1. Approaches to estimation of the number of people with undiagnosed HIV infection in a country - based on prevalence surveys - based on reported numbers of HIV diagnoses - based on reported simultaneous HIV/AIDS cases

2. Approach based on reported simultaneous HIV/AIDS cases 1000 people undiagnosed CD4 count < 200

3. Approach based on reported simultaneous HIV/AIDS cases Rate of development of AIDS for people with CD4 count < 200 ~ 25 per 100 person years 1000 people undiagnosed CD4 count < 200

4. Approach based on reported simultaneous HIV/AIDS cases Rate of development of AIDS for people with CD4 count < 200 ~ 25 per 100 person years 1000 people undiagnosed CD4 count < 200 250 people expected to develop AIDS over a 1 year period….

5. Approach based on reported simultaneous HIV/AIDS cases Rate of development of AIDS for people with CD4 count < 200 ~ 25 per 100 person years 1000 people undiagnosed CD4 count < 200 250 people expected to develop AIDS over a 1 year period…..and hence present with simultaneous HIV/AIDS

6. Approach based on reported simultaneous HIV/AIDS cases So if we observe 250 cases of simultaneous HIV/AIDS in people with CD4 count < 200 in a year then …..

7. Approach based on reported simultaneous HIV/AIDS cases …this implies there are 1000 people with undiagnosed HIV and CD4 count < 200 So if we observe 25 cases of simultaneous HIV/AIDS in people with CD4 count < 200 in a year then……..

8. With knowledge of the distribution of CD4 count in undiagnosed people can use this approach to estimate total number of undiagnosed Approach based on reported simultaneous HIV/AIDS cases 0 50 200 350 500 650 CD4 count in undiagnosed

9. With knowledge of the distribution of CD4 count in undiagnosed people can use this approach to estimate total number of undiagnosed Approach based on reported simultaneous HIV/AIDS cases 0 50 200 350 500 650 CD4 count at diagnosis in those diagnosed while asymptomatic

10. Issues to consider - Distribution of CD4 count in undiagnosed - Under-diagnosis and under-reporting of AIDS Approach based on reported simultaneous HIV/AIDS cases

11. Advantages - Particularly well suited to estimating number of undiagnosed people with low CD4 count See poster: Lodwick et al PE 18.1/5 Approach based on reported simultaneous HIV/AIDS cases

12. How does this relate to UK CHIC ? We have requested to use data from CHIC to provide: - Data on CD4-specific AIDS rates - Data on CD4 at diagnosis in people without AIDS to use in writing up this new method(s)