Enhancements to the National HIV Surveillance System, United States, 2013-2023

Abstract

HIV infection is monitored through the National HIV Surveillance System (NHSS) to help improve the health of people with HIV and reduce transmission. NHSS data are routinely used at federal, state, and local levels to monitor the distribution and transmission of HIV, plan and evaluate prevention and care programs, allocate resources, inform policy development, and identify and respond to rapid transmission in the United States. We describe the expanded use of HIV surveillance data since the 2013 NHSS status update, during which time the Centers for Disease Control and Prevention (CDC) coordinated to revise the HIV surveillance case definition to support the detection of early infection and reporting of laboratory data, expanded data collection to include information on sexual orientation and gender identity, enhanced data deduplication processes to improve quality, and expanded reporting to include social determinants of health and health equity measures. CDC maximized the effects of federal funding by integrating funding for HIV prevention and surveillance into a single program; the integration of program funding has expanded the use of HIV surveillance data and strengthened surveillance, resulting in enhanced cluster response capacity and intensified data-to-care activities to ensure sustained viral suppression. NHSS data serve as the primary source for monitoring HIV trends and progress toward achieving national initiatives, including the US Department of Health and Human Services’ Ending the HIV Epidemic in the United States initiative, the White House’s National HIV/AIDS Strategy (2022-2025), and Healthy People 2030. The NHSS will continue to modernize, adapt, and broaden its scope as the need for high-quality HIV surveillance data remains.

High-quality data to guide decision-making and response are essential for improving the health of people with HIV and for reducing HIV transmission. One of the most comprehensive and extensive public health surveillance programs in the United States is the Centers for Disease Control and Prevention’s (CDC’s) National HIV Surveillance System (NHSS). NHSS data are critical to understanding where HIV is occurring, how it can be prevented, and which groups are most affected. NHSS data are crucial components of the federal funding algorithm for HIV prevention, care, and other HIV-related initiatives across federal agencies, such as CDC and the US Health Resources and Services Administration^{1 -4} and are used to help allocate resources effectively and to ensure that funding is directed to areas with the greatest need. NHSS data are also used for monitoring the National HIV/AIDS Strategy, the Ending the HIV Epidemic in the United States initiative, and HIV measures for Healthy People 2030. These initiatives call for coordinated efforts to eliminate HIV transmission in the United States.^{5 -7}

When Cohen et al ⁸ described the status of HIV surveillance in the United States in 2013, all 50 states, the District of Columbia, and 6 US territories and freely associated states (American Samoa, Guam, Northern Mariana Islands, Puerto Rico, Republic of Palau, and the US Virgin Islands) had implemented confidential name-based reporting of HIV infections, and CDC was using NHSS data to estimate annual HIV case numbers for the entire country. ⁸ CDC had also expanded NHSS data collection to include all values of CD4+ T-lymphocyte (CD4) and viral load test results, allowing HIV surveillance data to be used to link individuals to care and ensure continued engagement in care. Additional supplemental HIV surveillance activities included HIV incidence surveillance, molecular HIV surveillance, perinatal HIV exposure reporting, and geocoding of HIV surveillance data. Since 2013, CDC has further advanced the NHSS by integrating HIV surveillance funding with funding for HIV prevention programs.^{1 -3} Integration of funding for HIV surveillance and prevention programs has strengthened surveillance efforts to achieve high-quality data, enhanced response capacity, and intensified data-to-care activities aimed at supporting sustained viral suppression.

Purpose

This case study describes the status of the NHSS since the 2013 update, during which time CDC revised the HIV surveillance case definition, expanded data collection to include information on sexual orientation and gender identity, enhanced processes to improve data quality, and expanded reporting to include social determinants of health and health equity measures. This case study aims to highlight how these updates have affected the utilization of NHSS data to track and monitor HIV transmission, plan and evaluate public health interventions, inform policy development, allocate resources for prevention and treatment programs, identify clusters and respond to rapid transmission, and design and implement national programs, strategies, and guidance to address HIV.

