It is less well known than kennel cough, but it can be serious, and it is a risk in the outdoors.
What it is
The CDC explains that leptospirosis is caused by Leptospira bacteria. Infected animals pass the bacteria in urine, and people and animals pick it up from contaminated water or soil. Without treatment it can damage the kidneys and liver. Dogs can carry the bacteria without signs and shed it for months. Antibiotics help when started early.
Risk for Northern California dogs
Wet ground, standing water and wildlife all raise exposure. Dogs that swim, walk creeks or drink from puddles are more exposed. Heavy rain and flooding increase risk in the CDC's description. The Central Valley has a mix of farms, ditches and wildlife, so ask your vet whether the vaccine suits your dog's life.
The Happy Paws position
The kennel lists leptospirosis as a recommended vaccine, not a required one. Required vaccines for dogs are rabies, distemper/parvo and Bordetella. The recommended group also includes canine influenza, heartworm prevention and flea prevention. Records for the required vaccines must be current through the stay. See the leptospirosis vaccine page.
Related reading
Read heartworm prevention in the Delta and flea and tick prevention. The CDC page also covers prevention for people, such as avoiding contact with contaminated water.
Talking it over with your vet
Whether to vaccinate depends on your dog's life: swimming, hiking, farm exposure, standing water, wildlife in the yard. Your vet knows the local picture. Ask how many doses the first year needs, and how often a booster is due. If your dog is vaccinated, bring the record so the staff have it, even though it is not required.
People can catch the disease too, so wash hands after cleaning up after animals, avoid swimming in standing water, and tell your doctor if you have symptoms after exposure.
Why the kennel only recommends it
The kennel lists the vaccine as recommended because the decision depends on each dog's exposure. Dogs that spend a lot of time near water or wildlife gain the most, while a dog that stays in a clean yard may gain less. Your vet makes that call, and the kennel respects it.