Prevalence and Trends in HIV Infection and Testing Among Adults in the United States: The National Health and Nutrition Examination Surveys, 1999-2018.

BACKGROUND: HIV antibody testing has been included in the National Health and Nutrition Examination Survey, for ages 18-49 since 1999 and for ages 18-59 years since 2009 enabling estimation of trends in HIV prevalence as part of national surveillance in the U.S. household population. Self-reported HIV testing and antiretroviral use was also included in the survey since 1999. SETTING: A continuous household-based probability sample of the U.S. population. METHODS: From 1999 to 2018, 29,020 participants age 18-49 years were tested for HIV antibody and 34,092 participants age 18-59 years were asked about self-report of any previous HIV testing. RESULTS: HIV prevalence was 0.41% among those aged 18-59 in 2009-2018 with a nonsignificant trend over time among those aged 18-49 years from 1999-2002 to 2015-2018. However, significant declines in prevalence were seen among those aged 18-39 years (0.37%-0.11%), women (0.22%-0.06%) and non-Hispanic black persons (2.14%-0.80%). Participants aged 18-39 years self-reported a decline in HIV testing, whereas those aged 40-49 and 50-59 years, non-Hispanic black persons and women reported an increase in getting a HIV test. Prevalence of infection and self-reported history of HIV testing varied by demographic and risk groups. HIV testing among HIV-positive persons was 83.9%. Antiretroviral therapy among those HIV-positive was under 50%. CONCLUSION: Although total HIV prevalence and previous self-reported HIV testing remained stable for the last 20 years, there were significant declines in age and demographic subgroups. Prevalence for both outcomes varied by demographic and risk variables.

Assessing consent for and response to health survey components in an era of falling response rates: National Health and Nutrition Examination Survey, 2011-2018.

Response rates for national population-based surveys have declined, including the National Health and Nutrition Examination Survey (NHANES). Declining response to the initial NHANES interview may impact consent and participation in downstream survey components such as record linkage, physical exams, storage of biological samples and phlebotomy. Interview response rates dropped from 68% in 2011-2012 to 53% in 2017-2018 for adults age 18 and older. Response was higher for children (1-17 years) but with a similar downward trend (2011-2012, 81%; 2017-2018, 65%). Despite declining interview response rates, changes in consent and response rates for downstream components over time have been mixed. Among those interviewed, the examination response rate was over 93%, consent for record linkage was over 90%, and consent for storage of specimens for future research was over 99%. The availability of a blood sample for storage ranged between 60%-65% for children and 78%-85% for adults.

Prevalence and Trends in Hepatitis B Virus Infection in the United States, 2015-2018.

Hepatitis B virus (HBV) is a type of viral hepatitis transmitted through sexual contact, contaminated blood, or from an infected mother to her newborn (1). HBV may cause a liver infection that is acute or short-term, but may also cause chronic or long-term infection. Vaccination was targeted to high-risk groups in 1982, and universal vaccination of newborns was recommended beginning in 1991 in the United States (2). This report provides 2015-2018 prevalence estimates of past or present HBV infection and evidence of hepatitis B vaccination, based on blood collected in the National Health and Nutrition Examination Survey (NHANES).

Prevalence of Herpes Simplex Virus Type 1 and Type 2 in Persons Aged 14-49: United States, 2015-2016.

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are common, lifelong infections, which often have no symptoms (1). People with symptoms may have painful blisters or sores at the site of infection (2,3). The viruses are transmitted through contact with an infected person's lesion, mucosal surface, or genital or oral secretions. This report provides recent national estimates of HSV-1 and HSV-2 antibody prevalence from the 2015­2016 National Health and Nutrition Examination Survey (NHANES) among persons aged 14­49 by age, sex, and race and Hispanic origin, and examines trends in prevalence by race and Hispanic origin from 1999­2000 to 2015­2016.

Toxoplasma gondii Infection in the United States, 2011-2014.

