Data from salivary assay to investigate the epidemiology of H pylori suggest that factors relating to the type of community in which the child lives may now be as important for acquisition of this infection as features of the family home. The greater reduction of growth among infected girls raises the possibility that H pylori infection may delay or diminish the pubertal growth spurt.

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The factors that determine which Helicobacter pylorn infected subjects develop duodenal ulcer (DU) are unclear. This study tested the hypothesis that infection density and urease activity are higher in DU than non-DU subjects. Fifty five DU and 55 age and sex matched non-DU subjects were studied. Quantitative methods were used for measuring infection density (viable organism count) and urease activity (Berthelot reaction). DU subjects had a greater antral infection density ( Studies have attempted to explain the outcome of H pylori infection on the basis of differences in strain virulence.6-8 A cytotoxin obtained from some strains of H pylori has been shown to produce vacuolation in cultured cell lines.9 The association between DU and carriage of cytotoxic strains of H pylori is strong, however, such strains also occur in most subjects without DU7 and therefore can only provide part of the explanation for the development of ulceration.H pylori produces large amounts of urease, the ammonia generated by this has been shown to have cytopathic effects on different cultured cell lines in a concentration dependent manner,10 11 and to be toxic to the gastric mucosa of experimental animals.'2 It is possible that strains of H pylori associated with ulceration produce greater amounts of urease.Histological assessment of the distribution and density of H pylori in the stomach has suggested that there may be greater colonisation of the gastric antrum in DU patients than subjects without DU,13 however, one study has produced conflicting results, showing no significant difference between the two groups. 14 The patchy nature of the distribution of the organism and the tendency of H pylori to colonise gastric glands in large clumps renders semi-quantitative histological studies inadequate for the measurement of a potentially immense range of infection densities in vivo. In addition, no assessment of organism viability is possible on histological sections.In this study we aimed to assess by quantitative methods H pylori infection density and urease activity in patients with DU and in those without; and the relation of infection density to factors associated with DU.

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