How is Helicobacter pylori transmitted?

Helicobacter pylori is one of the world's most common pathogens. It colonizes about 60% of the world's population, causes gastritis and peptic ulcer, and is strongly associated with gastric adenocarcinoma and lymphoma. However, most individuals never develop clinical disease. Thirteen years after the culture of H. pylori by Marshall and Warren, we still do not know its major mode of transmission. Childhood represents the major period of acquisition of infection in the third world, but infection is rare in children in the developed world. Possible routes of infection include either oral-oral or fecal-oral, iatrogenic spread with inadvertent use of unsterile pH probes and endoscopes, and vectorial spread by flies. Evidence to support each route of transmission is provided, but there is no predominant route. The only significant reservoir of infection appears to be humans themselves. The organism has been found in some domestic cats and in nonhuman primates, but the opportunities for human interaction with the latter are rare, making infection from this source an unlikely possibility. The organism has the propensity to become a coccoid form. This may represent a persistent form in which H. pylori can exist in the environment, but it has yet to be shown that it can revert to the replicative form.