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Updated 12-10-2013
Human Immunodeficiency Virus – HIV
HIV is a double-stranded RNA retrovirus that primarily infects lymphocytes, monocytes and
macrophages. It is transmitted by the exchange of bodily fluids through activities such as sexual
contact, injection drug use, transfusion of blood products, and occupational exposure. HIV may
also be transmitted from mother to infant during pregnancy and at the time of delivery.
What HIV does in your body
Researchers believe that the virus attaches to a specific type of immune system cell called a
dendritic cell. These cells are found in mucocutaneous (mucosal membranes) areas that line the
mouth, the vagina, rectum, penis, and the upper gastrointestinal tract. Scientists think that these
dendritic cells transport the virus from the site of the infection to your lymph nodes where HIV
can infect other immune system cells. HIV can infect multiple cells in your body, including brain
cells, but its main target is the CD4 lymphocyte, also called a T-cell or CD4 cell. When a CD4
cell is infected with HIV, the virus goes through multiple steps to reproduce itself and create
many more virus particles.
HIV disease has a well-documented progression. If you are infected with HIV and don’t get
treatment, HIV will eventually overwhelm your immune system—and this will lead to your being
diagnosed with Acquired Immune Deficiency Syndrome (AIDS).
Here’s what typically happens:

Acute Infection: Within 2-4 weeks after infection with HIV, you can experience an acute
illness, which is often described as “the worst flu ever.” This is called acute retroviral
syndrome (ARS) or primary HIV infection and it’s the body’s natural response to the HIV
infection. (Not everyone develops ARS, however—and it can take up to 3 months for it to
appear in some people who do.) During this period of infection, large amounts of virus are
being produced in your body. The virus uses CD4 cells to replicate and destroys them in the
process. Because of this the CD4 count can fall rapidly. Eventually your immune response
will begin to bring the level of virus in your body back down to a level called a viral set point,
which is a relatively stable level of virus in your body. At this point, your CD4 count begins to
increase, but it may not return to pre-infection levels

Clinical Latency: After the acute stage of HIV infection, the disease moves into a stage
called clinical latency. This period is sometimes called asymptomatic HIV infection or chronic
HIV infection. During this phase, HIV reproduces at very low levels, although it is still active.
You may be able to maintain an undetectable viral load and a healthy CD4 cell count without
the use of medication during the earlier years of this phase. You may not have symptoms or
opportunistic infections. This period can last up to 8 years or longer. Some people progress
Updated 12-10-2013
through this phase faster than others. It is important to remember that you are still able to
transmit HIV to others during this phase. Toward the middle and end of this period, your
viral load begins to rise and your CD4 cell count begins to drop. As this happens, you may
begin to have constitutional symptoms of HIV as the virus levels increase in your body.

