Geraldine McQuillan, Ph.D., and Deanna Kruszon-Moran, M.S., Division of Health and Nutrition Examination Surveys 

HIV Infection in the United States Household Population 

Aged 18–49 Years: Results from 1999–2006 

NCHS Data Brief

Importance 

Measurement of HIV prevalence in a nationally representative sample of the United States population provides an understanding of the background level of infection in the general household 

population aged 18–49 years as well as in demographic subgroups. This information can also be 

used to monitor trends in infection in the household population over time. Other public health 

surveillance systems address the impact of HIV infection among high risk groups including the 

homeless and prisoners that are not included in surveys of the general household population 

(1,2). The combination of information from these surveillance systems with estimates from 

surveys of the general household population provides a more complete picture of the HIV/AIDS 

epidemic in the United States. 

Herpes simplex-virus type 2 (HSV-2) infection is associated with HIV infection; some studies 

have shown that HSV-2 infection doubles the risk of HIV acquisition (3–5). Estimates of the 

prevalence of both HSV-2 and HIV infection can provide further understanding of the risk of 

HIV infection in higher risk subgroups of the general household population. 

CD4 counts (also known as T-helper cells) provide a measure of a person’s immune function. 

Among HIV-infected individuals, measurement of CD4 counts is often used to demonstrate how 

well anti-HIV drugs are working. Estimates of this measure in the general population can provide a picture of health among HIV-infected individuals. 

Keywords: HIV ● CD4 ● seroprevalence ● trends 

Findings 

What is the prevalence of HIV infection among U.S. adults ? 

●		 In 1999–2006, the prevalence of HIV infection among adults aged 18–49 years in the 

civilian noninstitutionalized household population of the United States was 0.47%. 

Figure 1. Prevalence of HIV infection among adults by age, sex, and race/ethnicity: 

United States, 1999–2006 

(1) 

(2) 

(4) 

(3) 

Percent 

Mexican American 

Non-Hispanic black 

Non-Hispanic white

 40–49 years

 30–39 years

 18–29 years 

Female 

Male 

All 

0 1 2 3 1

Significantly different from females.

2

Significantly different from ages 18–29 years.

3

Significantly different from the non-Hispanic white and Mexican-American population.

4

Estimate unstable. Based on fewer than 10 HIV-positive persons. See Appendix table. 

NOTE: Nationally representative sample of the civilian, noninstitutionalized household population. 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys, 1999–2006. 

No. 4 January 2008 

Highlights 

Data from the National 

Health and Nutrition 

Examination Surveys 

(NHANES) 

► The prevalence of HIV 

infection among adults 

aged 18–49 years residing in 

households in the United States 

was 0.47% for the period 

1999–2006. 

► Men were more likely to 

be HIV positive than women. 

Race/ethnic disparities in HIV 

infection were also seen. 

Non-Hispanic blacks were more 

likely to be HIV positive than all 

other race/ethnic groups. 

► Infection with HSV-2 was 

significantly associated with 

HIV infection among the total 

population aged 18–49 years and 

especially so among the non-Hispanic black population. 

► In 1999–2006, nearly 

one-quarter of HIV-positive 

individuals but only 1% of the 

HIV-negative individuals aged 

18–49 years had low CD4 counts 

(a marker of decreased immune 

function). Approximately onethird of HIV-positive persons 

had healthy immune systems as 

compared with 90% among those 

HIV negative. 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Center for Health Statistics 
No. 4 January 2008

NCHS Data Brief 

The prevalence among men was 0.72% and was significantly higher than the prevalence 

in women 0.22%. 

Adults aged 40–49 years were more likely to be HIV positive compared with those aged 18–29 

years. Approximately 0.61% of adults aged 40–49 years were HIV positive, compared with 0.55% 

of 30–39 year-olds and 0.25% of 18–29 year-olds. 

●		 In 1999–2006, the non-Hispanic black population had an increased prevalence of HIV

 infection compared with other population subgroups. 

The prevalence of HIV infection among the non-Hispanic black population was 2.01%, which 

was significantly higher than among the non-Hispanic white population (0.23%) and the MexicanAmerican population (0.30%). 

Among the non-Hispanic black population, the prevalence of HIV infection was higher among men 

(2.64%) than among women (1.49%). 

Is Herpes simplex-virus type 2 (HSV-2) infection associated with HIV infection? 

●		 HIV status was associated with HSV-2 infection, especially among the non-Hispanic black 

population. 

