An AIDS patient complains of headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made, and Toxoplasma cysts are observed in a brain section. Which of the following antibody results would be most likely in this patient?

One of the leading causes of death among AIDS patients is CNS toxoplasmosis. It is thought that Toxo-plasma infection is a result of reactivation of old or preexisting toxoplasmosis. Occasionally, the infection may be acquired by needle sharing. Because the disease is a reactivation of old or preexisting toxoplasmosis, routine quantitative tests for IgM antibody are usually negative, and IgG titers are low (<1:256, IFA). More sophisticated methods, such as IgM capture or IgG avidity, may reveal an acute response.