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March 2011

Over the years, the Division of HIV/AIDS Prevention (DHAP) at the Centers for Disease Control and Prevention (CDC) has developed various surveillance systems for collecting, analyzing, and disseminating data on HIV infection and AIDS. Through these surveillance systems, DHAP monitors many facets of the evolving HIV epidemic in the United States.

This fact sheet contains information on the six surveillance systems—all part of CDC’s national HIV surveillance system—that DHAP currently uses. The data from these systems inform and guide the critical decisions that ensure HIV prevention funds are directed to those populations most affected by the disease.

Core HIV Surveillance

In 1981, CDC first reported cases of a rare pneumonia in young gay men. This condition was subsequently determined to be AIDS, which in turn was a result of infection with the human immunodeficiency virus (HIV). AIDS reporting started in 1981; by 1986, all 50 states, the District of Columbia, and several U.S. dependent areas had instituted AIDS case reporting. Beginning in 1985, many states implemented HIV case reporting as part of an integrated HIV and AIDS surveillance system; as of 2008, all states had implemented confidential, name-based HIV reporting.

Process: Using a uniform surveillance case definition and report form, all 50 states, the District of Columbia, and 5 U.S. dependent areas (American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands) report confirmed diagnoses of HIV infection and AIDS to CDC. Case reports from these jurisdictions are sent to CDC after removal of personally identifying information.

Which jurisdictions participate: As of April 2008, all jurisdictions report cases of both HIV infection and AIDS to CDC. However, jurisdictions need to have 4 years worth of name-based surveillance data before the data can be statistically adjusted for reporting delays and for the redistribution of cases initially reported without risk factors. For the 2009 HIV Surveillance Report, adjusted data on diagnoses of AIDS were available from 50 states, the District of Columbia, and 5 U.S. dependent areas; adjusted data on diagnoses of HIV infection, regardless of the stage of disease, were available from 40 states and 5 U.S. dependent areas.

All 50 states and the District of Columbia will have adjusted data on diagnoses of HIV infection for the 2012 HIV Surveillance Report.

What data are collected: HIV reporting provides information on demographic characteristics (i.e., sex, race/ethnicity, age, and place of diagnosis), transmission category (mode of exposure), initial immune status, and viral load.

In addition, core HIV surveillance activities allow jurisdictions to monitor HIV disease progression, utilization of care services, and trends in the epidemic through the ongoing collection of data on laboratory immunology (viral load and CD4 counts), opportunistic infections and illnesses, and vital status.

The national HIV Surveillance Report is published annually. View the current report.

How this surveillance contributes to HIV prevention: Core surveillance data provide the basis for our understanding of the epidemic and are used to guide public health action at the federal, state, and local levels. Knowing how many people are diagnosed with HIV infection each year—and their stage of disease at diagnosis—is important for planning and resource allocation and for monitoring trends within the epidemic and disparities between groups.

HIV Incidence Surveillance

In 2004, as an extension of core HIV surveillance activities, CDC first funded selected state and local health departments to begin data collection and systems development for HIV incidence surveillance.

Process: State and local health departments that conduct HIV incidence surveillance collect testing and treatment history information as a part of routine surveillance activities. Case reports from these jurisdictions are sent to CDC after removal of personally identifying information. In addition, incidence surveillance coordinators at state and local health departments work closely with commercial/private, public, and hospital-based laboratories to acquire leftover diagnostic blood specimens to test for recent infection. By applying new technology to leftover blood specimens from persons newly diagnosed with HIV infection in the funded jurisdictions, CDC is able to identify the number of new HIV infections in a given year.

Which jurisdictions participate: Since 2008, HIV incidence surveillance areas have included 25 jurisdictions.

What data are collected: In addition to data collected through core surveillance, data on HIV testing behaviors and results from tests for recent HIV infection, collected from the jurisdictions participating in HIV incidence surveillance, are used to estimate HIV incidence. The incidence estimates, which are stratified by age, race/ethnicity, sex, and mode of transmission, describe the number of new HIV infections in the United States.

The data from the jurisdictions that conduct incidence surveillance are extrapolated to yield a national estimate. In 2011, CDC published estimates indicating that HIV incidence has remained essentially stable over the period 2006–2009. Read more about the HIV incidence estimates.

