Outbreak Identification

Day 6: Wednesday May 13, 2020

You attend a weekly teleconference call with Ontario and they note that they are seeing an increase in Salmonella Newport cases. The provincial public health laboratory conducted whole genome sequencing (WGS) on the case isolates to determine if they are genetically related, and shared the sequence information with PulseNet Canada to check for matches in other provinces or territories.

PulseNet Canada is a critical surveillance system used to quickly identify and respond to enteric outbreaks in Canada. It is an electronic network that connects the provincial public health laboratories and some federal laboratories together by linking their computers and databases. This national network is dedicated to tracking sequence information obtained through WGS. By finding isolates related by WGS through PulseNet Canada, scientists can determine whether an outbreak is occurring, even if the affected persons are geographically distant. PulseNet Canada is coordinated by the National Microbiology Laboratory (NML) located in Winnipeg, Manitoba.     

According to Ontario’s provincial public health laboratory, five of the Ontario isolates were considered related by WGS. PulseNet Canada is working on comparing these isolates to isolates in their national database to determine if they are genetically related to isolates from other provinces or territories.

Ontario notes that they have begun investigating these cases. In Canada, laboratory-confirmed cases of Salmonella are investigated by local public health authorities. This investigation typically involves interviewing cases over the telephone and filling out a questionnaire. These questionnaires usually include questions on the case’s illness, potential risk factors, food exposure history, and travel history. The interview also provides an opportunity to identify people in occupations that should be excluded from work until their illness clears (e.g., food handlers, daycare workers), provide education on risk factors (e.g., hand washing, safe food handling) and to answer any questions the case may have. Key information from the case interview, such as age, sex, date of illness onset, and potentially risk factors and food exposures, may be shared with provincial/territorial health officials.

If it is suspected that the case is part of an outbreak spanning beyond the local level, provincial/territorial health officials may also request that local health authorities share the complete case questionnaire.

Ontario has requested case questionnaires from the local health authorities to determine if there are any common exposures. They report that questionnaires are available for three of the five cases. The questionnaire is pending for one case, and the other case is lost to follow up. From looking at the information currently available, they note that baby spinach, chicken, and eggs are commonly reported exposures. In addition, two of the cases reported purchasing chicken thighs from the same local butcher shop.

A local health authority followed up with the butcher shop and learned that they only receive chicken from a provincially registered slaughter plant. This slaughter plant does not distribute chicken outside of Ontario.

Ontario notes that chicken is one of the leading hypotheses. Although one of the three cases for which a questionnaire is available reported being vegetarian, cross-contamination may be a possibility, as this case is roommates with another case that reported consuming chicken. They are currently waiting for the pending case questionnaire and are looking at following up with cases to learn if more specific information is available (e.g., brand, lot codes, purchase dates and locations) on the common foods consumed.

<Previous Next>