Helicobacter pylori infection has been reported to increase the risk of cholera. This nested case-control study was conducted to determine whether H. pylori infection is associated with occurrence of typhoid fever. Eighty-three case subjects of culture-proven typhoid fever were identified through a 1-year surveillance of subjects aged 0-40 years in an urban slum. Two age-and sex-matched neighborhood control subjects were concurrently selected for each case subject. Serum anti-H. pylori

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... bulin G antibodies were measured in case and neighborhood control subjects. For determining other risk factors, 2 additional community control subjects per case were selected. There was a significant association between the presence of serum anti-H. pylori immunoglobulin G antibodies and typhoid fever (adjusted odds ratio, 2.03; 95% confidence interval, 1.02-4.01). Illiteracy, being part of a nuclear family, nonuse of soap, and consumption of ice cream were also associated with a significantly greater risk of typhoid fever. This study provides the first empiric evidence that H. pylori infection is associated with an increased risk of typhoid fever. Helicobater pylori infection was associated with epidemic Vibrio cholerae O1 infection in Peru [1] . A Bangladesh-based article reported an increased risk of endemic cholera of life-threatening severity in that country [2] . This effect is probably mediated through hypochlorhydria, which is a common finding in developing countries and an important risk factor for cholera. Acute H. pylori infection is known to cause hypochlorhydria that can persist for 18 months [3] . Chronic H. pylori infection can cause hypochlorhydria by causing atrophic gastritis. The gastric-acid barrier is an important determinant of the severity of salmonella and shigella infection [4] . We hypothesized that H. pylori infection would increase susceptibility to Salmonella typhi infection, as a result of the induced hypochlor-