**3. Epidemiology and burden of** *H. pylori* **infection**

The prevalence of *H. pylori* infection is low in childhood and has begun to increase to 20% in adults younger than 40 years of age, and to 50% at the age of 60 [9]. In 2015, approximately 4.4 billion individuals were infected with *H. pylori* [13]. The prevalence rate comprises roughly 4.3% [14]. A systematic review and meta-analysis by Hooi, et al reported that Africa has the highest pooled prevalence of *H. pylori* infection while Oceania has the lowest rate [10]. The prevalence tends to decrease recently due to improvements in sanitation [9, 10]. Similar result is reported by Sjomina et al. a few years later, showing the minimal change in the epidemiology of *H. pylori* infection [14]. In Europe, Northern countries report lower prevalence compared to Southern and Eastern countries. The highest prevalence in Europe is reported in Portugal, reaching 84.2%. In the American continent, Mexico holds the highest prevalence (52.2%) similar to Bhutan in the Asia continent (86%). A study from Nigeria reported a very high prevalence of *H. pylori* infection, which is 93.6% [13]. In the Australia and Oceania region, the highest prevalence is detected on Pacific Island (49%). Minor differences are observed regarding the epidemiology of H. infection in several studies and it is due to the different diagnostic methods utilized from one study to another [8].

*H. pylori* is associated with 92% of duodenal ulcers and 70% of gastric ulcers. It is also related to 50% of gastric cancer and raises the risk for gastric cancer six times higher compared to those without *H. pylori* infection [11]. The odd for ulcer disease is even higher, reaching 10 times higher than *H. pylori*-negative subjects [9]. A study by Plummer et al. reported that 6.2% of estimated 12.7 million new malignancy cases in 2008 are attributed to *H. pylori* infection [15]. The incidence of gastric cancer is associated with geographical factors, strain diversity, and host immunological responses. The highest incidence of gastric cancer is reported in East Asian countries [16]. In 2017, there were 1.22 million new cases of gastric cancer with 865.000 deaths and 19.1 million disability-adjusted life-years. Not all, but the majority of gastric cancers are related to *H. pylori* infection therefore the microorganism is responsible for the burden of the disease [17]. Eradication of *H. pylori* will give a significant impact from an economic perspective [8, 17]. Eradication leads to decreased consultation with medical practitioners and is proven as an effective cost-saving method [8]. Screening and eradication of *H. pylori* infection in China might prevent one gastric cancer in every four to six cases [10].