Toxoplasma gondii can cause severe neurologic and ocular disease when transmitted congenitally and in immunosuppressed persons. Sera collected in the National Health and Nutrition Examination Survey 2011 through 2014 in 13,507 persons ≥ 6 years old were tested for T. gondii immunoglobulin (Ig) G and IgM antibodies, and in those both IgG and IgM antibody positive, for IgG avidity. Overall, 11.14% (95% confidence limits [CL] 9.88%, 12.51%) were seropositive for T. gondii IgG antibody (age-adjusted seroprevalence 10.42% [95% CL 9.19%, 11.76%]); in women aged 15-44 years, the age-adjusted T. gondii IgG seroprevalence was 7.50% (95% CL 6.00%, 9.25%). In multivariable analysis, risk for IgG seropositivity increased with age and was higher in males; persons living below the poverty level; persons with ≤ a high school education compared with those with > a high school education; and non-Hispanic black, Mexican American, and foreign born non-Hispanic white persons compared with U.S.-born non-Hispanic white persons. Overall, 1.16% (95% CL 0.94%, 1.42%) were T. gondii IgM antibody positive and 0.71%, (95% CL 0.54%, 0.92%) were both IgM and IgG antibody positive. In multivariable analysis, the significant risk factors for being both IgM and IgG positive were older age, crowding, and non-U.S. birth origin compared with U.S.-born persons. Among those positive for both IgM and IgG antibody, almost all had high avidity (all women aged 15-44 years had high avidity). Toxoplasma gondii antibody prevalence remains relatively low in the United States, although it is higher in non-U.S.-born persons, males, and some minority and socioeconomically disadvantaged groups.

Prevalence, Change Over Time, and Comparison With U.S. Estimates of Selected Infectious Diseases in Los Angeles County: Findings From the National Health and Nutrition Examination Survey, 1999-2006 and 2007-2014.

Objective-This report compares prevalence of and change over time for five infectious disease outcomes for the Los Angeles County (LAC) and the U.S. populations. The infectious disease outcomes examined are: herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), any hepatitis B virus (HBV) infection, HBV immunization, and hepatitis A virus (HAV) from infection or immunization, available for 1999-2006 and 2007-2014, as well as any human papillomavirus (HPV) and high-risk HPV infection, available for the 2007-2014 period only. Methods-LAC was sampled in every 2-year cycle of the current National Health and Nutrition Examination Survey, enabling creation of two 8-year samples (1999-2006 and 2007-2014). Demographic differences associated with disease prevalence were examined between LAC and the United States. Changes over time and differences in prevalence, unadjusted, age adjusted, and "fully" adjusted by direct standardization for these demographic variables, were evaluated between the United States and LAC for 2007-2014. Results-Compared with the United States, persons in LAC were more likely to be Mexican American, born outside of the United States, and live below the poverty level. Prevalence varied significantly by demographic subgroup for each outcome in the United States and for some outcomes in LAC. Differences between LAC and the United States existed for some outcomes but varied with adjustment. Over time, prevalence of HSV-1, HSV-2, and HBV infection decreased, and HBV immunization and HAV infection or immunization increased for the U.S. population. The direction of changes over time were mostly similar for LAC, but significance varied.

Prevalence of HPV in Adults Aged 18-69: United States, 2011-2014.

KEY FINDINGS: Data from the National Health and Nutrition Examination Survey Human papillomavirus (HPV) is the most common sexually transmitted infection in the United States (1). Some HPV types can cause genital warts and are considered low risk, with a small chance for causing cancer. Other types are considered high risk, causing cancer in different areas of the body including the cervix and vagina in women, penis in men, and anus and oropharynx in both men and women (2). This report provides the most recent national estimates of oral HPV prevalence among adults aged 18-69 from the National Health and Nutrition Examination Survey (NHANES) 2011-2014, as well as prevalence of genital HPV among adults aged 18-59 from NHANES 2013-2014. Estimates of any HPV (37 types tested) as well as high-risk HPV (14 of the 37 types) are provided.

TPrevalence of HPV in Adults Aged 18-69: United States, 2011-2014.

KEY FINDINGS: Data from the National Health and Nutrition Examination Survey ● During 2011-2014, prevalence of any oral human papillomavirus (HPV) for adults aged 18-69 was 7.3%; high-risk HPV was 4.0%. ● Overall, prevalence of any and high-risk oral HPV was lowest among non-Hispanic Asian adults; any oral HPV was highest among non-Hispanic black adults. ● Prevalence of any and high-risk oral HPV was higher in men than women except for high-risk HPV among Asian adults. ● During 2013-2014, prevalence of any and high-risk genital HPV for adults aged 18-59 was 45.2% and 25.1% in men and 39.9% and 20.4% in women, respectively. ● Prevalence of any and high-risk genital HPV was lower among non-Hispanic Asian and higher among non-Hispanic black than both non-Hispanic white and Hispanic men and women. Human papillomavirus (HPV) is the most common sexually transmitted infection in the United States (1). Some HPV types can cause genital warts and are considered low risk, with a small chance for causing cancer. Other types are considered high risk, causing cancer in different areas of the body including the cervix and vagina in women, penis in men, and anus and oropharynx in both men and women (2). This report provides the most recent national estimates of oral HPV prevalence among adults aged 18-69 from the National Health and Nutrition Examination Survey (NHANES) 2011-2014, as well as prevalence of genital HPV among adults aged 18-59 from NHANES 2013-2014. Estimates of any HPV (37 types tested) as well as high-risk HPV (14 of the 37 types) are provided.