Figure 2. HIV prevalence among adults aged 18–49 years, by Herpes simplex-virus 

type 2 (HSV-2) status and race/ethnicity: United States, 1999–2006 

% HIV positive among HSV-2 positive % HIV positive among HSV-2 negative 

Percent 

1

Significantly different from HSV-2 negative subgroup.

2

Estimate unstable. Based on fewer than 10 HIV-positive persons. 

NOTE: Nationally representative sample of the civilian, noninstitutionalized household population adjusted for age. 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys, 1999–2006. 

0 

1 

2 

3 

4 

5 

Total Non-Hispanic black

(1) 

(1) 

(2) 

HSV-2 infection among persons aged 18–49 years was much higher among non-Hispanic blacks 

(46.6%) as compared with all other race/ethnic groups combined (15.3%) (data not shown). 

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No. 4 January 2008

NCHS Data Brief 

HIV prevalence was higher among all persons aged 18–49 years who were infected with HSV-2 

compared with those who were not infected (1.99% and 0.13%, respectively). 

The higher risk of HIV infection among those HSV-2 positive was especially true for non-Hispanic 

blacks, where the HIV prevalence was 3.69% among HSV-2 positive non-Hispanic blacks. 

How does the immune function of HIV-positive individuals compare with HIV-negative 

individuals? 

●		 The CD4 count (also known as T-helper cells) is a measure of a person’s immune status. 

The immune function among HIV-infected individuals is often different from HIV-negative 

individuals. 

Figure 3. CD4 count, by HIV status: United States, 1999–2006 

NOTE: Nationally representative sample of the civilian, noninstitutionalized household population aged 18–49 years. 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Surveys, 1999–2006. 

HIV positive 

Greater than 

or equal 

to 500 

34% 

350-499 

22% 

Less than 

200 

23% 

200–349 

20% 

HIV negative 

Greater than or 

equal to 500 

90% 

350–499 

7% 

Less than 200 

1% 

200–349 

2% 

In 1999–2006, the majority (90%) of HIV-negative individuals had CD4 counts within the normal 

range (CD4 counts greater than or equal to 500 cells/mm3). 

As expected, many more HIV-positive persons had lower CD4 counts (counts less than 200 

cells/mm3 or between 200 and 349 cells/mm3) (43% combined) as compared with HIV-negative 

persons (3% combined). 

In 1999–2006, 23% of HIV-positive individuals had depressed immune function (CD4 counts less 

than 200 cells/mm3) and only 34.4% of HIV-positive individuals had healthy immune systems 

(CD4 counts greater than or equal to 500 cells/mm3). 

3 
 

 

No. 4 January 2008

NCHS Data Brief 

Summary 

In 1999–2006, the prevalence of HIV infection among U.S. adults aged 18–49 years residing in 

households was 0.47%. In addition, race/ethnic and gender disparities were present. HIV infection 

was higher among non-Hispanic blacks compared with other race/ethnic groups and higher among 

men than women. 

HIV infection was significantly associated with HSV-2 infection. The association was especially 

strong among non-Hispanic blacks where infection with HSV-2 is significantly higher than in all 

other race/ethnic groups. 

Low CD4 counts (less than 200 cells/mm3), a marker for depressed immune function, were much 

more frequent among those who were HIV positive than those HIV negative. Conversely, higher 

CD4 counts (greater than or equal to 500 cells/mm3 ) indicative of normal immune function, were 

much lower among individuals HIV positive as compared with those HIV negative. 

Since the HIV/AIDS epidemic was first recognized in 1981, the Centers for Disease Control and 

Prevention (CDC), in coordination with all states and U.S. dependent areas has conducted AIDS surveillance. As part of the national surveillance program to monitor the HIV/AIDS epidemic, CDC’s 

NHANES survey data provide prevalence estimates from the general household population aged 

18–49 years. Information on risk factors for HIV infection, such as sexual activity and intravenous 

drug use, were not addressed in this analysis, but are collected as part of the NHANES survey. 

Definitions

HIV positivity: Presence of antibody to human immunodeficiency virus (HIV) in blood or urine 

(6). 

CD4 counts: Enumeration of CD4 T-lymphocytes (also called T-helper cells, a measure of immune 

function) in blood (7). Counts greater than or equal to 500 cells/mm3 represents a healthy immune 

system. Counts less than 200 cells/mm3 represent adults with depressed immune function (6). 

HSV-2 positivity: Presence of antibody to Herpes simplex virus type-2 (HSV-2) in blood (6,8–10). 

