Toxoplasmosis, Active- Reactivation Disease
2024 Case Definition

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 women.

Presumptive Laboratory Evidence:

• Detection of Toxoplasma-specific IgG antibodies in blood.

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.

Probable

In the absence of another more likely etiology:

• Reactivation toxoplasmic encephalitis: Meets toxoplasmosis presumptive laboratory evidence AND toxoplasmosis clinical criteria of brain imaging that demonstrates typical toxoplasmic encephalitis radiographic appearance (e.g. ring-enhancing lesion[s]), AND has compatible clinical syndrome (e.g. headache, mental status changes or other neurologic symptoms) AND is immunocompromised AND criteria for probable active toxoplasmosis- primary infection are not already met, OR
• Reactivation ocular toxoplasmosis: A person with retinochoroiditis with evidence of a scar⁸, OR clinician diagnosis of new onset of recurrent toxoplasmosis ocular lesion.

Confirmed

• Meets toxoplasmosis confirmatory laboratory evidence AND has previous evidence of toxoplasmosis (such as a previous positive Toxoplasma-specific IgG, previous clinical diagnosis of toxoplasmosis, or clinician diagnosis of new onset of recurrent toxoplasmosis ocular lesion).

⁸This may appear as a single discrete, yellow-white focus of dense inflammatory material within and overlying the retina arising from the border of a scar. Findings of intraocular inflammation, such as transient elevation of intraocular pressure at onset of activity, cellular reactions in ocular fluids (aqueous humor, vitreous humor), or retinal vascular sheathing (anywhere in the fundus) would be further evidence of active disease.

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