Prevalence of Hepatitis B Virus infection Markers Among a Working Population in a Coastal City of Yantai, China

Three markers of hepatitis B virus (HBV) infection, HBsAg, anti-HBs and anti-HBc, were investigated in the sera from 426 factory workers of both sexes in a coastal city of Yantai in China. The investigation showed that the rate of those positive to HBsAg was 25.4% (25.9% in men and 24.6% in women), and that the rate when two sexes were combined was highest (i.e., 29.5%) at the ages of 20s followed by gradual decrease at higher ages (below 20%). The over-all HBV infection rate as calculated by those positive to any of the three markers studied was 70.4%. Comparison with rates reported in literature indicated that the rate of HBsAgpositive cases in the present study are probably among the highest values in China, whereas over-all rate of HBV infection was almost comparable to the values for other provinces. It should be added that other reports on other parts of Shandong Province describe HBsAg+ prevalence of about 6%. No explanation is currently available for the high HBsAg prevalence among the study population. J Epidemiol, 1991 ; 1 : 11-17.


Persistent
infection of hepatitis B virus (HBV) is among the known risk factors of primary hepatocellular carcinoma (PHC). Accordingly, increasing attention has been given in public health to the prevalence of the HBV infection with intention for the prevention of this insidious disease1-7). It is generally understood that the prevalence is higher in many parts of the Asian and Pacific regions than in northern Europe and North America 1,2,4, [8][9][10]. Reports on HBV prevalence in China are also growing in numbers in recent years reflecting the large population, with focus to the areas of high PHC incidence such as Guangxi Province 6, 7,[11][12][13][14][15].
In continuation of seroepidemiological surveys by this study group on HBV infection in East Asia16-19), a study was conducted in a coastal city of Yantai in Shandong Province, China, the area where there still exists a paucity of data on HBV infection.

MATERIALS AND METHODS
Sera. In 1991, the survey was conducted in a port city of Yantai in Shandong Province, on the north coast of the Shandong Peninsula, as a part of an occupational health survey of factory workers. The workers both in production sections and in clerical sections were invited to participate in the study, and sera obtained from 426 workers (243 men and 183 women at the ages of 17 to over 50 years) were subjected to the seroepidemiological study.

Prevalence of the 3 HB V infection markers among the study population
The prevalence of cases positive to the three markers are summarized in Tables I and 2. Those positive to HBsAg accounted for one fourth of the population studied with no significant difference in the prevalence between the two sexes (p>0. 10), and about a half of the HBsAg+ people were negative to the 2 antibody items. In contrast, about one third of the people studied were anti-HBs+ and anti-HBc+ in both sexes, and somewhat less than one third was negative to all of the 3 infection markers (Table 1). Thus, well over two thirds of the study population were either currently or previously infected with HBV. Very few (1%) were positive to all the three markers, as theoretically expected. In such cases, they were very weakly anti-HBs+ with titers just above the cut-off point, whereas anti-HBc titers were high and HBsAg titers were various depending on the cases.

Age-dependent changes in HBV infection rates
The observed cases were further classified by sex and by decade of years of ages of the subjects (Table 2). There is a gradual age-dependent decrease in HBsAg+ prevalence both in men and women, albeit the rate for those at the ages of 19 years or less (18.8% for men and 31.8% for women) may be comparable to that for 20s ; no significant difference in the prevalence was detected between those at less than 20 years of age and those at 20-29 years, when the two sexes were combined (p> 0.10). A high rate of 28.6% for >50 year-old men should be considered not reliable because only 7 subjects were examined.
Both anti-HBs+ and anti-HBc+ rates gradually increased in parallel in both sexes as ages advanced, so that about 80% or more of the population acquired immunity to HBV infection at the age of 40 years (i.e., either anti-HBs+ or anti-HBc+, or anti HBs+ and anti-HBc+). When positive reaction in any of the three infection markers (i.e., HBsAg+, anti-HBs+ or anti-HBc+) were considered to to be indicative of past or current HBV infection, almost all subjects (more than 85%) had experienced HBV infection before the age of 50, whereas less than 15% of the people remained negative to any of the three HBV infection markers at this stage of life.

