E, T-test was employed to compare the viral loads between the male, female, Han, and non-Han groups. Lastly, to further detect the true factors that affect the viral loads in the genotype 6 group, multivariate regression analysis was performed. In all the analyses described above, any test with p value less or equal to 0.05 was indicated to be statistically significant. All these statistical analyses were performed using SPSS for Windows, version 16.0 (SPSS, Chicago, IL, USA).Results Detected HCV genotypesHCV genotypes were determined among the 299 donors who were HCV viremic. Among them 173 (57.9 ) had origins in Guangdong province, 121 (40.5 ) in areas other than Guangdong, while the birthplaces for five (1.7 ) were unknown. Table 1 and Figure S1 showed the patterns of HCV genotype distribution among these 299 donors: 1b and 6a were predominant (48.2 and 30.1 , respectively), followed by 2a (8.7 ), 3a (8.0 ), 3b (4.3 ), and 1a (0.7 ). Among those having origins in Guangdong province, the frequencies of 1b (43.4 ) and 6a (38.2 ) were comparable, while among those having origins in areas other than Guangdong, the proportions of 1b (55.4 ) and 6a (19.0 ) were remarkably different. These patterns resembled that we have recently described [12]. Once again it was verified that 6a has become a major HCV strain in China, particularly in Guangdong province.HCV genotypingHCV genotypes were determined as previously described [27]. In brief, partial NS5B or E1 region ML-281 biological activity sequences were amplified using the Primer STAR kit (Takara, Dalian, China). Among the 299 donors, 298 were amplified successfully and 1 was failed by NS5B primer. And then the only one was amplified by E1 primer. Amplicons were sequenced in both directions on an ABI Prism 3100 genetic analyzer (PE Applied Biosystems, FosterCity, CA, USA). Sequences were aligned using the CLUSTAL_X program (www.geneious.com). Phylogenies were estimated using the maximum-likelihood method under the HKY+I+C6 substitution model in the MEGA5 (http://www.megasoftware.net/mega.php). Bootstrap resampling was performed in 1000 replicates. Reference sequences used for analyses were retrieved from Genbank (Table S1).Donors’ demographic characteristicsBased on the detected HCV genotypes, 
the blood donors were divided into four Solvent Yellow 14 groups with each group being represented by one genotype: genotype 1, 2, 3, and 6, respectively. In addition, according to the donors’ gender and their ethnic origins, each genotype group was further divided into the male, female, Han, and non-Han groups (Table 2). Since 15 donors lacked these pieces of information, only 284 donors were here analyzed. Based on the policy of voluntary blood donation, only donors aged from 18?5 years were recruited. Thus, the donors’ overall mean age was 31.8. Among the genotype 1, 2, 3, and 6 groups, the mean ages were 30.2, 29.7, 33.4, and 34.2, respectively, and no statistical significance was shown (x2 = 4.936, P = 0.177). Of the 12926553 284 donors analyzed, 274 (96.5 ) were of Han origin while 10 (3.5 ) of minority ethnicities. Although among the four genotype groupsHCV 6a Presented a Higher Virus Titer in ChinaTable 1. HCV genotype distribution ( ).Subtype1a 2(0.7) Guangdong 1(0.6) 1(0.8)1b 144(48.2) 75 (43.4) 67 (55.4)2a 26 (8.7) 6 (3.5) 18(14.9)3a 24 (8.0) 19(11.0) 5 (4.1)3b 13(4.3) 6 (3.5) 7 (5.8)6a 90(30.1) 66(38.2) 23(19.0)Total 299(100.0) 173(100.0) 121(100.0)BirthplaceOther areas Missing datadoi:10.1371/journal.pone.0052467.tsimilar ethnic compositions.E, T-test was employed to compare the viral loads between the male, female, Han, and non-Han groups. Lastly, to further detect the true factors that affect the viral loads in the genotype 6 group, multivariate regression analysis was performed. In all the analyses described above, any test with p value less or equal to 0.05 was indicated to be statistically significant. All these statistical analyses were performed using SPSS for Windows, version 16.0 (SPSS, Chicago, IL, USA).Results Detected HCV genotypesHCV genotypes were determined among the 299 donors who were HCV viremic. Among them 173 (57.9 ) had origins in Guangdong province, 121 (40.5 ) in areas other than Guangdong, while the birthplaces for five (1.7 ) were unknown. Table 1 and Figure S1 showed the patterns of HCV genotype distribution among these 299 donors: 1b and 6a were predominant (48.2 and 30.1 , respectively), followed by 2a (8.7 ), 3a (8.0 ), 3b (4.3 ), and 1a (0.7 ). Among those having origins in Guangdong province, the frequencies of 1b (43.4 ) and 6a (38.2 ) were comparable, while among those having origins in areas other than Guangdong, the proportions of 1b (55.4 ) and 6a (19.0 ) were remarkably different. These patterns resembled that we have recently described [12]. Once again it was verified that 6a has become a major HCV strain in China, particularly in Guangdong province.HCV genotypingHCV genotypes were determined as previously described [27]. In brief, partial NS5B or E1 region sequences were amplified using the Primer STAR kit (Takara, Dalian, China). Among the 299 donors, 298 were amplified successfully and 1 was failed by NS5B primer. And then the only one was amplified by E1 primer. Amplicons were sequenced in both directions on an ABI Prism 3100 genetic analyzer (PE Applied Biosystems, FosterCity, CA, USA). Sequences were aligned using the CLUSTAL_X program (www.geneious.com). Phylogenies were estimated using the maximum-likelihood method under the HKY+I+C6 substitution model in the MEGA5 (http://www.megasoftware.net/mega.php). Bootstrap resampling was performed in 1000 replicates. Reference sequences used for analyses were retrieved from Genbank (Table S1).Donors’ demographic characteristicsBased on the detected HCV genotypes, the blood donors were divided into four groups with each group being represented by one genotype: genotype 1, 2, 3, and 6, respectively. In addition, according to the donors’ gender and their ethnic origins, each genotype group was further divided into the male, female, Han, and non-Han groups (Table 2). Since 15 donors lacked these pieces of information, only 284 donors were here analyzed. Based on the policy of voluntary blood donation, only donors aged from 18?5 years were recruited. Thus, the donors’ overall mean age was 31.8. Among the genotype 1, 2, 
3, and 6 groups, the mean ages were 30.2, 29.7, 33.4, and 34.2, respectively, and no statistical significance was shown (x2 = 4.936, P = 0.177). Of the 12926553 284 donors analyzed, 274 (96.5 ) were of Han origin while 10 (3.5 ) of minority ethnicities. Although among the four genotype groupsHCV 6a Presented a Higher Virus Titer in ChinaTable 1. HCV genotype distribution ( ).Subtype1a 2(0.7) Guangdong 1(0.6) 1(0.8)1b 144(48.2) 75 (43.4) 67 (55.4)2a 26 (8.7) 6 (3.5) 18(14.9)3a 24 (8.0) 19(11.0) 5 (4.1)3b 13(4.3) 6 (3.5) 7 (5.8)6a 90(30.1) 66(38.2) 23(19.0)Total 299(100.0) 173(100.0) 121(100.0)BirthplaceOther areas Missing datadoi:10.1371/journal.pone.0052467.tsimilar ethnic compositions.