Preparing for Biological and Chemical Attacks - Bioattack: The Dalles Incident

Civilians are vulnerable to foodborne or waterborne bioterrorism, as demonstrated by the intentional salmonella contamination of restaurant salad bars in and around The Dalles, Oregon, in September and October 1984. A total of 751 people developed salmonella gastroenteritis from eating or working at those salad bars.

The outbreak occurred in two waves: September 9–September 18 and September 19–October 10. Most cases occurred in ten restaurants. Epidemiological studies of customers at four restaurants and of employees at all ten restaurants indicated that eating from salad bars was the major risk factor for infection. Eight of the ten affected restaurants (80%) operated a salad bar, compared with only three of the twenty-eight nonaffected restaurants (11%) in The Dalles.

The investigation did not identify any water supply, food item, supplier, or distributor common to all affected restaurants, nor were the employees exposed to any single common source. Infected employees may have contributed to the spread of the illness, but they did not initiate the outbreak, nor did food-rotation errors or inadequate refrigeration of the salad bars (although they may have promoted bacteria growth).

A criminal investigation revealed that members of a religious commune, the Rajneeshees, had deliberately contaminated the salad bars with salmonella bacteria as part of a plan to influence a county election in favor of candidates they endorsed. By making residents of The Dalles too ill to go to the polls on election day, the group hoped to seize control of the county government. According to most accounts, commune members planned to contaminate The Dalles's municipal water system just before election day. About a month before the election, they began experimenting with the bacteria by poisoning the refreshments they served to two county commissioners who were visiting the Rajneeshees' compound. Later, commune members sprinkled salmonella on produce in grocery stores. Finally, the Rajneeshees sprinkled salmonella bacteria in and around the salad bars of the town's ten most popular restaurants. Within a few weeks, more than seven hundred people had become ill.