Epidemiology

Update on the Epidemiology of HIV/AIDS in the United States

Michael Campsmith, DDS, MPH

Copyright 2001 Journal of the California Dental Association.

During the past 20 years, the epidemic of human immunodeficiency virus and acquired immunodeficiency syndrome in the United States has continually evolved. Beginning in the mid-1990s, the numbers of annual AIDS cases and AIDS deaths have decreased, due in large measure to effective combination anti-retroviral therapies, which prolong the survival of people infected with HIV and delay progression to AIDS. This has resulted in an increase in the number of people living with HIV infection or AIDS. Increasing proportions of AIDS cases are occurring among women, racial/ethnic minorities, and people infected through heterosexual transmission. Dental care professionals are faced with the challenge of providing quality dental care to this ever-increasing population.

In the two decades since the initial reports of opportunistic infections in previously healthy young men,^1,2 it has become clear that the epidemic of acquired immunodeficiency syndrome in the United States actually consists of many smaller epidemics, each with its own dynamic characteristics. First thought to affect only homosexual men, the epidemic was soon found to occur in other populations, including injection drug users,³ hemophiliacs,⁴ heterosexuals,⁵ and children born to infected mothers.⁶ AIDS is the end stage of a disease syndrome that begins with infection with human immunodeficiency virus. People infected with HIV can remain asymptomatic for varying lengths of time before developing the severe immune cell suppression and opportunistic infections that currently define a diagnosis of AIDS.⁷

Although a number of anti-retroviral agents to treat HIV have been identified, at present there is no cure for HIV or AIDS. However, in the mid-1990s, combination anti-retroviral regimens including a protease inhibitor (termed highly active anti-retroviral therapy, or HAART) began to show promise for treating HIV infection. Due in large part to these treatment advances, there has been a sharp decline in annual deaths due to AIDS and, to a lesser extent, new cases of AIDS, since 1996. Longer survival of HIV-infected persons has resulted in an increase in the number of people living with HIV and AIDS.

This paper provides an update on the epidemiology of HIV and AIDS from 1996 through 1999. Data are provided on the overall demographic profile of HIV and AIDS in the United States, as well as data specific for California.

Surveillance of AIDS in the United States

Health departments in all 50 states, the District of Columbia, and U.S. dependencies (including Puerto Rico and the U.S. Virgin Islands) collect data on cases of AIDS using a uniform case definition and report form. These data are forwarded, without personal identifiers, to the Centers for Disease Control and Prevention. Surveillance data are used at the local, state, and national levels to estimate the size and scope of the epidemic, identify populations at risk, and direct resource allocation. The AIDS reporting criteria have been periodically revised as new knowledge on HIV disease and its medical treatment has been discovered. Revisions to the original case definition occurred early in the epidemic, first in 1985,⁸ and again in 1987.⁹ A more significant change in the case definition came in 1993, when laboratory markers of severe immune suppression (CD4+ T-lymphocyte count of less than 200 cells/F l or percent of total lymphocytes of less than 14) were also used to define cases of AIDS.¹⁰ Severe immunosuppression occurs at an earlier stage of disease than do most AIDS-defining opportunistic infections. Thus, this expanded case definition created a large increase in the reported number of AIDS cases (Figure 1), as prevalent as well as incident cases were reported. The AIDS epidemic curve (Figure 1) illustrates the rapid spread of AIDS in the 1980s, a peak in 1993 associated with the expanded case definition, and then declining incidence as the effect of the expanded definition waned. From 1996 on, the annual incidence of AIDS and deaths among people with AIDS declines. These declines are primarily attributed to the use of combination anti-retroviral therapy, which delays progression of HIV infection to AIDS and death.^11-13

The Epidemiology of AIDS

Through the end of 1999, a total of 733,374 cases of AIDS had been reported to the CDC.¹⁴ Overall, 82 percent of reported AIDS cases have occurred in men and 17 percent in women; 1 percent of AIDS cases have been reported in children younger than 13. Classified by race/ethnicity, 43 percent of all AIDS cases have occurred in whites, 37 percent in blacks, 18 percent in Hispanics, and less than 1 percent each in Asian/Pacific Islanders and American Indians/Alaska natives. Mode of exposure to HIV is classified according to a hierarchical scheme; to date among people 13 and older, 47 percent of AIDS cases have been reported in men who have sex with men, 25 percent in injection drug users, 10 percent in people infected through heterosexual contact, and 2 percent infected through contaminated blood or blood products.

These cumulative figures help to define the magnitude of the AIDS epidemic in the United States. However, the burden of AIDS is not distributed equally among the population. Analysis of recent trends helps to more clearly define where the epidemic may be heading and which groups are most at risk.

