June 17, 2002 -- Dipping your tortilla chips in the guacamole or salsa at your table at Mexican restaurants may be tempting. But sampling these sauces may also tempt fate and make you a target for Montezuma's revenge. A new report shows many tabletop sauces collected from popular restaurants in Guadalajara, Mexico, and Houston, Texas, were contaminated with E. coli.
Overall, 66% of the sauces from restaurants in Guadalajara and 40% of those from Houston were contaminated with the bacteria, which commonly causes traveler's diarrhea.
Researchers say about 80% of the cases of traveler's diarrhea are caused by contaminated food, and these sauces may be an overlooked source of infection. Their findings appear in the June 18 issue of the Annals of Internal Medicine.
The researchers analyzed 71 sauces (including guacamole, pico de gallo, and other green and red sauces) from 36 independently owned Mexican-style restaurants in Guadalajara that are known to be popular with U.S. travelers and 25 similar sauces from 12 non-chain Mexican restaurants in Houston.
Researchers say they found a big difference between the two cities in the number and severity of contaminated samples.
The Mexican sauces from Guadalajara more frequently contained fecal contaminants and higher levels of the bacteria than that of the sauces from Houston, according to the researchers from the University of Texas-Houston Medical School.
Researchers say all of the sauces were already sitting on the table when they arrived at the restaurants in Mexico and were at room temperature, which creates a fertile breeding ground for dangerous bacteria.
"Moreover, we believe that the sauces were more likely to be handled by multiple workers and patrons (reuse of same sauce) in Mexico than in Houston," write the authors. "We feel that travelers to Mexico should be cautious about consuming sauces served on the table, particularly if previous refrigeration cannot be assured."
In contrast, all of the sauces from Houston restaurants were brought to the table after being seated and were refrigerated before serving.
Unlike the Guadalajara sauces, none of the Houston samples contained any of the more potent forms of E. coli that are known to be the major causes of traveler's diarrhea in Mexico.
Guacamole was the most frequently contaminated sauce in both cities, but pico de gallo contained the highest level of contamination among the Guadalajara restaurant samples. Researchers say the fact that an acidic sauce containing tomatoes and other acids, such as pico de gallo, was found to have high levels of E. coli contamination also dispels the popular notion that such foods are protected from bacterial contamination.