Veterinarians doubt study linking dog walking to COVID-19

Infectious disease expert cautions that study conclusion is unsupported

November 20, 2020 (published)
By Jennifer Fiala

VIN News Service photo
A new study from Spain concluding that walking a dog raises a person's risk of contracting COVID-19 is drawing skepticism.

Researchers in Spain made headlines this week with a study concluding that dog walking raises the risk of contracting COVID-19 by 78%, giving rise to speculation that dogs might touch contaminated surfaces in public and bring the virus home.

Veterinarians and others who scrutinized the study, however, said the authors' interpretation of their findings is flawed. Meanwhile, pet advocates voiced concerns that the sensationalized reports might elicit panic and result in dog owners relinquishing their pets.

"I think it's a middling study with bad/overreaching conclusions," said Dr. Kevin Jepsen-Grant of Sacramento, California, in a discussion on the Veterinary Information Network, an online community for the profession and parent of the VIN News Service. 

"The spread of SARS-CoV-2 in Spain: Hygiene habits, sociodemographic profile, mobility patterns and comorbidities" was published this month in an online issue of the journal Environmental Research dated January 2021. Based on results of an online survey, the study examines the hygiene habits and mobility of 2,086 people confined during government-ordered lockdowns imposed last spring to slow spiraling coronavirus infections. The authors, mass-emailing a survey to addresses from University of Granada mailing lists, social networks and mobile phone devices, said most respondents were graduate or postgraduate students living with their families. More than 40% ranged in age from 40 to 54.

During the time the survey was conducted — April 4 to May 5 — jogging or walking in public was restricted unless done with a pet. Of those polled, 491 owned dogs, and 407 reported walking them. "Among all the sociodemographic variables analyzed, walking the dog has shown to have the strongest effect" of increasing risk, the study said.

However, the single greatest of all risk factors was living with a COVID-19 patient, "which raised the risk of contagion by 60 times," the study said. That is an increase of 5,900%.

While the researchers noted limitations of the study, such as the online format and the fact that half of the cases are based on self-diagnosis for presenting symptoms compatible with COVID-19, they concluded that "living with dogs, working on-site, purchasing essential commodities by using home delivery service, and especially, living with a COVID-19 patient, have been the main routes of transmission of SARS-CoV-2 during the most restrictive period of confinement in Spain." 

The VIN News Service was unable to reach the study's lead author, Miguel Rodriguez Barranco, research coordinator of the Granada Cancer Registry of The Andalusian School of Public Health, to comment on the methodology and findings of the study, which has been characterized as "overall pretty weak" by an infectious disease veterinarian. 

Dr. J. Scott Weese, a zoonotic disease expert who heads infection control at the University of Guelph veterinary teaching hospital in Ontario, Canada, wrote in a blog post Tuesday that the researchers' study does not support their conclusion — and subsequent reports by some media — that "living with dogs" increases the risk of contracting COVID-19. 

The study looked at whether dog walkers contract COVID-19; it did not assess whether living with a dog is a risk factor. "In fact," Weese told VIN News by email, "their data showed that living with a pet was not a risk factor," which leads him to conclude that the researchers mischaracterized their own work.

Weese further analyzed aspects of the study on his Worms and Germs Blog, stating: "Even though the paper said that, it's not what they actually found. Unfortunately, a lot of people are reading that headline, or worse, they're reading '… yada yada … dogs spreading SARS-CoV-2 … yada yada.' "

His post outlines his concerns, starting with the fact that the poll of university students asks whether they walk "pets," not dogs: "It's reasonable to assume that the pets were mostly dogs, but they don't actually specify that."

For Weese, the study raises more questions than it provides answers. Among the questions:

  • People who used home delivery for food reportedly were almost twice as likely to have had COVID-19. Does that mean they were getting infected by delivery people and would have been safer shopping? "Presumably not," he said. "My concern is that there was some reason that people were more likely to order food, and that was also a risk factor for COVID-19. For example, if they knew they had been exposed or were in some other high-risk situation, that might lead people to avoid stores and also be at higher risk of being infected."

  • People with COVID-19 were presumably more likely to order delivery after being diagnosed, but the survey doesn't ask what they did before getting infected (if they had COVID-19), just what they did during Spain's period of restrictions. "So, finding increased risk from home delivery might actually be because people who were more likely to use home delivery were otherwise higher risk or already had COVID-19."

  • Another concern is whom they surveyed and whether the respondents represent the overall population. "You need to understand the study population to understand the results and any potential bias. You can get really misleading information or not understand your results."

The Pet Industry Joint Advisory Council expressed similar concerns in a statement Wednesday by Mike Bober, president and chief executive officer: "It is essential to note that the activity that was reported in the study to increase the risk of contagion was walking a dog outdoors, NOT interacting with the animal itself. The only correlation to a greater risk of infection that could reasonably have been drawn, given the limited information collected, was leaving the home and therefore being exposed to a greater number of potentially infected individuals." 

In a telephone interview, Weese concluded that the study did not provide much reliable information 

"It maybe suggests that people who are going out and doing things are going to pick up the virus," he said, "but I don't think we need a study to tell us that."

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