Viral Hepatitis Among Non-Hispanic Asian Adults in the United States, 2011-2014.

KEY FINDINGS: Hepatitis A (HAV), B (HBV), and C (HCV) viruses are common types of viral hepatitis. HBV and HCV infection can lead to liver disease, cancer, and serious health consequences. HAV and HBV infections are high among Asian persons, especially those born outside the United States (1-3). This report provides 2011- 2014 National Health and Nutrition Examination Survey (NHANES) estimates on prevalence of antibody to HAV (from infection or immunization), past or current HBV infection, and current HCV infection, by race and Hispanic origin.

HIV Infection in U.S. Household Population Aged 18-59: Data From the National Health and Nutrition Examination Survey, 2007-2012.

OBJECTIVES: This report presents estimates of HIV prevalence, the association of HIV status with key risk factors, and the prevalence of antiretroviral drug use among HIV-infected adults, based on the 2007­2012 National Health and Nutrition Examination Survey (NHANES). METHODS: HIV prevalence was estimated based on 10,466 NHANES respondents aged 18­59 during 2007­2012. Starting in 2009, the NHANES age range for HIV antibody testing was expanded from age group 18­49 to age group 18­59. HIV prevalence for 2007­2012 was estimated using 6 years of data and corresponding weights for participants aged 18­49 from NHANES 2007­2012, and 4 years of data and corresponding weights for participants aged 50­59 from NHANES 2009­2012. This HIV prevalence calculation assumes that HIV prevalence, and the relationship between prevalence and levels of all relevant cofactors, were the same between survey periods 2007­2008 and 2009­2012 for adults aged 50­59. HIV antibody status was measured using an enzyme-linked immunosorbent assay (ELISA) to detect antibody to HIV, followed by confirmatory Western blot for those with a positive ELISA test. RESULTS: During 2007­2012, the overall HIV prevalence among adults aged 18­59 residing in U.S. households was 0.39%. Men were more likely to be HIV-infected than women, and non-Hispanic black persons were more likely to be HIV-infected than all other race and Hispanic origin subgroups combined. HIV infection was associated with high-risk populations, including those with herpes simplex virus type 2 infection, 10 or more lifetime sexual partners, a history of prior sexually transmitted infection, or a history of same-sex sexual contact among men. One-half of HIV-infected adults were on antiretroviral therapy (51.9%). Among HIV-infected adults, 86.1% reported any lifetime history of HIV testing outside of blood donations.

National Health and Nutrition Examination Survey Biospecimen Program: NHANES III (1988-1994) and NHANES 1999-2014.

BACKGROUND: The National Health and Nutrition Examination Survey's 9NHANES) biospecimena program was formed to manage the collection of biospecimena (including serum, plasma, urine, and DNA) from NHANES cycles, the storage of biospecimens in NHANES biospecimens, accessing of biospecimens by researchers and the providing of resulting data to future researchers. Data from biospeceimen research can be combined with existing NHANES data. OBJECTIVE: This report provides background on the development of NHANES biorepositories and describes the collection, processing, and storing of biospecimens; ethical considerations and informed consent; and the proposal process for accessing biospecimens and resulting data. The number and types of biospecimens collected in each survey cycle from NHANES III (1988- 1994) through NHANES 1999-2014 are discussed so that researchers can understand what biospecimens are available if they are considering using NHANES biospecimens in their research.

Did CDC's 2006 revised HIV testing recommendations make a difference? Evaluation of HIV testing in the US household population, 2003-2010.

