HIV Infection and AIDS, An Overview, NIAID Fact Sheet: NIAID
Article title: HIV Infection and AIDS, An Overview, NIAID Fact Sheet: NIAID
HIV Infection and AIDS: An Overview
acquired immunodeficiency syndrome - was first reported in the
United States in 1981 and has since become a major worldwide
epidemic. AIDS is caused by the human immunodeficiency virus (HIV).
By killing or damaging cells of the body's immune system, HIV
progressively destroys the body's ability to fight infections and
certain cancers. People diagnosed with AIDS may get life-threatening
diseases called opportunistic infections, which are caused by
microbes such as viruses or bacteria that usually do not make
healthy people sick.
More than 700,000 cases of AIDS have
been reported in the United States since 1981, and as many as
900,000 Americans may be infected with HIV. The epidemic is growing
most rapidly among minority populations and is a leading killer of
African-American males. According to the U.S. Centers for Disease
Control and Prevention (CDC), AIDS affects nearly seven times more
African Americans than whites and three times more Hispanics than
whites (CDC HIV/AIDS Surveillance Report
, Vol. 12,
How is HIV transmitted?
HIV is spread most commonly by
having unprotected sex with an infected partner. The virus can enter
the body through the lining of the vagina, vulva, penis, rectum, or
mouth during sex.
HIV also is spread through contact with
infected blood. Before donated blood was screened for evidence of
HIV infection and before heat-treating techniques to destroy HIV in
blood products were introduced, HIV was transmitted through
transfusions of contaminated blood or blood components. Today,
because of blood screening and heat treatment, the risk of getting
HIV from such transfusions is extremely small.
frequently is spread among injection drug users by the sharing of
needles or syringes contaminated with very small quantities of blood
from someone infected with the virus. It is rare, however, for a
patient to give HIV to a health care worker or vice-versa by
accidental sticks with contaminated needles or other medical
Women can transmit HIV to their babies during
pregnancy or birth. Approximately one-quarter to one-third of all
untreated pregnant women infected with HIV will pass the infection
to their babies. HIV also can be spread to babies through the breast
milk of mothers infected with the virus. If the mother takes the
drug AZT during pregnancy, she can reduce significantly the chances
that her baby will get be infected with HIV. If health care
providers treat mothers with AZT and deliver their babies by
cesarean section, the chances of the baby being infected can be
reduced to a rate of 1 percent.
A study sponsored by the
National Institute of Allergy and Infectious Diseases (NIAID) in
Uganda found a highly effective and safe drug regimen for preventing
transmission of HIV from an infected mother to her newborn that is
more affordable and practical than any other examined to date.
Interim results from the study show that a single oral dose of the
antiretroviral drug nevirapine (NVP) given to an HIV-infected woman
in labor and another to her baby within three days of birth reduces
the transmission rate by half compared with a similar short course
Although researchers have found HIV in the saliva of
infected people, there is no evidence that the virus is spread by
contact with saliva. Laboratory studies reveal that saliva has
natural properties that limit the power of HIV to infect. Research
studies of people infected with HIV have found no evidence that the
virus is spread to others through saliva by kissing. No one knows,
however, whether so-called "deep" kissing, involving the exchange of
large amounts of saliva, or oral intercourse increase the risk of
infection. Scientists also have found no evidence that HIV is spread
through sweat, tears, urine, or feces.
Studies of families
of HIV-infected people have shown clearly that HIV is not spread
through casual contact such as the sharing of food utensils, towels
and bedding, swimming pools, telephones, or toilet seats. HIV is not
spread by biting insects such as mosquitoes or bedbugs.
can infect anyone who practices risky behaviors such as
- sharing drug needles or syringes
- having sexual contact with an infected person without using a
- having sexual contact with someone whose HIV status is unknown
Having a sexually transmitted disease such as syphilis,
genital herpes, chlamydial infection, gonorrhea, or bacterial
vaginosis appears to make people more susceptible to getting HIV
infection during sex with infected partners.
What are the early symptoms of HIV infection?
