Register      Login
Sexual Health Sexual Health Society
Publishing on sexual health from the widest perspective
REVIEW

Syphilis transmission: a review of the current evidence

Juliet E. Stoltey A C and Stephanie E. Cohen B
+ Author Affiliations
- Author Affiliations

A University of California, San Francisco – Division of Infectious Diseases, 513 Parnassus Avenue, Box 0654, San Francisco, CA 94143, USA.

B San Francisco Department of Public Health, 356 7th Street, San Francisco, CA 94103, USA.

C Corresponding author. Email: juliet.stoltey@ucsf.edu

Sexual Health 12(2) 103-109 https://doi.org/10.1071/SH14174
Submitted: 31 August 2014  Accepted: 22 December 2014   Published: 23 February 2015

Abstract

Syphilis remains widespread worldwide, with increasing rates among men who have sex with men. This paper reviews available evidence regarding syphilis transmission, including data on: sexual transmission (transmission probability per sexual partnership), vertical transmission, transmission via blood products and organ donation, and other rare modes of transmission. In addition, host susceptibility to syphilis infection is discussed. Syphilis screening and treatment, condoms and risk-reduction counselling and how they modify syphilis transmission dynamics are considered.


References

[1]  World Health Organization. Global incidence and prevalence of selected curable sexually transmitted infections – 2008–2012. Available online at: http://apps.who.int/iris/bitstream/10665/75181/1/9789241503839_eng.pdf [verified 20 January 2015].

[2]  Centers for Disease Control and Prevention. Syphilis - CDC fact sheet 2014. Available online at: http://www.cdc.gov/std/syphilis/STDFact-Syphilis-detailed.htm [verified 24 July 2014].

[3]  Fenton KA. A multilevel approach to understanding the resurgence and evolution of infectious syphilis in Western Europe. Euro Surveill 2004; 9 3–4.
| 15677857PubMed |

[4]  Fenton KA, Breban R, Vardavas R, Okano JT, Martin T, Aral S, et al Infectious syphilis in high-income settings in the 21st century. Lancet Infect Dis 2008; 8 244–53.
Infectious syphilis in high-income settings in the 21st century.Crossref | GoogleScholarGoogle Scholar | 18353265PubMed |

[5]  Garnett GP. The transmission dynamics of sexually transmitted infections. In Holmes KK, Sparling PF, Stamm WE, Piot P, Wasserheit JN, Corey L, et al., editors. Sexually transmitted diseases, 4th edn. New York: McGraw-Hill; 2008. pp. 27–39.

[6]  De Santis M, De Luca C, Mappa I, Spagnuolo T, Licameli A, Straface G, et al Syphilis infection during pregnancy: fetal risks and clinical management. Infect Dis Obstet Gynecol 2012; 2012 430585
Syphilis infection during pregnancy: fetal risks and clinical management.Crossref | GoogleScholarGoogle Scholar | 22829747PubMed |

[7]  Genc M, Ledger WJ. Syphilis in pregnancy. Sex Transm Infect 2000; 76 73–9.
Syphilis in pregnancy.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3czhs1Gisg%3D%3D&md5=b46234c8c952bce14ec558858941af10CAS | 10858706PubMed |

[8]  Dorfman DH, Glaser JH. Congenital syphilis presenting in infants after the newborn period. N Engl J Med 1990; 323 1299–302.
Congenital syphilis presenting in infants after the newborn period.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK3M%2FhsFaksA%3D%3D&md5=0f364595af14ca013c5f3193275c5a4bCAS | 2215616PubMed |

[9]  Chambers RW, Foley HT, Schmidt PJ. Transmission of syphilis by fresh blood components. Transfusion 1969; 9 32–4.
Transmission of syphilis by fresh blood components.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaF1M%2FosFCgtA%3D%3D&md5=2167d57289147192da0db2d53e2485d5CAS | 5762537PubMed |

[10]  Owusu-Ofori AK, Parry CM, Bates I. Transfusion-transmitted syphilis in teaching hospital, Ghana. Emerg Infect Dis 2011; 17 2080–2.
Transfusion-transmitted syphilis in teaching hospital, Ghana.Crossref | GoogleScholarGoogle Scholar | 22099108PubMed |

[11]  Perkins HA, Busch MP. Transfusion-associated infections: 50 years of relentless challenges and remarkable progress. Transfusion 2010; 50 2080–99.
Transfusion-associated infections: 50 years of relentless challenges and remarkable progress.Crossref | GoogleScholarGoogle Scholar | 20738828PubMed |

[12]  Epstein E. Extragenital syphilis in physicians. Calif Med 1952; 77 149–50.
| 1:STN:280:DyaG3s%2FgtlWhtQ%3D%3D&md5=85a3357fce10361470609188fcc3176eCAS | 12978898PubMed |

[13]  Oh Y, Ahn SY, Hong SP, Bak H, Ahn SK. A case of extragenital chancre on a nipple from a human bite during sexual intercourse. Int J Dermatol 2008; 47 978–80.
A case of extragenital chancre on a nipple from a human bite during sexual intercourse.Crossref | GoogleScholarGoogle Scholar | 18318701PubMed |

[14]  Chiu HY, Tsai TF. A crusted plaque on the right nipple. JAMA 2012; 308 403–4.
A crusted plaque on the right nipple.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38Xht1CksLjN&md5=5909642ea586b392b5ad60c0744444b6CAS | 22820793PubMed |

[15]  Fanfair RN, Wallingford M, Long LL, Chi KH, Pillay A, Chen CY, et al Acquired macrolide-resistant Treponema pallidum after a human bite. Sex Transm Dis 2014; 41 493–5.
Acquired macrolide-resistant Treponema pallidum after a human bite.Crossref | GoogleScholarGoogle Scholar | 25013977PubMed |

[16]  Zhou P, Qian Y, Lu H, Guan Z. Nonvenereal transmission of syphilis in infancy by mouth-to-mouth transfer of prechewed food. Sex Transm Dis 2009; 36 216–7.
Nonvenereal transmission of syphilis in infancy by mouth-to-mouth transfer of prechewed food.Crossref | GoogleScholarGoogle Scholar | 19265744PubMed |

[17]  Gray RT, Hoare A, McCann PD, Bradley J, Down I, Donovan B, et al Will changes in gay men’s sexual behavior reduce syphilis rates? Sex Transm Dis 2011; 38 1151–8.
Will changes in gay men’s sexual behavior reduce syphilis rates?Crossref | GoogleScholarGoogle Scholar | 22082727PubMed |

[18]  Von Werssowetz AJ. The incidence of infection in contacts of early syphilis. J Vener Dis Inf 1948; 29 132–7.
| 1:STN:280:DyaH1c%2FlslKgsg%3D%3D&md5=d3d966ca0b1d09e55c7b21594928799cCAS | 18913883PubMed |

[19]  Schober PC, Gabriel G, White P, Felton WF, Thin RN. How infectious is syphilis? Br J Vener Dis 1983; 59 217–9.
| 1:STN:280:DyaL3s3lvVClsg%3D%3D&md5=09ac4a462f15fd407e6692dfe32d810eCAS | 6871650PubMed |

[20]  Garnett GP, Aral SO, Hoyle DV, Cates W, Anderson RM. The natural history of syphilis. Implications for the transmission dynamics and control of infection. Sex Transm Dis 1997; 24 185–200.
The natural history of syphilis. Implications for the transmission dynamics and control of infection.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK2s3ls1aqug%3D%3D&md5=11dec31f3714b2efeb9b12030ee80115CAS | 9101629PubMed |

[21]  Alexander LJ, Schoch AG. Prevention of syphilis; penicillin calcium in oil and white wax, U.S. P., bismuth ethylcamphorate and oxophenarsine hydrochloride in treatment, during incubation stage, of persons exposed to syphilis. Arch Derm Syphilol 1949; 59 1–10.
Prevention of syphilis; penicillin calcium in oil and white wax, U.S. P., bismuth ethylcamphorate and oxophenarsine hydrochloride in treatment, during incubation stage, of persons exposed to syphilis.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaH1M%2Fht1Wnug%3D%3D&md5=f51918c09ea80eabad127dfb8bcdaa28CAS | 18110552PubMed |

[22]  Moore MB, Price EV, Knox JM, Elgin LW. Epidemiologic treatment of contacts to infectious syphilis. Public Health Rep 1963; 78 966–70.
Epidemiologic treatment of contacts to infectious syphilis.Crossref | GoogleScholarGoogle Scholar | 14084872PubMed |

