EAL

MHFS: Food Safety (2012-2013)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To summarize the study implicating consumption of undercooked eggs and home-prepared frozen chicken nuggets and strips as leading risk factors for Salmonella Heidelberg infections in Canada.

Inclusion Criteria:

Canadian residents with laboratory confirmed Salmonella Heidelberg infections diagnosed from January 1, 2003 to May 31, 2003
One control was selected for each case using forward/backward digit dialing from the case's home telephone number
Controls were matched to cases by age group (zero to six, seven to 17 and 18 years or more).

Exclusion Criteria:

If subject:
- Had traveled outside of Canada in the week prior to becoming ill
- Were unable to communicate in English or French
- Had been eligible for the British Columbia case-control study conducted from January 1 to April 1, 2003
If they had been ill with diarrhea in the month prior to interview.

Description of Study Protocol:

Recruitment

In April 2003, all provinces and territories were invited to participate in a national case-control study.

Design

Case-control study.

Statistical Analysis

Data were managed using Epi-Info version 6.04d and analyzed using Statistical Analysis System version 8.02
Matched case-control data were analysed by conditional logistic regression using the SAS procedure
Exposures demonstrating P<0.25 in univariate analyses were further analysed by multivariate modeling using a manual stepwise approach
P-values and likelihood ratio tests were used to confirm the significance of variables and potential interactions between variables
Population attributable fractions were calculated using matched odds ratios (mORs) derived from multivariate conditional logistic regression and the prevalence of exposure among all cases interviewed.

Data Collection Summary:

Timing of Measurements

Case-control study conducted from January to May 2003.

Dependent Variables

Salmonella Heidelberg infections in Canada:

Local and provincial public health laboratories confirmed cases by routine culture methods and serotyping
Phage-typing analysis was performed on case isolates forwarded to the National Laboratory for Enteric Pathogens, Health Canada.

Independent Variables

A case-and-control questionnaire addressed demographic information, case illness, 25 food exposures in the week prior to symptom onset (cases) or exposures in the week prior to symptom onset cases or interview (controls), brand date, location of purchase and cooked state (full or not) or food items consumed, information about how processed chicken products were perceived (raw vs. pre-cooked), handled, stored and prepared, and exposure to other potential risk factors including pets, day-care settings or zoos
Interviews were conducted by telephone
Parents or guardians were used as proxies for cases and controls under 18 years of age, except where cases or controls were 16 or 17 years of age and the parent or guardian requested that the case or control respond on their own behalf.

Description of Actual Data Sample:

Initial N: 95 matched pairs were interviewed and 16 unmatched cases from Quebec (52% of cases were male)
Attrition (final N): 95 matched pairs and 16 unmatched cases
Age: Median age of cases was 14 years (range zero to 95) and 31% of cases were less than six years old
Other relevant demographics: The median length of illness was 10 days (range zero to 90) and 47% of cases were admitted to a hospital as a result of infection for a median stay of five days
Anthropometrics: Controls were pair-matched by age group and telephone exchange to cases
Location: British Columbia, Canada.

Summary of Results:

Key Findings

Consumption of home-prepared chicken nuggets and strips and undercooked eggs increased the risk of illness (matched OR=4.0; 95% CI=1.4 to 13.8 for chicken and mOR=7.5; 95% CI=1.5 to 75.5 for undercooked eggs)
Exposure to a farm setting lowered the risk (mOR=0.22; 95% CI=0.03 to 1.0)
The population-attributable fraction associated with chicken nuggets/strips was 34% and with undercooked eggs was 16%
One third of study participants did not perceive, handle or prepare chicken nuggets and strips as high-risk products although the majority of the products on the Canadian market are raw
The most common types of cases were PT19 (29 cases), PT26 (16 cases), PT29 (nine cases), PT4 (seven cases) and PT35 (four cases)
When participants (both cases and controls) were asked who in the household typically eats frozen, processed chicken products such as chicken nuggets, 40% reported their whole family, 23% indicated the children or teenagers in the home, 13% said that only adults eat these products and 25% reported that nobody eats these products
40% of participants considered frozen, processed chicken products to be pre-cooked
30% of both cases and controls reported washing their hands less often after handling processed chicken products than after handling raw, whole chicken
11% of participants reported using the microwave for cooking chicken nuggets or strips
25% of chicken nugget and strip consumers reported repackaging large boxes of the product into smaller freezer portions at least some of the time, of whom 32% did not retain the box instructions
Among cases and controls, 57% always read the instructions, 31% read the cooking instructions often or sometimes and 12% never read them.

Author Conclusion:

This study demonstrates the value of research examining sources for sporadic food-borne infections. The study further indicated that a substantial proportion of Salmonella Heidelberg infections in Canada can be attributed to consumption of home-prepared chicken nuggets and strips, and provides a target for high-impact intervention.

Funding Source:

Government:

Public Health Agency of Canada

Reviewer Comments:

The authors noted that some provinces were unable to participate due to resource limitations and no information was requested for those cases not enrolled within participating provinces who may have not been contacted, refused to participate or were excluded for some other reason.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		Yes
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	Yes
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	Yes
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	N/A
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	Yes
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	Yes
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		N/A
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		Yes
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	Yes
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	Yes
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	Yes
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes