Human Immune Deficiency Virus (HIV) (updated 3/07)

What is HIV?

Human Immunodeficiency virus (HIV) is a virus that infects certain white blood cells.


When the virus infects these cells, called T-helper cells of CD4 cells, the virus takes over the cell’s ability to reproduce.


These “compromised” cells start making new copies of the virus. The infected cells die, releasing new copies of the virus that in turn infect new white blood cells.


This destruction of white blood cells damages the infected person’s immune system and compromises his/her ability to fight off infections and other immune system challenges.


In the USA, HIV infection is relatively uncommon, but in terms of morbidity (illness and suffering) and mortality (death), the toll is substantial. Outside the U.S. – and particularly in developing countries – the rates of new HIV infections are rising and the numbers of currently infected people are incredibly large. In some sub-Saharan countries in Africa, HIV prevalence among young adults is 15% or higher…


The History of HIV

In 1981, news of a strange syndrome of immune suppression and death in young, otherwise healthy, homosexual males began to appear in the medical literature and news media. This condition was initially called Gay Related Immune Disorder (GRID); but in 1982, the name was changed to Acquired Immune Deficiency Syndrome (AIDS) as individuals other than homosexual men were noted to have this same condition.


Efforts were begun to identify the cause of the condition and the manner in which the condition was spread. Epidemiologic investigations determined that an infectious agent transmitted by exposure to infected blood or blood products, by intravenous drug use, or through sexual activity, caused the condition.


In 1983, the HIV virus was discovered and isolated. Blood tests to detect viral antibodies and confirm the diagnosis of HIV infection were soon developed and marketed. The screening of blood donors for HIV risk behaviors and blood products for HIV antibodies both became routine.


Health educators promoted “safe sex” (use of latex condoms during sexual activities) to reduce the spread of HIV. Mention of HIV/AIDS in the media became commonplace. The first effective drug for delaying the inevitable progression from HIV infection to full-blown AIDS, and from AIDS to death was introduced in 1987 – it was called zidovudine, or AZT.


As treatment became available, the definition of AIDS changed (in 1993) and infected individuals were encouraged to initiate drug treatment at earlier stages in the disease process.


As those infected became visibly “sick” and died, a fear of HIV infection gripped the country and particularly impacted the high-risk communities.


This fear seemed to change behavior and probably led to a decrease in promiscuous sexual activity and other risky behaviors. Eventually, in the early1990s, the number of new HIV infections leveled out, and in 1993 the number of new AIDS cases began to decline. With the introduction of highly active anti-retroviral therapy (HAART) in 1995, AIDS-related deaths declined substantially.


[The number of newly diagnosed HIV cases has again been on the rise in 2003-2005]… the total number of people living in the USA with HIV infection is still on the rise.


HIV: What You Need To Know

Risk Factors

Exposure to infected blood or other body fluids is required for HIV transmission to occur. The highest concentrations of HIV occur in blood, semen and vaginal secretions.


Contact with these infected body fluids puts one at risk for becoming infected. Intravenous drug users and men who have sex with men (MSM) are at the highest risk of HIV, followed by those who have vaginal or oral sex with multiple partners, particularly high-risk partners.



Many people are surprised to find that HIV is among the least infectious STDs. The risk of acquiring HIV through vaginal intercourse with an infected individual is approximately 7 percent per year, when condoms are not used.


The risk of acquiring infection from one act of receptive anal sex is probably between one in 10 and one in 100, and the risk from one skin puncture by an infected needle is probably between one in 100 and one in 1000. Reliable estimates of the risk of acquiring infection from one act of oral sex are lacking, but oral sex is less likely to transmit the infection than vaginal intercourse.




In the year 2000, there were 21,704 new HIV infections reported in the USA. The CDC estimates that there are actually closer to 40,000 new infections yearly, but many infected people are unaware of their infection.


[Most recent figures, in 2006, indicate 40,000+ new infections per year, with actual numbers likely up to 60,000 per year in the USA.] Between 45-50% of new HIV infections are transmitted by sexual activity (approximately 30% homosexusal and 17% heterosexual), and about 10% are transmitted by intravenous drug use. A very small proportion of new infections are transmitted from infected mothers to their newborn children or by other means, and in 40% of new infections, the route of transmission is not known.



The CDC estimates that there are currently 800,000 to 900,000 Americans living with HIV infection, but roughly half of these people do not know they are infected. Approximately 323,000 Americans have AIDS.



Within the first few weeks following exposure, many infected people experience a “flu-like” syndrome and feel tired, feverish, achy or nauseated. Most of those people have no idea that a deadly virus has entered their bodies. At this time, the viral levels in the blood are very hight, so that people with sexual or bolld/body fluid exposure to infected individuals during this period are probably at greater risk of acquiring the infection than contacts occurring later.