Recent Trends

Adults and Adolescents (13 and older)

Men

Among all adults and adolescents in the United States with a diagnosis of AIDS, most have been men. Through June 1999, an estimated 610,134 cases of AIDS had been diagnosed among adult and adolescent men; of these an estimated 243,118 were still living.¹⁵ The proportion of new AIDS cases diagnosed among men has decreased in recent years (Table 1). Throughout the 1980s, the majority of cases were diagnosed in white men. However, black and Hispanic men have been disproportionately affected by AIDS, and this racial disparity has increased in recent years. In 1998 blacks accounted for 11 percent of the U.S. male population and Hispanics accounted for 10 percent. From January 1996 through June 1999, an estimated 42 percent of men diagnosed with AIDS were black and 20 percent were Hispanic (Asian/Pacific Islander men accounted for approximately 1 percent of recent AIDS cases, with less than 1 percent among Native American/Alaska native men). While the number of AIDS cases reported in 1999 was similar for white and black men, the case rate for black men was nearly eight times higher than for white men (125/100,000 vs. 16/100,000) (Table 2). The rate for Hispanic men was more than three times higher than for white men; rates for Asian/Pacific Islander men and Native American/Alaska Native men were similar to rates for white men.

Although the main HIV exposure risk for men has been and continues to be male-to-male sexual contact, recent estimates show this mode of transmission to be declining. Among AIDS cases diagnosed from July 1998 through June 1999, it is estimated that the proportion of cases among men who have sex with men has decreased to 53 percent. At the same time, the proportions attributed to injection drug use and heterosexual contact have increased to 27 percent and 13 percent, respectively (data adjusted for reporting delays and estimated proportional redistribution of cases initially reported without risk).¹⁵

Women

Through June 1999, an estimated 121,528 cases of AIDS had been diagnosed among adult and adolescent women in the United States.¹⁵ Of these, an estimated 61,203 were still living. The proportion of AIDS cases diagnosed among women has steadily increased, from 7 percent in 1985 to 13 percent in 1990 to 23 percent in 1999. As with men, black and Hispanic women are disproportionately affected by AIDS. Among recent AIDS cases in women, an estimated 62 percent have occurred in black women and 19 percent have occurred in Hispanic women (blacks represented 12 percent of the 1998 U.S. female population; Hispanics represented 10 percent). Similar to the pattern in men, in 1999 the AIDS case rates for black and Hispanic women were higher than the rate for white women; however, the disparities were even more pronounced. Black women had a case rate nearly 25 times higher than for white women, with Hispanic women having a case rate more than seven times higher than for white women (Table 3).

Through 1992, the predominant HIV exposure risk among women with AIDS was injection drug use, accounting for more than half of all cases. This has shifted in recent years, as heterosexual contact has now become the primary mode of HIV exposure for U.S. women. Among cases of AIDS diagnosed in women from July 1998 through June 1999, an estimated 62 percent were attributed to heterosexual contact and 36 percent to injection drug use.

Infants and Children

Through June 1999, an estimated 8,782 AIDS cases have been diagnosed among infants and children younger than 13. Of these, an estimated 3,681 infants and children with AIDS were still living. Ninety-two percent of these cases had been infected through perinatal transmission from an HIV-infected mother.

Perinatally acquired AIDS declined sharply in the 1990s as a result of the rapid implementation of the Public Health Service guidelines on the use of zidovudine (AZT) to reduce perinatal HIV transmission, as demonstrated in AIDS Clinical Trial 076.¹⁶ Efforts to further reduce -- and perhaps one day eliminate -- perinatal HIV transmission include educating health care providers about the importance of offering voluntary HIV counseling and testing to all pregnant women, public information campaigns regarding prevention of perinatal HIV infection, and intensifying outreach to increase prenatal care among high-risk women.

The Changing HIV/AIDS Epidemic in California

California was one of the first states in which a new syndrome of acquired immune deficiency was initially reported in 1981.¹ Through the end of 1999, the cumulative number of AIDS cases reported by the California Office of AIDS was 115,324.¹⁷ This number represents more than 16 percent of all cases reported in the United States since the start of the AIDS epidemic (second only to New York, with more than 18 percent of all AIDS cases). California has had a substantially larger cumulative proportion of AIDS cases among men who have sex with men compared to the rest of the United States (71 percent vs. 47 percent). Mirroring the U.S. trend, the proportion of AIDS cases in California among men who have sex with men has been decreasing in recent years, from 86 percent in 1990 down to 57 percent in 1999. Concurrently, the proportions due to injection drug use and heterosexual contact have increased to 13 percent and 8 percent, respectively (from 6 percent and 3 percent in 1990). Similarly to national trends, in California the proportion of recent AIDS cases among women continues to rise, accounting for 12 percent of AIDS cases reported in 1999 (up from 5 percent in 1990).

