Sometimes a persistent outbreak can feel challenging, like solving a 10,000-piece puzzle. With the complexity of multiple variables coming into play, identifying the transmission routes to find the source becomes a daunting task. You pull out the heavy artillery and do staff screening and environment swabbing, but you can’t seem to catch a break…

With the increasing use of whole genome sequencing in HAI investigations, we’ve definitely seen an increase in the categorization of outbreaks, once considered isolated events, as one long persistent outbreak. When that is the conclusion, most of our clients focus their efforts on periodic staff screening as the primary tool to identify the source of the outbreak. Some also add a comprehensive, but one time, environment swab. But, to really break open an investigation, we’ve been advising our clients to try and shift the focus to continuous environmental sampling.

Here’s why:

When you screen staff or do environmental swabs two factors reduce the chances of a positive ID, especially for certain species: 1. The possibility of a false negative for any sample tested at any given point in time, and 2. Transient carriage of the tested subject – for example, a staff member who may be colonized with the pathogen temporarily then clear the infection on their own before testing. So even if you sampled the transmission source, there is a chance it will turn out negative. Remember, each sample you take is just a “snapshot” of that specific time of collection. 

The solution? Routine, periodic sampling using low-cost, batched whole genome sequencing. And when you compare staff screening to environmental sampling, the choice is obvious. Environmental samples are less influenced by the transient nature of human carriage, it’s easier to perform logistically, and it doesn’t have any psychological implications – the ECMO device will not be offended by repeated tests, nor be afraid it will lose its job. Coincidentally, positive environmental isolates can also contribute to tracking and tracing epidemiological links and identification of persistent reservoirs of contamination.

When facing your next outbreak, think about the most effective long-term strategies that can help you deal with the high stakes of a persistent outbreak investigation. Feel free to connect with us for assistance.

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