Next Step in Outbreak Investigation
The next step is to conduct a case-control study to identify specific food items or exposures associated with illness (Option B). 1
Rationale for Case-Control Study
The outbreak investigation has already completed its initial phase—establishing that an outbreak exists with 15 of 50 staff ill with similar symptoms and common restaurant exposure. 1 The current phase requires systematic epidemiologic investigation to identify the specific vehicle of infection before pursuing environmental or control measures. 1
The CDC explicitly recommends conducting a formal case-control study to identify specific food items through systematic comparison of cases and controls, rather than pursuing broad interventions without epidemiologic direction. 1 The WHO warns that delaying the case-control study to pursue environmental investigations first wastes time and resources without epidemiologic direction. 1
Why Other Options Are Premature
Isolation (Option A)
- Isolation of affected individuals is not the immediate priority in a foodborne outbreak where the source remains unidentified. 1
- This would be appropriate later for specific pathogens with person-to-person transmission concerns, but only after identifying the vehicle of infection. 1
Quarantine Restaurant Staff (Option C)
- Quarantining restaurant staff without epidemiologic evidence identifying the specific food vehicle wastes time and resources. 1
- This determination comes after the case-control study identifies the implicated food and subsequent environmental investigation. 1
Detailed Restaurant Data Collection (Option D)
- Environmental investigation, including collecting samples of implicated foods for microbiologic testing and screening food handlers, occurs in the subsequent phase after the case-control study. 1
- The CDC warns against assuming all restaurant exposures are equal—the case-control study identifies specific high-risk items first. 1
Implementation of Case-Control Study
Define cases using clinical criteria (acute gastroenteritis with specific symptom onset timing) and identify controls from the same population (hospital staff who ate at the restaurant but remained well). 1
Conduct structured interviews about all specific food items consumed at the restaurant, then calculate odds ratios for each food exposure to identify the vehicle of infection. 1 Historical outbreak data demonstrates this approach can identify associations with odds ratios as high as 84.0 for specific implicated foods, guiding targeted interventions. 1
Collect stool specimens immediately from at least 10 ill persons during the first 48 hours of illness, as viral diagnostic yield drops precipitously after 2-3 days when viral shedding decreases below detectable levels. 1 Store bulk diarrheal specimens at +4°C rather than frozen to preserve viral morphology for electron microscopy. 1
Subsequent Control Measures
After the case-control study identifies the implicated food, subsequent phases will involve:
- Environmental investigation including collecting samples of implicated foods for microbiologic testing and screening food handlers for infection. 1
- Excluding infected food handlers until stool cultures are negative. 1
- Providing food handler education on hygiene practices to prevent future outbreaks. 1
Critical Pitfall to Avoid
Do not overlook asymptomatic food handlers, as they can be colonized and transmit infection without symptoms. 1 Pre-symptomatic food handlers have been documented as sources of transmission in multiple outbreaks. 2, 3