Challenge experiments have been an important method of studying the pathogenesis of many infectious diseases and of evaluating initial efficacy of vaccines before large scale field tests are conducted.^1,2 In challenge experiments, infections are deliberately induced under carefully controlled and monitored conditions to healthy research volunteers. Induced infections are usually either self limiting or can be fully treated within a short period of time. Because physicians should be dedicated to alleviating disease and avoiding harm to patients, this type of experiment may cause uncomfortable symptoms and evoke serious moral concerns. It should be appreciated however that clinical research commonly involves risks to subjects that are not outweighed by medical benefits but are justified by the potential to acquire new knowledge.³ In that regard, infection inducing challenges are not necessarily more ethically problematic than phase I trials aimed at determining maximum tolerated doses of medications. Like any clinical research, challenge experiments should be conducted by competent investigators according to sound protocols that incorporate appropriate safeguards to ensure the safety of volunteers. Because these experiments may provide valuable information that might not be otherwise obtained, lead to novel therapies, or speed up vaccine development that will ultimately spare morbidity or death from infectious diseases and reduce exposure of large groups in field trials, challenge experiments may be justified.⁴ However, the scientific rationale should be carefully examined for any given pathogen and model. When such a rationale exists, then the question of risks and discomforts should be addressed.

Twenty years after the first culture of Helicobacter pylori there are still many gaps in our knowledge of this worldwide infection. In particular, little information is available regarding the precise mode …