What's actually in the dirt
A 2016 study tested 300 dogs at three off-leash parks in Northern California. The findings explain why on-site washing isn't a luxury. It's a practical public health measure.
a pathogen
showed no symptoms
transmissible to humans
The study
Researchers at UC Davis collected fresh fecal samples from 300 dogs visiting three public off-leash areas in Yolo and Sacramento counties between August and November 2014. Each sample was tested for 11 known enteropathogens using three methods: fecal flotation, direct fluorescent antibody testing, and PCR. Dog owners completed a questionnaire covering health history, diet, park visit frequency, and recent symptoms.
The study was published in the Journal of Veterinary Internal Medicine and remains one of the most frequently cited pathogen prevalence studies specific to off-leash dog parks.
What they found
Of 300 dogs tested, 114 (38%) were positive for at least one enteropathogen. Almost half of those dogs were carrying more than one. The most common were:
| Pathogen | Prevalence |
|---|---|
| Clostridium perfringens (alpha toxin gene) | 35% |
| Giardia spp. | 9% |
| Circovirus | 9% |
| Cryptosporidium spp. | 5.3% |
| Coronavirus | 4.7% |
| Campylobacter spp. | 2.7% |
| Salmonella | 1% |
| Parasitic worms (whipworm, hookworm, roundworm) | <3% combined |
Bold names are zoonotic — transmissible from dogs to humans. Nearly 10% of all dogs tested carried at least one zoonotic pathogen.
The most important finding: 54% of infected dogs showed no symptoms at all. They looked healthy, acted healthy, and their owners had no reason to suspect a problem. A dog with normal stool can still be shedding pathogens that make other dogs — and people — sick.
Why this matters for parks
Off-leash areas concentrate dogs in shared space. Nose-to-ground, mouth-to-fur, paws-in-mud contact is constant. That's the whole point of the park. The study confirms what anyone who's spent time at an OLA already suspects: the environment carries risk, and most of it is invisible.
The researchers noted that frequency of park visits did not correlate with higher infection rates. Dogs aren't getting sick because they visit too often. They're picking up pathogens because the environment is shared and there's no decontamination step between the park and the car, the home, the couch, the bed.
Younger dogs showed higher infection rates, which matters because off-leash areas skew toward younger, more active dogs — exactly the population most likely to carry and spread pathogens.
What we do about it
An on-site wash station acts as a practical firewall. It intercepts dirt, parasites, and contaminants at the point of origin — before they reach cars, homes, and neighbors.
It doesn't eliminate risk. Nothing does. But it creates a convenient, affordable step between the park and everywhere else. When washing is easy and right there, more people do it. Regular post-visit washing reduces what dogs carry home and what they bring back to the park on their next visit.
That's the idea behind City Dog Wash: put the solution where the problem is.
Source
Hascall KL, Kass PH, Saksen J, Ahlmann A, Scorza AV, Lappin MR, Marks SL. Prevalence of enteropathogens in dogs attending 3 regional dog parks in Northern California. J Vet Intern Med. 2016;30(6):1838–1845. doi:10.1111/jvim.14603. PMID: 27859745.