NEW YORK (Reuters Health) - A recent study suggests that guacamole and hot sauce will join the ranks of fresh fruit, vegetables and tap water when it comes to dietary "don'ts" in Mexico.

The study found that 47 of 71 (66%) tabletop samples taken from popular tourist restaurants in Guadalajara, Mexico were contaminated with Escherichia coli, a leading cause of "traveler's diarrhea." E. coli is found in the intestines of humans and animals but some strains can cause diarrhea or even more dangerous infections.

While 10 of 25 samples (40%) of hot sauce and guacamole from Mexican-style restaurants in Houston, Texas also contained the bacteria, levels of contamination were 400 to 1,000 times greater in the Mexican restaurants, the study found. What's more, the type of E. coli that cause diarrhea were only found in the samples from Guadalajara, and not those from Texas restaurants.

In the US, sauces were more likely to be refrigerated before they were served, while in Mexico, the sauces tended to stay at room temperature. In both cities, guacamole was more likely than hot sauce to contain dangerous levels of E. coli, report researchers in the June 18th issue of the Annals of Internal Medicine.

The findings contradict the notion that acidic foods such as hot sauce are less prone to bacterial contamination and suggest that diners think twice when adding tabletop sauces to their dish, conclude Dr. Herbert L. DuPont, a professor at the University of Texas-Houston, and colleagues.

"People think that if it burns the mouth it might burn the bugs. Alas, this is not the case," said Herbert in an interview with Reuters Health.

He offered two pieces of advice to aficionados of Mexican fare: forego the tabletop hot sauces in Mexico but if the guacamole beckons, make sure the container is cold--indicating that it has spent time in the refrigerator.

SOURCE: Annals of Internal Medicine 2002;136:884-887.