Methods

In accordance with federal guidelines (eg, 45 CFR part 46.102[I][2]; 21 CFR part 56; 42 USC §241[d]; 5 USC §552a; 44 USC §3501 et seq), surveillance of cases of HIV infection is determined a public health activity and not human subjects research, and ethical consideration and institutional review board approval are not required for analyses or reporting of NHSS data. Thus, we did not seek institutional review board approval for this work.

HIV Case Surveillance

Conducting HIV case surveillance

States, territories, and freely associated states report HIV data according to state and local laws and regulations. States and territories voluntarily notify CDC of HIV cases but remove names and other directly identifying information before they report case information to CDC. HIV surveillance programs use document-based surveillance methods, which allow surveillance programs to monitor cases longitudinally. HIV surveillance programs collect demographic, clinical, laboratory, vital status, and behavioral data. Since the 2013 status update, HIV surveillance programs include sexual orientation and gender identity as part of demographic data. CDC and public health departments prefer electronic case reporting and electronic laboratory reporting because they are the most efficient methods to obtain information. ⁹

HIV surveillance case definition

The HIV surveillance case definition has evolved over time. In the current (2014) definition, CDC and the Council of State and Territorial Epidemiologists have (1) applied a single case definition to people of all ages rather than separating children aged <13 years, (2) revised the laboratory criteria for a confirmed case, and (3) added “stage 0” based on a sequence of negative and positive test results indicative of early infection. ⁹ CDC will continue to update the HIV case definition, as needed, to ensure the most accurate monitoring of HIV infection.

Monitoring HIV infection

Because HIV is a chronic infection without a cure, longitudinal monitoring is essential to improve health and reduce transmission. HIV surveillance collection should include information on numerous sentinel events, such as first and subsequent measurements of CD4, viral loads, and HIV nucleotide sequences from drug resistance tests; HIV-negative test results for people who subsequently received an HIV diagnosis; immunologic and clinical classification of stage 3 disease (or AIDS); and death. Infants born to people with HIV infection (perinatally exposed) should be followed up to age 18 months to determine the infant’s HIV status. Public health departments and CDC use HIV surveillance data to determine stage of HIV infection, ¹⁰ assess transmission, and monitor care outcomes (Table 1).

Table 1.

Reportable events and key uses of data to monitor HIV infection in the National HIV Surveillance System

Key uses of data for reportable event
Perinatal exposure a	Diagnostic and prior HIV-negative test results b	First CD4, viral load, and genotype test results c	Subsequent CD4, viral load, and genotype test results d	Death e
—	Diagnose HIV infection	Monitor linkage to and receipt of HIV care and viral suppression		Identify cause of death
—	Determine stage of HIV infection, including early HIV infection (stage 0 or acute) and stage 3 (AIDS) f			—
—	Identify clusters and outbreaks of rapid HIV transmission g			—
—	Monitor HIV subtypes and drug resistance–associated mutations h			—
—	Estimate number of new HIV infections (HIV incidence) i		—	—

^aExposure of an infant to HIV infection is through the infant’s birthing person and applicable only for birthing person–to-child transmission.

^bHIV is diagnosed with HIV testing; some diagnosed cases are new (incident) infections and others are long-standing infections. Some people may be tested for HIV during stage 0 or during the acute stage of infection (ie, immediately after the person is infected and before antibodies have developed). Acute HIV infection can be identified by an indeterminate or negative supplemental test result that is part of the HIV diagnostic testing algorithm. Stage 0 or early HIV infection can be identified by a negative or indeterminate HIV test result ≤180 days before or ≤60 days after the first positive HIV test result.

^cAfter HIV diagnosis, laboratory testing for initial CD4+ T-lymphocyte (CD4) count (or percentage) and viral load serve as markers of the degree of immunosuppression. These laboratory results are also indicative of entry into HIV medical care. Genotype testing is part of the standard of care for people with HIV and is recommended at entry into care, before initiation of antiretroviral therapy, at treatment failure, and when clinically indicated.

^dLaboratory test results (eg, CD4, viral load, genotype) reported to HIV surveillance are used to monitor linkage to and receipt of HIV care and viral suppression among people with HIV.