Race/ethnicity: Race/ethnicity was based on self-report and categorized as non-Hispanic white, 

non-Hispanic black, and Mexican American. Persons not fitting into these categories were classified 

as “other” and included in the total population estimates. 

Data source 

National Health and Nutrition Examination Surveys (NHANES) data were used for these analyses. 

NHANES is a cross-sectional survey designed to monitor the health and nutritional status of the 

civilian, noninstitutionalized U.S. population (11). The survey consists of interviews conducted in 

participants’ homes, standardized physical examinations conducted in specially outfitted mobile 

examination centers, and laboratory tests utilizing blood and urine specimens provided by 

participants during the physical examination. 

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No. 4 January 2008

NCHS Data Brief 

The NHANES sample is selected through a complex, multistage design that includes selection of 

primary sampling units (counties), household segments within the counties, and finally sample persons from selected households. The sample design includes oversampling in order to obtain reliable estimates of health and nutritional measures for population subgroups. In 1999–2006, African 

Americans, Mexican Americans, persons with low income, persons 12–19 years of age, and persons 

60 years and older were oversampled. In 1999, NHANES became a continuous survey, fielded on an 

ongoing basis. Each year of data collection is based on a representative sample covering all ages of 

the civilian, noninstitutionalized population. Public-use data files are released in 2-year cycles. 

Sample weights, which account for the differential probabilities of selection, nonresponse and noncoverage, are incorporated into the estimation process (12). The standard errors of the percentages were estimated using Taylor Series Linearization in SUDAAN, a method that incorporates the 

sample weights and sample design (13). Ninety-five percent confidence intervals were estimated by 

using the logit transformation (14). 

HIV antibody positive status was measured in examined sample persons aged 18–49 years. To examine possible predictors of HIV positivity, differences in prevalence were evaluated by examining 

P-values calculated using a univariate t-statistic obtained from a general linear contrast procedure in 

SUDAAN. All differences reported are statistically significant (p < 0.05) unless otherwise indicated. 

When comparing race/ethnic groups, using linear contrasts and when examining the association of 

HSV-2 with HIV status among race/ethnic groups, estimates were age adjusted to the 2000 U.S. 

standard census population using three age groups, 18–29, 30–39, and 40–49 years. This adjustment 

enabled us to compare prevalence estimates between subgroups that differ with respect to their age 

distributions (15). 

All data analyses were performed using the statistical packages SAS version 9.1 (SAS Institute, Cary, 

N.C.) and SUDAAN version 9.0 (Research Triangle Institute, Research Triangle Park, N.C.) (13). 

The relative standard error (RSE), defined as the estimate divided by its standard error, is an indicator 

for statistical reliability. Most estimates in this study are of small magnitude relative to their standard 

errors (i.e., the RSE are large). All estimates whose RSE was greater than a cut point of 40% are designated with a footnote to indicate that the estimate is statistically unreliable. In addition, estimates 

based on fewer than 10 positive persons are also designated with a footnote to indicate statistical 

unreliability (16). 

Acknowledgments 

The data files for this report were prepared in the Division of Health and Nutrition Examination Surveys, Informatics Branch. This report was edited by Demarius V. Miller, CDC/CCHIS/NCHM/Division of Creative Services, Writer-Editor Services Branch; layout, graphic production, and Internet 

preparation by Zorica Tomic-Whalen, CDC/CCHIS/NCHM/Division of Creative Services, NOVA 

contractor; and Internet preparation and Internet posting by Christine Brown, Office of Information 

Services, Information Design and Publishing Staff. Printing management by Patty Wilson, CDC/ 

MASO. 

5 
No. 4 January 2008

NCHS Data Brief 

Suggested citation 

McQuillan GM, Kruszon-Moran D. HIV infection in the United States household population aged 

18–49 years: Results from 1999–2006. NCHS data brief no 4. Hyattsville, MD: National Center for 

Health Statistics. 2008. 

References 

1. Allen DM, Lehman JS, Green TA, et al. HIV infection among homeless adults and runaway youth, 

United States, 1989–1992. AIDS 1994; 81:1593–8. 

2. Maruschak LM. HIV in Prisons, 2001. Bureau of Justice Statistics, report number NCJ 202293. 

January 2004. 

3. McQuillan GM, Kruszon-Moran D, Kottiri BJ, et al. Prevalence of HIV in the U.S. Household 

Population: The National Health and Nutrition Examination Surveys, 1988–2002. J Acquir Immune 

Defic Syndr 2006; 41:651–656. 

