In a rare occurrence of locally acquired typhoid fever in Canada, health officials in Ottawa recently traced an outbreak back to a chronic Salmonella Typhi carrier working as a food handler. The outbreak involved seven confirmed cases from Oct. 2018 to May 2022 and was linked to the asymptomatic carrier through whole genome sequencing (WGS) and social network analysis.
Typically, cases of typhoid fever in Canada are linked to international travel, making this localized outbreak unusual. The investigation led by Ottawa Public Health underscores the potential for chronic carriers, who may shed bacteria without symptoms and unintentionally transmit the disease over an extended period. All eight outbreak-related isolates matched genetically, confirming the cluster.
Initial cases and detection The outbreak investigation began when Ottawa Public Health identified two non-travel-related cases of typhoid fever in 2021. The patients, residing only 2.6 km (1.
6 miles) apart, had a common link to a grocery store ready-to-eat counter. One patient was an employee, and the other was a customer. An outbreak was declared after initial interviews, and WGS analysis confirmed the cases were part of the same cluster.
The early stages of the investigation were challenging because of the infrequent and spaced-out patients. Public health inspectors initially focused on the grocery store’s ready-to-eat counter, where three food handlers were identified for testing. However, the food samples and sto.
