An increase in stomach illnesses and diarrhea in the United States over the past 50 years could signal the need for a closer watch over the nation's food supply.

The rise in gastrointestinal illness is expected to continue despite scientific advancements, Mi-chael Osterholm, the Minnesota state epidemiologist, told the International Conference on Emerging Infectious Diseases on Monday.Scientists found an average of one stomach illness per person per year in a study of 86 families done in Cleveland between 1948 and 1957. The same rate held up in a 1965-71 study of 850 families in Tecumseh, Mich.

But in the past two years, studies in five places around the United States have found a rate of 1.4 illnesses per person per year. In Minnesota, the rate is 1.8, Osterholm said.

The problem may be even worse because many illnesses go un-re-ported.

"I believe that what we are currently missing is many times larger than what we are currently detecting," Osterholm said. "Given our global food supply, international outbreaks will, in many instances, be our own outbreaks."

Osterholm called for more community studies of food-borne illnesses and for state-of-the art laboratories to study the bacteria and parasites that cause them. Keeping watch for new outbreaks and finding their cause is essential to solving the problem, he said.

Current efforts to monitor the problem are fragmented at the local, state and federal levels. For example, a government-initiated surveillance system called Food-Net is being used in only seven areas of the country, Osterholm said.

Almost half the money Americans set aside for food is spent in cafes and restaurants, where diners are vulnerable to the safety practices of workers who are young, paid minimum wage and may not wash their hands, Os-ter-holm said.

Another factor is the push to eat more fresh fruits and vegetables year-round, which forces the United States to shop for produce in other countries with less stringent standards, Osterholm said.

In 1996, more than a third of all cantaloupes, 74 percent of green onions and 79 percent of cucumbers from Mexico were sold in the United States.

"We have seen a whole transformation in the way our food comes to us," said Robert Toaxe, chief of food-borne and diarrheal diseases at the Centers for Disease Control and Prevention.

Scientists are researching ways to wipe out harmful bacteria before food leaves the pasture, Toaxe said.

But ultimately, people must use common sense, Osterholm said. "It is not OK to eat pink hamburgers or pink pork, and we need to communicate that to the public."