4. McQuillan GM, Khare M, Karon JM, et al. Update on the seroepidemiology of human immunodeficiency virus in the United States household population: NHANES III, 1988–1994. J AIDS 

1997; 14:355–60. 

5. Wald A, Link K. Risk of human immunodeficiency virus infection in herpes simples virus type 2 

persons: a meta-analysis. J Infect Dis. 2002;185:45–52. 

6. National Center for Health Statistics. Available from: 

http://www.cdc.gov/nchs/about/major/nhanes/nhanes2003-2004/lab_methods_03_04.htm. 

7. Fiebig EW, Johnson DK, Hirschkorn DF, Knape CC, et al. Lymphocyte subset analysis on frozen 

whole blood. Cytometry 29:340–50. 1997. 

8. Xu F, Sternberg MR, Kotirri BJ, et al. Trends in Herpes simples virus type 1 and 2 seroprevalence 

in the United States. JAMA. 2006;296:964–73. 

9. Lee FK, Coleman RM, Pereira L, Griffin C, Reid E, Nahmias A. Detection of herpes simplex virus 

type-2-specific antibody with glycoprotein G. J Clin Microbiol 1985; 22:641–44. 

10. Fleming DT, McQuillan GM, Johnson RE, et al. Herpes simplex virus type 2 in the United States, 

1976–1994. N Engl J Med. 1997;337:1105–11. 

11. National Center for Health Statistics. NHANES 1999-2006. Available from: 

http://www.cdc.gov/nchs/about/major/nhanes/datalink.htm. 

12. Mohadjer L, Montaquila J, Waksberg J. National Health and Nurtition Examination Survey III: 

Weighting and examination methodology. Prepared for National Center for Health Statistics, Hyattsville, MD. Westat Inc, February 1996. 

13. Shah BV, Barnwell BG, Bieler GS, LaVange LM. SUDAAN Users Manual release7.0. Research 

Triangle Park, NC: Research Triangle Institute, 1996. 

14. Wolter K. Introduction to Variance Estimation. New York, New York, Springer-Verlag Inc 1985. 

15. Kahn HA, Sempos CT. Statistical Methods in Epidemiology. New York, NY: Oxford University 

Press Inc; 1989. 

16. National Center for Health Statistics. NHANES 1999–2002. Available from: 

http://www.cdc.gov/nchs/data/nhanes/nhanes_general_guidelines_june_04.pdf. 

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No. 4 January 2008

NCHS Data Brief 

Appendix 

Prevalence of HIV infection from NHANES 1999–2006, by age, gender, and race/ethnicity 

 Number Percent N 95% CI positive positive RSE 

Total1 11928 67 0.47 0.34–0.64 15 

Gender 

Males 5529 47 0.72 a 0.49–1.06 19

 Non-Hispanic

 black 1327 29 2.64 b 1.88–3.70 17 

All other 

race/ethnic groups2 4202 18 0.48 b 0.26–0.86 29 

Females 6399 20 0.22 a 0.14–0.36 23

 Non-Hispanic

 black 1478 17 1.49 c 0.91–2.43 24 

All other race/ 

ethnic groups2 4921 3 0.03 c,3 0.01–0.13 67 

Age1 

18–29 5696 15 0.25 d 0.13–0.48 32 

30–39 3147 23 0.55 0.32–0.94 27 

40–49 3085 29 0.61 d 0.38–0.98 23 

Race/Ethnicity

 Non-Hispanic

 white 4838 10 0.23 e 0.11–0.48 39

 Non-Hispanic

 black 2805 46 2.01 e,f 1.50–2.69 14

 Mexican 

 American 3228 7 0.30 f,3 0.13–0.69 40 

1 Totals differ from the sum for the non-Hispanic white, non-Hispanic black, and Mexican-American 

populations because those in the “other” race/ethnic category are included in the totals.
 2

 Includes non-Hispanic white, Mexican American, and “other” race/ethnicity.
 3 RSE greater than 40 or number of positive cases less than 10.
 a p<0.05 for difference between gender. b p<0.05 for difference between non-Hispanic black males and males in “All other race/ethnic groups.”
 c p<0.05 for difference between non-Hispanic black females and females in “All other race/ethnic groups.”
 d

 p<0.05 for difference between ages 18–29 and 40–49 years.
 e p<0.05 for difference between the non-Hispanic black and non-Hispanic white populations.
 f

 p<0.05 for difference between the non-Hispanic black and Mexican-American populations.
 

NOTES: CI is confidence interval. RSE is relative standard error. 7 
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