NCHS Data Brief ■ No. 90 ■ April 2012

Infectious Disease Prevalence in Los Angeles County–A 

Comparison to National Estimates, 1999–2004

Deanna Kruszon-Moran, Sc.M.; Kathryn S. Porter, M.D., M.S.; Geraldine McQuillan, Ph.D.; 

Veena Goud Billioux, Sc.M.; Robert Kim-Farley, M.D., M.P.H; and Rosemarie Hirsch, M.D., M.P.H.

Antibody prevalence estimates, markers of infection with T. gondii, HAV, 

CMV, HSV-1 or HSV-2, or vaccination to measles, mumps, rubella, or 

varicella have been available for the United States but not at the local level 

(1–8). Los Angeles County (LAC) was the only county selected each year 

into the NHANES sample. Six years of data (1999–2004) were combined 

to provide sufficient sample size to create the first estimates of antibody 

prevalence to these nine infectious diseases based on direct laboratory 

measures for LAC. These estimates of disease burden or immunization 

success are compared between LAC and the United States. 

Keywords: Seroprevalence • National Health and Nutrition Examination 

Survey • cross-sectional study

How does LAC compare with the total United States with 

respect to race and ethnicity?

LAC had significantly more persons of Mexican American (34.7%) or “Other” 

(29.2%) race and ethnicity then the total U.S. population (10.2% and 12.1%, 

Key findings

Data from the National 

Health and Nutrition 

Examination Survey 

1999–2004

• Los Angeles County 

(LAC) had more Mexican 

American or “Other” and fewer 

non-Hispanic white persons 

as compared with the U.S. 

population.

• Seropositivity, measured as 

the presence of antibody, to 

hepatitis A virus (HAV) was 

greater among the total and 

Mexican-American populations 

in LAC as compared with the 

United States.

• There were no significant 

differences in seropositivity 

to measles, mumps, rubella, 

varicella, herpes simplex virus 

type 1 (HSV-1) and type 2 

(HSV-2) between LAC and the 

U.S. total populations.

• Differences in seropositivity 

to cytomegalovirus (CMV) 

and to Toxoplasma gondii (T. 

gondii) between LAC and the 

U.S. total populations were 

no longer significant when 

comparing the two MexicanAmerican populations. 

Figure 1. Race and ethnicity in LAC and U.S. populations, ages 6–49 years,1999–2004

* p-value for differences between the United States and the LAC total populations is < 0.05.

NOTE: LAC is Los Angeles County.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2004.

LAC

United States

0 20 40

Percent

60 80 100

Other*

29.2

12.1

Mexican

American*

10.2

34.7

NonHispanic

Black

13.0

8.9

NonHispanic

White*

64.6

27.2

Confidence interval.

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics
NCHS Data Brief ■ No. 90 ■ April 2012

■  2  ■

respectively) (Figure 1). LAC also had fewer persons of non-Hispanic white (27.2%) race 

and ethnicity as compared with the race and ethnicity distribution in the total U.S. population 

(64.6%). Differences in the race and ethnicity demographic distribution observed between the 

United States and LAC are supported by census data. 

How does LAC compare with the total United States with respect to 

seropositivity to vaccine preventable diseases such as measles, mumps, 

rubella, and varicella? 

Seropositivity to all four vaccine preventable diseases, measles, mumps, rubella, and varicella 

was above 90% for both the U.S. and LAC populations (Figure 2). No significant differences 

between the United States and LAC were found in seropositivity for these four diseases in both 

the total population and the Mexican-American subgroup.

NOTE: LAC is Los Angeles County.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2004.

Figure 2. Seropositivity to measles, mumps, rubella, and varicella in LAC and the United States total populations and 

among the Mexican-American populations, ages 6–49 years, 1999–2004

0 80 90

Percent

100

LAC Mexican 

American

U.S. Mexican

American

LAC

United States

Measles

Mumps

Rubella

Varicella

Confidence interval.

96.0

94.7

95.4

95.7

91.2

91.6

91.5

91.3

90.0

91.0

92.2

94.0

95.9

96.2

94.2

94.4
NCHS Data Brief ■ No. 90 ■ April 2012

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How does LAC compare with the total United States with respect 

to seropositivity to the enteric diseases hepatitis A virus (HAV) and 

Toxoplasma gondii (T. gondii)?