^eDeath information is routinely collected as a part of HIV surveillance from state vital statistics registries, the National Death Index, ¹¹ and the Social Security Administration Death Master File. ¹²

^fPublic health departments can use information included in surveillance case reports and laboratory results to monitor cases of HIV infection longitudinally on a population basis for progression to stage 3 (AIDS), determined by a CD4 count <200 cells/mL or <14% or the occurrence of an AIDS-defining condition.

^gPublic health departments can use surveillance data to identify clusters and outbreaks of rapid transmission by analyzing HIV sequence data to identify groups of people with extremely similar HIV sequences (molecular clusters) or by analyzing diagnosis data to identify increases in HIV diagnoses in a particular geographic area or population (time–space clusters).

^hHIV sequences are used to monitor HIV subtypes, assess transmitted drug-resistance–associated mutation prevalence, and predict susceptibility to common HIV drugs.

ⁱHIV diagnoses, the first CD4 test result after HIV diagnosis, and other HIV surveillance data are used to estimate the number of new HIV infections (incidence) during a specified time. Estimates of HIV incidence include people with diagnosed and undiagnosed HIV infection. Estimates are used to assess changes in characteristics of people with newly acquired HIV infection.

Laboratory reporting

CDC and public health departments use HIV laboratory test results to determine whether the case definition is met, determine disease stage, detect clusters of HIV infection, monitor HIV prevention and care outcomes, and estimate HIV incidence and prevalence. HIV surveillance programs of all reporting jurisdictions (states, the District of Columbia, and 6 territories and freely associated states) require reporting of HIV-related test results indicative of infection; however, all jurisdictions do not require the reporting of all values of CD4 (counts and percentages) and viral load (detectable and nondetectable) test results, which are used to monitor HIV progression and care-related outcomes (eg, linkage to care, viral suppression). ¹³ As of January 2023, 49 states, the District Columbia, and Puerto Rico had implemented laws and regulations requiring the reporting of all values of CD4 and viral load test results to public health departments. ¹³

HIV surveillance system evaluation and data quality

Jurisdictions use information entered into their local Enhanced HIV/AIDS Reporting System for annual assessment of their surveillance processes and outcome standards and then submit a standard evaluation report to CDC. CDC uses this information to evaluate the performance of state and local HIV surveillance systems and to provide technical assistance and support. CDC, in collaboration with the Council of State and Territorial Epidemiologists and staff from state and territorial HIV surveillance programs, routinely revises and updates process and outcome standards. From 2013 through 2017, collaboration resulted in 8 outcome standards; in 2018, collaboration resulted in 9 more outcome standards. Collaborative efforts resulted in 17 updated outcome standards in 2023, with outcomes to be evaluated using the updated standards in 2025 (Table 2).

Table 2.

