prophylaxis for Pneumocystis carinii is indicated in HIV positive patents When CD4 count is-

Low CD4 count correlated with risk of PCP (p < 0.0001); 79% had CD4 counts less than 100/microl and 95% had CD4 counts less than 200/microl. Bacterial pneumonia has been linked to several HIV-related factors, including CD4 counts, having an uncontrolled viral load, and not being on antiretroviral therapy. HIV-positive people with a weak immune system, paicularly a CD4 count below 200 cells/mm3, are at greatest risk. Ref Harrison20th edition pg 1107