Many people do
not have any symptoms when they first become infected with HIV. Some
people, however, have a flu-like illness within a month or two after
exposure to the virus. This illness may include fever, headache,
tiredness, and enlarged lymph nodes (glands of the immune system
easily felt in the neck and groin). These symptoms usually disappear
within a week to a month and are often mistaken for those of another
viral infection. During this period, people are very infectious, and
HIV is present in large quantities in genital fluids.
persistent or severe symptoms may not surface for a decade or more
after HIV first enters the body in adults, or within two years in
children born with HIV infection. This period of "asymptomatic"
infection is highly individual. Some people may begin to have
symptoms within a few months, while others may be symptom-free for
more than 10 years.
Even during the asymptomatic period, the
virus is actively multiplying, infecting, and killing cells of the
immune system. HIV's effect is seen most obviously in a decline in
the blood levels of CD4+ T cells (also called T4 cells) - the immune
system's key infection fighters. At the beginning of its life in the
human body, the virus disables or destroys these cells without
As the immune system deteriorates, a
variety of complications start to take over. For many people, their
first sign of infection is large lymph nodes or "swollen glands"
that may be enlarged for more than three months. Other symptoms
often experienced months to years before the onset of AIDS include
- lack of energy
- weight loss
- frequent fevers and sweats
- persistent or frequent yeast infections (oral or vaginal)
- persistent skin rashes or flaky skin
- pelvic inflammatory disease in women that does not respond to
- short-term memory loss
Some people develop frequent
and severe herpes infections that cause mouth, genital, or anal
sores, or a painful nerve disease called shingles. Children may grow
slowly or be sick a lot.
What is AIDS?
The term AIDS applies to the most advanced
stages of HIV infection. CDC developed official criteria for the
definition of AIDS and is responsible for tracking the spread of
AIDS in the United States.
CDC's definition of AIDS includes
all HIV-infected people who have fewer than 200 CD4+ T cells per
cubic millimeter of blood. (Healthy adults usually have CD4+ T-cell
counts of 1,000 or more.) In addition, the definition includes 26
clinical conditions that affect people with advanced HIV disease.
Most of these conditions are opportunistic infections that generally
do not affect healthy people. In people with AIDS, these infections
are often severe and sometimes fatal because the immune system is so
ravaged by HIV that the body cannot fight off certain bacteria,
viruses, fungi, parasites, and other microbes.
opportunistic infections common in people with AIDS include
- coughing and shortness of breath
- seizures and lack of coordination
- difficult or painful swallowing
- mental symptoms such as confusion and forgetfulness
- severe and persistent diarrhea
- vision loss
- nausea, abdominal cramps, and vomiting
- weight loss and extreme fatigue
- severe headaches
Children with AIDS may get the same opportunistic
infections as do adults with the disease. In addition, they also
have severe forms of the bacterial infections all children may get,
such as conjunctivitis (pink eye), ear infections, and tonsillitis.
People with AIDS are particularly prone to developing
various cancers, especially those caused by viruses such as Kaposi's
sarcoma and cervical cancer, or cancers of the immune system known
as lymphomas. These cancers are usually more aggressive and
difficult to treat in people with AIDS. Signs of Kaposi's sarcoma in
light-skinned people are round brown, reddish, or purple spots that
develop in the skin or in the mouth. In dark-skinned people, the
spots are more pigmented.
During the course of HIV
infection, most people experience a gradual decline in the number of
CD4+ T cells, although some may have abrupt and dramatic drops in
their CD4+ T-cell counts. A person with CD4+ T cells above 200 may
experience some of the early symptoms of HIV disease. Others may
have no symptoms even though their CD4+ T-cell count is below 200.
Many people are so debilitated by the symptoms of AIDS that
they cannot hold steady employment or do household chores. Other
people with AIDS may experience phases of intense life-threatening
illness followed by phases in which they function normally.
A small number of people (fewer than 50) first infected with
HIV 10 or more years ago have not developed symptoms of AIDS.
Scientists are trying to determine what factors may account for
their lack of progression to AIDS, such as particular
characteristics of their immune systems or whether they were
infected with a less aggressive strain of the virus, or if their
genes may protect them from the effects of HIV. Scientists hope that
understanding the body's natural method of control may lead to ideas
for protective HIV vaccines and use of vaccines to prevent the
disease from progressing.
How is HIV infection diagnosed?
