Outbreak reportcited by the Tayebat archivefull text checked A-CHK-17 in-depth review
US Salmonella outbreak from one chicken company
National Outbreak of Multidrug Resistant Salmonella Heidelberg Infections Linked to a Single Poultry Company.
Overview
Gieraltowski L et al.. PLoS One 2016 · PMID 27631492 · DOI 10.1371/journal.pone.0162369
634 people fell ill from resistant Salmonella traced to one company's chicken.
Does the study support the specific claim? Yes · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
What caused a large multistate MDR Salmonella Heidelberg outbreak?
- How was the study done?
Outbreak investigation (epidemiological, laboratory, traceback)
- How many people, animals or samples were studied?
634 cases; 435 interviewed; 634 US case-patients
- What was actually found?
634 sick (38% hospitalised, no deaths); 87% of those with brand data ate Company A chicken; 67% of tested patient isolates resistant, 35% multidrug-resistant; Salmonella in 26% of samples at the implicated plants, down to about 5% after fixes.
- How large was the observed effect?
Descriptive
- What do the results mean in everyday life?
Shows why safe handling of raw chicken matters.
- What are the study's limitations?
Single outbreak
- What does it say about Elawady's specific claim?
Supports existence of hazard.
- Do the results apply to Germany and Europe?
Moderate.
- What can explicitly not be concluded from this study?
Cannot give routine prevalence in chicken and does not support an 80-85% contamination rate.
Scientific in-depth review
1. Full reference
- Authors
- Gieraltowski L, Higa J, Peralta V, Green A, Schwensohn C, Rosen H, Libby T, Kissler B, Marsden-Haug N, Booth H, Kimura A, Grass J, Bicknese A, Tolar B, Defibaugh-Chávez S, Williams I, Wise M, Salmonella Heidelberg Investigation Team
- Journal
- PLoS One
- Year
- 2016
- Identifier
- PMID 27631492 DOI 10.1371/journal.pone.0162369 · PMC5025200
- Verification
- verified – PubMed E-utilities efetch, 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- full text
- Conflicts of interest and funding
Authors (CDC, state health departments, USDA-FSIS) declare no competing interests; no separate funding statement in the retrieved text (public-health agency investigation).
2. Research question
What caused a large multistate MDR Salmonella Heidelberg outbreak?
3. Study design and population
- Study design
- Outbreak report – Multistate outbreak investigation (PulseNet PFGE case-finding, case-patient interviews compared with FoodNet Population Survey via binomial tests, shopper-card traceback, product and in-plant testing, NARMS susceptibility testing)
- Population
634 case-patients with laboratory-confirmed S. Heidelberg (1 of 7 PFGE patterns) in 29 states and Puerto Rico (77% California); median age 18 years (<1-93)
- Country
USA
- Period
March 2013-July 2014
- Sample size
634 cases; 435 interviewed (273 with focused questionnaire); 175 with brand information; 69 clinical isolates tested for resistance; 2,649 in-plant product samples
- Inclusion and exclusion criteria
Lab-confirmed S. Heidelberg with one of 7 outbreak PFGE XbaI patterns and onset 1 March 2013-11 July 2014; the nationally common pattern JF6X01.0022 counted only for California residents.
4. Methods and endpoints
- Exposure / intervention
Consumption of Company A (single US poultry company) chicken, mostly raw parts prepared at home, plus rotisserie chicken cooked in one store
- Comparator
Healthy persons in the 2006-2007 FoodNet Population Survey (65% ate chicken prepared at home in 7 days)
- Endpoints
Illness; hospitalisation; resistance
- Statistical methods
Descriptive proportions; binomial comparison against FoodNet population survey; CUSUM outbreak detection; no formal analytic (case-control) study
5. Actual results
- Results
634 cases; 200/528 (38%) hospitalised; 15% bloodstream isolates; no deaths. 371/435 (85%) ate chicken in the prior 7 days; 201/273 (74%) ate chicken prepared at home vs 65% in FoodNet (p=0.0004); 152/175 (87%) with brand information ate Company A chicken; 86% of home-chicken eaters ate parts. One store sub-cluster of 32 cases linked to rotisserie chicken. Outbreak strains in 9 of 19 leftover raw Company A chicken samples from 13 homes. In-plant testing September 2013: Salmonella in 26% (116/450) of samples at the 3 California establishments vs 1% (2/149) in Washington; declined to ~5% by October 2014 after control measures. Of 69 clinical isolates, 46 (67%) resistant to >=1 antimicrobial and 24 (35%) MDR (ampicillin, chloramphenicol, gentamicin, kanamycin, streptomycin, sulfisoxazole, tetracycline).