The initial flu-like syndrome quickly fades, after which infected individuals typically experience no recognizable symptoms. During this asymptomatic period, blood levels of the virus are at lower levels, but the infection can still be transmitted.


Although HIV infection causes AIDS, AIDS is a distinct clinical syndrome from HIV infection.


AIDS typically appears 10 years after the actual HIV infection, though new treatments may further delay the development of AIDS.


The defining conditions for AIDS include numerous infections that are rare among people with normal immune systems. Such infections include tuberculosis (TB), pneumocystis pneumonia, certain types of fungal and yeast infections, and persistent and unusual intestinal infections. AIDS patients also experience high rates of cancer, including lymphomas and Kaposi’s sarcoma.


The CD4 count (the concentration of T helper cells in the blood) is another factor used to determine that a person has AIDS. The presence of AIDS defining conditions is typically preceded/accompanied by a decrease in the CD4 count and an increase in the “viral load” (the concentration of HIV in the blood).


Death usually occurs within a few years following the onset of AIDS. Most AIDS deaths are due to infection of cancer. Treatment can slow the progression of HIV infection to AIDS and from AIDS to death, but treatment cannot cure either HIV infection or AIDS.[Sexual Health Update, Fall 2001, The Medical Institute,]



Has no symptoms in most patients, other than flu-like symptoms; but to date, infected persons ultimately develop full-blown AIDS.  HIV is relatively difficult to contract: there is only a 1 in 500 encounters chance of being infected.  However, once another STD is present, such as HPV, Herpes, chlamydia, gonorrhea, etc., the chances of contracting HIV are dramatically increased.


to the CDC:  In the United States, HIV-related death has the greatest impact on young and middle-aged adults, particularly racial and ethnic minorities. In 1999, HIV was the fifth leading cause of death for Americans between the ages of 25 and 44. Among African American men in this age group, HIV infection has been the leading cause of death since 1991. In 1999, among black women 25-44 years old, HIV infection was the third leading cause of death. Many of these young adults likely were infected in their teens and twenties. It has been estimated that at least half of all new HIV infections in the United States are among people under 25, and the majority of young people are infected sexually (Rosenberg PS, Biggar RJ, Goedert JJ. Declining age at HIV infection in the United States [letter]. New Engl J Med 1994;330:789-90).

In 2000, 1,688 young people (ages 13 to 24) were reported with AIDS, bringing the cumulative total to 31,293 cases of AIDS in this age group. Among young men aged 13- to 24-years, 49% of all AIDS cases reported in 2000 were among men who have sex with men (MSM); 10% were among injection drug users (IDUs); and 9% were among young men infected heterosexually.

In 2000, among young women the same age, 45% of all AIDS cases reported were acquired heterosexually and 11% were acquired through injection drug use. Among both males and females in this age group, the proportion of cases with exposure risk not reported or identified (26% for males and 43% for females) will decrease and the proportion of cases attributed to sexual contact and injection drug use will increase as follow-up investigations are completed and cases are reclassified into these categories.

Surveillance data analyzed from 25 states with integrated HIV and AIDS reporting systems for the period between January 1996 and June 1999 indicate that young people (aged 13 to 24) accounted for a much greater proportion of HIV (13%) than AIDS cases (3%). These data also show that even though AIDS incidence (the number of new cases diagnosed during a given time period, usually a year) is declining, there has not been a comparable decline in the number of newly diagnosed HIV cases among youth.

Scientists believe that cases of HIV infection diagnosed among 13- to 24-year-olds are indicative of overall trends in HIV incidence (the number of new infections in a given time period, usually a year) because this age group has more recently initiated high-risk behaviors. Females made up nearly half (47%) of HIV cases in this age group reported from the 34 areas with confidential HIV reporting for adults and adolescents in 2000—and in young people between the ages of 13 and 19, a much greater proportion of HIV infections was reported among females (61%) than among males (39%). Cumulatively, young African Americans are most heavily affected, accounting for 56% of all HIV cases ever reported among 13- to 24-year-olds in these 34 areas. ["Young People at Risk: HIV/AIDS Among America’s Youth", ]

Early symptoms of AIDS may include an acute mononucleosis-like (severe flu-like) syndrome; however, many infected people have no symptoms. The incubation period  from exposure to manifestation of HIV has ranged from five days to three months or longer. A negative blood test for HIV in the first six months does not verify that a person is free from the virus. Also, many new strains of  non-HIV forms of AIDS are beginning to appear, forms for which no tests are  yet available.

Also, new reports detail that drug-resistant HIV is emerging at a worrisome rate, and that many HIV-infected people who now use the retroviral drugs are getting less value from them. 

