Patients at Sexually Transmitted Disease Clinics

Because STD clinics provide comprehensive HIV prevalence data for MSM and high-risk heterosexual patients who attend these clinics, they are important sites for evaluating HIV prevention programs and for monitoring emerging patterns and trends in the HIV epidemic. These STD clinics, most of which are supported by state or local health departments, generally provide services to low-income patients in urban areas. They serve large numbers of persons at increased risk for HIV infection because the patients typically have engaged in unprotected sex or other high-risk behaviors, such as sex with multiple partners. Persons at the greatest risk of acquiring HIV infection sexually are also those at risk of acquiring other STDs; thus, surveys in STD clinics provide useful information on the sexual transmission of the HIV epidemic among high-risk persons.

Depending on the number of patients visiting a particular clinic, the survey period for data collection ranged from 6 weeks to 1 year. The survey included serum specimens from patients who had not visited the clinic either during the preceding 3 months (applies to data collected from 1993–1996) or since the current survey period (beginning in 1997) and who had blood drawn for routine clinical purposes other than HIV testing, usually for serologic syphilis testing. Through 1996, specimens were excluded from patients who attended the clinics for (1) follow-up visits for diseases that had been diagnosed during the current survey period, (2) HIV testing and counseling only, or (3) for treatment of HIV infection. Beginning in 1997, the eligibility criteria were modified to include specimens from all patients who had not previously attended the clinic during the current survey period and for whom a routine blood test was ordered. Specimens from clients who attended the clinics only for HIV testing were included if blood had been drawn at that visit for routine purposes other than for HIV testing.

Men whose medical records indicated that they had ever had homosexual or bisexual contact were classified as MSM. Men who were not classified as MSM and all women were classified as heterosexual. It is important to recognize that misclassification of even a few MSM as heterosexual men would probably increase the observed prevalence among the men classified as heterosexual.

Patients whose records indicated injection drug use were excluded from the analyses for MSM and heterosexual men and women so that we could better analyze the sexual transmission of HIV. Of course, misclassifying IDUs as persons who do not inject drugs would most likely increase the observed HIV prevalence among heterosexual patients and, to a lesser extent, among MSM.

To control for changing populations over time, we standardized data for the trends analyses to the 1993 STD clinic population by sex (for heterosexuals), region, race/ethnicity (black, Hispanic, white), and age group (<25 years, 25–34 years, and ≥35 years). Therefore, all HIV prevalence rates for the STD clinic trends analyses are presented as adjusted rates, standardized to the population of MSM or heterosexual men and women at the clinics in 1993.

This report includes only data from clinics that (1) collected data for each year of the 5-year survey and (2) reported at least 500 total eligible specimens or 200 eligible specimens from MSM collected during a survey period and tested according to CDC protocol. The criteria for inclusion in this report were met by 23 STD clinics in 13 metropolitan areas. From January 1993 through December 1997, serum specimens from 12,593 MSM and 198,861 heterosexual men and women were tested. Unadjusted HIV prevalence rates from STD clinics in all metropolitan areas combined for the 5-year survey period were 26% (range, 8%–39%) among MSM and 2.3% (range, 0.3%–5.5%) among heterosexual men and women (Table 2).

Men Who Have Sex With Men

Overall standardized HIV prevalence rates decreased among MSM at STD clinics from 32% in 1993 to 21% in 1997 (Figure 2). Although HIV prevalence was high among MSM in all regions, there were downward trends in the Northeast, the South, and the West. (Annual data for MSM in the Midwest are not included because the numbers of MSM tested per year were too small for meaningful analysis). In 1993, prevalence among MSM was 36% in the Northeast, 32% in the South, and 30% in the West. Prevalence in the same clinics in 1997 was 19% in the Northeast, 25% in the South, and 19% in the West (Figure 3).

