CPH (Other exams): A Gastrointestinal Illness Cluster After a Church Potluck

The median 28-hour incubation with prominent vomiting and a wide range (4–60 h) fits Staphylococcus aureus or Bacillus cereus toxin-mediated illness poorly on timing (those are typically 1–6 h and 0.5–16 h respectively), so the leading hypothesis is a short-incubation invasive/toxin pathogen with a longer range - most consistent with Clostridium perfringens (typically 8–16 h, diarrhea-predominant) or norovirus (12–48 h, vomiting-predominant, secondary person-to-person spread). The vomiting predominance and 28-h median favor norovirus, with the carved turkey and hand lesion raising S. aureus as a competing hypothesis (toxin from the wound contaminating the meat).

Alternatives: Salmonella (6–72 h, often fever), Campylobacter (2–5 d, less likely given timing), B. cereus emetic type if rice-based dish present (none here).

The wide range and 28-h median argue against a single pre-formed toxin and for either an organism that replicates in food or a viral agent with person-to-person amplification. The volunteer's recent 'stomach bug' could be a norovirus source (shedding can precede and follow symptoms), making him a plausible index rather than only the hand lesion.

Do not name a food yet. Naming a vehicle without evidence risks reputational harm to the volunteer, false reassurance if wrong, and may suppress future cooperation.

Required steps:

1. Case definition and line list: define a case (attendee with vomiting or diarrhea within 72 h), interview all attendees, and compute attack rates by food item.
2. Cohort analysis: calculate attack rates for exposed vs unexposed for each dish; a food is implicated when attack rate is high among eaters and low among non-eaters, with a plausible dose-response (amount eaten).
3. Specimen collection: stool from ill persons (including the two hospitalized) for bacterial culture and norovirus PCR; the volunteer's hand lesion and a stool specimen if symptomatic.
4. Environmental assessment: interview the carver about the wound, glove use, and the potato salad's holding time/temperature (car trunk for 3 h - temperature unknown).
5. Secondary spread: ask about household illness to assess person-to-person transmission.

Communication: acknowledge the cluster, state that the investigation is ongoing, give practical guidance (hydration, hand hygiene, stay home while ill, seek care for dehydration), and commit to sharing findings. Explain that with no food samples left, the epidemiologic analysis and clinical specimens are the evidence base, and that 'the potato salad' cannot be confirmed or excluded until attack rates are computed.

This materially shifts the hypothesis. Bloody diarrhea with fever is inconsistent with typical norovirus and points to an invasive bacterial pathogen; a Salmonella isolate from an attendee is supportive but not yet definitive (could be coincidental).

Immediate actions:

• Pulse the case definition: add fever and bloody stools as severe-case criteria; re-interview all cases for these features and for healthcare contact.
• Serotype and match: request serotyping/WGS of the Salmonella isolate and compare with any other isolates (including the hospitalized patients) to see if they are indistinguishable.
• Re-examine the menu: turkey is a classic Salmonella vehicle; ask about thawing, cooking temperature, and cross-contamination. The carver's hand lesion remains relevant for S. aureus but less so for Salmonella.
• Notify and coordinate: inform the state health department and CDC if a multistate match emerges; alert clinicians to consider stool cultures and report invasives.
• Protect the public: advise attendees with fever/bloody stools to seek care; exclude symptomatic food handlers from food work until 48 h after symptoms resolve (and per jurisdiction rules for Salmonella).

Revise the public message: the investigation now centers on a possible bacterial source; do not name a food, but flag the turkey as a focus of inquiry pending isolate comparison.