1 El Paso County Department of Health and Environment, Colorado Springs, CO.
2 Interdisciplinary Scientific Research, Seattle, WA.
3 Department of Family and Preventive Medicine, Emory University School of Medicine, Atlanta, GA.
4 Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany.
Received for publication September 10, 2003; accepted for publication November 24, 2003.
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ABSTRACT |
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acquired immunodeficiency syndrome; HIV; homicide; mortality; overdose; prostitution; substance abuse, intravenous; violence
Abbreviations: Abbreviations: HIV, human immunodeficiency virus; NDI, National Death Index; SSDI, Social Security Death Index; SSN, Social Security number.
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INTRODUCTION |
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For three decades, continuous, community-wide surveillance of prostitutes in Colorado Springs, Colorado, has generated information on a large cohort of prostitute women (8, 9). These data and the availability of national mortality databases permitted assessment of cause-specific mortality among these women.
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MATERIALS AND METHODS |
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Enhanced monitoring of prostitution in Colorado Springs began in the 1960s in response to a rapidly growing gonorrhea epidemic associated with prostitution (5, 8). In mid-1970, the health department instituted a mechanism for examining arrested prostitutes for sexually transmitted infections, termed the Health Hold Order (8). At about the same time, the police created a vice squad to monitor prostitution. Their activities included arrest and field surveillance (including the recording of personal identifiers) of persons engaged in prostitution. Colorado statutes urged coordination between public health officials and police officers in suppressing sexually transmitted infections and prostitution (5). This relationship was unilateral: Police provided health officers access to prostitution records but not vice versa. Between 1970 and 2000, health department and police prostitution records were periodically compared.
Health department records for prostitute women were also based on women identified independently in our sexually transmitted infection, human immunodeficiency virus (HIV), and drug treatment clinics (through self-report); in observations of prostitutes during public health outreach activities; and through contact tracing for sexually transmitted infections/HIV. In our clinics, we recorded standard information on each woman as part of routine clinical and epidemiologic evaluation. Starting in mid-1985, women visiting the sexually transmitted infection clinic or the HIV testing clinic who provided histories of prostitution were queried about injecting drug use and offered HIV testing; such information was unavailable for prostitutes ascertained solely by means of other sources.
The study cohort included women in Colorado Springs identified by police or health department surveillance as prostitutes, that is, as women who exchanged sex for money or drugs. These women were known to have engaged in prostitution between approximately 1967 and 1999. Most women ultimately appeared in multiple data sources during their prostitution careers (9). Both the prevalence and number of sexual partners of prostitute women in Colorado Springs appear to be representative of prostitutes in the United States (9, 12).
Mortality data sources
As a first step, we searched the Social Security Death Index (SSDI) in mid-1999 regarding people who had died between 1967 and 1999. The SSDI records information on decedents with Social Security numbers (SSNs) for whom survivor claims have been processed (13, 14). It lists the decedents first name (at least first initial), surname, birth date, date of death, postal codes of last residence and last Social Security benefit, and SSN; it does not record information on sex, race, birth name (for women), death location, or cause of death. The staff of the sexually transmitted infection clinic requested the SSN as an optional item; 79 percent (981/1,245) of the women seen at the clinic provided it. Many (565/1,969) records of women in our cohort contained multiple names. Thus, we queried the SSDI systematically, beginning with SSN only and then using combinations of surname, first name/initial, and birth date to identify likely matches.
The National Death Index (NDI) registers deaths that have occurred in the United States since 1979. It is maintained by the Centers for Disease Control and Prevention. Source documentation consists of death certificate information provided by state and territorial registries. Minimum data required for searches include first name and surname and either SSN or month/year of birth. Provision of middle initial, day of birth, fathers surname, age at death, sex, race, marital status, state of residence, and/or state of birth improves search accuracy. NDI algorithms identify possible matches; the quality of matches depends on the completeness of submitted data.
