To the Editor: Helicobacter pylori (H. pylori) infection is probably the most common chronic bacterial infection in humans.¹ H. pylori has been implicated as a major etiological factor in chronic type B gastritis, peptic ulcers and is indirectly related to gastric adenocarcinoma and primary gastric B cell lymphoma.² The infection may be acquired in early life. Person-to-person contact in crowded living conditions during childhood may play an important role in transmission.³ Several methods of transmission for H. pylori have been proposed, including the feco-oral and oro-oral routes.⁴ In developing countries, the infection is transmitted mainly by the feco-oral route.⁵ The emerging pattern of the epidemiology of H. pylori infection seems similar to that of the hepatitis A virus (HAV). HAV is transmitted predominantly through the feco-oral route and has a high incidence in populations with poor hygiene practices and low socioeconomic status.⁶

Since H. pylori is transmitted by the feco-oral and oro-oral routes and HAV is known to be a sensitive marker of feco-oral exposure, HAV infection could be associated with an increased risk of H. pylori acquisition. The association between these infections requires further investigation. Indeed, similar age-specific prevalence curves for H. pylori and HAV have been documented, suggesting a shared feco-oral transmission common for H. pylori and HAV.⁵

We assessed the seroprevalence of H. pylori and HAV in a group of Iranian people in the north of Iran, and compared the relationship of different risk factors, including age, gender, level of education, occupation, source of water supply, place of residence and type of housing with these two pathogens. We also investigated the association between seropositivity of antibodies against H. pylori and HAV, to assess whether these organisms might share similar modes of transmission.

Three hundred and seventy-four serum samples were collected from healthy volunteers (239 from females, 135 from males, ranging in age from 3 to 81 years, mean and SD, 34±16.7 years) who participated in a health check program in 2002 planned by the Public Health Center of Mazandaran Province, which is affiliated with Mazandaran University of Medical Sciences. Serum samples were obtained randomly from healthy volunteers living in four rural areas (Hamid Abad, Soorak, Asram and Zoghal Chall Counties) of Sari Township and four districts of Sari city. At interview, we collected questionnaire data, including age, gender, place of residence (urban or rural), source of water supply (city or well), type of housing (single dwelling, multifamily dwelling or apartment), level of education (literate or illiterate) and occupation (employed or unemployed). The last two last factors were used as a surrogate for socioeconomic status. In this study, subjects who had graduated from high school or had higher levels of education were considered literate and those who had graduated from primary school or had no schooling were considered illiterate. Serum samples were analysed for H. pylori IgG antibody by means of enzyme-linked immunosorbent assay (ELISA) using the GAP-IgG Test (Biomerica, Newport Beach, CA). The procedures were performed according to the manufacturers instructions with the cut-off point determined at 20 U/mL.⁷ Samples were considered positive for H. pylori antibody when antibody levels were >20 U/mL and negative when they were <12.5 U/mL. The intermediate range was considered indeterminate for evaluating the seropositivity of H. pylori. Anti-HAV antibodies were assayed by microparticle enzyme immunoassay (Radim, Rome, Italy) in the same samples. Serum samples with a cut-off value >30 U/mL were considered positive for hepatitis A infection, those between 15 to 30 U/mL were considered indeterminate for evaluating the presence of HAV infection, and those with a cut-off value <15 U/mL were considered negative. The seroprevalence of anti-H. pylori and anti-HAV were determined and the relation between seropositivity of these two pathogens and different risk factors were examined.

The statistical significance between different environmental factors and seropositivity of anti-H. pylori and anti- HAV antibodies, and the differences in seropositivity for antibodies against these two infectious agents were examined by Fishers Exact Test. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to indicate the magnitude of any association. Multiple logistic regression analysis was used to derive multivariate adjusted OR and its 95% CI.

