Line Lists

Examine the PulseNet Canada line list for the nine cases here.

While reviewing the line list, you note that the nine cases range in age from 17 to 57 years (median = 22 years), seven are female and two are male. The laboratory received dates (e.g., the dates the samples were received at the local or provincial laboratory for initial testing) range from April 28 to May 8, 2020.

Cases genetically related by whole genome sequencing (WGS) have been found now in three provinces. Based on your cluster assessment, you decide to contact Ontario to let them know the cluster is now multi-jurisdictional. Ontario offers to share their available exposure information as a next step and you let Ontario know that you will follow up with the other provinces for available exposure information. Additional exposure information on the British Columbia and Alberta cases, such as whether or not the cases travelled to Ontario, will help inform next steps in the investigation process. The number of Newport cases pending WGS (if any), either from P/Ts with cases or others, will provide an estimate to investigators of the number of potential cases that could match the outbreak cluster over the next one to two weeks.  

You share the available laboratory information with the other affected provinces by email and ask them to share their available exposure information, including whether or not the BC and AB cases travelled to ON. Here are the responses that you receive:

  • Ontario (n=6) reports that they received questionnaires for five of the six confirmed cases. One case is lost to follow up (ON-03).
    • Two of the cases (ON-01 and ON-02) are university students and are roommates (a 20-year-old female and a 21-year-old female) with the same illness onset date (April 22). They both reported eating similar food items including many fresh fruits and leafy greens including baby spinach; eggs, and a variety of supplements. ON-01 reported she is a vegetarian and does not consume beef, pork, or chicken. ON-02 reported eating chicken purchased from a local butcher shop.
    • ON-04 is a 22-year-old male who reported fresh produce items – including baby spinach. He also consumed beef and chicken and noted that he purchased chicken from a local butcher shop (same butcher shop as ON-02).
    • ON-05 is a 50-year-old male who reported eating many fruits, nuts and seeds, as well as pork and chicken, and going out to local diners frequently.
    • The most recent case (ON-08) is a 17-year-old female who reported veganism, as well as consuming different nuts and seeds and many vegetables. The questionnaire also noted that the case was on a “raw food diet” for two weeks prior to illness onset.
  • British Columbia (n=2) reports they have the questionnaires for the two cases.
    • One of their cases (BC-06) is a 27-year-old female with limited food history aside from consumption of blueberry-baby spinach smoothies, nuts and seeds, and an aversion to dairy products. The case did not report travel.
    • The other case (BC-09) is a 20-year-old female who reported fresh fruits including berries, nuts and seeds, whole grain cereal blends, oatmeal, and psyllium husk supplements. The case did not report travel.
  • Alberta (n=1) reports that the case questionnaire is pending for AB-07.

Question 1-5: Based on the information provided, is it reasonable to suspect that a common food item is the source of the illnesses? What additional information would you like to obtain in order to determine whether there is a common food source?

  • Based on the available food history, baby spinach, nuts, and seeds were frequently reported making these plausible hypotheses worth investigating further. After searching the literature, you discover that fresh produce, nuts, and seeds have all been identified as the sources of Salmonella outbreaks in the past.
  • As the British Columbia cases did not travel to Ontario, a common exposure source across provinces is likely, such as a food product that is distributed within British Columbia, Alberta and Ontario.
  • In order to determine if there is a common food source, further details on the food items of interest should be collected (e.g., type, brand, size, lot numbers, packaging, purchase dates and locations). If any of the cases have leftover product available, samples should be collected for testing.
  • Remember that baby spinach, nuts and seeds are just a few hypotheses of many. There are many other food items that could also be plausible sources for the outbreak. At this stage in the investigation there is not enough information available, hence alternative hypotheses should continue to be explored.

Question 1-6: How would you organize this information coming from the provinces? What key data elements would you want to capture?

The information collected during the interview should be entered into a line list or database.

A line list contains the information needed to describe an outbreak in terms of person, place, and time. It is a table that contains key information about each case in an outbreak, with each row representing a case and each column representing a descriptive variable such as demographic, clinical and epidemiologic information.

For this outbreak, variables you should consider adding include:

  • Unique ID number/case identifier
  • Case status (e.g., not a case, suspect, secondary, probable, or confirmed)
  • Demographic information and outcome:
    • Age
    • Sex
    • Geolocator(s) (e.g., province, region, city)
    • Date of illness onset
    • Death
    • Hospitalized
  • Laboratory information:
    • Pathogen
    • Serovar/serotype
    • Typing results (e.g., PulseNet Canada cluster code)
    • Date of specimen collection
    • Date case was reported to federal public health
  • Exposures: This text field can be used to capture food exposures of interest as well as information such as lot codes, purchase dates and purchase locations, which are important for guiding food safety investigations. From the beginning of the investigation, you may want to capture each exposure of interest in its own section, with two columns per exposure. One column would capture if they had eaten the food (with a Y/N/P/DK), and the second would be used for free text to capture details on the food item.
  • Notes: This text field can be used to capture information which is believed to be relevant but is not captured in any of the above variables.

A line list for this case study can be viewed here. 

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