OBJECTIVE: To examine changes in the prevalence of HIV testing among adults following the Centers for Disease Control and Prevention's 2006 revised HIV testing recommendations. DESIGN: The 2003-2010 National Health and Nutrition Examination Survey, a nationally representative cross-sectional survey of the noninstitutionalized US population. METHODS: Weighted estimates and multivariable modeling to assess the prevalence of lifetime HIV testing, outside of blood donations, based on 13,975 respondents aged 18-59 years, comparing the 2003-2006 and 2007-2010 National Health and Nutrition Examination Survey. RESULTS: Overall, HIV testing was 42.1% during 2003-2006 and 44.5% during 2007-2010 (P > 0.05). After adjusting for significant predictors in a multivariate model, HIV testing increased from 2003-2006 to 2007-2010 (adjusted odds ratio [aOR] 1.14, P < 0.05), mostly among males (aOR 1.33, P < 0.001) as compared with females (aOR 1.02, P > 0.05). HIV testing also increased significantly among non-Hispanic blacks, heterosexuals, those aged 50-59 years, those without a sexually transmitted infection history, those without health insurance, and those who did not access health care in the past year. HIV testing did not change significantly among high-risk groups, including men who have sex with men, those with a history of injection or illicit drug use, and those with a sexually transmitted infection history. CONCLUSIONS: In multivariate modeling, we found a modest but significant increase in HIV testing overall and among males after publication of the revised recommendations for HIV testing. The significant increase in non-high-risk groups suggests an expansion in generalized HIV testing, as recommended. However, even in 2007-2010, 56% of the US population has never been tested for HIV.

Chronic hepatitis C virus infection in the United States, National Health and Nutrition Examination Survey 2003 to 2010.

BACKGROUND: Knowledge of the number of persons with chronic hepatitis C virus (HCV) infection in the United States is critical for public health and policy planning. OBJECTIVE: To estimate the prevalence of chronic HCV infection between 2003 and 2010 and to identify factors associated with this condition. DESIGN: Nationally representative household survey. SETTING: U.S. noninstitutionalized civilian population. PARTICIPANTS: 30,074 NHANES (National Health and Nutrition Examination Survey) participants between 2003 and 2010. MEASUREMENTS: Interviews to ascertain demographic characteristics and possible risks and exposures for HCV infection. Serum samples from participants aged 6 years or older were tested for antibody to HCV; if results were positive or indeterminate, the samples were tested for HCV RNA, which indicates current chronic infection. RESULTS: Based on 273 participants who tested positive for HCV RNA, the estimated prevalence of HCV infection was 1.0% (95% CI, 0.8% to 1.2%), corresponding to 2.7 million chronically infected persons (CI, 2.2 to 3.2 million persons) in the U.S. noninstitutionalized civilian population. Infected persons were more likely to be aged 40 to 59 years, male, and non-Hispanic black and to have less education and lower family income. Factors significantly associated with chronic HCV infection were illicit drug use (including injection drugs) and receipt of a blood transfusion before 1992; 49% of persons with HCV infection did not report either risk factor. LIMITATION: Incarcerated and homeless persons were not surveyed. CONCLUSION: This analysis estimated that approximately 2.7 million U.S. residents in the population sampled by NHANES have chronic HCV infection, about 500,000 fewer than estimated in a similar analysis between 1999 and 2002. These data underscore the urgency of identifying the millions of persons who remain infected and linking them to appropriate care and treatment. PRIMARY FUNDING SOURCE: None.

Prevalence of hepatitis C virus infection in US Hispanic/Latino adults: results from the NHANES 2007-2010 and HCHS/SOL studies.

Prevalence of hepatitis C virus (HCV) antibody has been reported in Mexican Americans, but its prevalence in other US Hispanic/Latino groups is unknown. We studied 2 populations of US Hispanic/Latino adults; 3210 from the National Health and Nutrition Examination Survey (NHANES) 2007-2010 and 11 964 from the Hispanic Community Health Study/Study of Latinos (HCHS/SOL). Age-standardized prevalence of HCV antibody was similar in NHANES 2007-2010 (1.5%) and HCHS/SOL (2.0%) but differed significantly by Hispanic/Latino background in HCHS/SOL (eg, 11.6% in Puerto Rican men vs 0.4% in South American men). These findings suggest that the HCV epidemic among US Hispanics/Latinos is heterogeneous.

Seroprevalence of herpes simplex virus types 1 and 2--United States, 1999-2010.