AIDS: As the number of your CD4 cells begins to fall below 200 cells per cubic millimeter of
blood, you will be diagnosed as having AIDS. (Normal CD4 counts are between 500 and
1,600 cells/mm3.) This is the stage of infection that occurs when your immune system is
badly damaged and you become vulnerable to opportunistic infections. Without treatment,
people who are diagnosed with AIDS typically survive about 3 years. Once someone has a
dangerous opportunistic infection, life-expectancy falls to about 1 year.
HIV in the United States: At A Glance
CDC estimates that 1,144,500 persons aged 13 years and older are living with HIV infection,
including 180,900 (15.8%) who are unaware of their infection1. Over the past decade, the
number of people living with HIV has increased, while the annual number of new HIV infections
has remained relatively stable. Still, the pace of new infections continues at far too high a
level— particularly among certain groups.
HIV Incidence (new infections): The estimated incidence of HIV has remained stable overall in
recent years, at about 50,000 new HIV infections per year2. Within the overall estimates,
however, some groups are affected more than others. Gay, bisexual, and other men who have sex with
men (MSM) continue to bear the greatest burden of HIV infection, and among races/ethnicities,
African Americans continue to be disproportionately affected.
HIV Diagnoses (new diagnoses, regardless of when infection occurred): In 2011, an estimated
49,273 people were diagnosed with HIV infection in the United States. In that same year, an
estimated 32,052 people were diagnosed with AIDS. Overall, an estimated 1,155,792 people in
the United States have been diagnosed with AIDS3.
Deaths: An estimated 15,529 people with an AIDS diagnosis died in 2010, and approximately
636,000 people in the United States with an AIDS diagnosis have overall3. The deaths of
persons with an AIDS diagnosis can be due to any cause—that is, the death may or may not be
related to AIDS.
Additional information is available on the CDC website
(http://www.cdc.gov/hiv/default.html)
1
CDC. Monitoring selected national HIV prevention and care objectives by using HIV surveillance data—United
States and 6 U.S. dependent areas—2011. HIV Surveillance Supplemental Report 2013;18(No. 5). Published
October 2013.
2
CDC. Estimated HIV incidence in the United States, 2007–2010. HIV Surveillance Supplemental Report
2012;17(No. 4). Published December 2012.
3
CDC. HIV Surveillance Report, 2011; vol. 23. http://www.cdc.gov/hiv/topics/surveillance/resources/reports/.
Published February 2013.
Updated 12-10-2013
Hepatitis B Virus - HBV
HBV is a partially double-stranded DNA virus and is acquired by contact with body fluids during
sexual activity, injection-drug use, occupational exposure, hemodialysis, and transfusion of
blood products. HBV is also spread from mother to infant during pregnancy and childbirth.
HBV infects the cells of the liver causing inflamation and disrupting its function. Here is what
typically happens:
Acute infection
Symptoms of acute hepatitis may develop shortly after you first become infected with the virus
(within 1-6 months, which is the incubation period). Symptoms include: feeling sick (nausea),
being sick (vomiting), tummy (abdominal) pains, high temperature (fever) and feeling generally
unwell. You may look yellow (become jaundiced). This is due to a build-up of the chemical
bilirubin which is made in the liver and spills into the blood in some liver conditions. (With
jaundice due to hepatitis your urine goes dark and your stools (feces) may go pale.)
Symptoms of acute hepatitis B infection usually go after a few weeks, as the immune system
either clears the virus or brings it under control. Rarely, an acute severe hepatitis develops
which is life-threatening.
However, in about half of cases, no symptoms, or only mild flu-like symptoms, develop in the
acute phase. You may not even be aware that you have been infected with hepatitis B.
Following the initial acute phase:

In more than 9 in 10 cases in adults, the virus is cleared from the body by the immune
system within 3-6 months. In this situation you are no longer infectious and you are immune
to further infection.

In up to 1 in 10 cases in adults, the virus remains long-term (chronic hepatitis B infection).
This may occur whether or not you have symptoms in the acute phase.

In more than 9 in 10 babies infected from their mothers, the virus remains long-term.
Chronic infection
Of those people who develop chronic hepatitis B infection:

Up to 2 in 3 people remain well. You can have the virus in your body but develop no
damage or problems to the liver or other organs. This is called being a carrier and is
sometimes called chronic inactive hepatitis B. You may not know that you are infected and
are a carrier. However, even if you have no symptoms, you can still pass on the virus to
others. About 1 in 5 carriers eventually clear the virus from their body naturally, but this may
be after several years.

Some people develop persistent liver inflammation (sometimes called chronic active
hepatitis B). Symptoms include muscle aches, tiredness, feeling sick, lack of appetite,
intolerance of alcohol, pains over the liver, jaundice and depression. Symptoms vary in
severity and some people have liver inflammation without having any symptoms.

