Hepatitis A infection is caused by hepatitis A virus (HAV) that is a positive–sense RNA virus belonging to the family picornaviridae, genus hepatovirus.1 Most HAV infections occur through fecal-oral transmission, either by direct contact with an infected person or by ingestion of food or water contaminated with HAV.[2] Infection in children is usually asymptomatic or presents with mild symptoms, whereas adults infected with HAV develop fever, fatigue, malaise and jaundice that lasts for a period of 4 to 10 weeks. Irrespective of the presentation, lifelong immunity is conferred after infection.[1]
The prevalence of HAV is closely linked to the socioeconomic status and sanitation level, therefore a further decline in HAV infection is expected in many countries following improvement in living conditions.[3,4] As HAV infections in childhood decreases, the pool of susceptible adults increases.[5] It is well known that infection in adulthood carries substantially increased risk of mortality and morbidity.[6]
Over the last 20 years, the epidemiology of HAV has shown a shifting pattern in most Asian and Middle Eastern countries.[7,8,9] In the early 1980s, most of these areas were classified as areas of high endemicity where infection was common in childhood and this resulted in life-long immunity in adulthood. With seroepidemiological shift, more of these countries recommend hepatitis A in the schedule of routine childhood vaccination.
There are few studies on the epidemiology of hepatitis A in the Iranian population.[10,11] Also in recent years we faced many cases of acute hepatitis A in adulthood and middle age that shows the possibility of lower incidence in childhood. The objective of this study is to evaluate the seroprevalnce of antihepatitis A in Isfahan-Iran in 2006.
Methods
In a cross-sectional study we assessed anti-HAV Antibodies in 816 cases over the age of 6 years in Isfahan, Iran in 2006. Isfahan is a big province in the center of Iran, where 79.3% of residents live in the urban areas.
The population sample was obtained in a three stage process. Firstly, 41 clusters and in each clusters 20 samples were selected randomly after stratification into urban and rural areas (32 urban and 9 rural areas). Secondly, families in each cluster were selected randomly from the Department of Health census list. Thirdly, we selected randomly one person in every age group in a family. Participants were divided into age groups of 6-9, 10-19, 20-29, 30-39, 40-49 and >50 years for the analysis. The subjects were given detailed information about the study and written consents were obtained. A 5 ml venousblood sample was drown from each subject and transferred to the health care centres in less than 3 hours. Whole blood was centrifuged at 3000 rpm for 15 min and after serum isolation, they were freezed by the Alicot method. After this, they were transferred to the Isfahan Infectious Diseases and Tropical Medicine Research Centre by the cold chain method and were stored at -70 ºC.
The assay is based on the principle of competition where the antibodies in the sample compete with an anti-HAV specific antibody. The limit of detection of the assay has been calculated by means of the 2nd international standard supplied by the WHO. The sensitivity shown by the assay is <10 WHO mIu/ml. The value found for the test is used for the interpretation of results. Demographic variables were collected by a questionnaire that included sex, age group, number of family members, education status and place of residence.
Finally, collected data were coded, analysed and computed, using the Statistical Package for Social Sciences (SPSS) version 13. Chi-square, odds ratio (95% confidence intervals: CI) and logistic regression were calculated and a p-value = 0.05 was considered significant.
The study was approved by the Ethics Committee of the research department of Isfahan University of Medical Sciences.
Results
There were 428 female (52.5%) and 388 male (47.5%) subjects. 77.7% resided in urban and 22.3% in rural areas. The overall anti-HAV seroprevalence rate was 8.33%. The difference in the anti-HAV seroprevalence between the two sexes was not significant (p= 0.24, OR: 1.42 95% CI: 0.85- 2.36) .Comparing the prevalence of anti-HAV positive cases in the city of Isfahan and other districts we found out 5.77% versus 9.63 % (p<0.05).
No statistically significant difference was seen between the various age groups (p=0.18). Education level and number of persons per household (p=0.49) had no effect on HAV prevalence Detailed data was presented in Table 1. After dividing household numbers into two groups, one group included populous families with 5-6 and =7 participants) and second group for other families, no significant difference was detected (OR: 1.47 95% CI: 0.87-2.46).
Discussion
In 2006, the overall anti-HAV prevalence in Isfahan province was 8.33%. Kiyohara et al reported the prevalence of anti-HAV as 12.2% in Japan.1 This rate for the total German population was 46.5%[12] and 68.2% for catalonia-Spain.[13] Seroprevalence of hepatitis A varies among different Middle Eastern countries. In some, it is very high such as Egypt with 100%,[14] Iraq and Turkey borders with 94.4%[15] and Syria with 89%.[16] In a study in Lebanon, hepatitis A virus seroprevalence rates were about 78% for subjects aged 1 to 30.[17] In a similar study in Erzurum- Turkey seroprevalence was 84.2%.[18]
There is no study on the prevalence of HAV infection in the Iranian adult general population. Higher prevalences were reported in other studies in Iran. In a study on paediatric hospital patients in Tehran, 22.3% of the studied sample was positive for HAVAb.[10] This study differs from our study in the sampling and target populations. Like any other study in referral patients the available population was the major confounding factor. In another study in Zanjan, children showed 7.3% and 13.6%positivity in 6-9 and 10-19 years age groups, respectively;[11] the prevalence is somehow comparable to our results.
Low prevalence of HAV infection in our study population is mostly due to of the early establishment of healthy water supply and widespread sanitation and waste water treatment. For the last fifty yars Isfahan province was also the leading area within Iran in developing hygienic water and sanitary system, community health education and ducational level.[19]
In Germany,[12] Japan[1] and Spain,[13] the prevalence of anti- HAV increases with age. In our study the prevalence reached a climax in childhood and did not differ thereafter. It seems that highest risk of infection is in early childhood possibly due to higher exposure and insufficient prevention and that there is greater case to case transmission than in an epidemic. The epidemiology is not fully compatible to previously assumptions of WHO.[20]
Seroprevalence of anti-HAV varies among different districts in Isfahan province. The highest prevalence is observed in Borkhar and a possible explanation for this is the high proportion of immigrants in this district.
In conclusion, the results of this study show seroprevalence of anti-HAV is not high in Isfahan province. This may lead to a high prevalence of susceptible persons in adulthood that may cause a major problem in an epidemic. Thus, there is meagre information about HAV infection in Iran and further research is required to reach a decision of whether or not and when and how the vaccine should be used.
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19. http:// WWW .Mohme .gov.ir/health/index.htm.
20. http://WWW.CDC. gov/ ncidod/ diseases/ hepatitis..