Editor,—A major advance in gastroenterology was the discovery that Helicobacter pylori causes chronic active gastritis, and is associated with duodenal ulcers and with gastric cancer. In an international study on 17 populations from 13 countries, it was concluded that there is a roughly six-fold risk of gastric cancer in populations with 100% H pylori infection.1 ,2 In Africa, a puzzling feature is that although there is a very high prevalence of the infection, associated complications are very uncommon. In unpublished investigations carried out in the Soweto environs, it was found that at the age of 1 year, 46% of African infants were infected withH pylori, and that this proportion reaches 100% by the age of 12 years. Accordingly, it would be expected that stomach cancer should be common. However, Baragwanath hospital records from 1940 show a low occurrence of the disease. From 1948 to 1964 gastric cancer accounted for 2.2% of all cancers diagnosed,3 and in 1992 the figure was 2.8%, an average of 40 cases annually (National Cancer Registry, unpublished data). The hospital mentioned serves Soweto, which has grown from half a million people in 1940 to 3–4 million in 1995. Between 1990 and 1996, 280 cases of gastric cancer were diagnosed. It should be noted that endoscopy has been available at Baragwanath Hospital since 1975.

The problem becomes more puzzling because vitamin C status another risk for stomach cancer—the former is very low in Sowetans.4Thus the milieu for a high incidence of stomach cancer seems propitious, but other factors must be present preventing this from happening. Although age of acquisition was found to be an important risk factor for gastric cancer in developed countries, one hypothesis is that in Africa, acquisition of H pyloriat an early age leads to immunological tolerance, resulting in a low grade gastritis which has little or no clinical relevance.

Inexplicable behaviour in Africa respecting health/ill-health is not unusual. In Soweto, coronary heart disease is very uncommon, in spite of high levels of plasma homocysteine.5 Hip fracture in elderly African women is very uncommon despite, inter alia, a habitually low intake of calcium and losses of the element from high parity and long lactations.6 In brief, an outwardly unfavourable parameter can have a widely varying degree of noxiousness.