Initial criteria for gauging the probability of a correct match are based on data concordance: 1) either first name or surname and SSN; 2) SSN and surname (for men) or SSN and surname or fathers surname (for women); or 3) first name and surname and month and year of birth. The NDI program compensates for spelling subtleties by using phonetic codes. Possible matches include state of death and certificate number. The NDI search algorithm generates many potential matches, especially if the submitted information is incomplete, as well as a score (0100). For all searches, we classified matches as definite (concordance of four of the following: SSN (within one digit), name, birth date, race, and sex); probable (among data items other than SSN, no more than two items slightly discordant (e.g., birth date one digit off or name slightly different)); and possible (manual review aiming for a preponderance of evidence using data from the NDI, the death certificate, and our records). We considered definite and probable deaths to be confirmed. Most NDI matches were eliminated using logic (e.g., males were automatically excluded) and a conservative NDI score cutoff point (less than 45 out of a possible 100 in the absence of an SSN).
Our list was searched at the NDI in late 1999 and compared with decedent records for 19791997. We sought death certificates from relevant registries in the United States for confirmed, probable, and possible matches emanating from the SSDI or NDI searches. Our NDI search was approved by the Colorado Health Sciences Center Institutional Review Board; in addition, death certificate requests were subject, in some states, to local institutional review. The Colorado Springs Police Department supplied a list of homicides that occurred in Colorado Springs between 1968 and 1999. We also requested information about death circumstances from other US jurisdictions for other murdered women in our cohort.
Statistical analyses
Mortality rates were based on the 1,633 women for whom year of first observation of local prostitution was available. Nearly all of the missing data on year of first local prostitution were attributable to women who did not have dated records in police files during the early part of the observation period, women identified only through visits to the HIV testing clinic or the drug treatment clinic (where dates of first local prostitution were not systematically collected), women who engaged in prostitution elsewhere, and women for whom the locale of prostitution could not be determined. Our calculations of person-years of observation took into account the fact that actual dates of first observation and death (when dates precise to the day and month were available) were uniformly distributed across a given year (resulting in 0.5 of a person-year, on average, for the first year a woman was observed or the year of her death) and that the final SSDI search occurred in mid-1999 (also resulting in 0.5 of a person-year for a woman censored by that endpoint).
Rates were computed for two sets of women: the cumulative cohort (which grew steadily from 1967 to 1999) and a subcohort classified as active prostitutes. The latter consisted of a shifting set of women. We created this "moving cohort" by including, for a given year, only women who were within 3 years of first being observed engaging in prostitution. Among prostitute women in our cohort known to reside in Colorado Springs for several years or more at some point prior to 1995 (n = 449), 50 percent had a time span between first and last observation of local prostitution (based on police surveillance, observation in the field or health department clinics, and/or reports from other active prostitute women) of 3 or more years. Fifteen percent had a span of prostitution of 2 years, and 35 percent had a span of less than 2 years. Thus, we inferred that the majority of living women in the cohort continued to work as prostitutes while in the moving cohort.
We calculated the expected number of deaths (using the "prospective model" (15)) in the cumulative and active cohorts using sex-, age-, and race-specific mortality tables for all causes of death (16) and homicide (1719). We computed standardized mortality ratios by dividing the observed number of deaths by the expected number of deaths. In addition, we estimated the average annual number of murdered prostitutes in the United States between 1981 and 1990 by multiplying the homicide rate we observed by the estimated number of prostitute women in the United States (23 per 100,000 population, derived from our local capture-recapture study (9)). Then we divided this product by the mean number of females, overall and between ages 15 and 44 years, murdered annually during this period (1719) to estimate the percentage of female murder victims in the United States who were prostitutes. We estimated the typical prostitutes risk of murder during her prostitution career by means of the formula 1 (1 active prostitutes crude homicide rate)5, because prostitutes in Colorado Springs worked for 5 years, on average (9).
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RESULTS |
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We classified the majority of prostitute women (1,795/1,969; 91 percent) as evanescent, short-term, or long-term residents. Evanescent prostitutes (n = 1,012; 56 percent) resided and solicited locally for a few days or weeks in any given year. Short-termers (n = 315; 18 percent) solicited for many weeks to months in any given year, and long-termers (n = 468; 26 percent) solicited for years even if they did not solicit continuously (9). Ninety-one percent were known to have engaged in prostitution locally, 4 percent reported histories of prostitution elsewhere only, and for 5 percent, locale was not recorded. The mean age at first observation of working locally was 24 years for those for whom we had data on date of first observation (n = 1,633; median, 23; standard deviation, 6.0; interquartile range, 2027; range, 1154).
