Scientists are still learning about how people get PCP. Studies have shown that many people are exposed to the fungus as children, but they do not get sick because their immune systems are strong. Some healthy adults carry the fungus in their lungs and never develop symptoms of PCP. However, if a person's immune system stops working normally, the fungus can start causing symptoms.
TMP-SMX prophylaxis is currently recommended for:
All HIV-infected patients with CD4 < 350 cells / µL
Infants born to HIV-infected mothers
Children with a history of PCP
Stem cell transplant patients