Figure 2. HIV Prevalence Among Patients at Sexually Transmitted Disease Clinics, by Sexual Orientation, 1993–1997

Note. Standardized to 1993 STD clinic population by region, race/ethnicity, and age group.

Figure 3. HIV Prevalence Among Men Who Have Sex With Men at Sexually Transmitted Disease Clinics, 1993–1997

Note. Standardized to 1993 STD clinic population by race/ethnicity and age group. Midwest not included because of small numbers.

The highest observed prevalence of any group included in this report was among black MSM at STD clinics. The overall standardized prevalence for this group was stable at 42% to 44% from 1993 through 1995 and then decreased significantly to 29% in 1997. There was a downward trend for Hispanic MSM with rates decreasing from 30% in 1993 to 19% in 1997. Although prevalence rates were higher among Hispanic MSM than among white MSM for each of the 5 years, rates for the two groups were similar by 1997 (Figure 4).

Figure 4. HIV Prevalence Among Men Who Have Sex With Men at Sexually Transmitted Disease Clinics, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by region and age group.

Although overall HIV prevalence for white MSM decreased from 1993 to 1997, the trends varied among the 12 clinics with sufficient data for analysis by individual clinic. Although not statistically significant, prevalence rates were relatively stable in one of these clinics and tended to increase in one other clinic. For the remaining 10 clinics, prevalence declined (Appendix I). For the combined analysis, standardized HIV prevalence rates for white MSM decreased from 26% in 1993 to 17% in 1997 (Figure 4).

Prevalence was markedly higher among MSM who were 25 years of age or older than among those who were younger. However, there were downward trends among MSM in all age groups. Prevalence decreased among MSM who were 35 years of age or older, from 36% in 1993 to 26% in 1997, and decreased among those who were 25–34 years, from 34% in 1993 to 20% in 1997. Overall prevalence decreased from 16% in 1993 to 10% in 1997 among MSM who were under 25 years old (Figure 5).

Figure 5. HIV Prevalence Among Men Who Have Sex With Men at Sexually Transmitted Disease Clinics, by Age Group, 1993–1997

Note. Standardized to 1993 STD clinic population by region and race/ethnicity.

Heterosexual Men and Women

Overall unadjusted prevalence rates were less than 2% among women and less than 3% among heterosexual men at the participating STD clinics for each year of the 5-year survey period (Figure 2). Because the HIV prevalence rates and trends were similar for women (regardless of sexual orientation) and for heterosexual men, we included both populations in the analysis of heterosexual patients. There were strong regional variations in standardized HIV prevalence for this group: approximately 4% in the Northeast, 3% in the South, and 1% in the West and the Midwest. Prevalence decreased slightly over time in all regions (Figure 6).

Figure 6. HIV Prevalence Among Heterosexual Patients at Sexually Transmitted Disease Clinics, by Region, 1993–1997

Note. Standardized to 1993 STD clinic population by sex, race/ethnicity, and age group.

Prevalence among heterosexual patients at the STD clinics was highest among blacks, followed by Hispanics and whites. For black heterosexual patients, overall standardized prevalence was approximately stable at 2.9% from 1993–1995 and then decreased slightly to 2.4% in 1997. Rates for Hispanics increased slightly from 1.8% in 1993 to 2.1% in 1995 and then decreased to 1.5% in 1997. For whites, prevalence decreased from 1.7% in 1993 to 1.1% in 1994, remained approximately stable through 1996, and then decreased to 0.7% in 1997 (Figure 7).

Figure 7. HIV Prevalence Among Heterosexual Patients at Sexually Transmitted Disease Clinics, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by region, sex, and age group.

As was true of prevalence among MSM, prevalence among heterosexual clinic patients was much higher among patients who were 25 years of age or older than among those who were younger. Among heterosexual men and women who were at least 35 years old, prevalence ranged from 4.5% and 4.7% from 1993 through 1996 and then decreased to 3.6% in 1997. For those 25–34 years of age, prevalence was stable at 3.2% from 1993–1995 and then decreased to 2.6% in 1997. For those younger than 25 years, prevalence during the study period remained stable at less than 1% (Figure 8).