[23]  Schroeter AL, Turner RH, Lucas JB, Brown WJ. Therapy for incubating syphilis. Effectiveness of gonorrhea treatment. JAMA 1971; 218 711–3.
Therapy for incubating syphilis. Effectiveness of gonorrhea treatment.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE38%2FmtlGltQ%3D%3D&md5=ac9f0b78353f956af712eb9751294431CAS | 5171497PubMed |

[24]  Patel P, Borkowf CB, Brooks JT, Lasry A, Lansky A, Mermin J. Estimating per-act HIV transmission risk: a systematic review. AIDS 2014; 28 1509–19.
Estimating per-act HIV transmission risk: a systematic review.Crossref | GoogleScholarGoogle Scholar | 24809629PubMed |

[25]  Gray RT, Hoare A, Prestage GP, Donovan B, Kaldor JM, Wilson DP. Frequent testing of highly sexually active gay men is required to control syphilis. Sex Transm Dis 2010; 37 298–305.
| 20393383PubMed |

[26]  Presidential Commission for the Study of Bioethical Issues. “Ethically impossible” STD research in Guatemala from 1946 to 1948. Washington, D.C.: Presidential Commission for the Study of Bioethical Issues; 2011.

[27]  Magnuson HJ, Thomas EW, Olansky S, Kaplan BI, De Mello L, Cutler JC. Inoculation syphilis in human volunteers. Medicine (Baltimore) 1956; 35 33–82.
Inoculation syphilis in human volunteers.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaG28%2FkvV2gug%3D%3D&md5=bb0b6c8eef29dfdc5e79b72fe4d4df45CAS | 13296652PubMed |

[28]  Shafii T, Radolf JD, Sanchez PJ, Schulz KF, Murphy FK. Congenital syphilis. In Holmes KK, Sparling PF, Stamm WE, Piot P, Wasserheit JN, Corey L, et al., editors. Sexually transmitted diseases, 4th edn. New York: McGraw Hill; 2008. pp. 1578–612.

[29]  Fiumara NJ, Fleming WL, Downing JG, Good FL. The incidence of prenatal syphilis at the Boston City Hospital. N Engl J Med 1952; 247 48–52.
The incidence of prenatal syphilis at the Boston City Hospital.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaG38%2FntFeqsw%3D%3D&md5=a24c89dab00c54816756371a365cdfa9CAS | 14941281PubMed |

[30]  Sanchez PJ, Wendel GD, Grimprel E, Goldberg M, Hall M, Arencibia-Mireles O, et al Evaluation of molecular methodologies and rabbit infectivity testing for the diagnosis of congenital syphilis and neonatal central nervous system invasion by Treponema pallidum. J Infect Dis 1993; 167 148–57.
Evaluation of molecular methodologies and rabbit infectivity testing for the diagnosis of congenital syphilis and neonatal central nervous system invasion by Treponema pallidum.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK3s7hsFGjsw%3D%3D&md5=db5599b649db6d15e6c1b54a12b0807aCAS | 8418161PubMed |

[31]  Hollier LM, Harstad TW, Sanchez PJ, Twickler DM, Wendel GD. Fetal syphilis: clinical and laboratory characteristics. Obstet Gynecol 2001; 97 947–53.
Fetal syphilis: clinical and laboratory characteristics.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3Mzht1ehsA%3D%3D&md5=76e3c2c3afa831efc0f21e0ac5b73267CAS | 11384701PubMed |

[32]  Nathan L, Bohman VR, Sanchez PJ, Leos NK, Twickler DM, Wendel GD. In utero infection with Treponema pallidum in early pregnancy. Prenat Diagn 1997; 17 119–23.
In utero infection with Treponema pallidum in early pregnancy.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK2s3hsFCjtA%3D%3D&md5=4e1bd844b59dbddcdf822a4df6825f9dCAS | 9061759PubMed |

[33]  Wicher V, Wicher K. Pathogenesis of maternal-fetal syphilis revisited. Clin Infect Dis 2001; 33 354–63.
Pathogenesis of maternal-fetal syphilis revisited.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MzosVCktQ%3D%3D&md5=03fad4356c9f0a9393d91db09e2cc36fCAS | 11438902PubMed |

