HTML
-
Among the 1505 human serum samples tested, 455 subjects (30.23%) from the study cohort were positive for anti-HEV IgG. Out of these, 30 (1.99%) were also positive for antiHEV IgM and 7 (0.47%) were positive for HEV RNA. Further analysis showed that the prevalence of anti-HEV IgG in the 273 workers with occupational swine contact was significantly higher than in the 1232 representatives from the general population (χ2 characteristic of independence [χ2] for this distribution = 51.908, with degrees of freedom [df] = 5, P < 0.001; Table 1). No participants had any history of travel abroad. Among the 276 swine serum samples, we found a prevalence of 6.52% (18/276) for HEV-Ag and 2.54% (7/276) for HEV RNA.
Variables No. detected Positive numbers Positive rate (%) Chi square test Crowd χ2 = 51.908 General population (GP) 1232 323 26.22 P = 0.00 Workers occupationally contact with swine 273 132 48.35 Total 1505 455 30.23 Gender in GP χ2 = 10.874 Male 582 178 30.58 P = 0.01 Female 650 145 22.31 Total 1232 323 26.22 Age grouping in GP (years) χ2 = 160.925 0–5 165 3 1.82 P = 0.00 6–10 89 5 5.62 11–15 61 4 6.56 16–20 96 9 9.38 21–30 104 24 23.08 31–40 131 43 32.82 41–50 133 49 36.84 51–60 113 48 42.48 61–70 99 44 44.44 71–80 181 69 38.12 81–90 60 25 41.67 Total 1232 323 26.22 Occupational grouping in GPs χ2 = 155.871 Preschool children 181 5 2.76 P = 0.00 Students 219 15 6.85 Peasants 129 60 46.51 Blue-collar workers 112 42 37.5 Managerial staffs 102 39 38.24 Medical staffs 84 18 21.43 Clerks in public place 121 45 37.19 Others 284 99 34.86 Total 1232 323 26.22 Table 1. The positive rates of anti-HEV IgG among recruited cases.
-
We divided the general population into 11 age subgroups, ranging from 0 to 90 years old. Table 1 shows that 323 (26.22%) out of the 1232 people from the general population had detectable anti-HEV IgG levels. Surprisingly, the prevalence of anti-HEV IgG ranged from its lowest value (1.82%) in the 0 to 5-years age group, up to its highest value (44.44%) in the 61 to 70-years age group, and the age-specific differences in prevalence were statistically significant (χ2 = 160.925, P < 0.001), with a linear distribution. The male:female ratio for anti-HEV IgG was 1.22:1, which indicated a significant difference by sex (χ2 = 10.874, P = 0.01), insofar as the prevalence was higher in men (30.58%, 178/582) than in women (22.31%, 145/650). Among the general population, we expected occupation to be a key differentiating factor for the antiHEV IgG positivity. In fact, we found a significantly higher occurrence of HEV infection in peasants (46.51%) than in other groups, whereas the prevalence was lowest in preschool children (2.76%). Our result showed high prevalence of HEV among blue-collar workers (37.50%), managerial staff (38.24%), and clerks in the public (37.19%) compared with the other occupational groups. Retirees and other people not belonging to specific occupational groups were classified into the "others" group, and the prevalence in this group was high, at 34.86% (Table 1).
-
Anti-HEV IgG is a standard marker of an immune response to previous HEV infection. We used a multivariable model to identify the factors that predicted anti-HEV IgG positivity among the 273 workers with occupational swine contact. We included age, working years, sex, education level, occupational pattern, and working hours per day in the model. Overall, younger workers were significantly less likely to show evidence of previous HEV infection (OR = 2.067, χ2 = 14.649, P < 0.001; Table 2), and people > 40 years old had a higher HEV-infection risk and were more likely to test positive for anti-HEV IgG than people < 30 years old. A similar trend was also detected in working years (OR = 6.0, χ2 = 11.903, P = 0.018), and more working years was associated with an increased risk of HEV. The statistical analysis showed no significant differences in the sex (P = 0.491), education level (P = 0.321), occupation (P = 0.163), or working hours per day (P = 0.331) among workers who had swine contact.
