Opportunistic Infections - The AIDS InfoNet

New Mexico AIDS InfoNet

Fact Sheet Number 500

OPPORTUNISTIC INFECTIONS

WHAT ARE OPPORTUNISTIC INFECTIONS?
TESTING FOR OIs
OIs AND AIDS
WHAT ARE THE MOST COMMON OIs?
PREVENTING OIs
TREATING OIs

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WHAT ARE OPPORTUNISTIC

INFECTIONS?

In our bodies, we carry many germs – bacteria, protozoa, fungi,

and viruses. When our immune system is working, it controls these

germs. But when the immune system is weakened by HIV disease or

by some medications, these germs can get out of control and cause

health problems.

Infections that take advantage of weakness in the immune defenses

are called “opportunistic”. The phrase “opportunistic

infection” is often shortened to “OI”.

TESTING FOR OIs

You can be infected with an OI, and “test positive”

for it, even though you don’t have the disease. For example, almost

everyone with HIV tests positive for Cytomegalovirus

(CMV). But it is very rare for CMV disease to develop unless

the T-cell count drops below

50, a sign of serious damage to the immune system.

To see if you’re infected with an OI, your blood might be tested

for antigens (pieces of the germ that causes the OI) or for antibodies

(proteins made by the immune system to fight the antigens). If

either the antigens or the antibodies are found, it means you’re

infected. If you are infected with a germ that causes an OI, and

if your T-cells are low enough to allow that OI to develop, your

doctor will look for signs of active disease. These are different

for the different OIs.

OIs AND AIDS

People who aren’t HIV-infected can develop OIs if their immune

systems are damaged. For example, many drugs used to treat cancer

suppress the immune system. Some people who get cancer treatments

can develop OIs.

HIV weakens the immune system so that opportunistic infections

can develop. If you are HIV-infected and develop opportunistic

infections, you might have AIDS.

In the US, the Center for Disease Control (CDC) is responsible

for deciding who has AIDS. The CDC has developed a list of about

24 opportunistic infections. If you have HIV and one or more of

these “official” OIs, then you have AIDS. The list is

available at <http://www.cdc.gov/mmwr/preview/mmwrhtml/00018871.htm>

WHAT ARE THE MOST

COMMON OIs?

In the early years of the AIDS epidemic, OIs caused a lot of sickness

and deaths. Once people started taking combination antiviral therapy,

however, a lot fewer people got OIs. It’s not clear how many people

with HIV will get a specific OI.

The most common OIs are listed here, along with the disease

they usually cause, and the T-cell count when the disease becomes

active:

Candidiasis (Thrush) is a fungal
infection of the mouth, throat, or vagina. T-cell range: can

occur even with fairly high T-cells.
Cytomegalovirus (CMV) is a viral
infection that causes eye disease that can lead to blindness.

T-cell range: under 50.
Herpes simplex viruses can cause oral herpes (cold sores)
or genital herpes. These are fairly common infections, but if

you have HIV, the outbreaks can be much more frequent and more

severe. They can occur at any T-cell count.
Mycobacterium avium complex (MAC or
MAI) is a bacterial infection that can cause recurring fevers,

general sick feelings, problems with digestion, and serious weight

loss. T-cell range: under 75.
Pneumocystis carinii pneumonia (PCP)
is a protozoal infection that can cause a fatal pneumonia. T-cell

range: under 200.
Toxoplasmosis (Toxo) is a protozoal
infection of the brain. T-cell range: under 100.
Tuberculosis (TB) is a bacterial
infection that attacks the lungs, and can cause meningitis. T-cell

range: Everyone with HIV who tests positive for exposure to TB

should be treated.