Because early HIV infection
often causes no symptoms, a doctor or other health care provider
usually can diagnose it by testing a person's blood for the presence
of antibodies (disease-fighting proteins) to HIV. HIV antibodies
generally do not reach detectable levels in the blood for one to
three months following infection. It may take the antibodies as long
as six months to be produced in quantities large enough to show up
in standard blood tests.
People exposed to the virus should
get an HIV test as soon as they are likely to develop antibodies to
the virus - within 6 weeks to 12 months after possible exposure to
the virus. By getting tested early, people with HIV infection can
discuss with a health care provider when they should start treatment
to help their immune systems combat HIV and help prevent the
emergence of certain opportunistic infections (see section on
treatment below). Early testing also alerts HIV-infected people to
avoid high-risk behaviors that could spread the virus to others.
Most health care providers can do HIV testing and will
usually offer counseling to the patient at the same time. Of course,
individuals can be tested anonymously at many sites if they are
concerned about confidentiality.
Health care providers
diagnose HIV infection by using two different types of antibody
tests, ELISA and Western Blot. If a person is highly likely to be
infected with HIV and yet both tests are negative, the health care
provider may request additional tests. The person also may be told
to repeat antibody testing at a later date, when antibodies to HIV
are more likely to have developed.
Babies born to mothers
infected with HIV may or may not be infected with the virus, but all
carry their mothers' antibodies to HIV for several months. If these
babies lack symptoms, a doctor cannot make a definitive diagnosis of
HIV infection using standard antibody tests until after 15 months of
age. By then, babies are unlikely to still carry their mothers'
antibodies and will have produced their own, if they are infected.
Health care experts are using new technologies to detect HIV itself
to more accurately determine HIV infection in infants between ages 3
months and 15 months. They are evaluating a number of blood tests to
determine if they can diagnose HIV infection in babies younger than
How is HIV infection treated?
When AIDS first surfaced in
the United States, there were no medicines to combat the underlying
immune deficiency and few treatments existed for the opportunistic
diseases that resulted. Over the past 10 years, however, researchers
have developed drugs to fight both HIV infection and its associated
infections and cancers.
The U.S. Food and Drug
Administration (FDA) has approved a number of drugs for treating HIV
infection. The first group of drugs used to treat HIV infection,
called nucleoside reverse transcriptase (RT) inhibitors, interrupts
an early stage of the virus making copies of itself. Included in
this class of drugs (called nucleoside analogs) are AZT (also known
as zidovudine or ZDV), ddC (zalcitabine), ddI (dideoxyinosine), d4T
(stavudine), and 3TC (lamivudine). These drugs may slow the spread
of HIV in the body and delay the onset of opportunistic infections.
Health care providers can prescribe non-nucleoside reverse
transcriptase inhibitors (NNRTIs), such as delvaridine (Rescriptor),
nevirapine (Viramune), and efravirenz (Sustiva), in combination with
other antiretroviral drugs.
More recently, FDA has approved
a second class of drugs for treating HIV infection. These drugs,
called protease inhibitors, interrupt virus replication at a later
step in its life cycle. They include
- ritonavir (Norvir)
- saquinivir (Invirase)
- indinavir (Crixivan)
- amprenivir (Agenerase)
- nelfinavir (Viracept)
- lopinavir (Kaletra)
Because HIV can become resistant
to any of these drugs, health care providers must use a combination
treatment to effectively suppress the virus.
available antiretroviral drugs do not cure people of HIV infection
or AIDS, however, and they all have side effects that can be severe.
Some of the nucleoside RT inhibitors may cause a depletion of red or
white blood cells, especially when taken in the later stages of the
disease. Some may also cause an inflammation of the pancreas and
painful nerve damage. There have been reports or complications and
other severe reactions, including death, to some of the
antiretroviral nucleoside analogs when used alone or in combination.
Therefore, health care experts recommend that people on
antiretroviral therapy be routinely seen and followed by their
The most common side effects associated with
protease inhibitors include nausea, diarrhea, and other
gastrointestinal symptoms. In addition, protease inhibitors can
interact with other drugs resulting in serious side effects.
