Foodborne giardiasis in a corporate office setting.

Giardiasis is the most commonly reported intestinal protozoal infection worldwide, but its relatively long incubation period and often insidious onset make detection of common-source outbreaks difficult. Few well-documented foodborne outbreaks of giardiasis have been reported. In November 1990, such an outbreak among insurance company employees resulted in 18 laboratory-confirmed and 9 suspected cases of giardiasis. A case-control study of 26 ill and 162 well employees implicated raw sliced vegetables served in the employee cafeteria and prepared by a food handler infected with Giardia lamblia as the probable vehicle (odds ratio, 5.1; 95% confidence interval, 1.4-22.7). This outbreak illustrates the potential for transmission of Giardia organisms to occur in commercial establishments through a frequently served food item.