I think establishing the benchmark between prevalence and incidence would deter the appropriate measure in which a possible set of specific guidelines will be used. This is a very good topic that i hope to hear and answered.

I strongly agree that as a measurement incidence is appropriate, but there are operational problems that must be solved to get a reliable incidence mostly because a new diagnosed case does not mean a new infected case.

I appreciate your valuable feedback, suppose we confine ourselves to HIV/AIDS, there are obviously operational dynamics that have to be heeded to so as to develop a more accurate measure of incidence but I believe it remains indisputably the correct yardstick for measuring the progress of a prevention intervention. I agree with you that a new diagnosed case does not necessarily mean a new infection case but for HIV, with well known epidemiology and natural history, that should not be much of a problem.

We also know that there are several factors that are determinants of incidence. Population size, health seeking behavior (for diagnosis), diagnostic techniques and their sensitivity among others. It is therefore possible to adjust through regression to develop a mathematical model unique to a particular region for determining incidence rates. Through this we can make a near accurate measure of how our interventions that target preventing HIV/AIDS are performing.

I have always felt so too and the age at diagnosis, age and duration of exposure to prevention programs may actually give a clue to whether the infection is new or not. add to this the statistical modelling it would help to determine the extent of prevention interventions working

I may and strongly agree that in this situation developing a strategic model in order to establish guidelines to measure new cases and old cases that would help researchers

Definitely incidence is what we try to change with our interventions and what should be considered in research; however, it should first be estimated and whether we have sufficient data to estimate incidence reliably depends on the country, the population and the situation.

The WHO has been working with partners including the US CDC in looking at using HIV incidence for monitoring HIV in populations. There has been quite a lot of progress in this area with diagnostic assays for HIV- 1 BED, and a new development for HIV-1 subtype C:

http://www.who.int/diagnostics_laboratory/links/hiv_incidence_assay/en/index.html

The use of incidence as an indicator for gauging HIV prevention efforts is a controversial one. This is more so for a chronic disease such as HIV because inicidence is the measure of new cases among those at risk per peron-time years. As a result, it is practically impossible to monitor everyone who is at risk for HIV infection. Besides, such individuals may die from HIV complications before diagnosis. Therefore we will miss many undiagnosed case. This means that we need another measure.

The best indicator would then be prevalence; The numerator consists of all those who test positive for HIV and the denominator will be the whole population. For a chronic disease, this would be the best indicator for public health interventions.

Thanks.

Both incidence and prevalence are problematic indicators in countries with generalised epidemics and high antiretroviral treatment coverage. For example in South Africa, prevalence is actually increasing, not because of changes in incidence, but dramatic increases in survival for person on ARVs. While there is no easy solution to handle this, mathematical models looking at changing prevalence patterns over age can be useful.

Thanks Ben for that observation. I however think otherwise. Don't you think we know who is at risk of HIV? It is the entire population under study which seems to also make the denominator in your argument for prevalence use. Those who test positive for HIV at a particular time are not entirely new cases. There should be alot of factors that contribute to prevalence and that consist of tested cases and already pre-existing cases. The success of an intervention aimed to prevent new cases should strictly show how it has prevented those new cases from occurring in terms of a reduction in the number of new cases or otherwise. If you take time to look at the WHO RITA regime (Recent Infection testing algorithm). It will expose you to the complex area of estimating incidence as a measure of intervention success. The WHO has recognized the need for that.

Thanks Joel. I think that underlines the importance of incidence use rather than prevalence. I noticed during a presentation in the AIDS 2012 Conference held in Washington DC end of July on Orange county and the increase in prevalence which would otherwise be construed to mean the lack of success in the interventions to prevent new cases while it should in essence indicate otherwise because some of the goals of the regimes is the availability of life prolonging HIV drugs which assure the population of a longer survival period hence higher prevalence.

This question becomes very cricial specially fpr counties with high HIV prevalence. The measure of incidence est warranted even if the actual tools are not completely accurate. I strongly feel that countries should adopt one method and repeatively use it to establish the trends of incidence rather than focusing on the actual rates. This will inform on the direction of the epidemic and need to adjust or reinforce prevention programs in place.

I agree with you Stephane. Which incidence method would you recommend?