Seroprevalence and predictors of hepatitis A infection in Nigerian children

Introduction: Hepatitis A infection is prevalent in developing countries where sanitation is still a public health issue. In Nigeria, there is no epidemiological data on children for this infection. A community based study was carried out to establish the seroprevalence and predictors of this infection in children. Methods: A community based cross sectional study was carried out in Akpabuyo local Government Area of Cross River State in southern Nigeria. Multistaged sampling technique was used to recruit 406 children aged 1-18 years. Blood samples were analysed for anti-HAV total antibody ( IgM and IgG) using a commercial Enzyme -Linked Immunoassay Assay(ELISA) . A multivariate logistic regression was used to identify factors that independently predicted the occurrence of anti-HAV total antibody. p value of < 0.05 was considered significant. Results: Two hundred and twenty four subjects tested positive for anti-HAV total antibody giving a prevalence rate of 55.2%. The median age for those positive was 9 years and for those without evidence of HAV infection was 4 years. One hundred and one (45.1%) males and 123 (54.9%) females were positive. The study population was mainly of the low social class with 94.1%. After multivariate analysis, predictors of HAV infection were age and social class. Conclusion: HAV infection was prevalent in the study population. Educational campaign is imperative and vaccine provision is advocated to further curb the spread of this infection. Pan African Medical Journal. 2015; 20:120 doi:10.11604/pamj.2015.20.120.5501 This article is available online at: http://www.panafrican-med-journal.com/content/article/20/120/full/ © Joanah Moses Ikobah et al. The Pan African Medical Journal ISSN 1937-8688. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Research Open Access


Introduction
Hepatitis E virus (HEV) is a non-enveloped RNA virus that is transmitted through the fecal-oral route [1,2]. HEV is noted to be responsible for epidemic and sporadic cases of enterically transmitted non-A, non-B viral hepatitis in many developing countries [3][4][5][6]. Areas with endemic infection and high incidence are found in Asia, Africa, Central America, and the Middle East [7], where the virus has been known to produce self-limiting acute viral hepatitis with mortality rates of 1%-3% [8].
The largest documented outbreak of HEV infection was in China between 1986 and 1988, involving over 100,000 individuals [9]. In industrialized countries, the disease occurs sporadically, and most infections occur in individuals who travel to countries where HEV is endemic [7]. Hepatitis E is endemic in the West African sub-region. Outbreaks of hepatitis E have been described in Chad and Cote d'Ivoire, and the virus was responsible for 66% of sporadic hepatitis cases in Chad, at least 22% in Cote d'Ivoire, and 44% of cases of acute hepatitis in Senegal [10]. The reported seroprevalence rates of anti-HEV antibodies in the West African region varies from 4.4% in Ghana [11] (increasing from 1% in school-age children to 8.1% in older adolescents) to 8% in Sierra Leone [12]. The case fatality rate in a reported outbreak in Ghana was 3.2% [10]. The 2010 World Health Organization (WHO)'s systematic review on the global prevalence of HEV infection did not report any prevalence or case fatality study in Nigeria. Furthermore, no outbreaks were recorded [10]. However, Adesina et al. [13], in a hospital-based study in Ekiti State, southwest Nigeria, reported a prevalence of 13.4% in individuals between 3 and 72 years of age. No community-based study has been done, to our knowledge, of HEV in Nigeria.
This study was therefore designed to provide the first community-based data on hepatitis E seroprevalence in Nigerian children.

Setting
The study was a community-based, crosssectional, analytical study in Akpabuyo Local Government Area (LGA) of Cross River State, southsouth geopolitical zone, Nigeria. Akpabuyo LGA is a suburb of LGA, bounded by Akamkpa LGA in the north, Calabar Municipality in the west, Bakassi LGA in the east, and the Cross River in the south. It comprises 10 electoral wards with a total population of 313,097. The occupations of the residents include farming, trading, civil service, and fishing. The aim of the study was to determine the seroprevalence and predictors of viral hepatitis E in children.

Study period
The study was carried out between April and June 2012.

Selection of subjects
The study population comprised children 1 to 18 years of age. A multi-stage sampling technique was used in this study and involved three stages. The first stage was a simple random sampling technique used to select four out of ten wards by balloting. In the second stage, a proportionate sampling method was used to select ten villages from the four selected wards. In the third stage, 40 children from alternate households in the selected villages were chosen from those eligible after a screening form was administered. Children who had resided in Akpabuyo for less than one year were excluded from the study. An interviewer administered a structured questionnaire to the heads of the households.

Ethical approval
The study was approved by the ethical review committee of University of Calabar Teaching Hospital and the Cross River State Health research ethics committee. Informed consent was obtained from each parent or legal guardian of the eligible participants prior to enrolment.

Data collection
The following data were collected using a structured, interviewer-administered questionnaire: 1) General characteristics (age, sex); 2) Family socioeconomic characteristics and sanitation : parent's/guardian's occupation and education, total number of persons in the household, toilet types, method of disposal of domestic household waste, source of drinking water. The social class of parents/guardians was determined using the social classification proposed by Olusanya et al. [14] considering the parents/guardian's occupation and educational qualifications; and 3) Clinical history to determine eligibility for the study.

Laboratory investigations
Two milliliters of venous blood was collected from each participant into a clean, plain bottle, properly labeled. The sera were tested for anti-HEV IgG antibody by a competitive enzyme immunoassay (EIA) test with test kits from DRG International (Springfield Township, USA). The anti-HEV IgG antibody tested for IgG antibody for HEV. Test results were interpreted as a ratio of the absorbance of the sample (A s ) and the cut-off absorbance (A c ). A level of < 0.9 mIU/mL was considered negative; 0.9 to 1.1 mIU/mL equivocal; and > 1.1 mIU/mL positive. A negative result indicated that the subject was not infected with HEV. In subjects with equivocal results, a second sample taken two weeks later was retested. A positive result was indicative of previous HEV infection. The sensitivity and specificity of the test kits were over 98%.

Statistical analysis and presentation
The data obtained were analyzed using the Statistical Package for Social Sciences (SPSS) version 17.0. Quantitative variables were summarized as median (interquartile range [IQR]), and categorical data were summarized as frequency (percentage). Chi square was used to test for association between categorical variables. Likelihood ratio Chi square and Fisher's exact test were applied where required. Multivariate logistic regression analysis was used to control for anticipated confounders. A p value of < 0.05 was considered statistically significant. Results are presented in Tables 1-4.

General characteristics of the children
A total of 406 children between 1 and 18 years of age participated in this study. The 1-4 year age group was the most represented, with a total number of 150 (37.0%). The 15-18 year age group was least represented, with a total of 51 (12.6%). The median age was 6 years, and the interquartile range was 3-12 years. A total of 207 (51.0%) of the children were females and 199 (49.0%) were males, for a female-tomale ratio of 1:1.  (100) The 1-4 year age group was the highest represented with a total number of 150 (37.0%). The 15-18 year group was least represented, with a total of 51 (12.6%). The median age was 6 years, and the interquartile range was 3-12 years. Two hundred and seven (51.0%) were females and 199 (49.0%) were males, for a female-to-male ratio of 1:1.  There was no significant association with sex (p = 0.66). At the univariate level, age and duration of residence were significant predictors of HEV; for every one year increase in age, there was 8% increase risk of having anti-HEV IgG antibody (95% CI = 1.01-1.16, p = 0.02). Number of persons in the household was not statistically significant (95% CI = 0.80-1.04, p = 0.19) with positivity to anti-HEV IgG antibody at the univariate level; After multivariate analysis, duration of residence in the community predicted infection with HEV after adjusting for the effect of all the other factors in the model. Individuals who had spent 6-10 years (compared to those who spent 1-5 years) had a 3.6 times increased risk of having HEV infection after adjusting for other variables. Table 1 shows the age and sex distribution of the study population. Twenty-four (5.9%) of the subjects belonged to the middle class, and 382 (94.1%) were of the lower social class; no subjects were in the higher social class.

Results for HEV
Four hundred and six subjects were tested for the anti-HEV IgG antibody. Twenty-eight subjects were initially positive for HEV. Seven subjects had equivocal results, and a second test done two weeks later showed three positive results in two females and one male, while four subjects remained equivocal (two males and two females). These were excluded from further analysis. The total number of subjects positive was thus 31 out of 402, giving a seroprevalence rate of 7.7% (95% CI = 5.1-10.3). The median age of those positive was 9 years, with an interquartile range of 6-14 years, while the median age of those negative was 6 years, with an interquartile range of 3-12 years. Table  2 shows the prevalence of HEV antibody in relation to the age of the subjects. Age was significantly associated with anti-HEV IgG antibody positivity (p = 0.039). Table 3 shows the distribution of anti-HEV IgG antibody positivity with gender. There was no significant association with sex (p = 0.66). Table 4 shows the logistic regression of variables to anti-HEV IgG antibody positivity. At the univariate level, age and duration of residence were significant predictors of HEV; for every one-year increase in age, there was an 8% increased risk of having the anti-HEV IgG antibody (95% CI = 1.01-1.16, p = 0.02). Number of persons in the household was not statistically significant (95% CI = 0.80-1.04, p = 0.19) with positivity to anti-HEV IgG antibody at the univariate level. After multivariate analysis, duration of residence in the community predicted infection with HEV after adjusting for the effect of all the other factors in the model. Individuals who had lived for 6-10 years (compared to those who had lived 1-5 years) in the community had a 3.6 times increased risk of having HEV infection after adjusting for other variables.

Discussion
In this study, the prevalence of hepatitis E was 7.7%. This was similar to a prevalence of 8% reported by Hodges et al. [12] in Sierra Leone. Adesina et al. [13], working in Ekiti State in southwest Nigeria, found a prevalence rate of 22.2% in sick and healthy children. He studied only 20 children between the ages of 3 and 10 years, and these included sick children. Martinson et al. [11], working in Ghana, found a prevalence rate of 4.4% in children 6-18 years of age in a rural community. This rather lower value in rural Ghana may be due to variation in the sensitivity of the immunoassay kits in different laboratories. Colak et al. [15] found a prevalence rate of 0.9% in children in Turkey. Turkey is a country in the European Union, and socioeconomic conditions there are better than those in the community where this study was done. Goumba et al. [16] found a prevalence rate of 78% during an epidemic of HEV infection in Bangui, Central African Republic. The prevalence of hepatitis E in an epidemic period would obviously be higher than in a non-epidemic period. Age was significantly associated with the prevalence of the anti-HEV antibody in this study. The prevalence increased from 16.1% in the 1-4 year age group to 38.7% in the 15-18 year group. Martinson et al. [11] also showed increasing seroprevalence, from 1% in children between 6 and 7 years of age to 8.1% in adolescents 16 to 18 years of age. This age-specific antibody profile was also reported by Fix et al. [17], working in two rural Egyptian communities. Arrankalle [18] speculated that this age-specific antibody profile might be due to the increased exposure to HEV in young adults through exposure to high-risk environments through work and consumption of high volumes of contaminated food and water. In the present study, there was no significant association of sex with positivity to anti-HEV antibody. Females, however, had a prevalence rate of 54.8%, and the males had a rate of 45.2%. Adesina et al. [13] showed no significant difference in both sexes. This could be due to the fact that both sexes live in the same endemic environment and are exposed to the same predictors of the infection.
Source of drinking water, method of human waste disposal, and method of domestic waste disposal were not significantly associated with seropositivity to anti-HEV antibody in this study. It is important to note that in this study, 18 (58.1%) of the 31 subjects positive for anti-HEV antibody used a borehole as a source of drinking water and 12 (38.7%) got their drinking water from a stream. Twenty-six (83.9%) of the subjects positive for HEV used a pit latrine, and four (12.9%) used a water closet. Though these differences were not statistically significant, it is important to note that social amenities were generally poor, and it will be important for the community to be educated about how HEV infection is spread, about the need for improved personal hygiene, and also about boiling drinking water.
Social class was not significantly associated with positivity to anti-HEV antibody. However, In Spain, Buti et al. [19] showed a significant association of social class with positivity to anti-HEV antibody, using parents' professions and the English classification of social classes. HEV is endemic in areas with poor hygiene and among those of lower socioeconomic background who are not fully aware of the mode of transmission of the disease and the importance of improving personal hygiene [10]. In this study, 30 (96.8%) of the 31 subjects with positive anti-HEV antibody belonged to the lower social class, while one (3.2%) belonged to the middle class. None were of the upper social class. It would be therefore difficult to demonstrate statistically the effect of social class.
The number of persons in the household was not significantly associated with positivity to anti-HEV antibody. This is in keeping with the findings of Colak et al. [15] and Aggarwal et al. [20], who showed that intrafamilial transmission of HEV was rare. This could be due to the fact that there is a low level of fecal secretion of HEV [20], and so intrafamilial or personto-person transmission is low.
At the multivariate level, duration of residence was significantly associated with anti-HEV antibody in the community. Longer duration of residence increases the subjects' risk of re-exposure to risk factors, and the probability of infection increases.
A limitation of this study was that the kit used tested for the anti-IgG antibody and therefore made it impossible to test for new infections in the study populations.

Conclusions
An educational campaign about the mode of transmission of this virus and prevention of the infection is recommended. Though the effects of waste disposal systems and water sources were not demonstrated, probably because they were almost universally poor, provision of pipe-borne water and modern sewage disposal systems could help to curb the prevalence of this infection and prevent an epidemic.