title: Use of surveillance data on HIV diagnoses with HIV-related symptoms to estimate the number of people living with undiagnosed HIV in need of antiretroviral therapy.
abstract: BACKGROUND
  It is important to have methods available to estimate the number of people who have undiagnosed HIV and are in need of antiretroviral therapy (ART).
  
  
  METHODS
  The method uses the concept that a predictable level of occurrence of AIDS or other HIV-related clinical symptoms which lead to presentation for care, and hence diagnosis of HIV, arises in undiagnosed people with a given CD4 count. The method requires surveillance data on numbers of new HIV diagnoses with HIV-related symptoms, and the CD4 count at diagnosis. The CD4 count-specific rate at which HIV-related symptoms develop are estimated from cohort data. 95% confidence intervals can be constructed using a simple simulation method.
  
  
  RESULTS
  For example, if there were 13 HIV diagnoses with HIV-related symptoms made in one year with CD4 count at diagnosis between 150-199 cells/mm3, then since the CD4 count-specific rate of HIV-related symptoms is estimated as 0.216 per person-year, the estimated number of person years lived in people with undiagnosed HIV with CD4 count 150-199 cells/mm3 is 13/0.216 = 60 (95% confidence interval: 29-100), which is considered an estimate of the number of people living with undiagnosed HIV in this CD4 count stratum.
  
  
  CONCLUSIONS
  The method is straightforward to implement within a short period once a surveillance system of all new HIV diagnoses, collecting data on HIV-related symptoms at diagnosis, is in place and is most suitable for estimating the number of undiagnosed people with CD4 count <200 cells/mm3 due to the low rate of developing HIV-related symptoms at higher CD4 counts. A potential source of bias is under-diagnosis and under-reporting of diagnoses with HIV-related symptoms. Although this method has limitations as with all approaches, it is important for prompting increased efforts to identify undiagnosed people, particularly those with low CD4 count, and for informing levels of unmet need for ART.
authors.affiliation: Research Department of Primary Care and Population Health, University College London, London, United Kingdom.
authors.forename: Rebecca K
authors.initials: RK
authors.lastname: Lodwick
authors.affiliation: Research Department of Infection and Population Health, University College London, London, United Kingdom.
authors.forename: Fumiyo
authors.initials: F
authors.lastname: Nakagawa
authors.affiliation: Stichting HIV Monitoring, Amsterdam, Netherlands.
authors.forename: Ard
authors.initials: A
authors.lastname: van Sighem
authors.affiliation: Research Department of Infection and Population Health, University College London, London, United Kingdom.
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Sabin
authors.affiliation: Research Department of Infection and Population Health, University College London, London, United Kingdom.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Phillips
mesh_terms: D019380:Anti-HIV Agents / Q000627:therapeutic use*; D018791:CD4 Lymphocyte Count; D062665:Epidemiological Monitoring; D015658:HIV Infections / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology* / Q000276:immunology; D006301:Health Services Needs and Demand / Q000706:statistics & numerical data*; D006801:Humans
chemical_list: D019380:Anti-HIV Agents