PCP is a kind of pneumonia caused by Pneumocystis jiroveci (P. jiroveci). (Say the name this way: "new-mo-sis-tis yee-row-vet-zee-eye.") It used to be called Pneumocystis carinii pneumonia. Most people infected with P. jiroveci don't get pneumonia because their immune systems are healthy and strong. People whose immune systems are weak because of HIV infection can get PCP. PCP is less common than it used to be, but it's still the most common serious infection in people with advanced HIV disease in the United States.
If you get PCP, you probably will have fever, cough, trouble breathing (especially with exercise) or chest tightness. See your doctor right away if you have these symptoms. Most cases are mild, but people with severe PCP may die if the infection isn't treated quickly. PCP is diagnosed by lab tests of fluid or tissue from your lungs.
Most scientists believe PCP is spread in the air, but they don't know if it lives in the soil or someplace else. P. jiroveci is common all over the world. Since you can't help being exposed to P. jiroveci, you should get medical care so you won't get PCP. (PCP is not spread by sex.)
If you are at risk of PCP because you have HIV, PCP can be prevented. A good medicine for preventing PCP is trimethoprim-sulfamethoxazole (say the name this way: "try-meth-o-prim-sul-fa-meth-ox-uh-sole"), or TMP-SMX, for short. TMP-SMX is a combination of 2 medicines. It has different brand names, such as Bactrim and Septra. It comes in pill and liquid forms. Other medicines can also prevent PCP if you can't take TMP-SMX.
If you have HIV, your doctor will test your blood regularly to check how strong your immune system is. Your doctor will probably prescribe TMP-SMX to prevent PCP if your CD4 cell count goes below 200. Your doctor may also have you start taking TMP-SMX if you get certain symptoms, such as a temperature above 100°F that lasts for 2 weeks or longer, or a yeast infection in your mouth or throat (also called "thrush").
No. The pneumonia vaccine protects you against a different kind of pneumonia. It doesn't protect you against PCP. There is no vaccine for PCP.
TMP-SMX might cause a rash. It might make you feel sick. If you have just a mild reaction, you should keep taking TMP-SMX, because it works better than any other medicine to prevent PCP. Your doctor can give you another medicine for a while to help you with the side effects of TMP-SMX.
Yes. If you have already had PCP you can get it again. Taking TMP-SMX can prevent second infections with PCP.
Your doctor may let you stop taking medicine to prevent PCP if the following things are true for you:
Recent studies have shown that a strong immune system should protect you from PCP. It is not known whether it's safe to stop taking preventive medicine if you have had PCP before.
People with severe PCP are treated in a hospital with IV medicine (medicine put into a vein through a tube). As they get better--or if the illness was mild to begin with--they can take medicine in pill form. TMP-SMX is also a good treatment for PCP. If you can't take TMP-SMX, or if you don't get better quickly with TMP-SMX, you can take other medicines or combinations of medicines. Although these days the treatments for PCP are good, it's better to try not to get PCP at all.