OBJECTIVETo investigate the prevalence of occult HBV infection in the normal population in Xiamen.

METHODS4 437 registered permanent residents, aged 1-59 years old, were selected in Xiamen using stratified random sampling method from September to October in 2006. Serum samples were obtained, the basic characteristics, inoculation of HBV vaccine, and liver disease were surveyed. The serum samples were tested five HBV seroimmunological markers. The HBsAg-negative specimens were subjected to HBV-DNA detection by nested PCR targeting for multiple gene segments. The amplified products were sequenced and the sequence was used for determination of HBV genotype and mutation analysis of amino acids located in HBsAg "a" epitope. Subjects with serum detectable HBV-DNA and negative result of HBsAg were considered as occult HBV infection.

RESULTSAmong the 4 437 subjects, 482 individuals were observed HBsAg positive and 3 944 were observed negative. Of the 3 955 HBsAg- negative specimens, 27 occult HBV infections were determined with the positive rate of 0.68% (27/3 955). There were 16 samples with genotype B and 11 with genotype C. 3 types of amino acid (AA) mutation (M133T, T140I, G145R) that influence "a" epitope conformation were observed in 9 subjects with occult HBV infection. S region was successfully sequenced in 312 of the 482 HBsAg positive samples. In subjects with occult HBV infection, the infection rate of genotype C HBV (40.74%, 11/27), inoculation rate of HBV vaccine (62.96%, 17/27), positive rate of HBsAb (51.85%, 14/27), and mutation rate of critical amino acid of "a" epitope (33.33%, 9/27) were higher than HBsAg positive individuals (22.76% (71/312), 13.78% (43/312),0.32% (1/312),0.99% (31/312), respectively), and all the difference were significant (χ(2) = 4.29, 41.26, 156.00, 13.07, respectively, and P value = 0.038, <0.001, <0.001, <0.001, respectively). While the average age in subjects with occult HBV infection (18.3 ± 16.2) were lower than that in HBsAg positive infection (34.4 ± 11.6), and the difference was significant (t = 6.67, P < 0.001). The reactive rate of HBeAb (11.11%, 3/27) and HBcAb (62.96%, 17/27) in subjects with occult HBV infection were lower than that in HBsAg positive infection (74.36% (232/312), 98.40% (307/312)), and the difference were significant (χ(2) = 46.74, 73.78, respectively, and P value <0.001, <0.001, respectively).

CONCLUSIONIn normal population in Xiamen, the infection rate of genotype C, the positive rate of HBsAb, the HBV vaccination rate, and the key AA mutation rate in "a" epitope are significantly higher in occult HBV infection than in HBsAg positive infection, and the age, the positive rate of HBeAb and HBcAb are significantly lower.