Outcome standards for HIV surveillance in the United States, 2018-2023 ^a

Outcome standard	Evaluation
Cause of death b	• ≥85% of all deaths that occurred among people with diagnosed HIV infection during the evaluation year have an underlying cause of death, assessed 24 months after the evaluation year
Completeness of case ascertainment c	• ≥95% of the expected number of people with HIV infection diagnosed during the evaluation year are reported in the local HIV surveillance system, assessed 12 months after the evaluation year
Timeliness of case ascertainment c	• ≥90% of the expected number of people with HIV infection diagnosed during the evaluation year are reported in the local HIV surveillance system within 6 months after diagnosis, assessed 12 mo after the evaluation year
Data quality	• ≥97% of all people with HIV infection diagnosed during the evaluation year have no required fields missing and pass all standard data edit checks, assessed 12 months after the evaluation year
Risk factor ascertainment c	• ≥80% of all people with HIV infection who were first entered in the local HIV surveillance system during the evaluation year have sufficient HIV risk factor information to be classified into a known transmission category, assessed 12 months after the evaluation year
Intrastate duplicates	• ≤1% of all people with diagnosed HIV infection who were reported to the local surveillance program through the end of the evaluation year have duplicate case reports, assessed 12 months after the evaluation year
Interstate duplicatesb,d	• ≥98% of all potential duplicate case pairs identified on the Routine Interstate Duplicate Review (RIDR) process are resolved, assessed at the end of each 6-month RIDR cycle
Cumulative interstate duplicate reviewb,e	• ≥20% of all potential duplicate case pairs identified on the Cumulative Interstate Duplicate Review list are resolved, assessed in December of each of the 5 years of the funding cycle; this measure has cumulative standards for years 2018 (20%), 2019 (40%), 2020 (60%), 2021 (80%), and 2022 (100%)
CD4 reporting c	• ≥85% of all people aged ≥13 years with HIV infection diagnosed during the evaluation year have a CD4 test result based on a specimen collected within 1 month after HIV diagnosis, assessed 12 months after the evaluation year
Viral load reporting c	• ≥85% of all people aged ≥13 years with HIV infection diagnosed during the evaluation year have a viral load test result based on a specimen collected within 1 month after HIV diagnosis, assessed 12 months after the evaluation year
Timeliness of laboratory reporting b	• ≥85% of all laboratory results with a specimen collection date during the evaluation year for people with HIV infection diagnosed during the evaluation year are entered in the HIV surveillance system within 60 days of the specimen collection date, assessed at 12 months after the evaluation year
Completeness of nucleotide sequence b	• ≥60% of all people with HIV infection diagnosed during the evaluation year have an analyzable nucleotide sequence, assessed 12 months after the evaluation year
Antiretroviral history b	• ≥70% of all people with HIV infection diagnosed during the evaluation year have prior antiretroviral use history, assessed 12 months after the evaluation year
Previous negative HIV test b	• ≥70% of all people with HIV infection diagnosed during the evaluation year have a known value for previous negative HIV test result, assessed 12 months after the evaluation year ≥50% of all people with HIV infection diagnosed during the evaluation year who have a previous negative HIV test result have a valid date of documented negative test result, assessed 12 months after the evaluation year
Geocoding and data linkage b	• ≥90% of all people with HIV infection diagnosed during the evaluation year have their address at diagnosis geocoded to the census-tract level, assessed 12 months after the evaluation year
Perinatal HIV exposure reportingb,f	• ≥85% of all HIV-exposed infants born during the evaluation year have HIV infection status determined by 18 months of age
Data reporting and dissemination	• An HIV surveillance report is published and disseminated annually • A comprehensive integrated HIV epidemiologic profile is published and disseminated during the 5-year funding period

Abbreviations: CD4, CD4+ T-lymphocyte; CDC, Centers for Disease Control and Prevention.

^aOutcome standards were developed by CDC in collaboration with the Council of State and Territorial Epidemiologists and staff from state and territorial HIV surveillance programs.

^bOutcome standard implemented in 2018.

^cOutcome standard updated in 2018.

^dOngoing activity to identify duplicate cases reported in 6-month intervals.

^ePotential duplicate cases ever reported to CDC through December 2017.

^fOnly applies to areas conducting perinatal HIV exposure reporting.

CDC provides technical support and guidance, specialized tools, and resources to assist jurisdictions in achieving the outcome standards. For example, for assistance with laboratory reporting, CDC provides support and updates to the Logical Observation Identifiers Names and Codes (LOINC) ¹⁴ code mappings for in vitro diagnostic testing and provides SAS code (SAS Institute) to monitor laboratory data quality. For assistance with updates to vital status, CDC supports HIV surveillance programs with linking HIV cases to the National Death Index (NDI), ¹¹ NDI Plus, ¹¹ and Social Security Administration’s Death Master File ¹² and supports the implementation of requirements for timely ascertainment of cause or causes of death and the identification of people with HIV who were not previously reported to HIV surveillance programs. For assistance with identifying and resolving duplicate HIV case records, CDC distributes semiannual reports of potential duplicates to jurisdictions; provides a secure, online Soundex match application that allows for duplicate review of reported cases; and supports a secure data-sharing tool (the ATra Black Box) for more efficient identification and evaluation of duplicate cases. ¹⁵ From 2018 through 2023, jurisdictions improved data accuracy by resolving (determining if an HIV case represented the same person or different people) 98% (516 474 of 527 264) of potential duplicate cases in NHSS (unpublished data).

