Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 1999;60(6):1713-1714

See related article on Pneumocystis carinii pneumonia.

What is PCP?

PCP is a kind of pneumonia caused by the Pneumocystis carinii germ. (Say the name this way: new-mo-sis-tis ca-rin-nee-eye.) Most people infected with this germ 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.

How would I know if I have PCP?

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.

How do you “catch” PCP?

Most scientists believe PCP is spread in the air, but they don't know if it lives in the soil or someplace else. The PCP germ is common all over the world. Since you can't help being exposed to the PCP germ, you should get medical care so you won't get PCP. (PCP is not spread by sex.)

How can I protect myself from PCP?

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-SMZ, for short. TMP-SMZ is a combination of two medicines. It has different brand names, such as Bactrim, Septra and Cotrim. It comes in pill and liquid forms. Other medicines can also prevent PCP if you can't take TMP-SMZ.

When should I start taking medicine to prevent PCP?

You should have your blood tested regularly to check how strong your immune system is. Your doctor will probably prescribe TMP-SMZ to prevent PCP if your CD4 cell count goes below 200. Your doctor may also have you start taking TMP-SMZ if you get certain symptoms, such as a temperature above 100°F that lasts for two weeks or longer, or a yeast infection in your mouth or throat that is called “thrush.”

I already had a pneumonia vaccination. Won't that protect me against PCP?

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.

Does TMP-SMX have side effects?

TMP-SMZ might cause a rash. It might make you feel sick. If you have just a mild reaction, you should keep taking TMP-SMZ, 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-SMZ.

Can I get PCP more than once?

Yes. If you have already had PCP you can get it again. Taking TMP-SMZ can prevent second infections with PCP. That's why you should take TMP-SMZ after you've had PCP—so you won't get it again.

What if my CD4 cells go over 200 while I'm taking medicines to control HIV?

Your doctor may let you stop taking medicine to prevent PCP if the following things are true for you:

  • If you never had PCP before.

  • If your CD4 cell count stays above 200 for three to six months.

  • If blood tests show you have a low viral load or an undetectable viral load.

Recent studies have shown that a strong immune system should protect you from PCP. We don't know if it's safe to stop taking preventive medicine if you have had PCP before.

If I get PCP, how is it treated?

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-SMZ is also a good treatment for PCP. If you can't take TMP-SMZ, or if you don't get better quickly with TMP-SMZ, 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.

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