Some people develop cirrhosis. Cirrhosis is like a scarring of the liver, which can cause
serious problems and liver failure when it is severe. Cirrhosis usually takes many years to
develop after a person has been infected with hepatitis B.
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
A small number of people who develop cirrhosis then develop liver cancer after a further
period of time.
HBV in the United States: At A Glance
In 2011, 2,890 cases of acute Hepatitis B in the United States were reported to the CDC. The
overall incidence of reported acute Hepatitis B was 0.9 per 100,000 population. However,
because many HBV infections are either asymptomatic or never reported, the actual number of
new infections is estimated to be 18,800 (7,400 – 86,200) persons. Rates are highest among
adults, particularly males aged 25–44 years. An estimated 800,000–1.4 million persons in the
United States have chronic HBV infection.
HBV infection is the only bloodborne pathogen that is preventable by a vaccine. The vaccine is
safe, effective, and free to healthcare workers at risk from exposure to bloodborne pathogens.
Additional information is available on the CDC website
(http://www.cdc.gov/hepatitis/HBV/index.htm)
Updated 12-10-2013
Hepatitis C Virus - HCV
HCV is a single-stranded RNA virus and is acquired by contact with body fluids during injection
drug use, occupational exposure, hemodialysis, transfusion of blood products, or rarely sexual
activity. A few reports suggest that HCV may also be spread from mother to infant during
pregnancy and childbirth, although not as commonly as HBV. In the US, 10% of HCV patients
do not have an identifiable risk factor for infection.
HCV infects the cells of the liver causing inflamation and disrupting its function. Here is what
typically happens:
Acute phase
This phase lasts for the first six months. When first infected with the virus, most people have no
symptoms, or only mild ones. If symptoms do occur, they develop about 7-8 weeks after being
exposed to the virus and may include: feeling sick, vomiting and feeling generally unwell. Some
people become jaundiced (go 'yellow'). This is due to a build-up of the chemical bilirubin which
is made in the liver and spills into the blood in some liver conditions. It is unusual to get severe
symptoms.
Following the initial infection:

In about 1 in 5 cases the virus is cleared from the body by the immune system within 2-6
months. If this happens then you will have no long-term effects from the virus. Younger
people and women are more likely to clear the virus in this way.

In about 4 in 5 cases, the virus remains active in the liver and bloodstream long-term. This is
called chronic infection with hepatitis C.
Chronic phase
A chronic hepatitis C infection is when the infection lasts for longer than six months. The course
of the chronic infection varies considerably between people and it is very unpredictable. Of
those people who develop chronic infection:

Some people have mild or no symptoms. However, even if you have no symptoms, you can
still pass on the hepatitis C virus to others who may develop problems.

Some people develop some symptoms due to persistent inflammation of the liver. For
example, feeling sick, lack of appetite, intolerance of alcohol, pains over the liver, jaundice
and depression. The most common symptoms of chronic hepatitis C are extreme tiredness,
poor concentration and memory problems, and muscle and joint aches. There is actually no
relationship between the severity of symptoms and the degree of liver damage. This means
that some people can have liver inflammation without having any symptoms.

About one third of people with chronic hepatitis C infection develop cirrhosis over a period of
about 20-30 years. Cirrhosis is like a 'scarring' of the liver, which can cause serious
problems and 'liver failure' when it is severe. Some people with chronic hepatitis C have no
symptoms for many years until they develop cirrhosis. Only when the liver starts to fail with
cirrhosis do symptoms appear.

A small number of people who develop cirrhosis go on to develop liver cancer.
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HCV in the United States: At A Glance
In 2011, 1,229 cases of acute Hepatitis C in the United States were reported to the CDC (data
from 9 states was unreported). The overall incidence of reported acute Hepatitis B was 0.4 per
100,000 population. However, because many HBV infections are either asymptomatic or never
reported, the actual number of new infections is estimated to be 16,500 (7,200 – 43,400)
persons. Rates are highest among adults, particularly males aged 25–44 years. An estimated
3.2 million persons in the United States (approximately 1% of the population) have chronic HCV
infection. Infection is most prevalent among those born during 1945–1965, the majority of whom
were likely infected during the 1970s and 1980s when rates were highest.
A recent CDC analysis of death certificate data found that HCV-attributable deaths increased
significantly between 1999 and 2007. CDC estimates that there were 15,106 deaths caused by
HCV in 2007. The citation can be found at "The increasing burden of mortality from viral
hepatitis in the United States between 1999 and 2007." Ly, K., et al. Annals Of Internal
Medicine, 2012. 156(4): p. 271-278
Additional information is available on the CDC website
(http://www.cdc.gov/hepatitis/HCV/index.htm)