01.10.2009 - 01.10.2010

Determinants of Helicobacter pylori infection: a lifecourse approach



Ref
PTDC/SAU-ESA/103958/2008

Financing Instituitions
Administração Regional de Saúde do Norte

Participating Institutions
Instituto de Saúde Pública da Universidade do Porto (ISPUP)Unidade de Investigação e Desenvolvimento Cardiovascular (UIDC/FM/UP)Faculdade de Medicina da Universidade do Porto (FM/UP)

Summary

Helicobacter pylori infects more than half of the world adult population, with prevalence varying with age and socio-economic status, and across geographical areas.

Cross sectional data shows an increase in the proportion of the infected subjects with age, which has been attributed essentially to a cohort effect.

The incidence of infection is higher in children than in adults, especially in developing countries, and it has been suggested that acquisition occurs almost exclusively in the first five years of life. However, the annual rates of seroconversion among adults range from 0.2% to 1.1% in most populations, and the acquisition of infection in adulthood may not be negligible.

Additionally, the annual reinfection rates after H. pylori eradication have been reported to be as high as 13%- 24% in some low-income communities, and adults from affluent regions who visit or move to developing countries may seroconvert at rates similar to the observed in children from the host countries. The occurrence of Helicobacter pylori infection in adulthood results from the combined effect of a birth-cohort phenomenon and acquisition throughout life.

Intrafamilial transmission seems to be the main route of infection, and the finding that transmission appears to occur primarily between mothers and offspring and among siblings fits the hypothesis of close contact being important for transmission.

The relationship between low socioeconomic status and H. pylori infection is known, as the increasing standards of hygiene, including improved sanitation, less frequent close contacts, and increased antibiotic consumption shifted the age of H. pylori acquisition from early to late childhood, to adolescence and then to adulthood among consecutive generations.

Age at acquisition of infection has been postulated as an important determinant of the H. pylori-related gastric outcomes and it is reasonable to assume that some underlying trends of H. pylori infection have also been responsible for the birth cohort pattern in cancer.

The understanding of the determinants of H. pylori infection at different ages and the disclosure of finer relations between the dynamics of H. pylori infection and gastric cancer occurrence may contribute to a new life course framework for gastric pathology research.

This information is essential to develop preventive strategies aimed at accelerating the disappearance of infection in highprevalence populations, or at further increasing its extension in low-prevalence settings, and to predict the effect of interventions aiming the decrease in gastric cancer mortality.

These premises support the following research question: which factors contribute to the acquisition of H. pylori infection throughout life?

This project is organized to achieve the following specific objective:

Quantification of the incidence of H. pylori infection in two cohorts(newborns, adolescents), and identification of age-specific determinants.

The research team has a deep interest in the study of H. pylori infection and its association with gastric pathologies, focusing mainly on the determinants of gastric cancer and gastric precancerous lesions.

The team is also engaged in understanding the determinants of H. pylori infection throughout life-course, for which the infrastructures available at the Department of Hygiene and Epidemiology are essential. This project will rely on the evaluation of participants from a birth cohort (GXXI) and participants from a cohort of adolescents (EpiTeen), already assembled and being followed.

GXXI is a birth cohort assembled in Porto. All mothers resident in the metropolitan area who delivered a live-born baby between 01.05.2005 and 31.08.2006 in one of the five public hospitals were invited, and 8654 babies enrolled. Information on several socioeconomic factors was obtained, namely regarding the grandparents.

A blood sample was collected from the mother (n=1800) and the father (n=600). Anthropometric measures were performed in parents and in newborns. The first follow-up was conducted at six months of age, and information on breastfeeding and utilization of antibiotics was collected.

For the present study, 500 children and their parents will be evaluated at four years of follow-up. Blood samples will be collected from the children during the evaluation, to assess the H. pylori infection status.

The EpiTeen cohort includes 2161 urban adolescent born in 1990, and enrolled at public and private schools in Porto in 2003/2004.

Adolescents and parents fulfilled a structured questionnaire, including socioeconomic characterization and additionally allowed a blood sample collection (n=1300) and a physical examination.

The first follow-up was conducted in 2006/2007, and included the collection of a blood sample. We have successfully followed 300 subjects free of infection at baseline, allowing for incidence estimates.


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