The seroprevalences of anti-H. pylori and anti-HAV were approximately similar (33.1% and 30.5%). Subjects under the age of 9 years had lower seroprevalences of anti-H. pylori and anti-HAV than older age groups (Figure 1). The frequency of H. pylori seropositivity showed a sudden increase in the 10- to 19-year and 20- to 29-year age groups, increased slowly in each age group up to the 70-to 79-year group, and then slightly decreased in the oldest age group. The age-specific seroprevalence of anti-HAV was similar to that of anti-H. pylori with the exception that the increase in the seroprevalence of anti-HAV was low for the 10- to 19-year age group, but suddenly increased in the 20 to 29-year age group, reaching the highest level at the age of 80 years and older. Coprevalent infection showed a similar pattern. In the univariate analysis, a significant difference was found in the rate of H. pylori seropositivity between subjects living in urban and rural areas (P<0.002, OR=2.87, 95% CI=1.51-5.43), but the difference between rural and urban areas in the level of HAV seropositivity was not significant. The seroprevalences of anti-H. pylori and anti-HAV were higher in females than in males (P<0.05, OR-0.64, 95% CI=0.38 to 0.95 and P<0.05, OR=0.43, 95% CI=0.23 to 0.87, respectively). A statistically significant relationship was found between seropositivity for antibodies against H. pylori, HAV and the level of education (P<0.05, OR-1.69, 95% CI=1.4-3.51 and P<0.05, OR=0.89, 95% CI=0.37-0.93, respectively) as well as occupation (P<0.05, OR-1.6, 95% CI= 1.25- 2.64 and P<0.05, OR= 1.23, 95% CI=1.8-2.37, respectively).

The association between seropositivity for anti-H. pylori and anti-HAV remained statistically significant after adjustment by multiple logistic regression analysis for age, gender, occupation and level of education (P=0.003, OR=0.12, 95% CI=0.36–0.73). Eighty-three subjects (22.2%) were seropositive for both HAV and H. pylori (P<0.05, OR=0.01). Coprevalence was 14.6% among subjects under the age of 20 years, 24.3% among adults, 21% in males and 23% in females. Fifty-three subjects (14.2%) were seronegative for both HAV and H. pylori (P<0.05, OR=6.06, 95% CI=2.24-8.77). We found no significant association between type of housing and seropositivity of H, pylori and HAV.

Acquisition of HAV and H. pylori infections is established early in life⁸ and most children have been infected by the time they reach late adolescence.⁹ Increases in the seroprevalence rates of anti-HAV and anti-H. pylori with age in our study suggest continuous exposure of the population to these two microorganisms. We also found a significant relationship between the coprevalence of these infections and age (P<0.05). These data correlate with earlier studies.¹⁰ The seroprevalences of anti-H.pylori, anti-HAV and the rate of both infections occurring at the same time were higher in females than in males. These findings are different from those reported by other researchers.⁸ Our results indicate that females are at a higher risk for acquisition of these two organisms. Our data also could reflect a common mode of transmission of these two pathogens.

In this survey an inverse relation was found between seropositivity of H. pylori and occupation and educational level as surrogate markers for socioeconomic status. This finding is in agreement with those reported by others who have indicated that individuals of higher socioeconomic status are often less likely to be infected.^1,8 According to our findings, the higher rate of H. pylori seropositivity in lower socioeconomic groups is similar to that of HAV, which is transmitted by the feco-oral route. This result reflects the similarity in the route of transmission of these two organisms and supports the notion that one mode of transmission of H. pylori is feco-oral. Although an association has been reported between type of housing and H. pylori seropositivity,^11,12 we did not find an association between this factor and seropositivity for H. pylori and HAV. This could explain the similar mode of transmission of these two pathogens in the people under study. Epidemiological studies in South America have suggested that transmission of H. pylori occurs through water.¹² Researchers in Peru identified H. pylori in drinking water.¹³ In this study we did not find a significant relationship between seropositivity of H. pylori and source of water supply but this relation was statistically significant for HAV seropositivity. This result reveals that drinking water is not a vehicle for H. pylori transmission in people living in the areas under study. Place of residence (urban vs. rural) , which correlates with a poor level of hygiene and sanitation, has shown a significant relationship with anti-H. pylori seropositivity,¹⁴ but statistical evidence of this relationship has not been presented for anti-HAV seropositivity. According to our findings, 22.2% of subjects were seropositive for both anti-H. pylori and anti-HAV at the same time, which confirms that these two infectious agents share common routes of transmission.

In summary, this study compared different risk factors for acquisition of H. pylori and HAV infections and showed a strong association between seropositivity of antibodies against H. pylori and HAV. The latter is a sensitive marker of feco– oral exposure. Our findings are in agreement with an earlier report¹⁵ and support the hypothesis that these two microorganisms share common modes of transmission, including feco-oral. Still, common environmental factors could not completely explain the association between seropositivity of antibodies against H. pylori and HAV. Therefore, we are not able to fully explain the routes of transmission of H. pylori, whether feco-oral oro-oral, due to lack of information on all environmental factors.