A recent study looked at human illness associated with raw pet food and has led to headlines such as “It is safe to feed raw pet foods.”
Did the study say that? No, it did not.
If you asked 100 people if they had a foodborne disease in the past year, I assume few would say “yes,” despite the widespread estimate that about 30% of people get a foodborne illness every year. If you ask people if they got a foodborne disease from a specific food, the numbers would be even weaker / lower. People generally don’t have good recall for things like that, since we don’t usually recognize a cause when we get intestinal disease. The odds of someone linking their vomiting or diarrhea to their pet’s food are low, especially if they have no awareness that their pet’s food is a risk. Even if someone thinks about the source of their disease (which probably isn’t overly common), would they think about their pet’s food as the source, versus other foods in the house, versus a restaurant, versus anywhere else they ate? I suspect the average pet owner would not.
The problem isn’t the study, it’s how the study has been interpreted. It didn’t (and couldn’t) get a good estimate of the burden of disease associated with raw pet diets. The title of the study is Owners’ perception of acquiring infections through raw pet food: a comprehensive internet-based survey (Anturaniemi et al, Vet Rec, 2019). It looked at perceptions, which is useful, but has a lot of limitations.
The study was an internet survey of pet owners who fed raw diets. Internet surveys are easy to do, but are problematic for a few reasons. When you ask 1000 people to complete a survey and 990 respond, you know you captured your population well. If 10 respond, you know you haven’t and maybe you have a biased group of respondents (e.g. people that were more motivated / biased one way or another might be more likely to respond). With an internet survey, you generally have no idea how many people got the survey, and therefore no idea what percentage of people responded. The survey was disseminated through the research group’s Facebook page and through the researchers’ own academic, private and industrial contacts, so the people invited may not reflect the typical pet owning population. That doesn’t mean the results are useless (I’ve done internet surveys myself), it just means we need to be careful interpreting results. I tend to approach surveys as tools to get some basic information to figure out what questions to address more thoroughly, rather than tools to answer specific questions.
The main question that was asked in this study was “Are there/have there been people in your household that have become sick from handling raw pet food or that have become sick from contact with a raw pet food eating pet?”
That’s a question we want to answer. However, it’s not a question the general public is well equipped to answer themselves.
- The sample size was large (16,475 households), which is good, but there’s not much information about the households to determine how reflective they are of the broader population.
- Most had been feeding raw diets for years, but some were pretty recent (e.g. 0.1 years, which is not much time for someone to get sick as a result).
- Overall, 0.2% of households reported a “confirmed” transmission from the pet or food. That’s a relatively small number, but 0.2% per year means a lot of sick people. I’m actually surprised that people reported getting sick from their pet’s food at all. I’d expect massive under-recognition and under-reporting, so seeing any reports is interesting. If you consider that in most foodborne disease, reported cases usually account for less than 10% of the real number (and probably less than that here), the true burden of disease based on these numbers is quite a bit higher, to a level I’d certainly be concerned about.
- Salmonella and Campylobacter were most the commonly reported infections. However, most of the time, there was no effort to confirm the pet food as the source, so it’s hard to say what the numbers really mean.
- In situations where there was “confirmed” transmission, 31% of the time the pet was sick at the same time. That maybe strengthens the association between human and animal disease, but also maybe shows potential bias. Are people more likely to blame the pet/food if both they and their pet are sick at the same time, and blame human food or not consider pet food if the pet isn’t sick? I have no idea, but that could greatly influence self-reported data.
- Interestingly, raw foods were handled in the same place as human food and with human food utensils significantly more often in the negative households. That’s the opposite of what I’d expect. The counter argument might be that people who handle raw pet food poorly are not tuned into the risks and are therefore less likely to identify or blame the pet food if they get sick.
The authors sum things up in a more balanced manner than internet headline writers:
“As a conclusion, this large study population from all over the world shows that the transmission of zoonotic pathogens might happen, but it seems to be sporadic. It is clear that the precise source of the pathogen is often challenging to find, which makes the interpretation of the result difficult. However, studies using different kind of approaches should be conducted in the future to be able to get a better understanding of the true risks or possible health benefits of feeding raw food diets to pets. This way the true pros and cons can be accurately analysed, before asking pet owners not to feed their pets with a nutritionally balanced raw diet.”
That’s a good conclusion. This study provides some baseline information and can help tailor future studies. It helps us figure out how to get a good answer rather than giving us a good answer now.
More information about ways to reduce the risk from feeding raw diets is available on the Worms & Germs Resources – Pets page.