ulcers has invariably followed and not preceded recurrence of H. pylori infection (Logan et al., 1990).

Antibiotic treatment of gastritis, peptic ulcer, and duodenal ulcers associated with H. pylori currently is experimental. Results to date indicate that combinations of antibiotics are required to suppress or eradicate the bacterium.

Helicobacter pylori may also be associated with an increased risk of gastric carcinoma (Parsonnet et al., 1991; Nomura et al., 1991). The finding raises the possibility that this cancer, one of the world's most common, could be mitigated by screening for and treating H. pylori infection.

Malaria

Malaria, which had been eliminated or effectively suppressed in many parts of the world, has greatly increased in incidence over the past two decades. This parasitic disease results in some 1 million deaths each year, mostly among children, and is becoming increasingly difficult to treat and prevent. Many previously effective drugs no longer work against strains of the parasite that have become resistant. Particularly distressing is resistance to chloroquine, once the treatment of choice for the most severe form of malaria. Equally troubling is that a growing array of once-potent pesticides are no longer effective against mosquitoes that harbor the parasite. The use of other, still effective pesticides is often restricted.

Malaria occurs both in the tropics and, less frequently, in the temperate zones of the world. The disease was a major problem for early European settlers of North America. As recently as the early 1900s, half a million cases of malaria were recorded each year in the United States.

Currently, some 1,200 cases of malaria are diagnosed in the United States annually. The vast majority are individuals entering the country for the first time or returning from foreign travel. A very small number of cases are the result of direct transmission involving indigenous mosquitoes. Most of these have occurred among Mexican agricultural workers living in California in substandard conditions. The largest outbreak since 1952 involved 30 people in San Diego County in 1988. That experience and others like it, in conjunction with the rapid rise in drug-resistant strains of the malaria parasite, raise the possibility of even larger outbreaks in the future (see Chapter 2).

Malaria continues to pose a serious threat to the U.S. military. There were 500,000 cases of malaria among U.S. soldiers during World War II (Ognibene and Barrett, 1982; D. Robinette, Senior Program Officer, Medical Follow-up Agency, Institute of Medicine, personal communication, 1991), and more than 80,000 cases were diagnosed in American troops in Vietnam from 1965 to 1971 (Canfield, 1972). Troops sent to the Middle



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