Systematic reviewindependent cross-checkabstract checked I-EGG-123 standard review

Cages are one of many Salmonella risk factors on egg farms

Risk Factors Associated With Salmonella in Laying Hen Farms: Systematic Review of Observational Studies.

Overview

Denagamage T et al.. Avian Dis 2015 · PMID 26473681 · DOI 10.1637/10997-120214-Reg

Cage housing, large flocks, rodents and poor cleaning were linked to Salmonella on layer farms.

Does the study support the specific claim? Partly · Methodological quality: moderate

Study explained simply

What did the researchers want to find out?: Identify Salmonella risk factors in layer farms.
How was the study done?: Systematic review.
How many people, animals or samples were studied?: 17 studies.
What was actually found?: Multiple risk factors including cage housing.
How large was the observed effect?: Eggshell positivity 59x higher when faeces positive.
What do the results mean in everyday life?: Farm hygiene and size matter at least as much as cages.
What are the study's limitations?: Observational.
What does it say about Elawady's specific claim?: Partly supports it.
Do the results apply to Germany and Europe?: Moderate.
What can explicitly not be concluded from this study?: It cannot isolate a pure cage effect.

Authors: Denagamage T et al.
Journal: Avian Dis
Year: 2015
Identifier: PMID 26473681 DOI 10.1637/10997-120214-Reg
Verification: verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: not stated in abstract

Which farm factors are associated with Salmonella contamination of laying hens, premises and shell eggs?

Study design: Systematic review – Systematic review of observational studies (13 cross-sectional, 4 longitudinal) with evidence scoring
Population: Commercial laying hen farms
Country: Multinational
Period: not stated in abstract
Sample size: 17 studies
Inclusion and exclusion criteria: not detailed in abstract

Exposure / intervention: Management and housing factors, including cage housing
Comparator: Absence of factor
Endpoints: Salmonella in layer premises, hens and shell eggs
Statistical methods: Best-evidence synthesis; odds ratios

Results: Risk factors for contamination of laying hen premises included previous infection, absent cleaning/disinfection, rodents, induced moulting, larger flock size (>30,000), multi-age management and cage housing systems. For shell eggs: high manure contamination, later production phase, contaminated egg-handling equipment, flock size >30,000 and production rate >96%. Eggshell positivity was 59 times higher when faecal samples were positive.
Absolute risks: not reported
Authors' conclusion: Salmonella contamination of laying hen flocks and shell eggs is multifactorial.

Cage housing is one of many correlated risk factors (flock size, multi-age, hygiene).

Supports cage housing as a risk factor for farm Salmonella, while showing that size, hygiene and rodents matter as much.

Egyptian data (I-EGG-125) found closed battery farms with high biosecurity had cleaner eggs.

Mostly pre-2012 systems; EU conventional cages banned.

Supports the direction of the claim with important qualifications.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	moderate
Risk of bias	some concerns
Precision of results	not applicable
Directness	direct
Reproducibility	partly replicated
Consistency with the overall evidence	mixed
Regional transferability	moderate
Adequacy of the interpretation (by the archive)	not applicable

Effect of enriched cages.