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JAIDS Journal of Acquired Immune Deficiency Syndromes:
doi: 10.1097/QAI.0b013e31815e4062
Letters to the Editor

Decreases in AIDS Mortality and Increases in Primary and Secondary Syphilis in Men Who Have Sex With Men in the United States

Chesson, Harrell W PhD; Gift, Thomas L PhD

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Division of STD Prevention, National Center for HIV, STD, and TB Prevention Centers for Disease Control and Prevention Atlanta, GA

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

This is a US government work. There are no restrictions on its use with the exception of any previously printed figures and tables.

To the Editor:

The decrease in syphilis rates in the United States in the 1990s was likely attributable, at least in part, to sexual behavioral responses to the AIDS epidemic and disproportionate AIDS mortality in persons at high risk for acquisition and transmission of syphilis.1,2 If disproportionate AIDS mortality indeed reduced syphilis rates through the loss of high-risk persons from the population, decreases in AIDS mortality could facilitate increases in syphilis rates. Primary and secondary (P&S) syphilis rates have increased in the United States since 2001, particularly in men who have sex with men (MSM).3 The purpose of this analysis was to estimate how much of the recent increase in P&S syphilis in MSM in the United States might be attributable to the increased number of MSM at risk for acquisition of P&S syphilis as a result of decreasing AIDS mortality.

We estimated N, the number P&S syphilis cases in MSM with HIV in 2002 that would not have occurred if the number of AIDS deaths in MSM with AIDS had remained at peak 1994 levels, as follows: N = (M/100,000) × R, where M is the number of MSM with HIV younger than the age of 55 years in 2002 who would not have been alive at the start of 2002 if AIDS mortality in MSM had remained at 1994 levels and R is the estimated rate of P&S syphilis per 100,000 MSM with HIV in 2002. We focused our analysis on 2002, the only year for which estimates of the rate of P&S syphilis in MSM with HIV were available for the United States.4 We focused on syphilis cases in MSM younger than the age of 55 years in 2002, because P&S syphilis rates in men in 2002 were substantially lower in men aged 55 years and older than in younger men.5

The number of MSM with HIV younger than the age of 55 years in 2002 who would not have been alive in 2002 if AIDS mortality in MSM had remained at peak 1994 levels was calculated as

Equation (Uncited)
Equation (Uncited)
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where Dt is the number of deaths in MSM with AIDS in year t, θ (0.99) is an adjustment for the probability that death would have occurred in the absence of HIV infection, and P (0.73) is the proportion of deaths in men with AIDS in 1994 that occurred in men younger than the age of 45 years.6 We applied the age cutoff of 45 years for AIDS deaths in 1994, because men younger than the age of 45 years in 1994 would have been younger than the age of 55 years in 2002.

The number of deaths in MSM with AIDS was based on surveillance reports of the number of deaths in men with AIDS whose exposure category was MSM (including MSM who inject drugs).7 The base case value for R (the rate of P&S syphilis per 100,000 MSM with HIV in 2002) was 336 (range: 115 to 751).4

In 2002, there were an estimated 283 P&S syphilis cases in MSM with HIV attributable to the increased number of MSM with HIV at risk for acquisition of P&S syphilis as a result of decreasing AIDS mortality (Table 1). These 283 P&S syphilis cases make up approximately 8.7% of the estimated increase of 3257 P&S syphilis cases3 in MSM in 2002 compared with 1998. When varying R (the P&S syphilis rate in MSM with HIV), this estimate ranged from 97 to 632, or from 3% to 19% of the estimated increase in P&S syphilis cases in MSM in 2002 (compared with 1998).

Table 1
Table 1
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This range of estimates seems plausible in light of the substantial portion of P&S syphilis cases in MSM in recent outbreaks that occur in persons with long-standing HIV infection (ie, persons who might not have been alive without highly active antiretroviral therapy [HAART]).8,9

Our analysis considered only the acquisition of syphilis by MSM with HIV and not the transmission of syphilis after acquisition. If transmission dynamics were addressed, the estimated impact of the increased number of MSM with HIV on P&S syphilis incidence would have been more substantial.

We made several simplifying assumptions so that our estimates could be calculated with a simple model requiring few parameter values. The reasons for the increase in P&S syphilis in MSM are complex, and our analysis highlights the possible impact of decreased AIDS mortality through the increase in the number of MSM with HIV at risk for acquisition of syphilis. Decreased AIDS mortality can also have an impact on P&S syphilis incidence through other mechanisms, such as increased risky sexual behavior attributable to the decreased perceived risk of HIV.10 Thus, the role of decreased AIDS mortality on the increase in P&S syphilis cases in MSM could be more substantial than we estimated.

Although the increase in P&S syphilis in MSM is attributable in part to factors outside the control of sexually transmitted disease prevention programs, targeted prevention efforts can reduce syphilis in MSM.11

Harrell W. Chesson, PhD

Thomas L. Gift, PhD

Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention Centers for Disease Control and Prevention Atlanta, GA

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REFERENCES

1. Becker MH, Joseph JG. AIDS and behavioral change to reduce risk: a review. Am J Public Health. 1988;78:394-410.

2. Chesson HW, Dee TS, Aral SO. AIDS mortality may have contributed to the decline in syphilis rates in the United States in the 1990s. Sex Transm Dis. 2003;30:419-424.

3. Heffelfinger JD, Swint EB, Berman SM, et al. Trends in primary and secondary syphilis among men who have sex with men in the United States. Am J Public Health. 2007;97:1076-1083.

4. Chesson HW, Heffelfinger JD, Voigt RF, et al. Estimates of primary and secondary syphilis rates in persons with HIV in the United States, 2002. Sex Transm Dis. 2005;32:265-269.

5. Centers for Disease Control and Prevention. Sexually Transmitted Disease Surveillance, 2002. Atlanta, GA: US Department of Health and Human Services; 2003.

6. Centers for Disease Control and Prevention. HIV/AIDS Surveillance Report, 1995. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention; 1995.

7. Centers for Disease Control and Prevention. HIV/AIDS Surveillance Report, 2001. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention; 2002.

8. Paz-Bailey G, Meyers A, Blank S, et al. A case-control study of syphilis among men who have sex with men in New York City: association with HIV infection. Sex Transm Dis. 2004;31:581-587.

9. Centers for Disease Control and Prevention. Trends in primary and secondary syphilis and HIV infections in men who have sex with men-San Francisco and Los Angeles, California, 1998-2002. MMWR Morb Mortal Wkly Rep. 2004;53:575-578.

10. Stolte IG, Dukers NH, Geskus RB, et al. Homosexual men change to risky sex when perceiving less threat of HIV/AIDS since availability of highly active antiretroviral therapy: a longitudinal study. AIDS. 2004;18:303-309.

11. Centers for Disease Control and Prevention. The National Plan to Eliminate Syphilis from the United States. Atlanta, GA: Centers for Disease Control and Prevention; 2006.

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