This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Anatomy
Indication for prophylaxis in pneumocystis carinii pneumonia include 
Select and explain. 
A. CD4 count <200 /ul, B. Tuberculosis, C. Vital load >25000 copies/ml, D. Oral candidiasis
A: CD4 count <200 /ul
Answer: A: CD4 count <200 /ul 
Explanation: Defects in cellular and/or humoral immunity predispose to development of PCP. CD4+ T cells are critical in host defense against Pneumocystis. For HIV-infected patients, the incidence is inversely related to the CD4+ T cell count: at least 80% of cases occur at counts of <200 cells/mL, and most of these cases develop at counts of <100 cells/mL. Ref Harrison 19th edition pg 1017