[34]  Risseeuw-Appel IM, Kothe FC. Transfusion syphilis: a case report. Sex Transm Dis 1983; 10 200–1.
Transfusion syphilis: a case report.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaL2c7itFOrsQ%3D%3D&md5=3185ef3c54d8c620d4f45aae55050654CAS | 6665664PubMed |

[35]  Ko WJ, Chu SH, Lee YH, Lee PH, Lee CJ, Chao SH, et al Successful prevention of syphilis transmission from a multiple organ donor with serological evidence of syphilis. Transplant Proc 1998; 30 3667–8.
Successful prevention of syphilis transmission from a multiple organ donor with serological evidence of syphilis.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK1M%2FlsF2rug%3D%3D&md5=f985fbc0e5f972b4b10b4cf8a4f1dcf5CAS | 9838609PubMed |

[36]  Marek A, Inkster T. A syphilis-positive organ donor – management of the cardiac transplant recipient: a case report and review of the literature. Sex Transm Dis 2012; 39 485–6.
A syphilis-positive organ donor – management of the cardiac transplant recipient: a case report and review of the literature.Crossref | GoogleScholarGoogle Scholar | 22592837PubMed |

[37]  Tariciotti L, Das I, Dori L, Perera MT, Bramhall SR. Asymptomatic transmission of Treponema pallidum (syphilis) through deceased donor liver transplantation. Transpl Infect Dis 2012; 14 321–5.
Asymptomatic transmission of Treponema pallidum (syphilis) through deceased donor liver transplantation.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BC38nlvFaktQ%3D%3D&md5=d72447f44e29fd4444c63519cda059a5CAS | 22624823PubMed |

[38]  Raguse JD, Camerer C, Bergmann F, Schewe C, Schurmann D. Occupational syphilis following scalpel injury. Ann Intern Med 2012; 156 475–6.
Occupational syphilis following scalpel injury.Crossref | GoogleScholarGoogle Scholar | 22431685PubMed |

[39]  Meyer GS. Occupational infection in health care. The century-old lessons from syphilis. Arch Intern Med 1993; 153 2439–47.
Occupational infection in health care. The century-old lessons from syphilis.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK2c%2FivFensw%3D%3D&md5=aedfe4a1b6458c82e09dae38e4e1f782CAS | 8215748PubMed |

[40]  Peeling RW, Hook EW. The pathogenesis of syphilis: the Great Mimicker, revisited. J Pathol 2006; 208 224–32.
The pathogenesis of syphilis: the Great Mimicker, revisited.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XhsFGqu7c%3D&md5=62d39f6df9fb4c44974432d0831c93f2CAS | 16362988PubMed |

[41]  Ogilvie GS, Taylor DL, Moniruzzaman A, Knowles L, Jones H, Kim PH, et al A population-based study of infectious syphilis rediagnosis in British Columbia, 1995–2005. Clin Infect Dis 2009; 48 1554–8.
A population-based study of infectious syphilis rediagnosis in British Columbia, 1995–2005.Crossref | GoogleScholarGoogle Scholar | 19402790PubMed |

[42]  Brewer TH, Peterman TA, Newman DR, Schmitt K. Reinfections during the Florida syphilis epidemic, 2000–2008. Sex Transm Dis 2011; 38 12–7.
Reinfections during the Florida syphilis epidemic, 2000–2008.Crossref | GoogleScholarGoogle Scholar | 20739912PubMed |

[43]  Cohen SE, Chew Ng RA, Katz KA, Bernstein KT, Samuel MC, Kerndt PR, et al Repeat syphilis among men who have sex with men in California, 2002–2006: implications for syphilis elimination efforts. Am J Public Health 2012; 102 e1–8.
Repeat syphilis among men who have sex with men in California, 2002–2006: implications for syphilis elimination efforts.Crossref | GoogleScholarGoogle Scholar | 22095364PubMed |

[44]  Morgan CA, Lukehart SA, Van Voorhis WC. Protection against syphilis correlates with specificity of antibodies to the variable regions of Treponema pallidum repeat protein K. Infect Immun 2003; 71 5605–12.
Protection against syphilis correlates with specificity of antibodies to the variable regions of Treponema pallidum repeat protein K.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXnslylt78%3D&md5=fe4005fc0df8ab590875567ff69935b2CAS | 14500480PubMed |