BACKGROUND: Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) are common infections with serious sequelae. HSV-1 is an increasingly important cause of genital herpes in industrialized countries. METHODS: Using nationally representative data from the National Health and Nutrition Examination Survey (NHANES), we examined HSV-1 and HSV-2 seroprevalence among 14- to 49-year-olds in the United States. We estimated seroprevalence in 1999-2004 and 2005-2010, stratified by sociodemographic characteristics and sexual behaviors. We also reviewed HSV-1 and HSV-2 seroprevalence from 1976-1980 to 2005-2010. RESULTS: In 2005-2010, the seroprevalence of HSV-1 was 53.9%, and the seroprevalence of HSV-2 was 15.7%. From 1999-2004 to 2005-2010, HSV-1 seroprevalence declined by nearly 7% (P < .01), but HSV-2 seroprevalence did not change significantly. The largest decline in HSV-1 seroprevalence from 1999-2004 to 2005-2010 was observed among adolescents aged 14-19 years, among whom seroprevalence declined by nearly 23%, from 39.0% to 30.1% (P < .01). In this age group, HSV-1 seroprevalence declined >29% from 1976-1980 to 2005-2010 (P < .01). CONCLUSIONS: An increasing number of adolescents lack HSV-1 antibodies at sexual debut. In the absence of declines in HSV-2 infections, the prevalence of genital herpes may increase.

Reduction in human papillomavirus (HPV) prevalence among young women following HPV vaccine introduction in the United States, National Health and Nutrition Examination Surveys, 2003-2010.

BACKGROUND: Human papillomavirus (HPV) vaccination was introduced into the routine immunization schedule in the United States in late 2006 for females aged 11 or 12 years, with catch-up vaccination recommended for those aged 13-26 years. In 2010, 3-dose vaccine coverage was only 32% among 13-17 year-olds. Reduction in the prevalence of HPV types targeted by the quadrivalent vaccine (HPV-6, -11, -16, and -18) will be one of the first measures of vaccine impact. METHODS: We analyzed HPV prevalence data from the vaccine era (2007-2010) and the prevaccine era (2003-2006) that were collected during National Health and Nutrition Examination Surveys. HPV prevalence was determined by the Linear Array HPV Assay in cervicovaginal swab samples from females aged 14-59 years; 4150 provided samples in 2003-2006, and 4253 provided samples in 2007-2010. RESULTS: Among females aged 14-19 years, the vaccine-type HPV prevalence (HPV-6, -11, -16, or -18) decreased from 11.5% (95% confidence interval [CI], 9.2-14.4) in 2003-2006 to 5.1% (95% CI, 3.8-6.6) in 2007-2010, a decline of 56% (95% CI, 38-69). Among other age groups, the prevalence did not differ significantly between the 2 time periods (P > .05). The vaccine effectiveness of at least 1 dose was 82% (95% CI, 53-93). CONCLUSIONS: Within 4 years of vaccine introduction, the vaccine-type HPV prevalence decreased among females aged 14-19 years despite low vaccine uptake. The estimated vaccine effectiveness was high.

Change in Hepatitis A Seroprevalence among U.S. Children and Adolescents: Results from the National Health and Nutrition Examination Survey 2003-2006 and 2007-2010.

To examine changes in seroprevalence of antibodies to hepatitis A virus (HAV) during a period in which universal vaccine recommendations for all U.S. children were implemented, results from serologic testing from the National Health and Nutrition Examination Survey (NHANES) from 2003-2010 were analyzed among 7,989 participants age 6-19 years, born in the U.S. in two birth cohorts (1986-1996 and 1997-2004). Overall prevalence increased over time from 24.4% in 2003-2006 to the highest ever reported (37.6%) in 2007-2010. Specifically, increases reached statistical significance in the birth cohort born in the years after implementation of vaccine recommendations (1997-2004), among those of race/ethnicity other than white, non-Hispanic, and among states where recommendations were implemented later. The greatest increase over time was among the subgroup of persons in states with early implementation who were of race/ethnicity other than white, non-Hispanic. Geographic region and birth cohort based on vaccine recommendations as well as race/ethnicity were the main predictors of seropositivity in 2007-2010. The increase in Hepatitis A seroprevalence occurred during a time of decreasing incidence and increasing vaccination, however race/ethnic disparities persist.

Relationship of sex steroid hormones with body size and with body composition measured by dual-energy X-ray absorptiometry in US men.