How this surveillance contributes to HIV prevention: Annual estimates of the number of new infections in the United States can be used to monitor the leading edge of the epidemic. Monitoring HIV incidence is critical for evaluating progress in decreasing the number of new HIV infections that occur each year and for allocating resources and evaluating the effectiveness of HIV testing and other prevention programs. Improved surveillance methods allow us to better direct our programs and resources to the populations most affected.

Variant, Atypical, and Resistant HIV Surveillance (VARHS)

Since 2004, as an extension of core HIV surveillance activities, selected state and local health departments have been funded to collect HIV genetic sequence data to identify HIV subtypes and the presence of drug resistance mutations among persons newly diagnosed with HIV infection who have never taken antiretroviral medications.

Process: Health department surveillance staff partner with public health laboratories to acquire and sequence leftover diagnostic specimens from persons with newly diagnosed HIV infection, and with commercial/private and hospital-based laboratories to obtain electronic genetic sequence data from genotype testing that has been done as a part of HIV care. Case reports from these jurisdictions are sent to CDC after removal of personally identifying information.

Which jurisdictions participate: Currently, 11 jurisdictions are funded to collect genetic sequence data to determine HIV-1 drug resistance and subtypes.

What data are collected: In addition to data collected through core surveillance, genetic sequence data are reported to the state or local health department either from leftover blood specimens that are collected and genotyped from HIV diagnostic tests or from genotype testing conducted as a routine part of HIV care.

VARHS data are published periodically. The 2006 data were published in the May 2010 issue of AIDS (read the abstract), and the 2007 data were presented in February 2010 at the 17th Conference on Retroviruses and Opportunistic Infections.

How this surveillance contributes to HIV prevention: Data from VARHS are used to monitor the frequency of transmitted drug-resistance-associated mutations and HIV subtypes among persons for whom HIV infection is newly diagnosed. These data provide information on the variance of the transmitted strains of HIV and the emergence of resistant strains. To effectively monitor HIV drug resistance, state and local surveillance systems must work with laboratories in their jurisdictions to expand their surveillance activities to include reporting of HIV genomic data.

Enhanced Perinatal Surveillance (EPS)

In 1999, to further reduce perinatal HIV transmission in areas with high HIV prevalence, CDC created the EPS project as an extension of core HIV surveillance activities.

Process: Funded jurisdictions use a standard pediatric HIV case report form and a supplemental EPS data abstraction form to collect data on HIV-infected mothers and their perinatally exposed children, through the comprehensive review of maternal and pediatric medical records. Follow-up on mothers and their children is conducted every 6 months until the child is 18 months of age, unless the child receives a definitive HIV diagnosis (infected or not infected) before 18 months of age. Case reports from these jurisdictions are sent to CDC after removal of personally identifying information.

Which jurisdictions participate: Currently, 15 jurisdictions are funded to collect supplemental perinatal surveillance information.

What data are collected: In addition to data collected through core surveillance, supplemental maternal data include information on the use of antiretroviral therapy (during pregnancy, labor and delivery, and after childbirth), type of delivery (vaginal or cesarean section), access to and use of prenatal care, testing during pregnancy for other conditions, and substance use during pregnancy. Infant data include information on birth weight, use of antiretroviral prophylaxis after birth, date of first HIV test, all laboratory information, and presence of illnesses or birth defects. These data are used to identify and determine the HIV status of all HIV-exposed infants (i.e., infants born to HIV-infected mothers, regardless of whether the infant is infected).

EPS data are published periodically in surveillance supplemental reports. The most current report was published in 2011.

How this surveillance contributes to HIV prevention: These data are used to monitor implementation of U.S. Public Health Service recommendations for counseling and voluntary HIV testing of pregnant women, the use and efficacy of antiretroviral drugs to prevent perinatal HIV transmission as well as opportunistic infections among infants who become infected, and trends of HIV disease among children exposed to HIV perinatally. The surveillance system also collects data that enable state programs to respond to selected requirements of the Ryan White HIV/AIDS Treatment Extension Act of 2009 (Public Law 111-87, October 30, 2009).

National HIV Behavioral Surveillance System (NHBS)

In 2003, CDC created NHBS for conducting behavioral surveillance among persons at high risk for HIV infection.

Process: Surveillance is conducted in rotating annual cycles in three different populations at high risk for HIV: men who have sex with men (MSM), injection drug users (IDUs), and heterosexuals at increased risk for HIV infection (HET). Before each NHBS cycle, formative research is conducted to learn more about the populations and collect data to help with sampling procedures. MSM are sampled using venue-based, time-space sampling methods. Health department staff members first identify venues frequented by MSM (e.g., bars, clubs, organizations, and street locations) and days and times when men frequented those venues. Venues (and specific day/time periods) for recruitment are chosen randomly each month. IDUs and heterosexuals are recruited using respondent-driven sampling, a type of chain referral sampling. Health department staff members select a small number of initial participants, or “seeds,” who complete the survey and recruit their peers to participate. Recruitment and interviewing continue until the target sample size is reached.

Trained interviewers in all NHBS jurisdictions use a standardized anonymous questionnaire to collect information on HIV-related risk behaviors, HIV testing, and use of HIV prevention services. HIV testing is also offered to all participants. During each cycle, a minimum of 500 eligible persons from each participating jurisdiction are interviewed and tested for HIV infection. The first full round of NHBS, which comprised all three cycles (MSM, IDU, and HET), was conducted from 2003–2007. The second round was conducted during 2008–2010, and the third round began in January 2011.

Which jurisdictions participate: As of 2011, 20 jurisdictions with high AIDS prevalence are funded to conduct NHBS. Many of the health department grantees subcontract with local health departments, universities, or community-based organizations to implement NHBS activities

What data are collected: Data on behavioral risks for HIV, HIV testing behaviors, access to and use of prevention services, and HIV testing results are collected.

NHBS findings from the first round have been published in several issues of CDC’s Morbidity and Mortality Weekly Report (MMWR). In 2010, findings from the second cycle of NHBS for MSM were published in the September 24 issue of MMWR.

How this surveillance contributes to HIV prevention: NHBS data are used to provide a behavioral context for trends seen in HIV surveillance data. They also describe populations at increased risk for HIV infection and thus provide an indication of the leading edge of the epidemic. Through systematic surveillance in groups at high risk for HIV infection, NHBS will be critical for monitoring the impact of the National HIV/AIDS Strategy, which focuses on decreasing HIV incidence, improving linkage to care, and reducing disparities.

Medical Monitoring Project (MMP)

In 2005, CDC implemented MMP, a supplemental surveillance system designed to produce nationally representative data on clinical and behavioral outcomes among people living with HIV infection or AIDS who are receiving care in the United States.

Process: MMP uses a 3-stage sampling design to select an appropriate sample of persons from which locally and nationally representative data can be derived. The first stage is selecting geographic areas to participate; the second stage is selecting facilities providing HIV medical care within those participating project areas; and the third stage is selecting patients at least 18 years of age who are receiving care at selected facilities. Trained MMP interviewers and abstractors collect data through face-to-face interviews and medical record abstraction. The 45-minute interview includes questions about medical history, use of medical and social services, and risk behaviors. MMP abstractors then collect additional information on clinical outcomes and other health care services provided from the patient’s medical chart.

Which jurisdictions participate: Since 2009, 23 jurisdictions have been conducting MMP activities. The annual sample of facilities participating in MMP ranges from 600–800 health care facilities. Approximately 9,400 patients from these facilities are sampled annually. The project jurisdictions include over 75% of the total cases of HIV infection and AIDS in the United States.

What data are collected: Data include information on patient characteristics such as gender, age, and health insurance or medical coverage; injection drug use and sexual risk behaviors; reasons for delaying health care; and knowledge of HIV status of most recent sex partner. MMP data are used to provide estimates of risk behaviors and clinical characteristics of persons receiving HIV care; describe health-related behaviors; determine access to and utilization of prevention and support services; increase knowledge of the care and treatment provided; and examine variations of factors by geographic area and patient characteristics.

The current 5-year MMP cycle extends through May 31, 2013. A report on MMP data from the pilot cycle (2005) was published in 2010.

How this surveillance contributes to HIV prevention: Prevention planning groups, policy leaders, health care providers, and people living with HIV infection use the data to inform HIV prevention activities, highlight disparities in care and services, identify unmet needs, and evaluate services. The data are also used to guide policy and funding decisions aimed at reducing the spread of HIV and improving the quality of care for people living with HIV infection throughout the United States.

Surveillance Brief: Terms, Definitions, and Calculations Used in CDC HIV Surveillance Publications