Data analysis and dissemination

After improvements in data quality and duplicate processing, in 2016, CDC released the 2015 HIV Surveillance Report without statistical adjustment for reporting delays. ¹⁶ CDC publishes annual HIV surveillance reports, including provisional data with a 12-month reporting delay on HIV-related indicators, including incidence, diagnoses, deaths, prevalence, and care-related outcomes. CDC also releases preliminary data every quarter on HIV diagnoses and linkage to HIV medical care. CDC publicly releases national-, state-, and county-level data in AtlasPlus from the National Center for HIV, Viral Hepatitis, STD, and TB Prevention. ¹⁷ To ensure confidentiality of HIV surveillance data, CDC must adhere to specific levels of data suppression and data rerelease agreements established with state or local HIV surveillance programs.

HIV surveillance programs are now required to collect information on gender identity, and CDC reports national-level HIV data on people who identify as transgender or as a person of additional gender identity.^11,16-18 Improved HIV care data and timely identification of duplicate HIV cases in NHSS have led to increased accuracy of geographic data. Prevalence data are now presented based on a person’s most recently known jurisdiction of residence rather than jurisdiction of residence at the time of HIV diagnosis. With expansion of geocoding residential information to the census-tract level in all jurisdictions, CDC has incorporated data on social determinants of health into HIV surveillance reports. ¹⁹ CDC has also incorporated data on health equity into HIV surveillance reports, including routine presentation of absolute and relative disparity data; such data have helped identify and address disparities in HIV outcomes among different populations.^11,18,19

HIV incidence and prevalence estimation

In 2017, CDC discontinued the HIV Incidence Surveillance Supplemental Activity, which involved testing remnant HIV-positive blood specimens to determine the recency of infection. Instead, CDC now uses the first CD4 test after HIV diagnosis, along with an estimation method based on a CD4 depletion model, to estimate the incidence and prevalence of HIV in the United States.^20,21 Public health departments can use CDC-developed SAS programs for state and local HIV incidence and prevalence calculations.

Cluster detection and response

Public health departments and their community partners use HIV cluster detection and response (CDR) to identify clusters and respond to rapid transmission. ²² An HIV cluster or outbreak refers to rapid transmission among people in a sexual or drug-using network, which is often attributed to limited or no access to HIV prevention and care services. Stigma, discrimination, racism, poverty, and other social and structural factors all contribute to limiting access to HIV prevention and care services. Public health departments and their community partners respond to rapid HIV transmission by identifying and closing gaps in HIV prevention and care services for affected communities.

Since 2018, CDC requires HIV surveillance programs to collect and report HIV sequence data and to conduct monthly analyses of data to identify clusters. HIV molecular clusters (groups of people with extremely similar HIV sequences) and increases in diagnoses in a particular geographic area or population (time–space clusters) indicate rapid transmission.^23,24 CDC supports Secure HIV-TRACE, a secure, web-based application for public health departments to detect molecular clusters. ²⁵ Public health departments can use or adapt CDC-developed time–space SAS programs or develop their own approaches to detect, review, and prioritize clusters. For prioritized clusters, public health departments work with partners to gather information needed to guide response activities. Because rapid transmission can affect people beyond the identified cluster, public health departments recognize the importance of responding at individual, network, and systems levels.

CDC and public health departments recognize that community engagement and partnership are important parts of CDR. CDC has engaged with community members and partners extensively, and public health departments are required to engage with community members and partners to plan CDR activities and to implement responses to clusters. CDC has reemphasized that HIV surveillance data are and should be strongly protected from use for non–public health purposes. CDC has collected data indicating that no public health departments have released molecular sequence data for non–public health purposes (unpublished data).

