A patient has an increased antibody titer to delta agent. You would most likely suspect

Delta agent is a recently discovered antigen associated with HBsAg. Its presence usually correlates with HBsAg chronic carriers who have chronic active hepatitis. EIA and radioimmunoassay (RIA) tests are available to detect antibodies to delta agent. Fifth disease is a viral exanthem commonly seen in children 8 to 12 years old. Children are ill for a few days but recover without incident. Unfounately, if a pregnant female acquires the disease in the first trimester of pregnancy, the fetus is at risk. The causative agent is thought to be a parvovirus (parvovirus B 19). Adults with no titer to varicella (VZV) are at risk for acquisition of chickenpox. If they are health care workers, there is additional risk in transmitting VZV to immunodeficient children. Antibodies to VZV are readily detected by both enzyme immunoassay (EIA) and fluorescent-antibody (FA) techniques. SSPE is thought to be caused by a measles-related virus present in the central nervous system. Most SSPE patients show elevated measles virus antibodies in serum and CSF. In patients with multiple sclerosis (MS), lower CSF antibody titers have been observed, suggesting a possible etiologic role for measles virus in MS. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition