1 Division of HIV/AIDS Prevention, Surveillance, and Epidemiology, National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA.
2 Glades Health Initiative, Inc., Belle Glade, FL.
3 Department of Medicine, Dartmouth-Hitchcock Medical Center, Lebanon, NH.
4 Florida Department of Health, Tallahassee, FL.
5 Palm Beach County Health Department, Belle Glade, FL.
6 Department of Epidemiology, School of Public Health, Boston University, Boston, MA.
Received for publication September 23, 2003; accepted for publication April 6, 2004.
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ABSTRACT |
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acquired immunodeficiency syndrome; crack cocaine; HIV; HIV infections; risk factors; sexual behavior; sexually transmitted diseases
Abbreviations: Abbreviations: AIDS, acquired immunodeficiency syndrome; CI, confidence interval; HIV, human immunodeficiency virus.
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INTRODUCTION |
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The economy of western Palm Beach County, Florida, is predominantly agricultural, with sugar cane being the major crop. In 1986, a population-based study in Belle Glade, a rural community in western Palm Beach County, found that the prevalence of HIV infection was 28/877 (3.2 percent, 95 percent confidence interval (CI): 2.0, 4.4) (11). Independent predictors of HIV infection in men included a history of sexually transmitted diseases and sex with men, while independent predictors in women included a positive rapid plasma reagin test and microhemagglutination-Treponema pallidum test and having a male sex partner known to engage in sex with prostitutes. This was the first community in the United States in which heterosexual contact was identified as the predominant route of HIV transmission.
Beginning in 1987, an HIV prevention program was implemented in this community by the Palm Beach County Health Department, the Florida Department of Health, and the Centers for Disease Control and Prevention, in collaboration with local community-based organizations (12). Therefore, in 19982000, we performed a second population-based survey and a case-control study to determine HIV prevalence and risk factors and to compare them with the results from the 1986 survey.
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MATERIALS AND METHODS |
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The protocol was approved by the human subjects committees of the Florida Department of Health, Emory University, Boston University, Dartmouth Medical School, and the Centers for Disease Control and Prevention. At addresses that were households, one person was selected by means of a random selection table. Houses in which no one was found were visited at least six times during the survey period, including at least twice in the evening or on the weekend, before being categorized as unoccupied. After giving informed consent, each participant was administered a questionnaire in English, Spanish, or Haitian Creole by a trained interviewer, received pretest counseling, had blood drawn for HIV and syphilis serologic analysis, and was given a tuberculin skin test. Children aged 1217 years and their parents or legal guardians were asked to sign consent forms for the survey, and these adolescents were also asked to sign a second consent form for HIV testing and an assent form. Parents of children aged 11 years were asked to sign consent forms for a pediatric questionnaire and HIV testing, and children aged 811 years were asked to sign consent and assent forms. Children under the age of 1 year were excluded from the survey, as were persons with a history of blistering upon prior tuberculin skin testing.
Blood specimens were tested for HIV by means of enzyme immunoassay, and positive results on enzyme immunoassay were confirmed by Western blot. Serologic testing for syphilis included the rapid plasma reagin test and either the microhemagglutination assay or the fluorescent treponemal antibody-absorption test. HIV test results were given with posttest counseling 23 weeks after blood was obtained. Participants who tested positive for HIV or syphilis were referred to the local health clinic or private practitioners for treatment and care.
Case-control study
All HIV-infected residents of the community were also invited to enroll in a case-control study and were evaluated according to the same protocol as that used in the population-based study. These self-identified HIV-infected participants were identified by advertising in local media and by contacting local HIV/AIDS service organizations and care providers. Most of these participants were referred to the study staff from the local health clinic, by private practitioners, or by local HIV service agencies. To examine risk factors for HIV infection, we combined these 210 persons with the seven HIV-infected persons identified in the survey and compared them with the HIV-uninfected persons in the population-based survey. Because there were no cases of HIV infection among children, the case-control analysis was restricted to adults.