Perinatal HIV exposure reporting

Perinatal HIV exposure reporting (PHER) identifies and monitors infants who were perinatally exposed to HIV from their birth until their HIV status is determined. CDC requires jurisdictions that have increased numbers of perinatal HIV exposures, increased numbers of females (sex assigned at birth) of childbearing age with HIV, or increased rates of females with diagnosed primary or secondary syphilis to conduct PHER. CDC strongly encourages PHER in other jurisdictions where laws and regulations allow the collection of data on HIV-exposed infants. Public health departments can use PHER data to monitor outcomes in birthing people with HIV infection, longitudinal pediatric HIV outcomes, and the long-term effects of antiretroviral therapy on infants during pregnancy and after birth.

Security and confidentiality

Public health data are the foundation of public health practice and essential to helping people live healthy lives. Strong legal and scientific justifications have supported the conduct of surveillance without explicit individual consent, and protecting people’s privacy and confidentiality is an essential part of using public health surveillance data. ²⁶ CDC has strong security measures to ensure the privacy and confidentiality of HIV surveillance data. In addition, state, territorial, and local public health departments must comply with CDC data security and confidentiality guidelines. ²⁷

HIV-related criminalization laws are a concern in regard to whether public health surveillance data on HIV infection should be released. HIV-related criminalization laws do not reflect current scientific and medical evidence and can reinforce negative stereotypes and misconceptions about people with HIV. CDC protects HIV surveillance data from release by an assurance of confidentiality, and CDC guidelines indicate that public health departments should use public health data only for public health purposes. ²⁸ CDC continues to work with public health departments to enhance security and confidentiality of HIV surveillance data.

Integrated Funding of HIV Surveillance and Prevention Programs

In 2018, CDC aimed to strengthen the ability of public health departments to maximize the effects of federal funding by integrating public health department funding for HIV surveillance and HIV prevention into a single program. ¹ The integration of HIV surveillance and HIV prevention funding into a single program has accelerated progress toward ending the HIV epidemic in the United States through improved use of surveillance data to guide HIV prevention and care efforts.

HIV surveillance data play a crucial role in identifying HIV clusters, which allows for focused efforts to improve testing, treatment, and prevention in communities experiencing rapid transmission. ²⁹ HIV surveillance data are also a key driver of data-to-care activities; public health departments use data-to-care strategies to improve continuity of HIV care by identifying people with HIV not receiving medical care or other services and by facilitating linkage to these services. ³⁰ Integration of prevention and surveillance programs by CDC and public health departments has supported increased awareness of HIV infection, prompt linkage to care and treatment, and use of data-to-care strategies to support reengagement in HIV care and viral suppression and to prevent HIV transmission.

Outcomes

NHSS provides timely and comprehensive data to guide public health action at federal, state, and local levels. NHSS data are used to (1) monitor and characterize the trends and incidence of HIV infection; (2) identify determinants and disparities in HIV transmission to promote health equity; (3) inform HIV prevention and care efforts, resource allocation, and public health policy development; and (4) monitor and evaluate the effects of HIV prevention and care programs on the key outcome indicators of the Ending the HIV Epidemic in the United States initiative, the National HIV/AIDS Strategy, and Healthy People 2030.^5-7 The regular assessment and enhancement of NHSS will ensure that NHSS remains modern and effective in guiding public health actions to achieve national HIV prevention and care goals.

Lessons Learned

The continued enhancement of NHSS has provided valuable lessons, including:

1. State and local regulations should support the collection and timely reporting of key HIV data elements, such as laboratory results, demographic information, residential data, and vital status to public health departments and CDC to provide accurate and actionable data.

2. Modern, flexible, and interoperable data collection and analysis tools are needed to improve the accuracy, efficiency, and timeliness of reporting of HIV surveillance data to public health departments and CDC.

3. HIV surveillance data must be actively used for public health action to make progress in ending HIV transmission in the United States, including using HIV surveillance data to identify and respond to HIV clusters, direct HIV prevention and care services to people with HIV, and evaluate the effects of HIV interventions and programs.

4. Collaboration with public health department and community partners is essential for effectively using HIV surveillance data to identify and respond to HIV clusters and to improve HIV prevention and care services. Engagement with community partners helps to ensure that the needs and perspectives of affected populations are considered.

5. Partnership and collaboration between HIV surveillance and HIV prevention must continue to increase awareness of HIV infection and promote prompt linkage to HIV care and treatment.