Toxoplasmosis
2024 Case Definition

Clinical Criteria

In the absence of another more likely etiology, a person with new onset of one or more of the following clinical signs or symptoms:

• Fever,
• Lymphadenopathy,
• Muscle ache,
• Joint ache,
• Fatigue,
• Headache,
• Pharyngitis,
• Hepatosplenomegaly,
• Diffuse non-pruritic maculopapular rash,
• Pneumonitis,
• Myocarditis,
• Pericarditis,
• Polymyositis,
• Hepatitis,
• Retinochoroiditis without evidence of a scar, or
• Encephalitis

Laboratory Criteria

Confirmatory Laboratory Evidence:

• Detection of Toxoplasma-specific IgM antibodies in blood, confirmed at a reference laboratory,² with laboratory evidence of acute pattern of infection,³ OR
• Detection of Toxoplasma DNA (by NAAT [e.g., PCR]) performed on any tissue or body fluid, OR
• Visualization of Toxoplasma in any tissue or body fluid, OR
• Detection of Toxoplasma antigen in any tissue by immunohistochemistry, OR
• Isolation of Toxoplasma whole live parasite from any tissue or body fluid, OR
• A fourfold or greater increase in Toxoplasma-specific IgG antibody titer in paired sera samples collected at least three weeks apart, OR
• Evidence of Toxoplasma-specific IgG antibody seroconversion over two sequential samples collected up to 12 weeks apart, or during current pregnancy for pregnant persons.

Presumptive Laboratory Evidence:

• Detection of Toxoplasma-specific IgG antibodies in blood.

Supportive Laboratory Evidence:

• Detection of Toxoplasma-specific IgM antibodies in blood, not confirmed at a reference laboratory.²

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.
²In the United States, the toxoplasmosis reference laboratory is the Palo Alto Medical Foundation: Dr. Jack S. Remington Laboratory for Specialty Diagnostics
³This determination is made by the reference laboratory based on the results of additional Toxoplasma testing such as AC/HS differential agglutination, avidity, IgA and IgE.

Epidemiologic Linkage

Evidence of a shared exposure that is associated with at least one probable or confirmed case of active toxoplasmosis-primary infection.

Suspect

• Meets toxoplasmosis epidemiologic linkage criteria AND toxoplasmosis clinical criteria, OR
• Meets toxoplasmosis supportive laboratory evidence.

Probable

• Meets toxoplasmosis epidemiologic linkage criteria AND toxoplasmosis supportive laboratory evidence AND toxoplasmosis clinical criteria.

Confirmed

• Meets toxoplasmosis confirmatory laboratory evidence, OR
• Meets toxoplasmosis presumptive laboratory evidence.

• Toxoplasma gondii | 2024 Case Definition