I’m supposed to be in Rome for an antimicrobial resistance (AMR) meeting but a positive COVID test but a kink in my travel plans. So, I’ll take some unexpected time to catch up on some blog material. We’ll start with a pair of pet-food-linked Salmonella outbreaks, starting with a Canadian outbreak.

The Public Health Agency of Canada has issued a notice about an ongoing outbreak of extensively drug resistant (XDR) Salmonella I 4,[5],12:i:-infection. XDR Salmonella is a big concern because it’s resistant to a large number of antibiotics, including all those that are commonly recommended for treatment, when needed (i.e. ceftriaxone, azithromycin, trimethoprim/sulfamethoxazole, ampicillin, and ciprofloxacin), plus other drugs like aminoglycosides, chloramphenicol, and tetracycline.  While resistant Salmonella aren’t inherently more likely to cause severe disease than susceptible strains, and a lot of infections resolve without specific treatment or antibiotics, if someone is sick enough that they need antibiotics and the initial drugs don’t work because of resistance, that can lead to a greater risk of severe disease or death.

Here’s a quick synopsis of the investigation to date:

  • 40 cases have been identified, but presumably the actual number is much higher since only a small fraction of people with salmonellosis actually go to a doctor and get tested.
  • Most of the cases have been found in Quebec (21), followed by Ontario (14) and Nova Scotia (2), with single cases from New Brunswick, PEI and Manitoba.
  • To date, infections identified occurred between July 2020 and September 2023, but the investigation (and presumably the outbreak) is ongoing (see epidemiological graph below).
  • Thirteen (33%) of identified cases were hospitalized (that’s a pretty high rate), but fortunately no deaths were reported.
  • As is typical, young children bore the brunt of disease, with 43% of cases being children 5 years of age or younger.

Finding the source of an outbreak like this is often a challenge. It’s much simpler when it’s a nice, discreet outbreak in one town that’s quickly linked back to a single event, restaurant or food type. It’s harder when it’s an outbreak that involves numerous provinces and years, and when a lot of time has passed before the problem is identified. The investigation of this outbreak has identified links to contact with raw pet food diets (or dogs fed raw food diets) and contact with cattle, both of which make sense since they are well established risk factors for salmonellosis.

The outbreak strain was found in raw pet food from the home of a sick person. The notice indicates that “A single common supplier of raw pet food has not been identified.” It can be difficult to confirm the contamination of the pet food itself, because these investigations usually start well after infection is identified (especially in early cases), and it takes time to identify an outbreak and potential common sources. So, by the time we’re concerned about raw diets, the source food is usually long gone.

There’s also a statement that dogs and cattle have been infected and died. Some raw diet proponents continue to push false information that Salmonella doesn’t affect dogs. We know it does in some cases, and infection can kill animals too, so this is another reminder of that.

What does this change?

Not much. It’s more of a reminder of the issues about antimicrobial resistance (AMR) in animals and humans, the need to better understand the scope and impact of resistance, and the potential risks from raw food diets for pets. It’s also another reminder of the need to reduce AMR in livestock, which is a key issue here. Whether the infections came directly from cattle or indirectly from beef, it all started off with resistance in a Salmonella strain originating from cattle somewhere. We need to continue to try to find ways to reduce the incidence and impact of AMR across all species (including humans), as we are ultimately all interconnected.

My line about raw diets is that I’d rather they not be fed to pets at all, because the risks outweigh the benefits from my perspective. However, I realize it’s still going to be done, so I focus on trying to get people to avoid raw feeding in high risk households (e.g. those with young kids, elderly individuals, pregnant women and people with compromised immune systems), and making sure that people who feed raw diets take basic measures to reduce the risk to them and their pets. More information about raw diets and their associated risks (and how to mitigate them) is available on the Worms & Germs Resources – Pets page. The US CDC also recommends against feeding raw diets to pets. They also have some good resources on their website including an infographic for pet owners about raw diets.