[45]  Jaffe HW, Rice DT, Voigt R, Fowler J, St John RK. Selective mass treatment in a venereal disease control program. Am J Public Health 1979; 69 1181–2.
Selective mass treatment in a venereal disease control program.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaL3c%2Fmt1OktQ%3D%3D&md5=04887f8f2cbfb01b5151329822224ee6CAS | 583095PubMed |

[46]  Cates W, Rothenberg RB, Blount JH. Syphilis control. The historic context and epidemiologic basis for interrupting sexual transmission of Treponema pallidum. Sex Transm Dis 1996; 23 68–75.
Syphilis control. The historic context and epidemiologic basis for interrupting sexual transmission of Treponema pallidum.Crossref | GoogleScholarGoogle Scholar | 8801646PubMed |

[47]  Tuite AR, Burchell AN, Fisman DN. Cost-effectiveness of enhanced syphilis screening among HIV-positive men who have sex with men: a microsimulation model. PLoS ONE 2014; 9 e101240
Cost-effectiveness of enhanced syphilis screening among HIV-positive men who have sex with men: a microsimulation model.Crossref | GoogleScholarGoogle Scholar | 24983455PubMed |

[48]  Bissessor M, Fairley CK, Leslie D, Howley K, Chen MY. Frequent screening for syphilis as part of HIV monitoring increases the detection of early asymptomatic syphilis among HIV-positive homosexual men. J Acquir Immune Defic Syndr 2010; 55 211–6.
Frequent screening for syphilis as part of HIV monitoring increases the detection of early asymptomatic syphilis among HIV-positive homosexual men.Crossref | GoogleScholarGoogle Scholar | 20585261PubMed |

[49]  Bissessor M, Fairley CK, Leslie D, Chen MY. Use of a computer alert increases detection of early, asymptomatic syphilis among higher-risk men who have sex with men. Clin Infect Dis 2011; 53 57–8.
Use of a computer alert increases detection of early, asymptomatic syphilis among higher-risk men who have sex with men.Crossref | GoogleScholarGoogle Scholar | 21653303PubMed |

[50]  Bourne C, Knight V, Guy R, Wand H, Lu H, McNulty A. Short message service reminder intervention doubles sexually transmitted infection/HIV re-testing rates among men who have sex with men. Sex Transm Infect 2011; 87 229–31.
Short message service reminder intervention doubles sexually transmitted infection/HIV re-testing rates among men who have sex with men.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BC3M3ot1Wqug%3D%3D&md5=181971c5804980a3b21a82e757b447cdCAS | 21296796PubMed |

[51]  Workowski KA, Berman S. Sexually transmitted diseases treatment guidelines, 2010. MMWR Recomm Rep 2010; 59 1–110.
| 21160459PubMed |

[52]  Klausner JD, Kent CK, Wong W, McCright J, Katz MH. The public health response to epidemic syphilis, San Francisco, 1999–2004. Sex Transm Dis 2005; 32 S11–8.
The public health response to epidemic syphilis, San Francisco, 1999–2004.Crossref | GoogleScholarGoogle Scholar | 16205286PubMed |

[53]  Centers for Disease Control and Prevention. Internet use and early syphilis infection among men who have sex with men–San Francisco, California, 1999–2003. MMWR Morb Mortal Wkly Rep 2003; 52 1229–32.
| 14681596PubMed |

[54]  Hightow-Weidman L, Beagle S, Pike E, Kuruc J, Leone P, Mobley V, et al “No one’s at home and they won’t pick up the phone”: using the Internet and text messaging to enhance partner services in North Carolina. Sex Transm Dis 2014; 41 143–8.
“No one’s at home and they won’t pick up the phone”: using the Internet and text messaging to enhance partner services in North Carolina.Crossref | GoogleScholarGoogle Scholar | 24413497PubMed |

[55]  Steen R, Dallabetta G. The use of epidemiologic mass treatment and syndrome management for sexually transmitted disease control. Sex Transm Dis 1999; 26(Suppl) S12–20.
The use of epidemiologic mass treatment and syndrome management for sexually transmitted disease control.Crossref | GoogleScholarGoogle Scholar |

