HIV Risk and Prevention Estimates


This section of the CDC HIV Web site provides public health professionals and others with the state of the science regarding HIV prevention including estimates from the current scientific literature for HIV risk behaviors, effective prevention strategies to reduce the risk of acquiring or transmitting HIV, and factors increasing HIV risk. The estimates come from the published scientific literature and will be periodically updated as new research is completed.

If you are interested in learning more about your own risk of acquiring or transmitting HIV, you can also go to CDC’s HIV Risk Reduction Tool designed to help individuals make the best decisions for protecting themselves and their partners.

Principles for Selecting Estimates

Given different states of the science for the different prevention strategies reviewed, with a range of study designs (e.g., RCT, observational) and measurement methods used (e.g., self-report, blood levels of drug) in the literature, decision rules were made to be applied across strategies in an effort to select effectiveness estimates that were most closely aligned with each other and that most accurately represented effectiveness if the prevention strategy was optimally used.  More detailed principles are listed below, and the rationale for each specific estimate that was chosen is provided within the tables.

The choice of estimate was prioritized based on the following criteria:

  • Only evidence based on peer-reviewed published reports was considered when determining estimates. Unpublished data, including conference abstracts, were not considered to be as reliable as peer-reviewed publications because results may change as more data become available and data are re-analyzed or methods adjusted based on peer-review feedback. Additionally, the amount of information available for unpublished studies does not always allow us to adequately assess methods and quality of data and analysis. Non-peer reviewed publications may be used for supporting evidence.
  • Only evidence regarding HIV transmission (e.g., HIV outcomes) was considered. Data for non-HIV outcomes (e.g., pregnancy prevention, STD prevention) were considered not to be good proxies for HIV transmission because modeling or other methods that require complex assumptions would be required to equate proxies with HIV transmission rates and introduce additional uncertainty.
  • For the consensus estimates, a hierarchy was established for prioritizing the type of estimate to select.
  • The greatest priority was given to estimates based on “optimal use” of the strategy or intervention; that is, if the strategy or intervention was used as intended to achieve maximum protection. In most cases, this means evidence from restrictive or subset analyses from larger studies was prioritized if those findings were restricted to those participants with optimal adherence to the strategy or intervention.
  • “Optimal use” is typically determined by measuring level of adherence or exposure to the strategy or intervention (e.g. condom; PrEP); or it’s determined by measuring its intended virologic response (e.g. viral suppression is a result of effective ART).  Either way, priority was given to the most objective measure available for determining “optimal use” (e.g., maximum drug level in plasma).
  • In some cases, the most objective measure for determining “optimal use” may not be ideal but may be the most relevant objective measure available (e.g. pharmacy data; directly observed therapy).
  • If an objective measure for “optimal use” was not available, then we chose the best subjective measure available (e.g., self-report) based on assessing maximum adherence or “optimal use” (e.g., consistent use or always using) recognizing that self-report may overestimate actual use.
  • Other findings reflecting effectiveness of the intervention, if used recently or at all, were not used for selecting the most appropriate effectiveness estimate for “optimal use”.  However, these other findings were summarized when available to provide a broader context of the evidence available for each strategy or intervention.  In addition, findings from intent-to-treat, or modified intent-to-treat, (mITT/ITT) analyses from RCTs, comparing groups as assigned regardless of exposure or use were also summarized for broader context.  These findings tend to help illustrate the extent to which the intervention effectiveness depends on adherence.
  • An estimate from a published meta-analysis was used if available and relevant for the strategy/risk factor in question; otherwise the most appropriate estimate or range of estimates from relevant studies were used.


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