Guidelines for second generation HIV surveillance - World Health ...

Epidemic categories
Low-level epidemic
• HIV has not spread to significant levels in any subpopulation, including key populations at higher
risk for HIV, such as sex workers, clients of sex workers, men who have sex with men and persons
who inject drugs.
• The spread of HIV is slow and inefficient because there are infrequent and few repeated transmission
contacts among persons at higher risk for HIV. HIV may have only recently been introduced or
may not have entered a population network with behaviours that put them at higher risk for HIV
exposure.
Evaluating a National Surveillance System
Concentrated epidemic
• HIV transmission has taken root in one or more key populations whose behaviour puts them at
higher risk, such as sex workers, clients of sex workers, men who have sex with men and persons
who inject drugs.
• HIV is rarely transmitted to people outside of these key populations at higher risk of HIV exposure
or their regular sex partners.
• Unless there are behaviour changes or changes in the levels of other risk factors such as having
an STI, HIV transmission will continue among these key populations. Transmission will occur most
rapidly among persons who inject drugs or engage in unprotected anal sex.
• The size of key populations at higher risk for HIV and the degree of risk behaviours will determine
the number of new infections. Most new infections among the general population can be linked to
contact with a sex worker, men who have sex with men and persons who inject drugs.
Generalized epidemic
• HIV is established in the general population.
• A large proportion of transmission occurs outside the context of commercial sex, injecting drug
use or multiple partner male-to-male sex.
• Sex with multiple partners among the general population is at high enough levels to sustain
epidemic growth.
• Populations with specific behaviours that increase their risk for HIV infection may contribute to
more new HIV infections, even if the number of people with those behaviours is low.
The proxy thresholds for the different categories of epidemic have been discarded because some people
regarded the proxy numbers as extremely rigid and they were a source of confusion to policy-makers.
Categorization of a country or population as having a low-level epidemic should be done with caution. The
low-level designation is sometimes interpreted as “no cause for concern, action or resource allocation”. The
key message for low-level epidemics is the greater need for focused interventions, prioritizing geographical
areas and key population groups, and vigilance in monitoring the epidemic.
2.2.1. Step 1: Decide which key populations are important to track
In each geographical unit, determine whether there are key populations with known risk behaviours.
In the case of concentrated epidemics, the most relevant risk behaviours and key populations are those
associated with the main routes of HIV transmission, such as unprotected anal sex, unprotected vaginal sex,
and/or use of non-sterile injections or materials.
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