Comparison groups, for which HIV seroprevalence data in persons without syphilis were calculated, were reported in 17 studies. Fourteen odds ratios were calculated for men and women together (median odds ratio 4.5). Five odds ratios were obtained for men alone (median odds ratio 8.5) and eight odds ratios were obtained for women alone (median odd ratio 3.3). Table 2 shows odds ratios for these groups.
Human immunodeficiency virus seroprevalences for MSM and IDU ranged from 64.3% to 90.0% and 22.5% to 70.6%, respectively. Odds ratios ranged from 5.4-7.4 for MSM and 3.0-3.5 for IDU. These results are shown in Table 3..
The public health significance of STDs on the U.S. HIV epidemic is influenced by the amount of coinfection present, the effect that coinfection has on HIV transmission, and the prevalence of the STD in the population. While syphilis rates in the United States are at extremely low levels, recent history documents potential for major epidemics, regionally and nationally, in the future. The studies included in this review demonstrate that the HIV infection rate is high in persons with syphilis in the United States. Previous investigations have indicated that coinfected individuals are at elevated risk to transmit HIV. This combination of high dual infection rates and increased individual transmission risk demonstrates that cases of syphilis represent a strikingly high risk for HIV transmission in the United States wherever syphilis persists, especially if the prevalence of syphilis were to increase.
This review indicates that a high proportion of persons with syphilis are at risk for transmitting both diseases through sexual contact. The median HIV seroprevalence in patients with syphilis was 15.7% for men and women together, 27.5% for men alone, and 12.4% for women alone. The discrepancy of HIV seroprevalence by gender may be related to baseline HIV seroprevalence. The median HIV seroprevalences in persons without syphilis reported in the reviewed articles was 4.5 and 2.7 for men and women, respectively (data not shown). The majority of the studies showed an increased likelihood of HIV seroprevalence in persons with syphilis compared to similar populations without syphilis. One study with a newly emerging heterosexual epidemic of HIV infection found that HIV was exclusively present in the population with genital ulcer diseases, including syphilis.15 The two studies that showed no disease overlap were in populations in which the HIV seroprevalence was extremely low or nonexistent. One of these studies noted HIV infection only in the non-syphilis population.31 This may be due to the low number of patients with syphilis identified (n = 19) and the low seroprevalence of HIV in this population (0.4% in the referent group). The second study that noted no HIV seroprevalence in patients with syphilis was an outbreak investigation in rural Texas.47 The outbreak took place in four counties that had no cases of HIV identified among child-bearing women as part of a separate surveillance project (CDC, unpublished data). In addition, in the Texas outbreak, fewer than 20% of the identified cases of syphilis underwent testing for HIV. Overall, this review indicates that persons with syphilis are at substantially higher likelihood to be HIV seropositive than persons without syphilis.
Certain populations traditionally associated with increased prevalence of HIV (MSM and IDU) show high HIV coinfection with syphilis. In this study, HIV seroprevalences ranged from 64.3% to 90% and 22.5% to 70.6% for MSM and IDU, respectively. While these numbers reflect the high baseline HIV seroprevalence in these populations (data not shown), they also demonstrate a significantly increased prevalence of HIV infection in individuals with syphilis as shown in Table 3. Although some of these studies may have selected individuals with greater HIV seroprevalence because of their sampling techniques (i.e., persons actively seeking medical care), at least one study recruited participants from the community.53 These investigators reported a lower baseline HIV seroprevalence in the referent group compared to other studies, but they found a large increase in seroprevalence in persons with syphilis. Despite variable baseline seroprevalence, MSM and IDU consistently show an increased HIV seroprevalence in individuals with syphilis.
Because background HIV seroprevalence varies considerably across the United States and between subpopulations (such as persons who attend public STD clinics), we also calculated odds ratios when data were available. This study demonstrates a median odds ratio of 4.5 for men and women together. While the baseline HIV seroprevalences varied, all studies that provided information by sex showed increased odds of being HIV seropositive in the presence of syphilis. The odds ratios for men alone and women alone were 8.5 and 3.3, respectively. The reasons for the higher odds ratios in men are unclear, and might be an artifact of the populations from which the studies were chosen, an inherent increased risk based on gender, or additional factors not accounted for in this review. Increased odds ratios were also demonstrated for MSM and IDU.
This paper is unable to make any conclusion regarding causality or temporality of infections with HIV and syphilis. The biologic mechanisms involved in transmission were not investigated nor were other significant behavioral or clinical factors. We were unable to provide age-adjusted prevalences, and this may be a significant factor in the degree of overlap between HIV and syphilis. This article attempts to summarize the degree of concomitant HIV infection in individuals with syphilis compared to that in persons without syphilis. Given the relatively low prevalence of syphilis in the United States, it is unlikely that prospective studies that will clearly define the factors involved in this association would be feasible. Several states with the highest syphilis rates are not represented in the studies included in this paper. These areas are predominantly in the Southeastern United States and likely represented by the data presented.
There has been an 84% decline in primary and secondary syphilis rates in the United States from 1990 to 1997.54 This likely corresponds to a sharp decrease in syphilis-related HIV transmission. Recent outbreaks of syphilis are particularly concerning for the potential impact on local HIV transmission.24,25 The prospect remains that if the rates of syphilis return to the levels observed in the 1980s, there would likely be a substantial increase in the rate of HIV transmission.
The finding of increased HIV seroprevalence in persons with syphilis has significant public health implications. The value of detecting and treating a case of infectious syphilis goes beyond the medical and public health considerations of syphilis alone. Rather, timely and appropriate management of such cases eliminates an important facilitating factor for HIV transmission. Moreover, this intervention is “self-targeting” to individuals who often engage in high risk behavior and who may interact routinely with persons in high risk sexual networks. In addition, these results suggest that HIV counseling and testing, as recommended for all syphilis patients,21,22 will identify a number of persons who are HIV positive, and should be emphasized as a standard of care for all persons with syphilis. These findings also reinforce the potential impact of the national effort to eliminate syphilis from the United States as one highly targeted component of HIV prevention in the United States.22,26
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