WASHINGTON -- The efficient, worldwide food system that gives grocery shoppers more choices and lower prices carries a troubling cost: an upsurge in food poisoning. The rate of salmonella illness alone has doubled over the past 20 years.
The way outbreaks occur also is changing. In the past, most cases originated in restaurants or at events like church suppers -- caused by mistakes in the kitchen.
Such cases still happen -- one person died and 750 were sickened by salmonella at a Maryland church outing last month. But there is now a bigger problem: Food sometimes is tainted during processing at the growing number of huge food factories and is widely distributed before anyone gets sick.
The federal Centers for Disease Control and Prevention estimates that 9,000 people die every year from food poisoning in the United States. Millions more are sickened.
"Industry consolidation and mass distribution of foods may lead to large outbreaks of foodborne disease," Dr. Sean F. Altekruse, a veterinary epidemiologist with the Food and Drug Administration, said in a new CDC report on emerging microbes.
For example, about 224,000 people in many states were sickened by salmonella in 1994 because tanker trucks used to haul thousands of gallons of ice cream previously had been used to transport contaminated liquid eggs, according to the CDC.
"The huge epidemic was the result of a basic failure on an industrial scale to separate the raw from the cooked," said CDC researcher Robert Tauxe.
A single day's production at a modern ground beef plant can turn out hundreds of thousands of pounds of hamburger, which are then quickly trucked all over the country.
"That means any single problem that happens can be spread very quickly and cause massive illness before we even know about it," said Caroline Smith DeWaal, food safety director at the nonprofit Center for Science in the Public Interest.
Along with the industrial food processing system, Altekruse said the trend toward large-scale livestock operations in which thousands of animals are crowded together is another reason for increased problems with bacteria.
In 1945, for example, there were about 500 birds in a typical henhouse. By 1995, houses contained as many as 100,000 hens, which can spread salmonella through their eggs.
"Multiple houses were often linked by common machinery, resulting in large flocks with common risk," Altekruse said.
There have also recently been increases in food poisoning from imported and domestic produce such as cantaloupe, strawberries, raspberries and tomatoes. The CDC report identified several causes, including use of contaminated water to spray the produce and instances when animal manure containing E. coli touched fruit during picking.
Other factors cited by the CDC include: more people eating out, consumer ignorance about safe handling of food, and an increased chance of illness among the growing number of the elderly and people with suppressed immune systems, such as AIDS sufferers. Doctors are also getting better at diagnosing and reporting food illnesses.
One disturbing trend is that some microbes are developing resistance to antibiotics used to treat ill people. One reason: Antibiotics are frequently given to livestock to prevent disease, serving as an unintended inoculation for the bacteria that live with the animals.
In Britain, a strain of salmonella called DT104 has proven resistant to many antibiotics, including tetracycline, and has triggered a jump in human illnesses from the strain -- from 259 in 1990 to 3,837 by 1995 -- said E.M. Foster of the Food Research Institute in Madison, Wis.
More than one-third of the people infected with DT104 were hospitalized and 3 percent died, Foster said. The strain is now emerging in the United States.
"These figures are very unusual for ordinary salmonella infections and indicate serious problems ahead," Foster said.
Food safety experts say the world's governments and private industry must spend more money on research into the causes and prevention of food poisoning, from the farm to the dinner table, and on identifying how the bacteria are getting into the food system.
In the United States, a new surveillance system called FoodNet is being set up to monitor outbreaks. In addition, scientists are able to use DNA fingerprinting to trace microbes that sicken people in many places back to a single source.
That is how Colorado officials were able to discover that an unusually high number of people sickened with E. coli this summer had eaten tainted frozen hamburgers produced by Hudson Foods Inc., resulting in the recall of 25 million pounds of ground beef.