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Working Papers

Estimates of HIV Incidence

Incidence is a measure of the rate of new HIV infection for a given population. Incidence is critical for monitoring the status of an epidemic--if incidence falls the epidemic is declining, while if incidence increases, the epidemic is getting more serious. The incidence rate calculated in the attached working papers is based on yearly new HIV infections divided by the total population at risk (Total Population - Number of People Living with HIV/AIDS). Incidence should not be confused with prevalence which measures the proportion of a given population that is HIV positive. As more and more people with HIV receive anti-retroviral treatment (ART) prevalence can increase as AIDS patients who would otherwise have died, survive-- increasing prevalence-- although new infections could be decreasing at the same time.

Measuring incidence directly is difficult. A UNAIDS report examines issues related to calculating incidence directly. However, it is possible to estimate incidence using UNAIDS and World Bank data. A pdf report explaining calculation methods used in calculating HIV incidence is available here. A brief description of of 1991-2007 trends in HIV incidence at the regional level (World Bank regions) follows, while a comprehensive report on HIV incidence between 1991-2007 at the country and regional level will be posted shortly

The table and charts below show that in terms of level of incidence, SubSaharan Africa (SSA) has been and still is the most seriously HIV-affected region. Incidence in the SubSaharan Africa region peaked in 1994 and has been declining since. It is also clear that global incidence peaked in 1997 and has also been declining since. Incidence in other regions has been consistently lower than SSA and has been declining, with a clear peak for South Asia (SAS) in 1997 and for Europe and Central Asia (ECA) in 2002. Incidence in Latin America and the Caribbean (LAC) has been declining since 1991/92 while trends for the Middle-East and North Africa (MNA) and High Income Countries (HI) have varied within a narrow range at low levels. This data is particularly interesting in terms of the Millennium Development Goals (MDGs). MDG 6 has two targets, the first of which is to "Have halted by 2015 and begun to reverse the spread of HIV/AIDS". The regional data suggests that not only has this goal been achieved, but it was achieved at the global and SSA level before the goal was set by the UN in 2000. An Excel spreadsheet in 1997-2003 format (compatible with all more recent verions) of the table and two charts below is available here. An Excel spreadsheet with time-series estimates of HIV incidence for 1991-2007 at the national and regional level is available here.

REGIONAL HIV INCIDENCE--1991-2008--(PerCent)
Year EAP ECA LAC MNA SAS SSA HI WLD
1991 0.015% 0.003% 0.035% 0.001% 0.006% 0.313% 0.017% 0.050%
1992 0.014% 0.003% 0.035% 0.002% 0.012% 0.344% 0.015% 0.054%
1993 0.012% 0.002% 0.032% 0.002% 0.020% 0.375% 0.016% 0.058%
1994 0.012% 0.002% 0.032% 0.003% 0.033% 0.417% 0.016% 0.066%
1995 0.010% 0.005% 0.029% 0.004% 0.049% 0.409% 0.014% 0.067%
1996 0.011% 0.013% 0.031% 0.004% 0.052% 0.390% 0.012% 0.067%
1997 0.013% 0.021% 0.026% 0.006% 0.053% 0.396% 0.010% 0.068%
1998 0.011% 0.023% 0.029% 0.007% 0.037% 0.362% 0.007% 0.060%
1999 0.013% 0.030% 0.024% 0.007% 0.021% 0.359% 0.010% 0.056%
2000 0.013% 0.042% 0.023% 0.009% 0.021% 0.321% 0.009% 0.053%
2001 0.013% 0.064% 0.025% 0.009% 0.014% 0.332% 0.007% 0.054%
2002 0.013% 0.077% 0.021% 0.009% 0.014% 0.312% 0.007% 0.051%
2003 0.012% 0.069% 0.021% 0.008% 0.014% 0.291% 0.016% 0.050%
2004 0.012% 0.055% 0.019% 0.008% 0.007% 0.258% 0.006% 0.042%
2005 0.011% 0.043% 0.025% 0.007% 0.007% 0.260% 0.007% 0.043%
2006 0.012% 0.032% 0.016% 0.008% 0.013% 0.243% 0.005% 0.041%
2007 0.010% 0.032% 0.024% 0.007% 0.005% 0.241% 0.017% 0.041%
2008 0.040%
Source: Calculated by author from adjusted UNAIDS data


WORLD HIV INCIDENCE (PER CENT) --1991-2008

Source: Calculated by Author from UNAIDS data


REGIONAL HIV INCIDENCE (PER CENT)--1991-2008

Source: Calculated by Author from UNAIDS data

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