51.4 (35.6–67.0) | 75.5 (61.9–85.4) | 93.3 (82.1–97.7) | 96.7 (83.3–99.4) | 100.0 (91.8–100.0) | 100.0 (89.6–100.0) |
Female | 40.0 (23.4–59.3) | 46.7 (30.9–63.6) | 68.1 (53.8–79.6) | 95.1 (83.9–98.7) | 100.0 (90.6–100.0) | 100.0 (91.8–100.0) | 100.0 (90.1–100.0) |
GMT (95%CI) |
Male | 34.6 (12.1–98.5) | 83.8 (39.6-177.2) | 132.9 (87.2-202.6) | 217.1 (133.2-353.7) | 201.6 (125.5-323.9) | 315.7 (223.1-446.6) | 501.4 (379.6-662.1) |
Female | 45.3 (17.6-116.1) | 77.0 (41.3-143.6) | 133.7 (81.8-218.5) | 378.5 (240.9-594.6) | 303.0 (197.1–466.0) | 300.8 (214.4–422.0) | 331.2 (234.1-468.5) |
Table 2
Seroprevalence and GMT of nAb against EV-D68 in geographic regions
Regions | Seroprevalence% (95%CI) | GMT (95%CI) |
Downtown | 78.1 (71.5–83.5) | 170.1 (137.0-211.1) |
SM | 68.7 (58.1–77.6) | 134.4 (95.3-189.5) |
HL | 86.3 (78.0-91.8) | 200.3 (151.7-264.7) |
Suburb | 84.0 (79.7–87.5) | 249.8 (212.0-294.4) |
HC | 81.0 (71.3–87.9) | 344.0 (245.0-483.2) |
JM | 87.8 (79.0-93.2) | 217.4 (155.3-304.3) |
TA | 82.0 (72.8–88.6) | 217.8 (156.6-303.5) |
XA | 85.4 (76.2–91.4) | 243.6 (177.4-334.7) |