PURPOSE: To evaluate the association of body size-captured via whole-body dual-energy X-ray absorptiometry (DXA) and physical measurement-with serum sex steroid hormones and sex hormone binding globulin (SHBG), we utilized cross-sectional data and serum samples from the National Health and Nutrition Examination Survey (NHANES; 1999-2004). METHODS: Testosterone, androstanediol glucuronide (3-alpha-diol-G), estradiol, and SHBG were measured via immunoassay in serum samples from a total of 898 adult men (ages 20-90) participating in the morning examination. As part of the NHANES data collection, DXA scans and measurements of weight, height, and waist circumference were performed by trained staff. Linear regression was used to estimate associations between body size and hormone levels adjusted for potential confounders and NHANES sampling procedures. RESULTS: Total bone area (cm(2)) was inversely associated with total testosterone (ng/mL) [beta = -0.12; p value < 0.01], while bone mineral density (g/cm(2)) was inversely associated with SHBG (nmol/L) [beta = -17.16; p value = 0.01]. Increased percent body fat was associated with lower concentrations of total testosterone [beta = -0.16; p value < 0.01] and SHBG [beta = -1.11; p value < 0.01] and higher concentrations of free estradiol (fg/mL) [beta = 12.52; p value < 0.01]. CONCLUSIONS: Clinical measures of body fat (measured via DXA scan) and anthropometric measures of body fat (BMI and waist circumference) provided similar inferences regarding the association between increased body fat and hormone levels in men. Increased body fat was associated with lower circulating levels of testosterone (total and free) and SHBG and higher circulating levels of free estradiol in men, while decreased bone mineral density was associated with higher circulating levels of SHBG.

Infectious disease prevalence in Los Angeles county--a comparison to national estimates, 1999-2004 birth rates for U.S. teenagers reach historic lows for all age and ethnic groups.

This is the first time seroprevalence of antibody to these nine infectious diseases have been available for LAC. Differences in the race and ethnicity distribution of the United States and LAC were observed. Because disease prevalence varies by race and ethnicity, in some instances these demographic differences affected the population differences seen between the United States and LAC in the seroprevalence of the infectious diseases reported in this study. Seroprevalence for HAV was higher in LAC as compared with the United States among the total population and among the Mexican-American population. California is 1 of 11 states in which routine vaccination of children was recommended in 1999 by the Advisory Committee on Immunization Practices (ACIP) because mean incidence rates in these states were at least twice the national mean from 1987­1997 (9). Seroprevalence to CMV and T. gondii have been shown to be higher among Mexican-American persons then other race and ethnicity groups (1,3). The higher seropositivity for CMV and T. gondii among persons from LAC is due to the higher proportion of Mexican-American persons in the LAC population. No differences in seropositivity were observed when comparing Mexican-American persons in the United States and LAC for these two outcomes. No significant differences in seroprevalence between the United States and LAC were seen for measles, mumps, rubella, varicella, HSV-1, and HSV-2. Estimates of seropositivity from immunization or disease for LAC may assist in policy development, program planning, and measuring health disparities.

Awareness of infection, knowledge of hepatitis C, and medical follow-up among individuals testing positive for hepatitis C: National Health and Nutrition Examination Survey 2001-2008.

UNLABELLED: Many persons infected with hepatitis C virus (HCV) are unknown to the healthcare system because they may be asymptomatic for years, have not been tested for HCV infection, and only seek medical care when they develop liver-related complications. We analyzed data from persons who tested positive for past or current HCV infection during participation in the National Health and Nutrition Examination Survey (NHANES) from 2001 through 2008. A follow-up survey was conducted 6 months after examination to determine (1) how many participants testing positive for HCV infection were aware of their HCV status before being notified by NHANES, (2) what actions participants took after becoming aware of their first positive test, and (3) participants' knowledge about hepatitis C. Of 30,140 participants tested, 393 (1.3%) had evidence of past or current HCV infection and 170 (43%) could be contacted during the follow-up survey and interviewed. Only 49.7% were aware of their positive HCV infection status before being notified by NHANES, and only 3.7% of these respondents reported that they had first been tested for HCV because they or their doctor thought they were at risk for infection. Overall, 85.4% had heard of hepatitis C; correct responses to questions about hepatitis C were higher among persons 40-59 years of age, white non-Hispanics, and respondents who saw a physician after their first positive HCV test. Eighty percent of respondents indicated they had seen a doctor about their first positive HCV test result. CONCLUSION: These data indicate that fewer than half of those infected with HCV may be aware of their infection. The findings suggest that more intensive efforts are needed to identify and test persons at risk for HCV infection.