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New tests that promise to speed up diagnosis of food poisoning pose an unexpected problem: They could make it more difficult to identify dangerous outbreaks like the one that sickened people who ate a variety of Trader Joe’s peanut butter this fall.

The new tests could reach medical laboratories as early as next year, an exciting development for patients. They could shave a few days off the time needed to tell whether E. coli, salmonella or other food-borne bacteria caused a patient’s illness, allowing faster treatment of sometimes deadly diseases.

The problem: These new tests can’t detect crucial differences between different subtypes of bacteria, as today’s tests can. And that fingerprint is what states and the federal government use to match sick people to a contaminated food.

“It’s like a forensics lab. If somebody says a shot was fired, without the bullet you don’t know where it came from,” said E. coli expert Dr. Phillip Tarr of Washington University School of Medicine in St. Louis.

The federal Centers for Disease Control and Prevention expects private labs to rapidly adopt these next-generation tests – and warns that what is progress for individual patients could hamper the nation’s efforts to keep food safe. Already, 1 in 6 Americans gets sick from food-borne illness each year, and 3,000 die.

So even before these tests hit the market, the agency is searching for solutions. Unless one is found, the CDC’s Dr. John Besser said, the tests’ unintended consequence could be that ultimately, more people become sick.

It all comes down to what’s called a bacterial culture – whether labs grow a sample of a patient’s bacteria in an old fashioned petri dish or skip that step because the new tests don’t require it.

Here’s the way it works now: Someone with serious diarrhea visits the doctor, who gets a stool sample and sends it to a private testing laboratory. The lab cultures the sample, growing larger batches of any lurking bacteria to identify what’s there. If disease-causing germs such as E. coli O157 or salmonella are found, they may be sent on to a public health laboratory for more sophisticated analysis to uncover their unique DNA patterns.

Those patterns are posted to a national database that the CDC and state health officials use to look for food poisoning trends. If a few people in, say, Baltimore have salmonella with the same molecular signature as some sick people in Cleveland, it’s time to investigate, because scientists might be able narrow the outbreak to a particular food or company.

But culture-based testing takes time – as long as two to four days after the sample reaches the lab.

So what’s in the pipeline? Tests that could detect many kinds of germs simultaneously instead of hunting one at a time – and within hours of the sample’s reaching the lab. Those tests essentially work by searching for an identifying piece of a germ’s DNA without first having to grow a culture.

However, the CDC is asking the medical community to send samples to be cultured even when a new, nonculture test is performed. It’s not clear who would pay for that extra step. Private labs only can perform the tests that a doctor orders, noted Dr. Jay M. Lieberman of Quest Diagnostics.

A few first-generation nonculture tests are already available. When private labs in Wisconsin use them, they frequently ship leftover samples to the state lab, which grows the bacteria itself. But as more private labs switch over after the next-generation rapid tests arrive, the Wisconsin State Laboratory of Hygiene will be hard-pressed to keep up with that extra work before it can do its main job – fingerprinting the bugs, said deputy director Dr. Dave Warshauer.

Stay tuned: Research is beginning to look for solutions that one day might allow rapid and in-depth looks at food poisoning causes in the same test.

“As molecular techniques evolve, you may be able to get the information you want from nonculture techniques,” Lieberman said.

Associated Press reporter Mary Clare Jalonick contributed to this report.