WASHINGTON (AP) — 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 foodborne bacteria caused a patient’s illness, allowing faster treatment of sometimes deadly diseases.