Again, if STDs such as Herpes sores or HPV genital warts (or even chlamydia or gonorrhea) are already present, the HIV virus has a quick and easy route into the person's body through these infection sites and the chances of acquiring HIV are greatly increased.

Acquired Immune Deficiency Syndrome (AIDS) was first recognized in the 1980s. As of December 1996, nearly one million people with HIV were reported in the U.S. to the Centers for Disease Control. The number of deaths from AIDS at that time was over 581,400, about half the number of cases reported. The U.S. Public Health Service estimates that one million Americans are infected with HIV, the virus that causes AIDS. There have been 31,400 AIDS cases in young people under the age of 25, as of December 1996 (CDC, 12/96). Twenty-five percent (one in four) of all new diagnosed HIV infections are found in people under the age of 22 (MISH, 97).

According to the CDC HIV/AIDS Surveillance Report,  87 percent of those diagnosed with AIDS have been homosexual males and/or intravenous drug abusers (7/92). Other high risk groups include recipients of infected blood transfusions and women whose sexual partners are intravenous drug abusers or bisexual males.

Women infected with the HIV virus before or during pregnancy have about one chance in three of transmitting the HIV virus to the baby. There is no means to prevent this transmission (CDC, America Responds to AIDS), although certain drugs used during the pregnancy are showing promising results.



HIV Infection, Adult

By December 2003, all 50 states and the District of Columbia had implemented HIV surveillance systems, including both name-based and nonname-based systems. Since 2000, a total of 35 areas (33 states, Guam, and the U.S. Virgin Islands) have had laws or regulations requiring name-based confidential reporting for adults/adolescents with confirmed HIV infection, in addition to reporting of persons with AIDS. In 2002, CDC initiated a system to monitor HIV incidence; in 2003, CDC expanded this system and also initiated a national HIV behavioral surveillance system. CDC will assess the implementation and effectiveness of prevention activities through multiple monitoring systems, including use of new performance indicators for state and local health departments and community-based organizations (1).

At the end of 2004, a total of 209,937 adults and adolescents in the 35 areas
were living with HIV infection (not AIDS). Estimated prevalence of HIV infection (not AIDS) in this group was 136.7 per 100,000 population (2). In these areas, 2004 was the first year in which mature HIV surveillance data (i.e., available since at least 2000) could be used to allow for stabilization of data collection and for adjustment of the data in order to monitor trends. Data from additional areas will be included in analyses when >4 years of case reports have accrued.

CDC. Advancing HIV prevention: new strategies for a changing epidemic—United States, 2003. MMWR 2003;52:329–32.
CDC. HIV/AIDS surveillance report, 2004. Atlanta, GA: US Department of Health and Human Services, CDC; 2005. Available at [CDC, MMWR, June 16, 2006 / 53(53);1-79 Summary of Notifiable Diseases — United States, 2004]

HIV Infection, Pediatric

In the 35 areas (33 states, Guam, and the U.S. Virgin Islands) that have had laws or regulations since 2000 requiring confidential name-based reporting for children aged <13 years with confirmed HIV infection, an estimated 2,636 children were living with HIV infection (not AIDS) at the end of 2004. Estimated prevalence of HIV infection (not AIDS) in this group was 7.9 per 100,000 population (1).

CDC. HIV/AIDS surveillance report, 2004. Atlanta, GA: US Department of Health and Human Services, CDC, Vol. 16; 2005. Available at  
[CDC, MMWR, June 16, 2006 / 53(53);1-79 Summary of Notifiable Diseases — United States, 2004]


Racial/Ethnic Disparities in Diagnoses of HIV/AIDS

33 States, 2001–2005

During 2001–2004, blacks accounted for 51% of newly diagnosed human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) infections in the United States (1). This report updates HIV/AIDS diagnoses during 2001–2005 among black adults and adolescents and other racial/ethnic populations reported to CDC through June 2006 by 33 states† that had used confidential, name-based reporting of HIV and AIDS cases since at least 2001.

Of the estimated 184,991 adult and adolescent HIV infections diagnosed during 2001–2005, more (51%) occurred among blacks than among all other racial/ethnic populations combined. Most (62%) new HIV/AIDS diagnoses were among persons aged 25–44 years; in this age group, blacks accounted for 48% of new HIV/AIDS diagnoses. New interventions and mobilization of the broader community are needed to reduce the disproportionate impact of HIV/AIDS on blacks in the United States.

