A New Antibody Test Detects Serum Antibodies Against Virus X

A new antibody test detects serum antibodies against virus X (sensitivity 99%, specificity 90%) . When applied in a group of hospitalized patients diagnosed as having virus X infections, the test is found to have a positive predictive value of 85%. When used to screen a group of healthy blood donors for virus X infections, the test is found to have a positive predictive value of 30%. Which of the following best explains this difference between the positive predictive values?

A) Measurement error was introduced into the procedure.
B) The prevalence of virus X infection is higher among the hospital patients than among blood donors.
C) Cases of virus X infection are more severe in the hospital.
D) Lead time bias occurs among the blood donors.