Figure 8. HIV Prevalence Among Heterosexual Patients at Sexually Transmitted Disease Clinics, by Age Group, 1993–1997

Note. Standardized to 1993 STD clinic population by region, sex, and race/ethnicity.

The data from the STD surveys probably resulted in overestimations of the prevalence of HIV among all MSM and all heterosexuals because these clinics serve persons whose sexual behavior has put them at high risk for exposure to various STDs, including HIV infection. In addition, the participating clinics may not have been representative of all STD clinics in the United States, and the patients of these public clinics may not be representative of all patients at STD clinics. Therefore, the HIV prevalence rates among the STD clinic patients in these surveys cannot be generalized to all MSM or to all heterosexual patients or even to all patients at STD clinics. In addition, some of the patients who were classified as heterosexual could have been MSM or IDUs who did not disclose these behaviors. Because the prevalence rates for patients classified as heterosexual could be greatly elevated if MSM or IDUs were misclassified, prevalence rates among heterosexual patients should be interpreted with caution.

Injection Drug Users Entering Drug Treatment Centers

The transmission of HIV infection associated with injection drug use occurs directly through the sharing of drug injection equipment or indirectly through sexual and perinatal transmission from HIV-infected IDUs. Drug users entering treatment, typically an older population than patients at STD clinics, are an easily accessible subgroup of drug users. Unlinked prevalence surveys make use of remnant serum specimens that are routinely obtained as part of the medical assessment.

The DTC unlinked prevalence surveys included specimens from eligible clients who (1) entered treatment for illicit drug use, including use of prescription drugs for nonprescribed purposes, at least once during the past 12 months and (2) had a routine blood test performed for clinical purposes other than for HIV testing. Persons for whom alcohol was the only drug used within the past 12 months were not eligible for the survey. Only specimens from eligible clients who reported ever having injected drugs were included in the analyses for this report. To control for changing populations over time, data for the trends analyses were standardized to the 1993 population of IDUs entering the participating DTCs by region, sex, race/ethnicity (black, Hispanic, white), and age group (20–29 years, 30–39 years, and ≥40 years).

Only the data from centers that collected at least 35 eligible specimens from IDUs for each year of the survey period were analyzed. Data from 22 DTCs in 14 metropolitan areas were included in this report. Most of the persons in the study population were seeking methadone treatment for heroin addiction. Of the 22 DTCs, 14 were primarily methadone maintenance or methadone detoxification centers, 5 were therapeutic community programs or drug-free programs, 2 offered methadone detoxification and drug-free programs, and 1 offered treatment for cocaine use.

During the study period, 36,584 eligible specimens from IDUs entering these 22 DTCs were tested according to CDC protocol. Overall unadjusted prevalence for male IDUs entering participating treatment centers in all metropolitan areas was 19%, ranging from 1% in Denver and Los Angeles to 36% in New York City; for female IDUs, unadjusted prevalence was 17%, ranging from 2% in Denver and Los Angeles to 37% in New York City (Table 3).

Prevalence among IDUs entering DTCs differed markedly by region. In 1993, HIV prevalence among these IDUs was 39% in the Northeast, 28% in the South, 10% in the Midwest, and 3% in the West. By 1997, standardized prevalence rates had decreased to 28% in the Northeast and 17% in the South. Prevalence rates in the Midwest and the West remained approximately stable (Figure 9).

Figure 9. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers, by Region, 1993–1997

Note. Standardized to 1993 STD clinic population by sex, race/ethnicity, and age group.

Overall prevalence was slightly higher among male IDUs than among female IDUs and declined for both groups during the study period. The 1993 prevalence rate for male IDUs was 22% in 1993 and 15% in 1997; for female IDUs, the rate was 18% in 1993 and 14% in 1997 (Figure 10).

