Congenital Toxoplasmosis
2024 Case Definition

Clinical Criteria

In the absence of another more likely etiology, a fetus or liveborn child with one or more of the following clinical findings:

• Retinochoroiditis,
• Hydrocephalus, or
• Intracranial calcifications.¹

¹These 3 clinical findings (retinochoroiditis, hydrocephalus, intracranial calcifications) make up the classical triad of congenital toxoplasmosis. Other clinical findings (e.g., ocular [amblyopia, cataract, nystagmus, optic nerve atrophy, strabismus, visual impairment], neurologic [cerebral spinal fluid pleocytosis or elevated protein or eosinophilia or hypoglycorrhachia, developmental delay, hypotonia, macrocephaly or microcephaly, palsies, sensorineural hearing loss, seizures, spasticity], additional signs [anemia, hepatitis, hepatic calcifications, hepatomegaly or splenomegaly or hepatosplenomegaly, myocarditis, preterm birth, rash, sepsis-like illness, thrombocytopenia], fetal ultrasound findings [ascites, echogenic bowel, hepatosplenomegaly, intrahepatic densities/calcifications, intrauterine growth retardation, placenta hyperdensities, placenta increased thickness]) can be seen with congenital toxoplasmosis but are not included in the public health case classification criteria (3).

Laboratory Criteria

Confirmatory Laboratory Evidence:

• Detection of Toxoplasma-specific IgG antibodies AND (Toxoplasma-specific IgM antibodies OR Toxoplasma-specific IgA antibodies)⁴ in blood, confirmed at a reference laboratory,² OR
• Persistence in Toxoplasma-specific IgG antibody titer beyond one year of age in a patient being followed since infancy for possible congenital toxoplasmosis, OR reappearance of Toxoplasma-specific IgG antibodies after period of undetectable levels in a child who recently completed treatment for congenital toxoplasmosis, OR
• Increase in Toxoplasma-specific IgG antibody titer during the first year of life, OR
• Detection of Toxoplasma DNA (by NAAT [e.g., PCR]) performed on any tissue or body fluid (including placental tissue or amniotic fluid from birthing mother), OR
• Visualization of Toxoplasma in any tissue or body fluid (including placental tissue or amniotic fluid from birthing mother), OR
• Detection of Toxoplasma antigen in any tissue by immunohistochemistry (including placental tissue from birthing mother), OR
• Isolation of Toxoplasma whole live parasite from any tissue or body fluid (including placental tissue or amniotic fluid from birthing mother).

Presumptive Laboratory Evidence:

• Detection of Toxoplasma-specific IgG antibodies AND (Toxoplasma-specific IgM antibodies OR Toxoplasma-specific IgA antibodies) in blood, not confirmed at a reference laboratory.²

Supportive Laboratory Evidence

• Detection of Toxoplasma-specific IgG antibodies in blood.⁵

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
⁴Detection of Toxoplasma-specific IgM antibodies before 5 days of age or detection of Toxoplasma-specific IgA before 10 days age could represent false-positive results due to the possibility of contamination of the infant’s blood with maternal blood because of materno-fetal blood leak (3). Other possible reasons for false-positive test results (e.g., blood product transfusion or IVIG transfusion) should also be considered (3). If mother had evidence of an acute primary toxoplasmosis infection acquired late in gestation, then initially negative Toxoplasma IgM and IgA results in the newborn at birth could be due to delayed production of those antibodies (3). Antenatal and postnatal treatment can also affect the serologic profile of the infant (3).
⁵Detection of Toxoplasma-specific IgG in the newborn may represent congenital infection or maternal antibodies transferred transplacentally (3).

Epidemiologic Linkage

Fetus or infant delivered to a pregnant woman with evidence of Toxoplasma gondii infection or toxoplasmosis acquired or reactivated during current gestation or within 6 months prior to conception.

Suspect

• Meets congenital toxoplasmosis supportive laboratory evidence, OR
• In setting of fetal loss: meets congenital toxoplasmosis epidemiological linkage criteria.

Probable

• Meets congenital toxoplasmosis presumptive laboratory criteria AND (congenital toxoplasmosis epidemiologic linkage criteria OR congenital toxoplasmosis clinical criteria), OR
• Meets congenital toxoplasmosis clinical criteria AND congenital toxoplasmosis epidemiologic linkage criteria.

Confirmed

• Meets congenital toxoplasmosis confirmatory laboratory evidence.

Case Classification Comments

• The diagnosis of congenital toxoplasmosis after infancy is confounded by the small possibility of the child acquiring a toxoplasmosis infection postnatally (4).
• Clinical and laboratory evidence of congenital toxoplasmosis may evolve and take time to manifest throughout the infancy period.

• Toxoplasma gondii | 2024 Case Definition