EAL

MHFS: Food Safety (2012-2013)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To complete a case control investigation of frozen chicken nuggets and strips since Salmonella enterica var. Heidelberg was isolated from an unusual food source during routine case follow-up.

Inclusion Criteria:

Laboratory confirmed cases of Salmonella Heidelberg identified in British Columbia between January 1 and April 1, 2003
Only the person with earliest onset of symptoms per household in the case control analyses
Controls were individually matched to cases by age category to account for potential differences in food preparation practice.

Exclusion Criteria:

One individual was lost to follow-up and two cases were excluded as additional household cases.

Description of Study Protocol:

Recruitment

Laboratory-confirmed cases of Salmonella Heidelberg identified in British Columbia between January 1 and April 1, 2003 were included in epidemiologic and laboratory investigations
Controls were generated through forward-digit dialing and individually matched by age category.

Design

Case-control study.

Statistical Analysis

Frequency and matched analyses were performed by EpiInfo version 6.04d.

Data Collection Summary:

Timing of Measurements

Study took place between January and May 2003.

Dependent Variables

Presence of Salmonella Heidelberg:

Unopened packages of frozen processed nuggets and strips were selected for testing in a non-random fashion from among stores and brands most commonly cited by cases
The presence of Salmonella Heidelberg in unopened packages was detected by inoculating 25g of homogenized food into pre-enrichment broth followed by selective enrichment and plating onto differential agars.

Independent Variables

Three-page hypothesis-testing questionnaire was used to interview cases and controls by telephone
Information was collected regarding exposure to frozen processed chicken products, including nuggets, burgers, strips and wings and other raw chicken products
Consumption of other foods commonly associated with Salmonella outbreaks were assessed, including deli meats, beef, pork and turkey products
Participants were asked about exposure to pets, farm animals and petting zoos.

Description of Actual Data Sample:

Initial N: 23 cases (47.8% male)
Attrition (final N): 18 matched cases and controls
Age: Median age 16 years (range one to 85 years)
Other relevant demographics: 65% of cases were seen in an emergency room and 42% of cases were hospitalized with a median stay of five days
Anthropometrics: Controls were individually matched by age category
Location: British Columbia, Canada.

Summary of Results:

Key Findings

The odds of infection were 11 times higher in individuals who had consumed frozen processed chicken nuggets and strips (95% CI: 1.42; OR<85.20)
No other exposure, including unprocessed chicken, was significantly associated with illness
One third of cases and controls considered frozen nuggets and strips to be pre-cooked, requiring reheating only
Cases (33.3%) and controls (33.3%) were equally likely to consider these products pre-cooked (matched OR=1.00, 95% CI: 0.01 to 78.5)
When asked about cooking methods, 27.3% of all respondents replied that they either always used the microwave (15.2%) or sometimes used a microwave when heating these products, an ill-advised cooking method
35% of respondents reported washing their hands less frequently after handling frozen, processed chicken than after handling raw, uncooked chicken
37% of respondents reported repackaging nuggets and strips into smaller freezer portions, but of these, only 36% reported saving the cooking instructions off the original box for later use
No difference was detected in cooking practices, hand washing and repackaging habits between cases and controls.

Author Conclusion:

This case control study highlights the need not only to continue consumer education activities but to pursue regulatory changes that improve the clarity of labels. A thorough review of the manufacturing process should be undertaken to identify interventions that can succeed in reducing the substantial risk of infection posed by these products.

Funding Source:

Government:

British Columbia Centers for Disease Control

Reviewer Comments:

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)	Yes
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	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)?	N/A
	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