Figure 10. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers, by Sex, 1993–1997

Note. Standardized to 1993 STD clinic population by region, race/ethnicity, and age group.

Among IDUs entering treatment, there was substantial regional variation in HIV prevalence by race/ethnicity. In the Northeast, prevalence was high among IDUs in each race/ethnicity group, particularly among blacks and Hispanics. Among black IDUs, standardized prevalence rates remained approximately stable from 1993 (46%) through 1997 (40%). Rates decreased steadily among Hispanic IDUs, from 44% in 1993 to 31% in 1997. Among white IDUs, rates decreased from 1993 (24%) through 1995 (13%) and then remained stable through 1997 (Figure 11).

Figure 11. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers in the Northeast, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by sex and age group.

HIV prevalence was also high among black and Hispanic IDUs in the South. For each year of the survey period, except 1996, prevalence was higher among Hispanics in the South than among blacks. Although rates among Hispanics decreased steadily, from 32% in 1993 to 18% in 1997, this decline was primarily the result of a significant decline in one DTC in San Juan. Among blacks, prevalence decreased from 25% in 1993 to 16% in 1995, increased to 24% in 1996, and then decreased to 16% in 1997. Rates among whites varied from 1993 through 1995 (between 3% and 8%) and then increased from 3% in 1995 to 11% in 1997 (Figure 12).

Figure 12. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers in the South, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by sex and age group.

In the Midwest, the highest prevalence for IDUs entering treatment was among Hispanics. Prevalence for this group was 32% in 1993, decreased to 19% in 1995, and then increased to 31% in 1997. These fluctuations are probably due to the small number of Hispanics who attended the participating DTCs in the Midwest. Prevalence among black IDUs in the Midwest increased from 9% in 1993 to 14% in 1995 and then decreased to 9% in 1997. Among white IDUs, prevalence was relatively stable at 5% to 8% through 1996 and then decreased from 8% in 1996 to 4% in 1997 (Figure 13).

Figure 13. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers in the Midwest, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by sex and age group.

In the West, prevalence among IDUs entering treatment was substantially higher for blacks than for Hispanics or whites. Prevalence among black IDUs was stable at 10% to 13% for the 5-year period. Rates among Hispanic IDUs and white IDUs in the West were stable at 2% or less for each year (Figure 14).

Figure 14. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers in the West, by Race/Ethnicity, 1993–1997

Note. Standardized to 1993 STD clinic population by sex and age group.

HIV prevalence was higher among IDUs who were 30 years of age or older than among those who were younger. Among IDUs who were at least 40 years old, prevalence declined slightly, from 20% in 1993 to 17% in 1997. For those who were 30–39 years old, prevalence decreased from 23% in 1993 to 15% in 1997. For those who were 20–29 years old, prevalence decreased from 15% in 1993 to 7% in 1997 (Figure 15).

Figure 15. HIV Prevalence Among Injection Drug Users Entering Drug Treatment Centers, by Age Group, 1993–1997

Note. Standardized to 1993 STD clinic population by region, sex, and race/ethnicity.

The prevalence rates obtained from this survey may not represent HIV infection rates for all IDUs entering treatment programs, and they may not reflect HIV prevalence among IDUs who were not in treatment. Nearly all of the IDUs in the surveys were in treatment for heroin addiction; therefore, results cannot be generalized to IDUs who inject other drugs. Although the populations of IDUs in treatment and IDUs not in treatment overlap at any given time, drug use and sexual risk behaviors in these two groups may differ. A comparison of IDUs entering DTCs and IDUs at STD clinics in seven metropolitan areas shows that, in general, HIV prevalence is higher among the IDUs in drug treatment (Table 5). Because DTCs are likely to serve an older population of IDUs whose drug use has been consistent and long-term, the DTC population is more likely to be HIV-positive, especially in cities where HIV prevalence among IDUs is high.

Go to Youth Populations