Statistical methods
Statistical associations between HIV serostatus and categorical variables were tested by means of the chi-squared test or Fishers exact test. Ninety-five percent confidence intervals were calculated using a normal approximation of the binomial distribution. All tests of statistical significance were two-sided. Age and gender adjustment of HIV rates was carried out using the population distribution of the 2000 US Census (13). Associations with continuous variables were analyzed by means of the Wilcoxon rank-sum test. Variables that were associated with HIV infection were then analyzed by stepwise logistic regression using SAS, version 8.0 (SAS Institute, Inc., Cary, North Carolina). Attributable fractions and population attributable fractions were calculated as described by Rothman and Greenland (14), substituting odds ratios for risk ratios.
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RESULTS |
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DISCUSSION |
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Interpreting changes in HIV prevalence over time requires estimation of in- and out-migration of persons with HIV infection, as well as new acquisition of HIV infection and deaths among persons with HIV. When mechanized harvesting of sugar cane was introduced in the late 1980s, a decline in the importation of non-US-born laborers (largely Caribbean) began, and few such workers have come to the area since the early 1990s. Such persons were not likely to have imported HIV infection from outside the area, since they were screened for HIV infection prior to coming to the United States and were denied entry if found to be HIV-infected. In addition, the lack of economic resources in this population makes it unlikely that HIV-infected persons moved away from the area to obtain medical care or social services. Moreover, between 1986 and 1998, the overall number of persons living in the area remained stable (13). Therefore, the observed changes are not likely to have been caused by in- or out-migration.
A persisting cohort of HIV-infected persons from 1986 is suggested by the greater age of HIV-infected persons in 19982000 as compared with those studied in 1986. However, it is clear that the HIV epidemic in this area began well before 1986, since a large number of AIDS cases had already appeared by that time. The survival of those persons identified as having HIV in the 1986 survey can be expected to be similar to that of HIV-infected persons from other areas with high AIDS rates in 1986; such persons had only 4245 percent survival through 1995 (15). Survival to 19982000 among persons with HIV infection in 1986 in western Palm Beach County is likely to have been substantially lower than 45 percent, both because 4 additional years had elapsed and because new treatments for HIV and opportunistic infections were not available in that area as early as they were in major urban centers. In addition, the presence of HIV infection among persons as young as age 20 years in our survey suggests that new infections occurred in the intervening period. Therefore, we conclude that HIV transmission also contributed to the observed infection prevalence.
For the results of a population-based survey to be reliable and generalizable, a high participation rate is essential. In this survey, 85 percent of randomly selected residents were interviewed, and 73 percent were tested for HIV. In two previous population-based surveys of HIV infection in the United States, the reported participation rates were 84 percent and 82 percent, while 80 percent and 71 percent of the participants, respectively, were tested for HIV (16, 17). The high participation rate in this survey was attributable to the presence of the Glades Health Initiative, Inc., a community-based organization. Prior to the survey, a pilot study carried out in western Palm Beach County suggested that a high participation rate could not be achieved in the survey without active community involvement (12). Thus, the Glades Health Initiative was created to give the community fiscal and administrative control over the survey and to ensure widespread community acceptance and participation (12).
Despite this high participation rate, participants in the 19982000 survey were not similar to residents of western Palm Beach County in the 2000 US Census with respect to age or gender. Fifty-three percent of the population in the Census was male, as compared with 41 percent of those enrolled in the survey, and 23 percent of the Census population was under 12 years of age, as compared with 10 percent of those in the survey (18). The lower proportion of children was an anticipated result of the sampling strategy used, because children are not randomly distributed among households. Underenrollment of children is not likely to have introduced bias, since the reasons for underenrollment were not related to HIV status. Age-adjusted HIV prevalence rates among children were actually slightly lower than the crude values, so the observed prevalence of HIV infection may have been an overestimate.
Underenrollment of men in the population-based survey probably resulted from the absence of male migrant farmworkers from the area for prolonged periods of time, such that, despite our making at least six visits to each household during various seasons and on evenings and weekends, they were less likely to be offered participation in the survey. Western Palm Beach County is at the southern terminus of the East Coast migrant farmworker stream, and most farmworkers in western Palm Beach County have permanent residences in the area, leaving each spring to harvest crops elsewhere and returning to the area after the harvest. In a study of largely male farmworkers in a neighboring community, 5 percent of participants were infected with HIV (19). If men who were not reached by our survey had such a rate of HIV infection, little effect on the estimated prevalence would have been seen. If, on the other hand, men who spend long periods of time away from home have a substantially higher prevalence of HIV infection, the rate we observed may have been an underestimate.