Search results
The NDI search of 1,969 women used 2,883 names (mean = 1.47 per person; range, 19), yielding 9,926 potential matches, of which 1,223 met our initial matching criteria. Using the more rigorous matching criteria, we made 301 requests for death certificates for 165 women from 38 state registries. For the 33-year study interval, 117 women (6 percent) were classified as confirmed dead and 26 (1.3 percent) were classified as possibly dead (table 1). The 117 confirmed deaths were distributed in 26 states. Health department records and death certificates showed perfect concordance on SSN for 49 (86 percent) of the 57 confirmed-dead women who had an SSN in both sources. The NDI identified 100 confirmed deaths, with the SSDI corroborating only 57 of these; all deaths recorded by the SSDI appeared in the NDI. In reviewing the 43 deaths "missed" by the SSDI, at least 36 should have been listed, because a matching name or SSN was available. Predictably (7), none of the death certificates recorded any history or evidence of prostitution.
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Violent death
Of 21 murders, nine occurred within 3 years of the first observed prostitution. All of these nine women were active prostitutes at the time of death, and eight were killed while soliciting. The crude mortality rate for homicide in the cumulative cohort was 82.0 per 100,000 person-years; for the cohort of active prostitutes, it was 229 per 100,000 person-years (table 2). On the basis of this latter estimate, these women faced, on average, a 1 percent (0.0114) chance of being murdered during their prostitution careers. By extrapolation, this rate implies that between 1981 and 1990, approximately 124 prostitute women were murdered annually in the United States, accounting for 2.5 percent of female murder victims (3.7 percent of female murder victims aged 1544 years). The workplace homicide rate for prostitutes in the moving cohort (eight murdered on the job) was 204 per 100,000 person-years. The standardized mortality ratio for homicide in the cumulative cohort was 7.9, and in the moving cohort it was 17.7. Thus, active prostitutes were almost 18 times more likely to be murdered than women of similar age and race during the study interval. The nine deaths occurring among active prostitutes that were not deemed to be homicides included five drug overdoses, two suicides, and two deaths due to unknown causes.
Although murder accounted for 19 percent of all confirmed deaths, it accounted for half of the 18 deaths in the active subcohort. Of the 12 women murdered more than 3 years after the first observation of prostitution, eight died while still actively working as prostitutes (six were slain while soliciting and another was killed by a boyfriend who was jealous of her prostitution activity). One victim was not actively engaged in prostitution; death circumstances suggested that two were killed by clients while soliciting; and no information on prostitution status was available for the other. Thus, the vast majority of murdered women in our sample were killed as a direct consequence of prostitution.
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DISCUSSION |
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Our estimates of the all-cause crude mortality rate (459 per 100,000) and standardized mortality ratio (5.9) for presumed-active prostitutes are similar to earlier estimates from smaller groups of prostitute women followed in Colorado Springs in 19761977 (standardized mortality ratio = 3.3) (5), in Nairobi, Kenya, in 19982002 (n = 466; crude mortality rate = 310 per 100,000 (Stephen Moses, University of Manitoba, personal communication, 2003)), and in London, United Kingdom, in 19851994 (n = 402; crude mortality rate = 401 per 100,000; standardized mortality ratio = 12.2) (6). The London study was based on comparatively few (675) person-years, deaths were measured by incidental reports from other prostitutes, and the observation period for living women was the interval between the first and last clinic visits, truncating the observation period relative to women who died.