- Absolute risks
not applicable (outbreak case counts only; no denominator of consumers). In-plant Salmonella prevalence 26% at implicated plants during the outbreak, ~5% after interventions; national 2012 baseline for chicken parts 26%.
- Authors' conclusion
Company A chicken caused the outbreak; upstream reservoir suspected.
6. Strengths
- Convergent epidemiological, traceback and laboratory evidence (identical PFGE patterns in patients, leftover chicken, retail and in-plant samples)
- Large national case series with multi-agency investigation
- Documents regulatory follow-up (new USDA standards for chicken parts)
7. Weaknesses
- No formal analytic study; comparison with an older (2006-2007) population survey
- Recall bias for foods and brands (interviews weeks after onset); brand data available for only 175 cases
- Passive surveillance underestimates total cases
- PFGE is less discriminatory than whole-genome sequencing; 3 leftover samples carried a different outbreak strain than the patient
- Single outbreak in one company; not a measure of routine prevalence
8. Risk of bias
- Orienting tool
- none (outbreak investigation; no standard RoB tool applies)
- Type of assessment
- structured assessment based on the full text by a single reviewer (no formal double review)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Changed from not_assessable to a structured judgement (some_concerns): source attribution is strong but individual-level association was not formally tested. Single-reviewer structured judgement; a formal assessment would need two independent reviewers.
| Domain | Judgement | Rationale |
|---|---|---|
| Case ascertainment | some concerns | Passive PulseNet surveillance with PFGE definition; pattern 0022 restricted to California to reduce misclassification. |
| Exposure ascertainment | some concerns | Self-reported food and brand history weeks after onset; supported by shopper-card records. |
| Comparison/association | some concerns | No case-control study; historical FoodNet comparator. |
| Laboratory confirmation | low | Outbreak strains isolated from leftover, retail and in-plant chicken; NARMS susceptibility testing. |
Full-text review (25 October 2026): Added case definition, FoodNet comparison (74% vs 65%, p=0.0004), leftover-chicken testing (9/19), in-plant prevalence 26% (CA) vs 1% (WA) falling to ~5%, resistance profile, author-stated limitations; bias changed not_assessable -> some_concerns. Prevalence data contradict the 80-85% figure in C-CHK-08.
9. Assessment of the statistical interpretation
Descriptive outbreak data; the attribution to Company A chicken rests on convergent microbiological evidence rather than a measure of association. Prevalence figures (26% at implicated plants during the outbreak, ~5% afterwards) are far below 80-85%.
10. Relevance to the specific claim
11. Independent contrary findings
Outbreak, not routine prevalence.
12. Transferability to Germany and Europe
Moderate.
13. Overall methodological judgement
Strong, well-documented example that raw chicken from one company caused a large multidrug-resistant Salmonella outbreak; it demonstrates a real hazard and the role of handling/cooking and plant controls. It does not support the claim that 80-85% of chickens carry Salmonella (in-plant prevalence 26% at the implicated plants, 1% elsewhere, ~5% after interventions).
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | not applicable |
| Directness | direct |
| Reproducibility | not replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Upstream (farm/hatchery) reservoir and source of resistance genes; current prevalence in EU/Egyptian chicken parts.
15. Linked fact checks
- Industrial chicken is raised with routine antibiotics, and antibiotic-resistant bacteria (e.g., ESBL E. coli, MRSA, resistant Campylobacter, mcr-1) spread from poultry to humans via the food chain. – Studies supporting the claim
- About 80-85% of chickens are contaminated with Salmonella, even with the cleanest slaughter methods (the blood is contaminated). – Studies contradicting or limiting the claim
- Chicken carries Campylobacter and Salmonella, which cause human infections. – Studies supporting the claim
Use by the Tayebat archive
Note: according to the archive, the studies were compiled by the archive operators. Whether Dr. Elawady himself cited this study is not established.
- What the archive says about the study
Listed in bibliography (no interpretation).
- A. What was actually studied?
Salmonella outbreak from chicken.
- B. What did the authors find?
634 cases (38% hospitalised, no deaths) traced to Company A chicken; 67% of 69 clinical isolates resistant, 35% MDR; Salmonella in 26% of in-plant samples at 3 implicated California plants (1% in Washington), reduced to ~5% after control measures.
- C. What conclusions do the authors themselves draw?
Food safety policies for chicken parts needed.
- D. What does the archive derive from it?
Supports hazard of industrial chicken.
- E. Is this derivation scientifically justified?
Justified as an example of a real food-safety hazard from raw chicken; it is a single outbreak and its prevalence data (26% at implicated plants, ~5% after controls) contradict rather than support claims that 80-85% of chickens carry Salmonella.
- Adequacy of the interpretation (by the archive)
- not applicable