Selection of cases for the case-control study may also have led to bias in that HIV-infected persons who did not know they were infected with HIV could not have been selected as cases. By applying the 19982000 HIV prevalence estimate to the population of western Palm Beach County in 2000, we estimated that there were between 140 and 870 HIV-infected persons in the area. If persons who do not know that they are HIV-infected have a different risk profile than those who do, the case-control analysis we performed may have failed to identify those risk factors.
Results from these two cross-sectional surveys covering a 14-year period provide us with a unique opportunity to learn about the natural history of the HIV epidemic in the rural United States. HIV prevalence did not continue to increase during the interval between the two surveys, and it probably decreased. Although the finding was of borderline statistical significance, the relative decline in HIV prevalence was more marked among women than among men. HIV prevention efforts in the area were not specifically targeted towards women, but it was recognized early in the AIDS epidemic that HIV transmission was a particular problem among pregnant women (9). This awareness may have resulted in a greater effect of prevention programs in women than in men. Thus, while the importance of community-wide prevention programs in limiting the spread of the epidemic cannot be conclusively established, it is likely that they contributed to slowing its growth.
In 19982000, many HIV risk activities were significantly associated with HIV infection, including heterosexual activity, intravenous drug use, and receipt of blood transfusions between 1977 and 1985. However, intravenous drug use and receipt of transfusions were uncommon, and only activities related to heterosexual HIV transmission were retained in the multivariate model. We conclude that HIV infection has remained a heterosexually transmitted infection in this community, facilitated by other sexually transmitted infections and crack cocaine use. Among men in 1986, a history of having sex with men was significantly associated with HIV infection in multivariate analysis, but by 19982000 this association was no longer statistically significant. These results are similar to those from urban areas, where HIV infection is endemic among marginalized populations and is strongly associated with syphilis and other sexually transmitted diseases (18, 2023). In contrast to the situation in urban areas, the contribution of intravenous drug use to HIV transmission in our population was minimal. Thus, essentially all transmission in this community can be attributed to heterosexual activity.
Residence in specific neighborhoods in the community also emerged as an independent predictor of HIV infection in 19982000. These high-risk neighborhoods are areas where prostitution and crack cocaine use occur. The persistence of neighborhood as an independent risk factor for HIV infection suggests that this variable may be a surrogate for the risk that an individuals sex partners are HIV-infected. This result indicates that HIV infection evolves over time into a disease that persists in focal geographic areas without spreading to the community at large.
Analysis of the attributable fractions for HIV infection for factors that were retained in the multivariate model demonstrates that the fraction of the exposed cases that would not have occurred if the exposure had not occurred is high for sexual behaviors. On the other hand, the population attributable fractions are lower for the sexual behaviors, reflecting the smaller fraction of the total number of cases that would not have occurred had the exposure not occurred, since the exposures were infrequent in the population. Nonetheless, a substantial proportion of the risk for HIV can be attributed to modifiable factors such as sexually transmitted diseases other than HIV and number of sex partners. In western Palm Beach County, the Glades Health Initiative has initiated a street outreach campaign in the highest-risk neighborhoods to provide HIV testing and counseling and risk reduction counseling for uninfected persons whose sexual activities place them at high risk for HIV and other sexually transmitted infections. Such programs have been shown to have a high level of acceptability among rural minority populations (24, 25). Further reduction in HIV prevalence may require a better understanding of the social networks that exist in these endemic neighborhoods (26, 27) and ethnographic studies focusing on the identification of factors affecting heterosexual HIV transmission (28).
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ACKNOWLEDGMENTS |
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The authors acknowledge the staffs of the Glades Health Initiative, Inc., the C. L. Brumback Health Center, and Neighbors Organized for Adequate Housing (all located in Belle Glade, Florida) for their assistance in performing the survey.
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NOTES |
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REFERENCES |
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