Food safety inspectors have pinpointed the problem that sickened patrons at Raleigh’s Evoo restaurant last month: Anchovies used in a Caesar salad dressing. At least 17 diners fell ill at the restaurant and in a nearby home, summoning multiple emergency medical teams to the scene.

Test results by federal Food and Drug Administration (PDF, 228 KB) revealed poisonous levels of histamine, an agent resulting from the decomposition of fish muscles, which causes nausea, vomiting and allergic-like reactions very quickly after exposure. The resulting illness is called scombroid food poisoning, and is most commonly associated with anchovies and sardines, as well as tuna, bluefish and mahi mahi.

The canned anchovies came from the manufacturer, Monarch, with histamine levels of 48 to 79 parts per million (ppm). The FDA considers levels of more than 50 ppm unsafe for consumption, and individual diners can experience sensitivity to the substance even at levels below that, says Andre Pierce, Wake County’s environmental health and safety director.

Monarch, a division of U.S. Foods, has issued a Class 1 (highest priority) recall of the anchovies, Pierce said.

“Today is a big sigh of relief for the restaurant,” said Evoo partner Robert Duffy. “We feel like we did everything right; there’s nothing we could have done to prevent this.”

Regulators tested both the anchovies and some tuna that were served on April 17, and while the tuna returned some results that could have caused some sensitive diners a problem, anchovies seem the more likely culprit because all of the ill patrons had eaten salad, Pierce said.

While not every diner had the Caesar salad, the same cutting board was used to prepare the anchovies and the salad greens, so other salads may have been cross-contaminated, Pierce said.

Duffy says Evoo has discontinued using anchovies in its salad dressing, and is inviting patrons affected by the illness to dinner on the house. The restaurant was cleared by inspectors to reopen the day after the incident, and continues to maintain its A rating.