On December 10th 2014, Fulton County Department of Health and Wellness (FCDHW) was notified of a cluster of persons with acute gastroenteritis. It was reported that illness was occurring in students, parents, staff and other guests who had attended an end-of-the-year high school sports team banquet on December 8th and that up to 150 attendees may have been ill. The epidemiology branch at FCDHW conducted a field investigation to determine the scope of the outbreak, find the source of illness, and recommend prevention and control measures. In order to gain experience in outbreak investigation, I was asked to initiate the investigation under the supervision of a senior epidemiologist and medical director. We first developed a case definition, carried out additional case finding, and created a questionnaire, which was distributed to all attendees. To identify potential sources of illness, we performed a case control study. Additionally, we collected stool samples from 12 persons who became ill. These were assessed by the Georgia Public Health Laboratory (GPHL). Staff from the Environmental Health Services Unit of FCDHW interviewed the individual who prepared the main meat entrees (pork and chicken) regarding the handling, cooking, and serving procedures used.
Responses to the survey were provided by 71 of the 200 attendees, and 69 observations were included in the analysis: 56 probable cases and 13 controls were identified. Onset of symptoms ranged from December 8th to December 10th (Fig.1) and illness lasted for an average of 5.09 days. The most common symptoms reported were headache (96.3%), diarrhea (93.0%), abdominal cramping (91.2%), body aches (91.1%), and chills (91.1%). The attack rate for attendees who ate the smoked chicken was 100% and was strongly associated with illness (OR= 155.77, 95% CI= 8.19, 2,962.97, p-value: <.005). Models using exact logistic regression indicate that only the smoked chicken was significantly associated with illness. GPHL bacteriology results identified 10 positive specimens for Salmonella Thompson. Pulsed-field gel electrophoresis (PFGE) indicated that nine of the 10 specimens had the same pattern. Findings from Environmental Health Service interviews revealed that the person preparing the chicken had limited knowledge regarding the required temperatures and procedures necessary to properly store or cook chicken for such a large number of people.
Figure 1.Probable cases of Salmonella Thompson infection by date of illness onset from December 7, 2014 to December 11th, 2014.
The epidemiologic, clinical, and environmental data collected indicate a point source outbreak due to contaminated smoked chicken as the probable transmission vehicle. The presence of two PFGE patterns in an outbreak such as this is not commonly reported in epidemiology literature – but it does occur. The use of PFGE can assist in identifying associated outbreaks. This facilitates quicker identification of contamination at the point of production rather than preparation. No other outbreaks of the main serotype with matching PFGE patterns were identified during the period of time around this event. This suggests that either bacterial contamination or amplification occurred during the preparation and storage of the chicken, rather than problems with bacterial contamination at the point of production and sale.
These findings indicate that proper food preparation and serving processes, such as temperature regulation, are highly important in the prevention of foodborne outbreaks. Furthermore, private entities that do not have permits for food service and catering events are not held to the same hygiene and food safety standards as professional caterers. These individuals should be educated on food safety regarding preparation and service before preparation of food for large numbers of people. This outbreak demonstrates the importance of prevention measures in food preparation to mitigate the hazards of preparing and serving food at large events.
As a result of this outbreak investigation, the following public health actions have been implemented: our team reported findings from the case control study to school administrators, distributed a USDA brochure “Cooking for Groups: A Volunteer’s Guide to Food Safety” and a flyer from the health department. Additional health communications regarding food safety at large events are in the development stage.
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