Screening

HIV-infected patients

HIV-infected patients with severe immunosuppression (CD4+ T lymphocyte count near 100 cells/microliter) who are unable to take trimethoprim/sulfamethoxazole for Pneumocystis jiroveci prophylaxis should be tested for prior exposure by measuring anti-Toxoplasma immunoglobulin (Ig) G.[42]

Patients with HIV and CD4+ T lymphocyte counts <100 cells/microliter with detectable anti-Toxoplasma IgG are at risk for reactivation of latent infection and should receive prophylactic treatment.[25]

Before antiretroviral therapy (ART) was available, patients who were seropositive for Toxoplasma, and who had advanced immunosuppression but were not receiving chemoprophylaxis, had incidence rates of symptomatic disease of 12% to 47%.[43][44] Incidence and associated mortality has decreased substantially since the availability of ART and initiation of prophylactic regimens.

Transplant recipients

In the US, Toxoplasma IgG testing is required for all donors, regardless of organ.[45]

Among organ transplant recipients, toxoplasmosis is most commonly seen in heart recipients but can also occur in recipients of other solid organs or stem cell transplants.[42] Thus, the serostatus of all donors and recipients should be checked prior to transplantation.[26] Cardiac transplant patients who have detectable anti-Toxoplasma IgG or who are recipients of hearts from seropositive donors should receive prophylaxis, as should all solid organ transplant recipients who are high risk for toxoplasmosis (donor Toxoplasma IgG+, recipient Toxoplasma IgG negative). 

Additionally, all recipients of allogeneic hematopoietic stem cell transplants should have baseline anti-Toxoplasma IgG testing. Prophylaxis prior to hematopoietic stem cell transplantation is recommended for all Toxoplasma seropositive recipients.[46]

For Toxoplasma seropositive individuals undergoing allogeneic hematopoietic stem-cell transplant who are unable to tolerate trimethoprim-sulfamethoxazole prophylaxis, weekly monitoring of blood for Toxoplasma polymerase chain reaction (PCR) for the first 3 months post-transplant is recommended.[47]​ 

Consideration should also be given to performing a PCR at regular intervals in other patients who are at high risk of disseminated disease (e.g., heart transplant recipients with seropositive donors who are not able to tolerate trimethoprim-sulfamethoxazole). While there is no consensus on the optimal treatment of patients who are asymptomatic and PCR positive (i.e., trimethoprim/sulfamethoxazole prophylaxis versus treatment dosing of pyrimethamine plus sulfadiazine), centers utilizing this surveillance strategy have higher survival rates than centers that do not screen with PCR.[41]

Pregnant women and newborns

The American College of Obstetricians and Gynecologists does not recommend universal screening for toxoplasmosis in women of childbearing age or those who are already pregnant.[48]  Instead, it is advised to focus on targeted screening for individuals exhibiting symptoms indicative of acute infection or those who have had high-risk exposures. Understanding the limitations of serologic testing, including the possibility of false-positive or negative results, is essential.[32]​ Some countries with a higher seroprevalence for Toxoplasma gondii, such as France, perform routine screening for women of childbearing age and during pregnancy.[11]

Certain US states (Massachusetts and New Hampshire) screen for toxoplasmosis in newborns by checking anti-Toxoplasma IgM.[49]

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