Context On January 5, 1999, the California Department of Health Services was
notified of the repeated occurrence (December 21, 1998, and January 2, 1999)
of gastrointestinal tract illness among patrons at a Thai restaurant in central
Objective To identify the source of the outbreak.
Design Case-control study; microbiological and toxicological laboratory testing
of samples of food, stool, and vomitus.
Setting Thai food restaurant in central California.
Participants Patrons of the restaurant. A case (n = 107) was defined as dizziness,
nausea, or vomiting occurring in a person who ate at the restaurant between
December 20, 1998, and January 2, 1999, with onset of symptoms within 2 hours
of eating. A control (n = 169) was a person who ate at the restaurant during
the same period but reported no symptoms.
Main Outcome Measures Odds ratios (ORs) of illness associated with food exposures; ORs of
shifts during which illness occurred associated with certain cooks; laboratory
Results The median latency period was 40 minutes from beginning eating to first
symptom and was 2 hours to onset of diarrhea. The median duration of symptoms
was 6 hours. Twenty-six persons (24%) visited the emergency department or
were treated by a physician; no person required hospitalization. Patients
reported nausea (95%), dizziness (72%), abdominal cramps (58%), headache (52%),
vomiting (51%), chills (48%), and diarrhea (46%). Fifty-one cases (48%) included
dizziness, lightheadedness, or a feeling of disequilibrium as the initial
symptom. Illness was statistically associated with several foods and ingredients,
but no single dish or ingredient explained a substantial number of cases.
The analysis of food exposures included salt added by cooks, as estimated
by using the amount of salt in the recipe for each dish and the amount of
each dish eaten by respondents. This association was stronger with increasing
levels of salt: ORs for illness among persons who consumed more than 0.42
to 0.84, more than 0.84 to 1.25, and more than 1.25 tsp of salt added to foods
in the kitchen were 1.9 (95% confidence interval [CI], 0.6-5.7), 3.0 (95%
CI, 1.0-8.8), and 4.0 (95% CI, 1.3-13.5) compared with persons who consumed
less than 0.42 tsp (P value for trend = .004). Methomyl,
a highly toxic carbamate pesticide, was identified in a sample of vomitus
(20 ppm) and in salt taken from containers in the storeroom (mean, 5600 ppm)
and the stovetop (mean, 1425 ppm). The oral toxic dose causing illness in
50% of those exposed to methomyl was estimated to be 0.15 mg/kg of body weight
(estimated range, 0.09-0.31 mg/kg of body weight). The presence of cook A
was associated with shifts during which cases of illness occurred (OR, 10.4;
95% CI, 1.2-157.4).
Conclusion This outbreak of gastrointestinal illness was associated with the consumption of food seasoned with
methomyl-contaminated salt. To allow rapid assessment for further
investigational and control measures by health officials, physicians
should report suspected outbreaks of illness to public health
departments, however trivial the symptoms or cause may seem.