HIV Cluster and Outbreak Detection and Response

HIV cluster detection and response (CDR) identifies communities affected by rapid HIV transmission. CDR helps public health agencies and communities identify where to boost HIV prevention and treatment services and programs. These services may include linking people to HIV testing, medical care, pre-exposure prophylaxis (PrEP), and syringe services programs. Real-time CDR is key to stopping HIV transmission and is a pillar of the federal Ending the HIV Epidemic in the U.S. initiative.

The Benefits of HIV Cluster Detection and Response

Many communities have successfully used CDR strategies to

  • improve HIV care and viral suppression outcomes,
  • increase HIV testing and use of prevention services, and
  • reduce HIV transmission.

CDR can reveal gaps in HIV prevention and treatment services. State and local health departments, medical and social service providers, community-based organizations, and others then work together to address these gaps.

An HIV cluster or outbreak signifies increased HIV transmission among a group of people in an area or in a sexual or social network. This can indicate gaps in HIV prevention or care for that group of people. Tailoring services to the people in the network helps bring HIV prevention and care to people who need it and helps prevent transmission.

Identifying HIV Clusters

HIV clusters or outbreaks refer to the rapid HIV transmission of HIV among a group of people in a sexual or social network, or in a specific geographic location. CDC and health departments can identify HIV clusters or outbreaks in a few different ways. Sometimes, public health agencies use more than one method to understand HIV transmission in a network. This approach provides more complete information to public health departments and communities to help people with a new HIV diagnose get the information and services they need and prevent further transmission.

Cluster detection can be done in different ways:

  • Medical providers, public health staff, or others in the community may notice an increase in HIV diagnoses among a specific group of people.
  • CDC and health departments analyze HIV surveillance data and may identify areas where HIV diagnoses are increasing.
  • Molecular data analysis can also help identify HIV clusters or outbreaks.
    • Health care providers conduct drug resistance testing as a routine part of clinical care to find the best HIV medication for their patients. This testing generates genetic sequences from the virus (not the person). These sequences are a portion of the larger HIV genome.
    • CDC and health departments can then analyze these sequences to identify groups, or clusters, of similar HIV sequences. Because HIV mutates quickly in each person’s body, similar genetic sequences in the virus indicate rapid transmission.
    • Molecular data analysis can help detect HIV clusters and outbreaks more rapidly and comprehensively than had previously been possible.

Molecular data analysis has helped to identify hundreds of growing HIV transmission clusters across the United States, many of which were not detected before. In some cases, health departments have noticed an increase in diagnoses and identified clusters. Later, molecular data revealed that these cluster were much larger than initially thought.

Molecular data can also be compared across geographic areas to help public health officials find out if a cluster or outbreak is contained. These data can tell if a cluster or outbreak is limited to a single community or expands across counties or even across states.

Responding to HIV Clusters

When public health agencies identify an HIV cluster or outbreak, they can work with local partners to address a community’s specific needs. The partners may include health care providers, advocates, and other community leaders and organizations. The response can be broad, reaching people in the affected networks, including

  • People with undiagnosed HIV,
  • People with diagnosed HIV who might not be accessing HIV care or other services, and
  • People without HIV who would benefit from prevention services.

Public health agencies can scale responses to the size of the cluster or outbreak and the needs of the people affected by it. CDR work routinely identifies and prioritizes clusters, responds to small clusters, and expands or escalates responses when needed. Responses can have long-lasting benefits beyond the people affected by the initial cluster. For example, agencies have established new community collaborations dedicated to HIV prevention, and expanded testing and PrEP services in an area.

CDC’s Role in HIV Cluster Detection and Response

CDC provides funding and guidance to health departments to support CDR work, including response preparation and planning. CDC also helps state and local public health staff identify and respond to clusters or outbreaks. In addition, CDC assists and advises public health staff who are responding to a cluster or outbreak, and may provide direct staffing to support response needs.