Factors Variables β Wald c2 P value OR (95% CI) Chi square test Gender 1 = male, 0 = female 0.15 0.474 0.491 1.162 (0.759–1.779) Age group (years) 24.699 0 2.067 χ2 = 14.649 1≦30 years -1.371 12.969 0 0.254 (0.120–0.535) P = 0.002 2 = 31–40 years -0.824 6.551 0.01 0.439 (0.234–0.825) 3 = 41–50 years -1.044 19.379 0 0.352 (0.221–0.560) Years of Working 23.243 0 6 χ2 = 11.903 1 = 0–5 years, -3.007 13.445 0 0.049 (0.010–0.247) P = 0.018 2 = 6–10 years, -2.772 11.946 0.001 0.063 (0.013–0.301) 3 = 11–15 years, -2.986 13.313 0 0.050 (0.010–0.251) 4 = 16–20 years, -1.576 2.881 0.09 0.207 (0.033–1.276) Educational background 3.5 0.321 0.923 χ2 = 1.749 1 = Primary school -0.811 1.987 0.159 0.444 (0.144–1.373) P = 0.417 2 = Junior school -0.483 0.769 0.381 0.617 (0.210–1.815) 3 = Senior school -0.826 2.067 0.151 0.438 (0.142–1.350) Job pattern 1.95 0.163 1.2 χ2 = 5.637 1 = pig farmers 1.713 7.134 0.068 5.545 (1.011–30.424) P = 0.060 2 = Slaughters 2.396 3.89 0.049 10.984 (1.650–73.130) 3 = Pork retailers 2.303 6.139 0.013 10.009 (1.533–65.349) Working hours per day 2.214 0.331 1.506 χ2 = 8.077 1≦6 h -0.008 0 0.985 1.008 (0.452–2.247) P = 0.018 2 = 7–9 h -0.398 1.012 0.315 0.670 (0.307–1.462) Table 2. Analysis for influent factors of the positive rates of anti-HEV IgG among workers occupationally contacted with swine using logistic regression model.
-
There was no significant difference in anti-HEV IgM prevalence between males and females (1.83% [14/767] and 2.17% [16/738], respectively). There was also no any significant age-related (χ2 = 0.268, P = 8.793) or occupation-related differences in anti-HEV IgM prevalence detected (Table 3). The epidemiological questionnaire showed that two out of the 30 patients with anti-HEV IgM were also diagnosed with liver dysfunction; one was female with no history of pig exposure and the other was a male swine worker. The female patient was coinfected with HBV and HCV, and presented with chronic liver disease without jaundice. Her alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), and direct bilirubin (DBIL) levels were 92.9 U/L, 108.9 U/L, 13.63 μmol/L, and 4.6 μmol/L respectively. The ALT, AST, TBIL and DBIL levels of the male patient were 462.5 U/L, 138.4 U/L, 155.37 μmol/L and 115.73 μmol/L, respectively, and were accompanied by evident clinical jaundice. Only two of the 30 people with anti-HEVantibody-positive sera had abnormal liver function, which suggests that HEV-infected people often have asymptomatic liver disease.
Variables No. detected Positive numbers Positive rate (%) Chi square test Gender χ2 = 0.634 Male 767 14 1.83 P = 0.226 Female 738 16 2.17 Age grouping (years) χ2 = 0.268 0–10 254 0 0 P = 8.793 11–20 161 1 0.62 21–30 132 0 0 31–40 174 7 4.02 41–50 246 7 2.85 51–60 189 4 2.12 61–70 107 4 3.74 71–80 182 5 2.75 81–90 60 2 3.33 Occupation grouping χ2 = 76.158 Preschool children 181 0 0 P = 0.000 Students 219 1 0.46 Peasants 129 10 7.75 Blue-collar workers 112 0 0 Managerial staffs 102 0 0 Medical staffs 84 0 0 Clerks in public place 121 11 9.09 Others 284 0 0 Pig farmers 137 3 2.19 Pork retailers 104 5 4.81 Slaughterers 24 0 0 Veterinarians 8 0 0 Table 3. The positive rates of anti-HEV IgM using Chi square test among general population and workers occupationally contacted with swine.
-
A sequence of 100% homology in the same species is considered to be the same sequence. There were 4 different sequences after comparing and analyzing the homology of 7 swine HEV ORF2 sequences. After the homology analysis of 7 human HEV ORF2 sequences, 4 different sequences were found. Homology and phylogenetic analyses were performed on the partial ORF2 sequences from pig samples (GenBank nos KX463414–KX463417) and human samples (GenBank nos KX463410–KX463413). The human and swine HEV isolates shared 97.04%–100% sequence homology, and ORF2 from a human sample (KX463411) shared 100% sequence identity with ORF2 from a swine sample (KX463417). The four human HEV isolates shared 97.04%–99.34% sequence homology and the swine isolates shared 98.68%–99.67% sequence homology. The eight HEV isolates also shared 75.33%–79.28%, 77.96%–78.95%, 75.33%–78.62%, and 82.89%–94.08% identity with GenBank reference sequences of HEV genotypes 1–4, respectively. Homology and phylogenetic analyses confirmed that the eight novel HEV sequences detected in this study were subtype 4d, and shared 96.05%–97.37% nucleotide sequence identity with the most closely matched strain (GenBank no. FJ46 1765), which was isolated from a person in Hubei Province (Fig. 1), and 89.14%–90.46% identity with another strain (GenBank no. FJ46 1762) that was isolated from a swine in Hubei Province. Further analysis of the ORF2 amplicons revealed higher sequence homologies (96.05%–97.04% and 95.72%–96.38% identity) with genotype 4d from Shandong (KF176370) and Beijing (KP196807) HEV swine strains, respectively.
Figure 1. Phylogenetic analysis of HEV isolates from human populations and swine herds. The phylogenetic tree was constructed by the neighbor-joining method and evaluated by interior branch test, based on partial nucleotide sequence of the ORF2 region. Forty-three known representative strains published in GenBank were used as references. The human or swine's isolates were signed with filled triangle or filled circle, respectively.