BERRY PUZZLING

As smears go, this was a nasty one. When health officials announced three weeks ago the outbreak of a rare gastrointestinal illness in 10 U.S. states and Canada, they fingered fresh strawberries as the likeliest source of the bug–and promptly turned a favorite summer fruit into a culinary pariah. Now, however, it looks as if strawberries may have gotten a bum rap. Investigators still haven’t located the infectious microbe outside its human hosts, but the intensifying search has come up with a new and equally delectable prime suspect: fresh raspberries.

What has prevented researchers from identifying a culprit more conclusively, they say, is the nature of the sickness itself. Caused by an exotic protozoan parasite known as , the infection takes several days to manifest its symptoms (primarily “explosive watery diarrhea” lasting up to two months, according to one advisory). By the time its victims seek treatment, their recollections of what they ate and when they ate it tend to have grown hazy, and any leftovers worth examining are usually long gone.

Health experts suspect as well that their initial tests on fruit may not have been sufficiently sensitive to spot the bug. Last week, however, the Food and Drug Administration started using a state-of-the-art technique known as the polymerase chain reaction, or PCR, that can detect minute quantities of the microbe’s genetic material. Raspberries and strawberries are both getting the pcr treatment (blueberries and blackberries are next in line), and medical gumshoes nationwide have their fingers crossed. It wouldn’t be the first time, after all, that a DNA test brought a naggingly unsettled investigation to a definitive conclusion.

–By Julian Dibbell. Reported by Christine Sadlowski/New York