It’s the Salsa!

If you want to know why you’re getting Montezuma’s revenge when you travel to Mexico and elsewhere, the answer is at Carlos and Charlie’s—in the salsa, jalapeno sauces, and guacamole.

Researchers from the University of Texas found E. coli in twothirds of the condiments they tested from Mexico, and on average the levels of contamination were one thousand times what they measured in restaurants in Houston. What’s more, they repeatedly found two particularly virulent strains of E. coli that together account for half of all cases of traveler’s diarrhea.

The bugs come from human feces and contaminate the sauces via unwashed hands, says Herbert DuPont, an expert in infectious diseases and chief of internal medicine at St. Luke’s Episcopal Hospital in Houston.

“Most people think it’s the water, but it’s not,” says DuPont, who’s been testing food for nearly three decades. He has found that bad food is responsible for about ninety percent of traveler’s diarrhea.

DuPont’s team collected samples of seventy-one sauces from thirty- six restaurants in Guadalajara and compared them with twenty-five sauces served in twelve Mexican-style restaurants in Houston. Of the many bugs that can cause food poisoning, they only found E. coli, but it was present in sixty-six percent of the sauces from Guadalajara and forty percent of those collected in Houston. While none of the Houston samples contained dangerous strains of E. coli, sauces from Mexico commonly contained two that wreak havoc in the gut. One releases a toxin, and the other causes inflammation.

DuPont’s group found that nine percent of Mexican samples harbored the first kind, and forty-four percent the second. The Mexican restaurants in Houston are probably safer because they serve their condiments either freshly made or from the refrigerator. In Mexico, the same sauces sit on the table all day. Not only are they unrefrigerated, but many consecutive diners may stick their fingers in them while dipping their chips, says DuPont.

Diane Martindale
New Scientist 27 July 2002