DISCUSSION
The present study of a Yantai population has shown that the rate of those positive to HBsAg was as high as 25.4% (25.9% in men and 24.6% in women), and that the rate when two sexes were combined was highest (i.e., 29.5%) at the ages of 20s followed by gradual decrease at higher ages (about 20% or less). The overall HBV infection rate as calculated by those positive to any of the three markers studied was 70.4%.
A growing number of papers have been published in recent years to report the prevalence of HBV infection especially in terms of HBsAg+, and in some cases as the positivities to the three infection markers, in various cities and provinces in Chinas5-7, [11][12][13][14][15][16][17][18][30][31][32][33][34][35][36][37][38][39][40] The results of the reviewing are summarized in Table 3. In comparative evaluation of the results in which radioimmunoassay, hemagglutination assay or the both in combination were employed, it should be taken into account that the sensitivity of the two methods vary and that hemagglutination method employed was reported to be less sensitive than the radioimmunoassay12,37. Nevertheless, it is conceivable from the table that the HBsAg+ rate for the present Shandong examinees, 25.4%, is markedly higher than the values reported for various provinces including Guangxi Province where PHC mortality is known to be very high especially in men41) ; the values higher than the present observation are usually associated with known HBV infection26) or inclusion of hepatitis cases38).
The anti-HBs+ and anti-HBc+ rates were not remarkably high so that the over-all rate of HBV infection of the present study population is only comparable to the values for other provinces. It was previously pointed out that the prevalence of HBV infection is lower in a large city like Beijing (although not in Shnaghai where PHC mortality is reported to be high41)) than in rural provinces17). Simple urban-rural difference, however, will not be sufficient to explain rather unusually high HBsAg rate among the working population in the present study (Tables 1 and 3).
For comparison with the present observation, 6 reports28-35) are available in addition to an early report of Beasley and his co-workers3) on HBV infection in Shandong Province in particular.
The reported HBV infection prevalence as defined by positive to any of the 3 markers reported in recent studies28-35) are in a wide range of 27.4%34) to 78.3%35). Nevertheless, the prevalence of HBsAg+ cases are all well below 10%.
Beasley et al.3) found that the HBsAg+ prevalence among former Shandong Province residents currently in Taiwan were 9.3%, the value being not higher as compared with the values for those from northern China (11.2% on an average) and probably lower than the values for those from southern China (17.7%). In agreement with rather low HBsAg+ prevalence, the rates of mortality from liver cancer (per 105 population, based on deaths in 1973 to 1975, and age-adjusted to 1964 census population of China41)) was 11.57 for men (4.24 for women) in Shandong Province; the values are not higher than the values for the whole country ( 14.52 for men and 5.61 for women), and quite lower than those for Guangxi Province (26.55 for men and 6.63 for women) where HBV infection prevalence  Figure 1 ; a high prevalence (33%) observed in less than 20 year-old subjects in Wuxi may be due to the fact that only a small number of people (15 subjects) were examined in this age group, and therefore not depicted in the figure. It is apparent from Figure 1 that the prevalence in Yantai subjects up to 49 years of age is much higher than their counterparts in other cities, indicating that HBV infection is endemic among this study population. In addition, the fact that the persistent carrier rate is almost 1.5-fold higher in younger people (those below In the former group, 12 cases out of 27 liver tissues (44.4%) were positive to the infection when P-labeled HBV-DNA was employed as a probe, suggesting that intra-uterine infection is also an important mode of HBV transmission42). In this connection, it is worthy to note that Duan et al.43) in fact succeeded to interrupt mother-to-baby transmission of HBV by the administration of HBV vaccine to the babies born to HBsAg+ mothers.
Regarding the latter possibility, In a study of babies born to HBsAg+ mothers in Taiwan, Stevens and others45) observed that the risk of babies to be HBsAg+ increased when his/her mother had high titer HbsAg, when the umbilical cord blood was HbsAg+, or when his/her sibling was HbsAg+, and concluded that the vertical transmission occur rather frequently.
In contrast, Lam et al. 16) observed a sharp increase in HBsAg+ prevalence from first (less than 10%) toward fourth decade (over 40%) of life (and then decrease thereafter) among Chinese population in Hongkong, and thought that the dominant mode of HBV transmission among Chinese people there was likely to be horizontal rather than vertical.
At the moment, no plausible explanation is available to understand the unusually high HBV infection prevalence among the population studied. Whether the prevalence is high in Yantai City in general or it is so among the study population only is still yet to be elucidated.
Careful observation of the local culture and the way of daily life appears to be extremely important in order to identify the social habits which enhance the risk of infection at an early stage of life.