An outbreak of food-borne illness associated with methomyl-contaminated salt.
BACKGROUND
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 California.


OBJECTIVE
To identify the source of the outbreak.


METHODS
Case-control study; microbiological and toxicological laboratory testing of samples of food, stool, and vomitus.


METHODS
Thai food restaurant in central California.


METHODS
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.


METHODS
Odds ratios (ORs) of illness associated with food exposures; ORs of shifts during which illness occurred associated with certain cooks; laboratory results.


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).


CONCLUSIONS
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.
Buchholz
Udo
U
Epidemic Intelligence Service, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, GA, USA. BuchholzU@rki.de
Mermin
Jonathan
J
Rios
Richard
R
Casagrande
Tim L
TL
Galey
Francis
F
Lee
Mark
M
Quattrone
Alfredo
A
Farrar
Jeff
J
Nagelkerke
Nico
N
Werner
S Benson
SB
D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D004196:Disease Outbreaks; D005506:Food Contamination; D005517:Foodborne Diseases / Q000453:epidemiology* / Q000209:etiology; D006801:Humans; D007306:Insecticides / Q000032:analysis / Q000506:poisoning*; D016015:Logistic Models; D008724:Methomyl / Q000032:analysis / Q000506:poisoning*; D016017:Odds Ratio; D012147:Restaurants; D017673:Sodium Chloride, Dietary / Q000032:analysis
D007306:Insecticides; D017673:Sodium Chloride, Dietary; D008724:Methomyl