December 15, 2010
New Estimates of Food Poisoning Cases
By WILLIAM NEUMAN

The federal government on Wednesday significantly cut its estimate of how many Americans get sick every year from tainted food.

But that does not mean that food poisoning is declining or that farms and factories are producing safer food. Instead, officials said, the government’s researchers are just getting better at calculating how much foodborne illness is out there.

In a pair of research reports made public on Wednesday, the Centers for Disease Control and Prevention said that about 48 million people a year get sick from tainted food, down from the previous, often-cited estimate of 76 million. The number of deaths estimated to come from food poisoning also went down, to about 3,000 a year from 5,000.

The revision means that one in six Americans gets sick each year from tainted food, not one in four, as the old study, conducted in 1999, projected.

The estimates were part scientific detective work and part guesswork. For both studies, government statisticians extrapolated the number of nationwide illnesses from data on tens of thousands of lab-confirmed illnesses in 10 states. They also used information from telephone surveys.

Some scientists said the new estimates on their own offered little new guidance on how to prevent major outbreaks, such as the outbreak of salmonella in eggs that sickened thousands of people this summer.

“Knowing the number of cases of salmonella is not that valuable unless you know what food that disease is linked with,” said Dr. J. Glenn Morris, director of the Emerging Pathogens Institute of the University of Florida in Gainesville. “The real question is how much of that salmonella is coming from chickens vs. eggs vs. beef vs. pork.”

The C.D.C. said it was working on a follow-up study with a range of pathogens, showing how often each is linked with a particular food. That will allow regulators to focus on the areas of greatest risk in the food system.

But Dr. Morris also said that the study signals the need for better data collection in general. Today, the C.D.C., the Food and Drug Administration and the Agriculture Department all gather data on food safety in separate databases, making it hard to share data.

“We are not where we need to be in terms of national data collection systems,” he said.

The new estimates of foodborne illness arrived as regulators and food-safety advocates were hoping for the Senate to take a new vote on stalled food safety legislation. The Senate approved the legislation last month and the House essentially agreed to the Senate’s version, but the bill was sidetracked by a procedural snafu that imperiled its final passage.

C.D.C. officials took pains to say that while their projections of the amount of foodborne illness were now lower, the problem was no less urgent.

“It would be really unfortunate if there were conclusions, looking at 76 million and 48 million, that foodborne disease is no longer a problem,” said Dr. Christopher R. Braden, director of foodborne, waterborne and environmental diseases at the C.D.C. “The fact is that tens of millions of illnesses and hospitalizations and deaths of this extent tells us we need to do more.”

The difference between the two estimates rests heavily on a reduced calculation of the national numbers of what researchers call acute gastroenteritis, or stomach illness. It also reflects a revised understanding, also lower, of how many of those cases are caused by foodborne pathogens, as opposed to other sources, like the flu or other viruses passed through person-to-person contact, or contaminated drinking water.

But the numbers also highlight how little is known about foodborne illnesses.

The new estimate, published in the journal Emerging Infectious Diseases, says that only about a fifth of all foodborne illness is the result of pathogens that scientists have been able to identify.

Researchers estimated that four-fifths of the foodborne illnesses each year, or about 38 million, are caused by what they called “unspecified agents.” That includes pathogens for which there is little data and those that have not yet been discovered. It also may include chemicals in foods that scientists have not yet identified as the cause of illness.

Of the remainder, a bug called norovirus is believed to cause 5.5 million cases of foodborne illness each year, making it the single most common known source of foodborne disease. Norovirus, whose symptoms include vomiting and diarrhea, is most often transferred from person to person but it can also be spread through foods.

The smallest category of illnesses is made up mainly of cases caused by bacteria, including salmonella and E. coli, which were behind many prominent outbreaks in recent years. This group, which also includes parasites like toxoplasma, accounts for 3.9 million cases of illness a year. Dr. Richard Raymond, who was formerly the head of food safety at the Agriculture Department, said this group was the one where regulators could have the greatest impact.

“We’ve got to keep this in perspective when we decide how much money to spend to get that number down,” said Dr. Raymond, who had criticized the earlier estimate of 76 million illnesses as being too high.

The new study sheds light on the prevalence and virulence of the headline-grabbing bacteria involved in numerous outbreaks.

Salmonella, the bacteria behind this summer’s extensive egg recall, is now estimated to be responsible for more than a million illnesses and 378 deaths a year.

Listeria, which is less common but far more likely to be fatal, was estimated to cause 1,591 illnesses, with 255 deaths.

A group of toxic forms of E. coli bacteria that have been found in hamburger meat and leafy greens were estimated to cause more than 175,000 illnesses and 20 deaths a year.

Researchers said that there was a great deal of guesswork in the new estimates. The 48 million figure is near the midpoint of the range of projections in the survey, which said the number of illnesses could be as few as 29 million or as many as 71 million.

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