Clinical, diagnostic, and epidemiological criteria used to classify cases of dogs with illness suspected to be caused by Leptospira spp between January 1, 2016, and June 30, 2017, whose owners’ primary residence was in Maricopa County, Ariz, and reported by veterinarians, owners of dog daycare or boarding facilities, and dog owners to the state veterinarian or state or local public health departments.^*

Clinical criteria 1,18–20
≥ 2 from the following list:	or	≥ 1 from the following list:
Fever (rectal temperature ≥ 39.4°C [103.0°F]) Lethargy Anorexia Vomiting, diarrhea, or abdominal pain Muscle or joint tenderness Chemosis or conjunctivitis Dyspnea, tachypnea, or cough		Acute kidney injury (high creatinine concentration with or without polyuria, polydipsia, oliguria, or anuria) Icterus or hyperbilirubinemia Acute increase in liver enzyme activities Uveitis Abortion Pulmonary hemorrhage or other unexplained bleeding

Diagnostic criteria 13–17	Confirmatory—positive PCR assay result from any clinical specimen or a confirmatory MAT titer or a 4-fold rise in MAT titer in an unvaccinated dog or a dog vaccinated ≥ 2 months prior to sample collection.
	Supportive—supportive MAT titer or positive IgM-IgG point-of-care test or ELISA result.

Vaccination status relative to diagnostic sample collection†	Confirmatory criteria MAT titer	Supportive criteria MAT titer	Detection of combined IgM-IgG anti-Leptospira antibodies via point-of-care test or ELISA
Not vaccinated	≥ 1:400	≥ 1:200 but < 1:400	Yes (meets criteria)
Vaccinated ≥ 6 months; or unknown vaccination status; or vaccinated but date of vaccination unknown	≥ 1:800	≥ 1:400 but < 1:800	Yes (meets criteria)
Vaccinated 3–6 months	≥ 1:6,400	≥ 1:1,600 but < 1:6,400	No (does not meet criteria)
Vaccinated 0–3 months	≥ 1:12,800	≥ 1:6,400 but < 1:12,800	No (does not meet criteria)

Epidemiological criteria

Dog that was exposed to another dog in the household with confirmed leptospirosis, was kenneled or attended daycare at a facility where a dog with confirmed leptospirosis had also been, or had direct contact with a dog with confirmed leptospirosis, as reported by the dog’s owner

^*Confirmed case = Met confirmatory diagnostic criteria. Probable case = Met ≥ 2 of the 3 criteria: clinical, supportive diagnostic, or epidemiological. Dogs that did not meet the clinical criteria were classified as probable cases only if they had never been vaccinated against Leptospira spp. Suspect case = Met clinical criteria alone or supportive diagnostic criteria alone but did not meet any other case definition. Not a case = No anti-Leptospira antibodies detected by means of MAT or IgM-IgG point-of-care test or ELISA in serum collected ≥ 10 days after illness onset.

^†Because serologic tests for Leptospira spp cannot differentiate between naturally occurring and vaccine-induced antibodies, diagnostic criteria for quantitative and qualitative serologic tests varied on the basis of time since vaccination and expected persistence of IgM and IgG antibodies.