title: Modelling the impact of chlamydia screening on the transmission of HIV among men who have sex with men.
abstract: BACKGROUND
  Recent studies have found high prevalences of asymptomatic rectal chlamydia among HIV-infected men who have sex with men (MSM). Chlamydia could increase the infectivity of HIV and the susceptibility to HIV infection. We investigate the role of chlamydia in the spread of HIV among MSM and the possible impact of routine chlamydia screening among HIV-infected MSM at HIV treatment centres on the incidence of chlamydia and HIV in the overall MSM population.
  
  
  METHODS
  A mathematical model was developed to describe the transmission of HIV and chlamydia among MSM. Parameters relating to sexual behaviour were estimated from data from the Amsterdam Cohort Study among MSM. Uncertainty analysis was carried out for model parameters without confident estimates. The effects of different screening strategies for chlamydia were investigated.
  
  
  RESULTS
  Among all new HIV infections in MSM, 15% can be attributed to chlamydia infection. Introduction of routine chlamydia screening every six months among HIV-infected MSM during regular HIV consultations can reduce the incidence of both infections among MSM: after 10 years, the relative percentage reduction in chlamydia incidence would be 15% and in HIV incidence 4%, compared to the current situation. Chlamydia screening is more effective in reducing HIV incidence with more frequent screening and with higher participation of the most risky MSM in the screening program.
  
  
  CONCLUSIONS
  Chlamydia infection could contribute to the transmission of HIV among MSM. Preventive measures reducing chlamydia prevalence, such as routine chlamydia screening of HIV-infected MSM, can result in a decline in the incidence of chlamydia and HIV.
authors.affiliation: National Institute of Public Health and Environment, P,O, Box 1, 3720, BA Bilthoven, the Netherlands. maria.xiridou@rivm.nl.
authors.forename: Maria
authors.initials: M
authors.lastname: Xiridou
authors.forename: Henrike J
authors.initials: HJ
authors.lastname: Vriend
authors.forename: Anna K
authors.initials: AK
authors.lastname: Lugner
authors.forename: Jacco
authors.initials: J
authors.lastname: Wallinga
authors.forename: Johannes S
authors.initials: JS
authors.lastname: Fennema
authors.forename: Jan M
authors.initials: JM
authors.lastname: Prins
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Geerlings
authors.forename: Bart J A
authors.initials: BJ
authors.lastname: Rijnders
authors.forename: Maria
authors.initials: M
authors.lastname: Prins
authors.forename: Henry J C
authors.initials: HJ
authors.lastname: de Vries
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Postma
authors.forename: Maaike G
authors.initials: MG
authors.lastname: van Veen
authors.forename: Maarten F
authors.initials: MF
authors.lastname: Schim van der Loeff
authors.forename: Marianne A B
authors.initials: MA
authors.lastname: van der Sande
mesh_terms: D000328:Adult; D002689:Chlamydia / Q000302:isolation & purification* / Q000502:physiology; D002690:Chlamydia Infections / Q000150:complications* / Q000175:diagnosis* / Q000382:microbiology; D015658:HIV Infections / Q000209:etiology / Q000635:transmission* / Q000821:virology; D018451:Homosexuality, Male / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008403:Mass Screening; D008962:Models, Theoretical
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