It is likely that we underestimated mortality in our current analysis. While the sensitivity of the SSDI relative to the NDI for the 19791997 period was only 57 percent, other research shows that the SSDI ascertained proportionally fewer deaths in the decades prior to 1979 than in the years after 1978 (23). Thus, the sensitivity of the SSDI for the 19671978 period in our study was probably lower than the sensitivity we estimated for the 19791997 period. Moreover, the NDI displayed only moderately high sensitivity (8193 percent) for samples of known female decedents (24, 25). Had NDI data been available for the periods 19671978 and 19981999, for which we relied solely on the SSDI, we estimate that another 10 (9.7) additional confirmed deaths would have been identified. The extent of underestimation is probably even greater than that suggested by these factors, given that we classified deaths conservatively and did not include 26 possible deaths when computing mortality rates.
The relatively low sensitivity of the death indexes for our cohort might have been due to the tendency of women to have multiple surnames, to some womens ineligibility for Social Security benefits (lack of sufficient legal employment), and to the dearth of information on fathers surnames in our database. Other factors may have prevented ascertainment of death for some women. For example, prostitutes who died in a foreign country or were murdered but never identified as dead (because the body was never found or the remains were not identifiable) (2628) would be unlikely to appear in death indexes. Some women also might have intentionally misreported identifying information to the health department or police.
To our knowledge, no population of women studied previously has had a crude mortality rate, standardized mortality ratio, or percentage of deaths due to murder even approximating those observed in our cohort. The workplace homicide rate for prostitutes (204 per 100,000) is many times higher than that for women and men in the standard occupations that had the highest workplace homicide rates in the United States during the 1980s (4 per 100,000 for female liquor store workers and 29 per 100,000 for male taxicab drivers) (29).
Our crude homicide mortality rate for presumed-active prostitutes (229 per 100,000) is also similar to the mortality rates extrapolated from passive and informal surveillance of prostitute women in Canada between 1992 and 1998 (30) (181 per 100,000 on the basis of our prostitute prevalence estimate (9) and national population figures (31)) and in the Canadian province of British Columbia between 1985 and 1990 (32) (112225 per 100,000). Parallel calculations for the 34 known prostitute women who were murdered on the job in Canada between 1992 and 1995 (30) yield a workplace homicide rate of 127 per 100,000. In our study, murder accounted for 50 percent of the deaths among presumed-active prostitutes. Murder accounted for 29100 percent of prostitute deaths observed in recent decades in Birmingham, United Kingdom (Hilary Kinnell, United Kingdom Network of Sex Work Projects, personal communication, 1999), Nairobi (Stephen Moses, University of Manitoba, personal communication, 2003), Vancouver (32), and London (6). However, prostitutes represented a greater share of all female murder victims in British Columbia between 1981 and 1990 (8 percent) (32) and in Canada overall between 1991 and 1995 (5 percent) (33) than in the United States between 1981 and 1990, by our estimate (3 percent).
The high homicide and overall mortality rates observed in our cohort probably reflect circumstances for nearly all prostitutes in the United States (where prostitution is illegal, except for a few rural Nevada counties where brothels are permitted (34)) and many other countries. Although these Colorado Springs prostitutes appeared to be representative of all US prostitutes in terms of prevalence and number of sexual partners (9, 12) and although they worked as prostitutes (and died) in many parts of the country, prostitutes elsewhere might have different mortality rates and profiles.
Clients perpetrate a large proportion of the lethal and nonlethal violence experienced by prostitutes (1, 32, 3541). For instance, clients were suspected perpetrators in 55 (64 percent) of the 86 murders of known prostitute women that took place in Canada between 1992 and 1998 (30). Moreover, clients who are serial murderers may account for a disproportionate fraction of prostitute murders (2628, 4244). Surveys also indicate that prostitute women encounter more violence from clients when working on the streets than in off-street contexts (32, 4547), and 84 percent of known prostitutes murdered in the United Kingdom in the 1990s worked on the streets (39).
Women engaged in prostitution face the most dangerous occupational environment in the United States. Research identifying individual and contextual factors that make prostitutes vulnerable to murder and drug overdose can inform the development of interventions for reducing harm (32, 37, 48, 49).
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ACKNOWLEDGMENTS |
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The authors thank Ken Basilio, formerly of the vital statistics office of the El Paso County Department of Health and Environment, for his exceptional tenacity in procuring death certificates.
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NOTES |
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REFERENCES |
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