For this report, cases of HIV or AIDS were analyzed together as HIV/AIDS (i.e., HIV infection with or without AIDS) and counted by year of diagnosis. Cases were classified according to the following transmission categories: 1) male-to-male sexual contact (i.e., among men who have sex with men [MSM]); 2) injection-drug use (IDU); 3) MSM with IDU; 4) high-risk heterosexual contact (i.e., with a person of the opposite sex known to be HIV infected or at high risk for HIV/AIDS [e.g., MSM or injection-drug user]); and 5) other (e.g., hemophilia or blood transfusion) and all risk factors not reported or not identified…

Although adult and adolescent blacks accounted for 13% of the population in the 33 states during 2001–2005 (3), they accounted for 50.5% of the 184,991 new HIV/AIDS diagnoses; whites accounted for 72% of the population and 29.3% of diagnoses, and Hispanics accounted for 13% of the population and 18.2% of diagnoses. Among racial/ethnic populations, blacks accounted for the largest percentages of cases diagnosed in both males (43.9%) and females (67.2%) (Table 1).

During 2001–2005, blacks had the largest percentage of HIV/AIDS diagnoses in all age groups and in the IDU and high-risk heterosexual transmission categories (Table 1). Among men and women with IDU and persons with high-risk heterosexual contact, more than half were black (men: 53.8% and 65.7%, respectively; women: 58.8% and 69.5%, respectively). More MSM with HIV/AIDS diagnoses were white (42.7%), with smaller proportions of blacks (36.2%) and Hispanics (19.0%).

During 2001–2005, adults aged 25–44 years accounted for a majority of HIV/AIDS diagnoses regardless of racial/ethnic population (Table 1). Among persons aged 25–34 and 35–44 years, blacks accounted for the greatest proportion of cases (48.0% and 47.5%, respectively). By region,†† blacks accounted for the majority of diagnoses in the South (54.3%) and Northeast (52.0%) (Table 1). Black males accounted for more new HIV/AIDS diagnoses than males of any other racial/ethnic population in the South (47.5%) and Northeast (46.1%). Among females, blacks accounted for the majority of HIV/AIDS diagnoses in the South (71.5%), Northeast (64.4%), and Midwest (63.5%), compared with other racial/ethnic populations.

Among black males and females, the age distribution of persons who had HIV/AIDS diagnosed varied by transmission category (Table 2). By transmission category, most HIV/AIDS diagnoses of black male adults and adolescents were classified as MSM (30,154 [51.7%]), followed by high-risk heterosexual contact (14,698 [25.2%]), IDU (10,415 [17.9%]), MSM with IDU (2,698 [4.6%]), and other (322 [0.6%]). Most HIV/AIDS diagnoses among black female adults and adolescents were classified as high-risk heterosexual contact (28,283 [80.4%]), followed by IDU (6,412 [18.2%]), and other (465 [1.3%]) (Table 2).

In 2005, the estimated annual HIV/AIDS diagnosis rate among black males was 127.6 per 100,000 population and among black females was 61.4 per 100,000, both higher than the rates for all other racial/ethnic populations. Among males, the annual HIV/AIDS diagnosis black/white RR of 6.9 was higher than the Hispanic/white RR of 3.1. Among females, the black/white RR was 20.5, and the Hispanic/white RR was 5.4.

In 2005, overall estimated HIV (i.e., without AIDS) and AIDS prevalences were higher among blacks than among all other racial/ethnic populations. Among blacks, the estimated HIV prevalence (in 33 states) was 515 per 100,000 population, ranging from 109 (Alaska) to 858 (New Jersey); the estimated AIDS prevalence (in the 50 states and DC) was 639 per 100,000 population and ranged from 79 (Wyoming) to 3,179 (DC) (Table 3).

Reported by: T Durant, PhD, K McDavid, PhD, X Hu, MS, P Sullivan, DVM, PhD, R Janssen, MD, Div of HIV/AIDS Prevention; K Fenton, MD, PhD, Office of the Director, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (proposed), CDC.

Editorial Note:

During 2001–2005, HIV/AIDS diagnoses, diagnosis rates, and RRs were higher among black males and females than among any other racial/ethnic population in the United States. In 2005, the annual rates of HIV/AIDS diagnosis among black men and women were seven and 21 times higher than rates among white men and women, respectively. For black men, sexual contact with men was the primary mode of HIV infection; for black women, high-risk heterosexual contact was the primary mode. In a recent study of MSM in five cities, 46% of blacks were infected with HIV, compared with 21% of whites and 17% of Hispanics (4). In 2004, HIV/AIDS was the fourth-leading cause of death among blacks aged 25–44 years in the United States (5).

During 2001–2004, HIV diagnosis rates among black males and females declined by 4.4% and 6.8%, respectively (1). A 2007 study reported similar declines among blacks in Florida (6). These declines were observed among black heterosexuals and injection-drug users but not among MSM. Although these declines in rates of new HIV diagnoses are encouraging, they might not directly reflect trends in HIV incidence because they are also affected by changes in testing behavior and surveillance practices. Regardless of the trends, blacks remain disproportionately affected by high rates of HIV/AIDS…
 [March 9, 2007 / 56(09);189-193; MMWR Weekly, CDC; full report:]