AIDS in California disproportionately affects some minority populations. Although whites still make up the largest proportion of cumulative AIDS cases (61 percent), their proportion of recent cases has been steadily declining. Among California AIDS cases diagnosed in 1998, 44 percent were in whites, 23 percent in blacks, 30 percent in Hispanics, 3 percent in Asian/Pacific Islanders and less than 1 percent in Native American/Alaska natives.¹⁸ (Although the overall proportion of cases among Native American/Alaska natives is low, approximately 25 percent of all cumulative AIDS cases in Native Americans have been reported in California.¹⁹) The number of AIDS cases diagnosed in California in 1998 and estimated incidence rates by race are shown in Table 4.

For men of all races in California, the main exposure risk continues to be male-to-male sexual contact. Among AIDS cases diagnosed in men in 1998, 65 percent were in men who have sex with men and 12 percent in injection drug users. These proportions differ by race as shown in Table 5. Among women, the trend has been toward an increasing proportion of cases attributed to heterosexual contact. For cases diagnosed in women in 1998, the main exposure modes were heterosexual contact (47 percent) and injection drug use (32 percent). As with men, these proportions differed by race (Table 5).

Estimates of HIV/AIDS Prevalence and Incidence

CDC estimates that the prevalence of HIV infection (people diagnosed with HIV or AIDS as well as those who are infected but not yet diagnosed) in the United States at the end of 1998 was between 800,000 and 900,000 infected people.²⁰ The California Office of AIDS estimates the number of people living with HIV or AIDS in California on Jan. 1, 1996, to have been between 94,300 and 130,500.²¹

The CDC estimates that approximately 40,000 people in the United States are becoming infected with HIV each year;^20,22 of these new infections, approximately 28,000 are in men and 12,000 are in women. Among newly infected men, approximately 50 percent are black, 30 percent are white, and 20 percent are Hispanic. An estimated 60 percent of new HIV infections in men are acquired through male-to-male sexual contact, 25 percent through injection drug use, and 15 percent through heterosexual contact. Among newly infected women, approximately 64 percent are black, 18 percent are white, and 18 percent are Hispanic. An estimated 75 percent of all new HIV infections in women are acquired through heterosexual contact and 25 percent through injection drug use.

Summary

Data from the HIV/AIDS surveillance system in the United States have revealed these highlights about the current state of the epidemic:

* Men still account for the largest proportion of people with HIV and AIDS, but women account for an increasing proportion of infected people. Women accounted for 12 percent of AIDS cases reported in California in 1999.

* Racial/ethnic disparities among people with HIV and AIDS continue to increase. Among men with a recent AIDS diagnosis, 62 percent were black or Hispanic; among women, 81 percent were black or Hispanic. Among men in California receiving an AIDS diagnosis in 1998, 51 percent were black or Hispanic; among women, 67 percent were black or Hispanic.

* The proportion of AIDS cases attributed to heterosexual contact continues to increase, accounting for 22 percent of all recently diagnosed cases (11 percent of cases among men and 59 percent of cases among women). Cases attributed to heterosexual contact accounted for 9 percent of AIDS cases diagnosed in California in 1998 (4 percent among men and 47 percent among women).

* Similarly, injection drug use accounts for an increasing proportion of recently diagnosed AIDS cases, with 30 percent attributed to injection drug use (27 percent of cases among men and 38 percent of cases among women). Cases attributed to injection drug use accounted for 14 percent of AIDS cases diagnosed in California in 1998 (12 percent among men and 32 percent among women).

* Perinatally acquired AIDS has declined significantly, due primarily to use of AZT.

Because of treatment advances, the number of HIV-infected people developing AIDS and dying from the disease has declined. However, the rate of new HIV infections has remained stable, with the result being more people living with HIV and AIDS every year.

In an era when effective prevention and treatment interventions are available, the HIV/AIDS epidemic will continue to evolve. Dental care professionals need to keep abreast of current recommendations for infection control practices and apply these in the treatment of all patients.^23,24

Author

Michael Campsmith, DDS, MPH, works in the Division of HIV/AIDS Prevention, National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention in Atlanta, Ga.

References

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2. Gottlieb MS, Schroff R, et al, Pneumocystis carinii pneumonia and mucosal candidiasis in previously healthy homosexual men. N Engl J Med 305:1425-31, 1981.

3. Masur H, Michelis MA, et al, An outbreak of community acquired Pneumocystis carinii pneumonia -- initial manifestation of cellular immune dysfunction. N Engl J Med 305:1431-8, 1981.

4. Davis KC, Horsburgh Jr CR, et al, Acquired immunodeficiency syndrome in a patient with hemophilia. Ann Intern Med 98:284-6, 1983.

5. Centers for Disease Control and Prevention, Epidemiologic notes and reports update on Kaposi’s sarcoma and opportunistic infections in previously healthy people -- United States. Morb Mortality Wkly Rep 31:294, 300-1, 1982.

