Seroprevalence of Helicobacter pylori infection in children is variable according to geographical location and family sanitation. A previous study in Bangkok showed an incidence of 25.5% in 1998. The higher incidence in the urban and rural area is predicted in lower economic classes and poor sanitation.
Objective: To study the occcurance of CagA and VacA genotype in Thai children using the Western blot technique.
Material and Method: Sera of 159 Thai native children aged 0-15 year without associated abdominal pain from different provinces in 4 parts of the Kingdom of Thailand were tested with the rapid screening test for H. pylori. The positive specimen was further tested with the Western blot technique for determination of Urea A (p37), CagA (p116) and VacA (p89).
Result: Fifty five and fifty two (34.6%) were tested positive by the rapid test while 32.7% were positive for the band of current infection marker (CIM).The 28 selected positive sera with complete history of housing and water supply were analysed. Thai children living in urban areas have a higher prevalence and the CagA+, VacA + are found in 96.43% of infected patients. The transmission may be through the water supply.
Conclusion: A high prevalence of Helicobacter pylori infection was found in childhood period in urban areas and may be associated with the local water supply.

Keywords: CagA, VacA, Helicobacter pylori, Water supply, Children, Thai