What is the next step in managing an outbreak of acute gastroenteritis among hospital staff who consumed food from the same restaurant?

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 as Immediate Priority

The outbreak has already been established with 15 of 50 hospital staff ill with similar symptoms and common restaurant exposure, completing the initial phase of investigation. 1 The current phase requires systematic epidemiologic investigation before implementing control measures. 1

Conducting a case-control study provides the epidemiologic direction needed to identify the specific food vehicle and guide targeted interventions, whereas pursuing environmental investigations or control measures first wastes time and resources without this critical information. 1

Why Other Options Are Premature

Isolation (Option A)

• Isolation of affected individuals is not the immediate priority in a foodborne outbreak investigation where the source remains unidentified. 1
• This intervention would be appropriate later for specific pathogens with person-to-person transmission concerns, but only after the epidemiologic investigation identifies the outbreak vehicle. 1

Quarantine of 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 confirms the findings. 1

Detailed Restaurant Data Collection (Option D)

• Collecting detailed data about food processing should not precede the case-control study, as you need epidemiologic direction to know which specific foods and processes to investigate. 1
• Environmental and laboratory investigation, including collecting samples of implicated foods for microbiologic testing and screening food handlers for infection, occurs in the subsequent phase after the case-control study identifies specific high-risk items. 1

Implementation of Case-Control Study

Case Definition and Control Selection

• Define cases using clinical criteria, such as acute gastroenteritis with specific symptom onset timing. 1
• Identify controls from the same population—hospital staff who ate at the restaurant but remained well. 1

Structured Interviews

• Conduct structured interviews about all specific food items consumed at the restaurant. 1
• Calculate odds ratios for each food exposure to identify the vehicle of infection. 1
• Historical data demonstrates that this approach can identify associations with odds ratios as high as 84.0 for specific implicated foods, as seen in the Connecticut outbreak where potato salad was strongly associated with illness. 2, 1

Laboratory Specimen Collection

• 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 Case-Control Study)

Once the case-control study identifies the specific food vehicle and environmental investigation confirms the source:

• Exclude infected food handlers until stool cultures are negative. 1
• Provide food handler education on hygiene practices to prevent future outbreaks. 1
• Do not overlook asymptomatic food handlers, as they can be colonized and transmit infection without symptoms, as demonstrated in the Connecticut outbreak where one asymptomatic food service worker had Salmonella-positive stool. 2, 1

Critical Pitfall to Avoid

Do not assume all restaurant exposures are equal—the case-control study identifies specific high-risk items that require targeted intervention rather than broad, resource-intensive measures. 1