Helicobacter pylori, a Gram-negative bacterium that colonizes human gastric mucosa is one of the most common chronic infections which occurs worldwide, with 50% of the world’s population estimated to be carriers of this organism [1] [2] . It is a major aetiological factor in chronic gastritis, peptic ulcer disease, gastric carcinoma, and gastric mucosal associated lymphoid tissue lymphoma [3] [4] [5] [6] [7] . The mode of transmission still remains unclear, but literature data suggest different modalities of transmission of the infection to include, person- to-person, faeco-oral, oro-oral, gastro-oral and gastro-gastric transmissions [1] [8] .

It has been established that Helicobacter pylori infection is commonly acquired during childhood [9] [10] [11] , thus, any differences in prevalence of the infection within or among populations likely result from factors that were in effect during childhood. Previous reports show that age, race, living in rural area, overcrowding, socioeconomic status, poor sanitary conditions, mothers with lower educational level, poor diet and poor water supply are some of the important risk factors for transmission of H. pylori [1] [2] [12] [13] [14] . Prevalence of H. pylori infection in developing countries is higher compared with developed countries [15] . The decline in prevalence in developed countries is a reflection of higher socio-economic status and improved hygiene and sanitation and the active elimination of carriership via antimicrobial treatment [16] [17] [18] . In Nigeria, one of the developing countries, a high prevalence of H. pylori has been reported among adult populations with gastric and duodenal ulcers [19] [20] [21] .

Diagnostic methods for Helicobacter pylori infection are classified as invasive and non-invasive. Invasive methods include culture, immunohistochemistry, rapid urease tests, or the polymerase chain reaction, which require upper gastrointestinal endoscopy for obtaining the diagnostic sample. On the other hand, non-invasive detection methods include the urea breath test, serological and stool antigen methods. It is not clear which method should be used as gold standard for the detection of H. pylori infection. However, of all the available tests, invasive tests are considered the most accurate. Serological methods are based on the detection of Helicobacter pylori specific antibodies in serum, saliva, or urine and are used for initial screening. The stool antigen test is particularly used when the urea breath test is not available.

Previous studies on the seroprevalence of H. pylori have focused mainly on children and symptomatic adult populations. Limited studies exist on the prevalence of H. pylori among asymptomatic adult population in Nigeria. In the light of the rising incidents of gastritis and duodenal ulcers in Nigeria, as well as the importance of H. pylori infection in the pathogenesis of gastroduodenal diseases, there is therefore a need to re-appraise its seroprevalence rate in a cross-section of asymptomatic adult population. This study therefore was aimed at evaluating the seroprevalence of H. pylori infection and its associated risk factors in asymptomatic adult population in a Niger-Delta region of Nigeria. It is believed that the result of the present study will be helpful to plan a future large-scale population survey in different sex, age and socioeconomic groups.

A total number of 408 apparently healthy volunteers, aged between 18 - 87 years were recruited for this study from the three senatorial districts of Delta state (Delta South, n = 141; Delta Central, n = 128 and Delta North, n = 139). A well-structured questionnaire was administered to every participant of this study to obtain their demographic information and health history. All volunteers with history of gastric ulcers were excluded from the study. Informed consents of participants were sought and obtained after explaining the purpose of the research. The Ethics committee of Ministry of Health, Delta State approved the study.

Five (5 mL) of venous blood sample was collected from each participant and the serum separated immediately into sterile tubes and stored at a temperature of 2˚C - 8˚C for up to 3 days prior to analysis. For a longer storage they were kept at −20˚C until analyzed for anti- Helicobacter pylori antibodies―IgG detection. All blood samples obtained from volunteers were screened qualitatively using aria Helicobacter pylori antibody combo rapid test kit (serum/plasma/whole blood) which is a sandwich lateral flow chromatographic immunoassay for the qualitative detection of antibodies against Helicobacter pylori in human serum/plasma or whole blood [22] . Serum/plasma samples were assayed quantitatively using the Accu-Bind ELISA Micro-wells for the detection of IgG Antibodies to H. pylori in human serum (system code, 1425-300; Monobind Inc., Lake Forest, CA 92630, USA).

Stool specimens were collected from the participants. Small piece of stool (~5 mm in diameter; ~150 mg) was transferred into 1 ml of Sample Treatment Solution in a test tube and mixed thoroughly. Stool samples obtained were screened qualitatively using aria Helicobacter pylori antigen rapid test kit (fecal specimen) which is a lateral flow chromatographic immunoassay for the qualitative detection of H. pylori antigen in human stool samples [23] . The stool samples were also assayed quantitatively using the stool antigen Accu-Diag^TM H. pylori Antigen ELISA Kit (Cat #1506-11, USA).

All assay procedures were carried out according to manufacturer’s instruction. All samples were analyzed at Shalom Medical Services, Warri-Delta State, Nigeria.

Data was expressed as percentages for categorical variables. Comparative analyses to evaluate differences in H. pylori positivity between categorical variables were done using Chi-square test. The association between each potential risk factor and the outcome (H. pylori status) was measured using logistic regression. Statistical significance was set at p < 0.05. All statistics were done using SPSS/ IBM statistical software (version 20).

Table 1 shows the socio-demographic characteristics of the study population. Data indicated that majority (81.6%) of the participants were aged between 18 - 39 years of age and followed by the age group, 40 - 59 years (13%). Those aged ≥60 years had the least percentage of the population (5.4%). The mean age of the study population was 32.55 ± 11.98 years (range 18 - 87 years). Majority (70.6%) of the study population were females, while the males constituted a smaller percentage (29.4%) of the population. The participants were selected from Delta South (34.6%), Delta North (34.1%) and Delta Central (31.4%) districts.

The overall prevalence of Helicobacter pylori colonization in 408 asymptomatics was 52.5% (n = 214) and 48.3% (n = 197) by qualitative (Combo rapid kits) and quantitative (Accu-Bind ELISA kits) serological test methods respectively (Figure 1).

The prevalence of H. pylori according to sex, age and geographical location of participants is summarized in Tables 2-4 respectively. Among the 408 subjects,