Prevalence of cytotoxin-associated gene a (CagA) positive helicobacter pylori among seropositive asymptomatic children attending Kenyatta National Hospital, Nairobi, Kenya

Abstract

Background: Helicobacter pylori is a curved, microaerophilic, gram negative bacterium that was isolated in 1983 from gastric biopsy specimens of patients with chronic gastritis. The bacterium colonizes the gastric mucosa of 20-80% of humans worldwide. In many developing countries, >50% of children and >70% of adults are H. pylori positive as compared with <15% of children and <40% of adults in most developed countries. Locally, studies done in asymptomatic children have shown a seroprevalence of between 45% and 51%. Infection is usually acquired in early childhood, is usually life-long unless eradicated and about 12-24% of those infected ultimately develop peptic ulcers and gastric malignancies. The mode of transmission from person to person is often feco-oral, and infection rate is highest in the developing world due to socio-economic factors. Risk factors significantly associated with H. pylori infection include: lack of clean water supply, poor sanitation, overcrowding, low maternal education level and low socio-economic status. Initial infection causes an acute superficial gastritis which may be followed by a chronic active gastritis, more severe forms of disease, such as peptic ulcer disease, atrophic gastritis, and gastric adenocarcinoma and mucosa associated lymphoid tissue (MALT) lymphoma in a minority of cases. Extra-gastric associations include: food allergy and chronic tonsillitis in children, hypertension and chronic prostatitis. Approximately 60-70% of H.pylori strains possess the Cytotoxin-associated gene A (CagA gene) and express the CagA protein, an oncoprotein and a highly immunogenic virulence factor that has been linked to gastric disease. Globally, few studies done on the prevalence of CagA positive strains in children have shown about 70% seropositivity. Eradication of H. pylori infection is of importance in prevention of the long-term severe forms of gastric disease. Studies have shown a high prevalence of H. pylori infection and acquisition early in life, thus, there is need to determine the local prevalence of the CagA positive H. pylori strains in the pediatric population in order to formulate strategies aimed at infection eradication. Objective: To determine the prevalence of CagA positive H. pylori among asymptomatic children at Kenyatta National Hospital, Nairobi. Study design: Cross-sectional descriptive study. Study area: This study was conducted at Kenyatta National Hospital (KNH), a tertiary, referral and teaching hospital in Nairobi, Kenya, between October 2012 and May 2013. The study xii participants were recruited from the general pediatric outpatient clinic and the pediatric wards. Laboratory analysis was done at the Immunology laboratory, University of Nairobi. Study population: Children aged 2-13 years attending KNH, mainly drawn from Nairobi and its environs and presenting with non-GIT conditions. Materials and methods: Socio-demographic information was collected by direct interview of the participants’ parents/guardians (respondents). A study questionnaire was administered to all the participants to collect the socio-demographic information. Two (2) milliliters of venous blood samples were drawn from the subjects and serum separated. The serum samples were tested by ELISA for the anti-H. pylori IgG antibody. Those that tested positive were tested for anti-CagA IgG antibody by ELISA. The data collected was entered into SPSS v.18 software for analysis. Results: A total of 175 children aged 2-13 years were enrolled on the study. 57.3% (101/175) were males with a male to female ratio of 1.4:1. The mean age was 7.5 years (±3.68) with a median (IQR) of eight years for both gender. The overall prevalence of H. pylori among the participants was 50.3% (88/175). CagA positive H. pylori prevalence among those who tested positive for H. pylori was 64.8% (57/88). 65% (113/175) of the participants lived in permanent houses with 66.9% (117/175) being urban dwellers. 70.9% (124/175) used tap water as their source of water. 70.3% (123/175) treated their drinking water, mainly by boiling. 32.6% (57/175) reported keeping domestic animals as pets with 29 keeping cats. As regards human waste disposal, 38.3% (67/175) used individual toilets and only1.1% (2/175) disposed of their human waste in the bush. Socio-demographic data was provided by the parents/guardians (respondents) of the study participants, 84.7% (148/175) of whom were females. 74.9% (131/175) had up to three children. 46.3% (81/175) had secondary education while 19.4% (34/175) had tertiary education. 5 (9/175) had not attained any formal education. 81.7% (143/175) were in marriages, 45.1% (79/175) were in formal employment with 48.1% (38/79) earning a maximum monthly income of Ksh.10,000. 22.3% (39/175) were the sole bread winners in the family. xiii There was positive correlation between H. pylori seropositivity with increasing age (p<0.001). Education level of the parent/guardian significantly correlated with infection (p = 0.030), seropositivity being highest among parents/guardians of study participants’ with informal and basic education. In addition, there was significant association between the participants’ human waste disposal practices and H. pylori infection, seropositivity was highest in those who lacked human waste disposal facilities (p=0.031). Participants in the rural areas had a significantly higher seroprevalence of H. pylori than the urban and semi-urban dwellers (p=0.043). Regarding gender, males had a higher prevalence of H. pylori, (53.5%) compared to females (45.9%), however, females had a slightly higher prevalence of CagA seropositivity (67.6%) than males (63.0%). However both findings were not statistically significant. There was no significant correlation between socio-demographic characteristics of the study participants and CagA status. Conclusions: 1. Prevalence of H. pylori was 50.3% and among the positive patients, prevalence of virulent strains was 64.8%. 2. H. pylori seropositivity increases with age and low social economic factors play a key role in contributing to the risk of H. pylori infection. 3. There was no significant correlation between socio-demographic characteristics of the study participants and H. pylori CagA status. Recommendations: H. pylori testing currently practiced in children should focus on the virulent strains only since half of the young population is infected by both virulent and non-virulent strains while only two thirds of infections are caused by the clinically significant virulent strains. Improvement of the socio-economic status of the population will reduce risk of infection acquisition