In Western countries, the percentage of people with "H. pylori" infections roughly matches age (i.e., 20% at age 20, 30% at age 30, 80% at age 80, etc.). Prevalence is higher in third world countries, where it is estimated at about 70% of the population, whereas developed countries show a maximum of a 40% ratio. Overall, "H. pylori" infections show a worldwide decrease, more so in developed countries. Transmission occurs via food, contaminated groundwater, or human saliva (such as from kissing or sharing food utensils).