[56]  Rekart ML, Patrick DM, Chakraborty B, Maginley JJ, Jones HD, Bajdik CD, et al Targeted mass treatment for syphilis with oral azithromycin. Lancet 2003; 361 313–4.
Targeted mass treatment for syphilis with oral azithromycin.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXmt1anug%3D%3D&md5=ee0b2b7ef2d41c3f5a3e4d25355389cdCAS | 12559870PubMed |

[57]  Chen JL, Callahan DB, Kerndt PR. Syphilis control among incarcerated men who have sex with men: public health response to an outbreak. Am J Public Health 2002; 92 1473–4.
Syphilis control among incarcerated men who have sex with men: public health response to an outbreak.Crossref | GoogleScholarGoogle Scholar | 12197977PubMed |

[58]  Farley TA, Cohen DA, Kahn RH, Lolis S, Johnson G, Martin DH. The acceptability and behavioral effects of antibiotic prophylaxis for syphilis prevention. Sex Transm Dis 2003; 30 844–9.
The acceptability and behavioral effects of antibiotic prophylaxis for syphilis prevention.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXoslWlurY%3D&md5=b7da84a15ce65fdd00cba1398ef03298CAS | 14603093PubMed |

[59]  Wilson DP, Prestage GP, Gray RT, Hoare A, McCann P, Down I, et al Chemoprophylaxis is likely to be acceptable and could mitigate syphilis epidemics among populations of gay men. Sex Transm Dis 2011; 38 573–9.
Chemoprophylaxis is likely to be acceptable and could mitigate syphilis epidemics among populations of gay men.Crossref | GoogleScholarGoogle Scholar | 21343845PubMed |

[60]  Bolan RK, Beymer M, Klausner JD, Flynn R, Leibowitz A. Doxycycline prophylaxis for syphilis in a persistently high risk HIV infected population; (Abstract P3.430). Sex Transm Infect 2013; 89 A283
Doxycycline prophylaxis for syphilis in a persistently high risk HIV infected population; (Abstract P3.430).Crossref | GoogleScholarGoogle Scholar |

[61]  Pourbohloul B, Rekart ML, Brunham RC. Impact of mass treatment on syphilis transmission: a mathematical modeling approach. Sex Transm Dis 2003; 30 297–305.
Impact of mass treatment on syphilis transmission: a mathematical modeling approach.Crossref | GoogleScholarGoogle Scholar | 12671548PubMed |

[62]  Mann JR, Stine CC, Vessey J. The role of disease-specific infectivity and number of disease exposures on long-term effectiveness of the latex condom. Sex Transm Dis 2002; 29 344–9.
The role of disease-specific infectivity and number of disease exposures on long-term effectiveness of the latex condom.Crossref | GoogleScholarGoogle Scholar | 12035024PubMed |

[63]  Koss CA, Dunne EF, Warner L. A systematic review of epidemiologic studies assessing condom use and risk of syphilis. Sex Transm Dis 2009; 36 401–5.
A systematic review of epidemiologic studies assessing condom use and risk of syphilis.Crossref | GoogleScholarGoogle Scholar | 19455075PubMed |

[64]  Vijayakumar G, Mabude Z, Smit J, Beksinska M, Lurie M. A review of female-condom effectiveness: patterns of use and impact on protected sex acts and STI incidence. Int J STD AIDS 2006; 17 652–9.
A review of female-condom effectiveness: patterns of use and impact on protected sex acts and STI incidence.Crossref | GoogleScholarGoogle Scholar | 17059633PubMed |

[65]  Morris M. Concurrent partnerships and syphilis persistence: new thoughts on an old puzzle. Sex Transm Dis 2001; 28 504–7.
Concurrent partnerships and syphilis persistence: new thoughts on an old puzzle.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MvnsFGlsA%3D%3D&md5=e2dfd4075c6c9b077bd3c208ab050630CAS | 11518866PubMed |

[66]  Koumans EH, Farley TA, Gibson JJ, Langley C, Ross MW, McFarlane M, et al Characteristics of persons with syphilis in areas of persisting syphilis in the United States: sustained transmission associated with concurrent partnerships. Sex Transm Dis 2001; 28 497–503.
Characteristics of persons with syphilis in areas of persisting syphilis in the United States: sustained transmission associated with concurrent partnerships.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3MrisVGktQ%3D%3D&md5=5d30fceb11d9ad8c50a1f8829634f673CAS | 11518865PubMed |