6. Centers for Disease Control and Prevention, Unexplained immunodeficiency and opportunistic infections in infants -- New Your, New Jersey, California. Morb Mortality Wkly Rep 31:665-7, 1982.

7. Levy JA, HIV and the Pathogenesis of AIDS, 2nd ed. ASM Press, Washington, DC, pp 401-3, 1998.

8. Centers for Disease Control and Prevention, Revision of the case definition of acquired immunodeficiency syndrome for national reporting -- United States. Morb Mortality Wkly Rep 34:373-5, 1985.

9. Centers for Disease Control and Prevention, Revision of the CDC surveillance case definition for acquired immunodeficiency syndrome. Morb Mortality Wkly Rep 36:1-15S, 1987.

10. Centers for Disease Control and Prevention, 1993 revised classification system for HIV infection and expanded surveillance case definition for AIDS among adolescents and adults. Morb Mortality Wkly Rep 41(RR-17):1-19, 1993.

11. Hammer SM, Squires KE, et al, A controlled trial of two nucleoside analogues plus indinavir in persons with human immunodeficiency virus infection and CD4 cell counts of 200 per cubic millimeter or less. N Engl J Med 337:725-33, 1997.

12. Fleming PL, Ward JW, et al, Declines in AIDS incidence and deaths in the USA: a signal change in the epidemic. AIDS 12:S55-S61, 1998.

13. McNaghten AD, Hanson DL, et al, Effects of antiretroviral therapy and opportunistic illness primary chemoprophylaxis on survival after AIDS diagnosis. AIDS 13:1687-95, 1999.

14. Centers for Disease Control and Prevention, HIV/AIDS Surveillance Report 11(No.2):1-44, Centers for Disease Control and Prevention, Atlanta, Ga, 1999.

15. Centers for Disease Control and Prevention, HIV/AIDS Surveillance Update 1(No.1):1-48, Centers for Disease Control and Prevention, Atlanta, Ga, 2000.

16. Centers for Disease Control and Prevention, Recommendations of the U.S. Public Health service task force on the use of zidovudine to reduce perinatal transmission of human immunodeficiency virus. Morb Mortality Wkly Rep 43(RR11):1-20, 1994.

17. California Department of Health Services, Office of AIDS, California and the HIV/AIDS Epidemic -- The State of the State Report, 1999. 1-11, California Department of Health Services, Office of AIDS: Sacramento, Calif, 2000.

18. California Department of Health Services, Office of AIDS, HIV/AIDS Among Racial/Ethnic Groups in California, 1999. 1-82, California Department of Health Services, Office of AIDS: Sacramento, Calif, 2000.

19. Centers for Disease Control and Prevention. HIV/AIDS among American Indians and Alaskan Natives -- United States, 1981-1997. Morb Mortality Wkly Rep 47:154-160, 1998.

20. Centers for Disease Control and Prevention, Guidelines for national human immunodeficiency virus case surveillance, including monitoring for human immunodeficiency virus infection and acquired immunodeficiency syndrome. Morb Mortality Wkly Rep 48(No. RR-11), 1999.

21. Tabnak F, Johnson, HIV prevalence estimates for California, 1996. California HIV/AIDS Update 10(1)1-7, 1997.

22. Rosenberg PS, Biggar RJ, Trends in HIV incidence among young adults in the United States. JAMA 279:1894-1899, 1998.

23. Centers for Disease Control and Prevention, Recommended infection-control practices for dentistry. Morb Mortality Wkly Rep 42(No. RR-8), 1993.

24. Department of Labor, Occupational Safety and Health Administration, 29 CFR Part 1910.1030, occupational exposure to bloodborne pathogens; final rule. Federal Register 56:64004-64182, 1991.

To request a printed copy of this article, please contact, Michael Campsmith, DDS, MPH, Centers for Disease Control and Prevention, Mailstop E-47, 1600 Clifton Road NE, Atlanta, GA 30333 or Mcampsmith@cdc.gov.

Figure 1.

Table 1. Estimated AIDS Incidence* Among Adults and Adolescents, United States, by Sex, Through June 1999

*Data adjusted for reporting delays.

**Includes 3 cases among people for whom sex was unknown because of missing information.

Table 2. AIDS Cases in Adult/Adolescent Men by Race/Ethnicity, United States, Reported in 1999

* Includes 98 men whose race/ethnicity is unknown.

Table 3. AIDS Cases in Adult/Adolescent Women by Race/Ethnicity, United States, Reported in 1999

* Includes 21 women whose race/ethnicity is unknown.

Table 4. AIDS Cases in California Diagnosed in 1998, by Race/Ethnicity

Table 5. Risk Distribution Among AIDS Cases Diagnosed in California in 1998, by Race and Sex

* Number of cases diagnosed in 1998 was too small to accurately estimate rates.

MSM = men who have sex with men
IDU = injection drug use