Extragastric manifestations of Helicobacter species infection. Do these bacteria act as triggers?

Since the latest decade, several studies have reported on the association between chronic Helicobacter pylori (H. pylori) or Helicobacter species (H. species) infection and a variety of extragastric manifestations. These include ischaemic heart disease (IHD), liver diseases, skin diseases, blood disorders and others. However, the hypothesis of an aetiological role has not yet been fully investigated. The epidemiological studies have frequently involved control selection bias, population of small sizes, and presence of confounders, like age and socio-economic conditions. Randomised, long-term and large studies on the follow-up of H. pylori eradication in extragastric diseases are lacking. The present paper attempts to highlight both the epidemiological source of the actual controversies and the biological plausibility for a causal role of H. pylori or H. species infection, in the pathogenesis of some of the most debated extragastric manifestations. Although currently available data do not provide proof of the role of H. pylori infection in the pathogenic mechanism of extragastric diseases, a potential relationship cannot be ruled out. Thus, the need for extensive studies with appropriate epidemiological and clinical approaches is evident.