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Heterosexual Transmission of HIV -- Puerto Rico, 1981-1991

Puerto Rico has the second highest overall rate of acquired immunodeficiency syndrome (AIDS) cases among states and territories of the United States and the second highest rate of cases among women (1,2). Although heterosexual transmission of human immunodeficiency virus (HIV) among persons reported with AIDS has increased throughout the United States -- accounting for 8% of all U.S. AIDS cases diagnosed in 1991 (2,3) -- the proportion of cases attributed to heterosexual transmission is highest in Puerto Rico (18%). This report summarizes data collected through the Puerto Rico AIDS Surveillance Program to characterize AIDS cases associated with heterosexual transmission during 1981-1991.

In Puerto Rico, AIDS case reporting includes the collection of data on behavioral and other risk factors for HIV exposure. A standard report form is completed by trained data abstractors and used to identify HIV-transmission categories. Persons with multiple exposure risks for HIV are assigned a probable mode of transmission using a standard hierarchy (4).

From 1981 through 1991, 7080 AIDS cases were reported in Puerto Rico residents aged greater than or equal to 13 years, including 1266 AIDS cases diagnosed and reported in 1991, for an annual incidence rate of 50.9 cases per 100,000 population. Of the total cases, 5782 (82%) occurred among males. Overall Patterns of Transmission

The primary mode of transmission for HIV in Puerto Rico was injecting-drug use (IDU), which was reported for 4639 (66%) of all cases among adults reported since 1981; 546 (8%) cases among adults were attributed to heterosexual contact with an injecting-drug user. Of all cases among adults, heterosexual transmission accounted for 11% and male-male transmission for 18%. *

The proportion of AIDS cases attributed to IDU declined from 70% before 1988 to 59% in 1991, and the proportion of cases attributed to heterosexual transmission increased from 5% to 18%. Of the 798 cases of AIDS attributed to heterosexual transmission since 1981, 546 (68%) occurred among persons who reported heterosexual contact with an injecting-drug user. Heterosexual Transmission

Overall, 553 (69%) AIDS cases attributed to heterosexual transmission were among women. Before 1988, the proportion of cases among women attributed to IDU (61%) was greater than that attributed to heterosexual transmission (28%). In 1991, however, 58% of AIDS cases among women were attributed to heterosexual transmission, and 39%, to IDU. In comparison, in the United States, heterosexual transmission accounted for 37% and IDU, for 48%. Among the 1268 women with AIDS in Puerto Rico, heterosexual contact with an injecting-drug user accounted for 423 (76%) of 553 cases attributed to heterosexual transmission. In addition, 105 (19%) cases among women were attributed to heterosexual contact with a person known to have been infected with HIV but who had no specified mode of HIV exposure.

Heterosexual transmission was less frequent among men with AIDS and accounted for 81 (8%) of 993 cases in 1991, compared with less than 1% before 1988. In 1991, heterosexual HIV transmission ranked far behind IDU (64% of all cases among men) and male-male sexual transmission (24% of all cases among men). Among all men with AIDS aged less than 40 years, approximately 2% were infected through heterosexual contact, compared with 9% among men aged greater than or equal to 40 years. The proportion of cases attributed to heterosexual transmission increased among men aged greater than or equal to 40 years from 2% before 1988 to 16% in 1991 and among men aged less than 40 years from 0.4% to 4%. Multiple Modes of Transmission

A substantial proportion of injecting-drug users reported high-risk sexual behavior: since 1981, 16% of all men with AIDS who reported IDU also reported having had sex with men. Among all persons with AIDS who reported IDU, 42% of women and 27% of heterosexual men also reported having had sex with another injecting-drug user or sex with someone known to have HIV infection or AIDS.

Reported by: S Martinez, MD, Central Office of AIDS Affairs and Communicable Diseases; J Rullan, MD, Commonwealth Epidemiologist, Puerto Rico Dept of Health. Div of Field Epidemiology, Epidemiology Program Office; Div of HIV/AIDS, National Center for Infectious Diseases; National Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Because of a high rate of AIDS and a substantial proportion of AIDS cases attributed to heterosexual contact, the epidemiologic profile of AIDS in Puerto Rico appears to be similar to that in Caribbean countries (5,6). However, the marked prevalence of IDU among persons with AIDS in Puerto Rico distinguishes it from other areas of the Caribbean.

In states with high proportions of IDU cases, such as New Jersey and Florida, the proportion of cases attributed to heterosexual transmission is as high as 16%. In some countries with high rates of IDU associated with HIV infection, such as Italy and Spain, increases in heterosexual transmission have also occurred (7).

The findings in this report indicate that, in Puerto Rico, the proportion of cases attributed to heterosexual transmission is increasing among men. These findings are consistent with an evolving pattern of the HIV/AIDS epidemic: the epidemic was initially characterized by transmission associated primarily with IDU and male-male sex. Transmission was subsequently propagated through heterosexual relations, and more women became infected. Finally, a substantial proportion of men with AIDS are becoming infected through sex with infected women.

Many persons with AIDS have multiple HIV-exposure risks, and it is often not possible to ascertain the specific mode of viral transmission. Consequently, more cases may be due to heterosexual transmission than are documented. Conversely, overestimation of the rate of heterosexual transmission among men may result from mis-classification of men who do not acknowledge having had sex with men or IDU (8).

The findings in this report underscore that efforts to prevent the spread of HIV infection in Puerto Rico should target injecting-drug users and their sex partners. Using combined local and federal funds to achieve this goal, the Puerto Rico Department of Health has implemented outreach programs in areas with a high prevalence of drug use. These programs have been instituted throughout the commonwealth and frequently use resources and personnel from community-based organizations to educate persons at risk regarding prevention of HIV transmission and risk reduction. As part of these outreach programs, former addicts now serve as peer educators to teach methods for safer sexual practice, refer for treatment, discourage needle sharing, and teach needle hygiene.


  1. CDC. HIV/AIDS surveillance report. Atlanta: US Department of Health and Human Services, Public Health Service, January 1992:1-18.

  2. CDC. Update: acquired immunodeficiency syndrome -- United States, 1981-1990. MMWR 1991; 40:358-63,369.

  3. Holmes KK, Karon JM, Kreiss J. The increasing frequency of heterosexually acquired AIDS in the United States, 1983-88. Am J Public Health 1990;80:858-63.

  4. CDC. AIDS reporting system user guide, version 5.0 B. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1992.

  5. Quinn TC, Narain JP, Zacarias FRK. AIDS in the Americas: a public health priority for the region. AIDS 1990;4:709-24.

  6. Piot P, Plummer FA, Mhalu FS, Lamboray J, Chin J, Mann J. AIDS: an international perspective. Science 1988;239:573-9.

  7. World Health Organization. Acquired immunodeficiency syndrome (AIDS): WHO European Region -- update to 30 September 1990. Wkly Epidemiol Rec 1991;6:33-40.

  8. CDC. Update: heterosexual transmission of acquired immunodeficiency syndrome and human immunodeficiency virus infection -- United States. MMWR 1989;38:423- 4,429-34.

    • For this report, IDU is considered the primary mode of transmission among the 628 persons reporting both male-male sex and IDU (9% of all AIDS cases among adults in Puerto Rico).

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