Researchers have credited highly active antiretroviral
therapy, or HAART, as being a major factor in reducing the number of
deaths from AIDS in this country by 47 percent in 1997. HAART is a
treatment regimen that uses a combination of reverse transcriptase
inhibitors and protease inhibitors to treat patients. Patients who
are newly infected with HIV as well as AIDS patients can take the
While HAART is not a cure for AIDS, it has
greatly improved the health of many people with AIDS and it reduces
the amount of virus circulating in the blood to nearly undetectable
levels. Researchers have shown that HAART cannot eradicate HIV
entirely from the body. HIV remains present, lurking in hiding
places such as the lymph nodes, the brain, testes, and the retina of
the eye, even in patients who have been treated.
A number of
drugs are available to help treat opportunistic infections to which
people with HIV are especially prone. These drugs include
- foscarnet and ganciclovir to treat cytomegalovirus eye
- fluconazole to treat yeast and other fungal infections
- trimethoprim/sulfamethoxazole (TMP/SMX) or pentamidine to
treat Pneumocystis carinii pneumonia (PCP)
addition to antiretroviral therapy, health care providers treat
adults with HIV, whose CD4+ T-cell counts drop below 200, to prevent
the occurrence of PCP, which is one of the most common and deadly
opportunistic infections associated with HIV. They give children PCP
preventive therapy when their CD4+ T-cell counts drop to levels
considered below normal for their age group. Regardless of their
CD4+ T-cell counts, HIV-infected children and adults who have
survived an episode of PCP take drugs for the rest of their lives to
prevent a recurrence of the pneumonia.
individuals who develop Kaposi's sarcoma or other cancers are
treated with radiation, chemotherapy, or injections of alpha
interferon, a genetically engineered naturally occurring protein.
How can HIV infection be prevented?
Because no vaccine for
HIV is available, the only way to prevent infection by the virus is
to avoid behaviors that put a person at risk of infection, such as
sharing needles and having unprotected sex.
infected with HIV have no symptoms. Therefore, there is no way of
knowing with certainty whether a sexual partner is infected unless
he or she has repeatedly tested negative for the virus and has not
engaged in any risky behavior.
People should either abstain
from having sex or use male latex condoms or female polyurethane
condoms, which may offer partial protection, during oral, anal, or
vaginal sex. Only water-based lubricants should be used with male
Although some laboratory evidence shows that
spermicides can kill HIV, researchers have not found that these
products can prevent a person from getting HIV.
The risk of
HIV transmission from a pregnant woman to her baby is significantly
reduced if she takes AZT during pregnancy, labor, and delivery, and
her baby takes it for the first six weeks of life.
What research is going on?
NIAID-supported investigators are
conducting an abundance of research on HIV infection, including
developing and testing HIV vaccines and new therapies for the
disease and some of its associated conditions. Investigators are
testing 29 HIV vaccines in people, and are developing or testing
many drugs for HIV infection or AIDS-associated opportunistic
infections. Researchers also are investigating exactly how HIV
damages the immune system. This research is suggesting new and more
effective targets for drugs and vaccines. NIAID-supported
investigators also continue to trace how the disease progresses in
Scientists are investigating and testing
chemical barriers, such as topical microbicides, that people can use
in the vagina or in the rectum during sex to prevent HIV
transmission. They also are looking at other ways to prevent
transmission, such as controlling sexually transmitted diseases and
modifying people's behavior, as well as ways to prevent transmission
from mother to child.
For information about Food and Drug
Administration-approved HIV-related clinical trials being conducted
throughout the United States, contact the AIDS Clinical Trials
federally approved treatment guidelines on HIV/AIDS, contact the
HIV/AIDS Treatment Information Service.
services operate from 9 a.m. to 5 p.m. Eastern Time, Monday through
Friday. Spanish-speaking specialists are available.
information specifically about clinical trials conducted by the
NIAID Intramural AIDS Research Program, call 1-800-243-7644 (https://clinicaltrials.gov/
For materials contact the National Prevention Information
NIAID is a component of the National Institutes
of Health (NIH). NIAID supports basic and applied research to
prevent, diagnose, and treat infectious and immune-mediated
illnesses, including HIV/AIDS and other sexually transmitted
diseases, tuberculosis, malaria, autoimmune disorders, asthma and
Press releases, fact sheets and other
NIAID-related materials are available on the NIAID Web site at https://www.niaid.nih.gov/default.htm.
Office of Communications and
National Institute of Allergy and Infectious
National Institutes of Health
Public Health Service
U.S. Department of Health
and Human Services