[67]  Chew Ng RA, Samuel MC, Lo T, Bernstein KT, Aynalem G, Klausner JD, et al Sex, drugs (methamphetamines), and the Internet: increasing syphilis among men who have sex with men in California, 2004–2008. Am J Public Health 2013; 103 1450–6.
Sex, drugs (methamphetamines), and the Internet: increasing syphilis among men who have sex with men in California, 2004–2008.Crossref | GoogleScholarGoogle Scholar | 23153138PubMed |

[68]  Truong HM, Kellogg T, Klausner JD, Katz MH, Dilley J, Knapper K, et al Increases in sexually transmitted infections and sexual risk behaviour without a concurrent increase in HIV incidence among men who have sex with men in San Francisco: a suggestion of HIV serosorting? Sex Transm Infect 2006; 82 461–6.
Increases in sexually transmitted infections and sexual risk behaviour without a concurrent increase in HIV incidence among men who have sex with men in San Francisco: a suggestion of HIV serosorting?Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD28jhsVKitQ%3D%3D&md5=46ba52d75b357342abda941dd0907299CAS | 17151031PubMed |

[69]  Sullivan PS, Drake AJ, Sanchez TH. Prevalence of treatment optimism-related risk behavior and associated factors among men who have sex with men in 11 states, 2000–2001. AIDS Behav 2007; 11 123–9.
Prevalence of treatment optimism-related risk behavior and associated factors among men who have sex with men in 11 states, 2000–2001.Crossref | GoogleScholarGoogle Scholar | 16767506PubMed |

[70]  Snowden JM, Wei C, McFarland W, Raymond HF. Prevalence, correlates and trends in seroadaptive behaviours among men who have sex with men from serial cross-sectional surveillance in San Francisco, 2004–2011. Sex Transm Infect 2014; 90 498–504.
Prevalence, correlates and trends in seroadaptive behaviours among men who have sex with men from serial cross-sectional surveillance in San Francisco, 2004–2011.Crossref | GoogleScholarGoogle Scholar | 24687128PubMed |

[71]  Golub SA, Kowalczyk W, Weinberger CL, Parsons JT. Preexposure prophylaxis and predicted condom use among high-risk men who have sex with men. J Acquir Immune Defic Syndr 2010; 54 548–55.
Preexposure prophylaxis and predicted condom use among high-risk men who have sex with men.Crossref | GoogleScholarGoogle Scholar | 20512046PubMed |

[72]  Grant RM, Anderson PL, McMahan V, Liu A, Amico KR, Mehrotra M, et al Uptake of pre-exposure prophylaxis, sexual practices, and HIV incidence in men and transgender women who have sex with men: a cohort study. Lancet Infect Dis 2014; 14 820–9.
Uptake of pre-exposure prophylaxis, sexual practices, and HIV incidence in men and transgender women who have sex with men: a cohort study.Crossref | GoogleScholarGoogle Scholar | 25065857PubMed |

[73]  Metsch LR, Feaster DJ, Gooden L, Schackman BR, Matheson T, Das M, et al Effect of risk-reduction counseling with rapid HIV testing on risk of acquiring sexually transmitted infections: the AWARE randomized clinical trial. JAMA 2013; 310 1701–10.
Effect of risk-reduction counseling with rapid HIV testing on risk of acquiring sexually transmitted infections: the AWARE randomized clinical trial.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhvVahs7nK&md5=7ab4fcdd0d2c46e6efbacf5b4abb1f10CAS | 24150466PubMed |

[74]  McCann PD, Gray RT, Hoare A, Bradley J, Down I, Donovan B, et al Would gay men change their sexual behavior to reduce syphilis rates? Sex Transm Dis 2011; 38 1145–50.
Would gay men change their sexual behavior to reduce syphilis rates?Crossref | GoogleScholarGoogle Scholar | 22082726PubMed |

[75]  Wohlfeiler D. What difference can we make in reducing syphilis among gay men? And how? Sex Transm Dis 2011; 38 1159–60.
What difference can we make in reducing syphilis among gay men? And how?Crossref | GoogleScholarGoogle Scholar | 22082728PubMed |