Seropositivity to HAV, due to either natural infection or vaccination, was greater in LAC (64.8%) 

as compared with the United States (35.9%) and this difference remained when we looked at the 

Mexican-American subgroups alone (76.6% for the United States and 71.3% for LAC) (Figure 

3). Seropositivity to T. gondii, due to natural infection, was greater in LAC (16.0%) as compared 

with the United States (11.0%). However, there was no significant difference in seroprevalence to 

T. gondii between the U.S. Mexican-American population compared with the Mexican-American 

population in LAC.

* p-value for differences between the United States and the LAC total populations is < 0.05.

^ p-value for differences between the U.S. Mexican-American population and the LAC Mexican-American population is < 0.05.

NOTES: LAC is Los Angeles County and HAV is hepatitis A virus. 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2004.

Figure 3. Seropositivity to HAV (ages 6 years and over) and T. gondii (ages 6–49 years) in LAC and the United States 

total populations and among the Mexican-American populations, 1999–2004

Percent

LAC Mexican 

American

U.S. Mexican

American

LAC

United States

0 20 40 60 80 100

T. gondii*

HAV*^

35.9

64.8

71.3

76.6

11.0

16.0

13.3

15.2

Confidence interval.
NCHS Data Brief ■ No. 90 ■ April 2012

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How does LAC compare with the total United States with respect to 

seropositivity to herpes viral infections such as cytomegalovirus (CMV), 

herpes simplex virus type 1 (HSV-1), and herpes simplex virus type 2 (HSV2)?

Seropositivity to CMV, due to natural infection, was greater in LAC (69.7%) as compared 

with the United States (50.9%) (Figure 4). However, there was no significant difference in 

seroprevalence to CMV between the Mexican-American population in the United States 

compared with the Mexican American-population in LAC (75.9% and 79.7%, respectively). No 

significant differences between the United States and LAC were found in seropositivity to HSV-1 

or HSV-2.

* p-value for differences between the U.S. and the LAC total populations is < 0.05.

NOTES: LAC is Los Angeles County, CMV is cytomegalovirus, HSV-1 is herpes simplex virus type 1 and HSV-2 is herpes simplex virus type 2.

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2004.

Figure 4. Seropositivity to CMV (ages 6–49 years) and HSV-1 and HSV-2 (ages 14–49 years) in LAC and the 

United States total populations and among the Mexican-American populations, 1999–2004

LAC Mexican 

American

U.S. Mexican

American

LAC

United States

0 20 40 60

Percent

80 100

HSV-1

HSV-2

CMV*

50.9

17.3

21.9

11.9

10.2

58.1

64.6

79.9

80.4

69.7

75.9

79.7

Confidence interval.

Summary

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 1987–1997 (9). 
NCHS Data Brief ■ No. 90 ■ April 2012

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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 MexicanAmerican 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. 

Definitions 

Race and ethnicity: Race and 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 (10). 

Measles positivity: Presence of antibody to measles in blood from either infection or 

immunization (5); measured on those persons ages 6–49 years.

Mumps positivity: Presence of antibody to mumps in blood from either infection or immunization 

(6); measured on those persons ages 6–49 years.

Rubella positivity: Presence of antibody to rubella in blood from either infection or immunization 

(7); measured on those persons ages 6–49 years.

Varicella positivity: Presence of antibody to varicella in blood from either infection or 

immunization (8); measured on those persons ages 6–49 years.

Toxoplasma gondii positivity: Presence of antibody to T. gondii in blood, a marker of past or 

current infection (1); measured on those persons ages 6–49 years.

Hepatitis A positivity: Presence of antibody to HAV in blood from either infection or 

immunization (2); measured on those persons ages 6–49 years and over.

Cytomegalovirus positivity: Presence of antibody to CMV in serum (3); measured on those ages 

6–49 years.

HSV-1 and HSV-2 positivity: Presence of antibody to HSV-1 or HSV-2 in blood, a marker of 

current or past infection (4); measured on those ages 14–49 years.

Data source and methods 

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 (10). 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.
NCHS Data Brief ■ No. 90 ■ April 2012

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

of primary sampling units (PSU-counties), household segments within the counties, and finally 

sample persons from selected households. The sample design includes oversampling 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 over were oversampled. Because of the size and population density 

of LAC and the large Mexican-American population, a PSU in LAC was chosen with certainty 

in each 1-year sample in NHANES. It was the only county sampled in NHANES every year. 

In 1999, NHANES became a continuous survey, fielded on an ongoing basis. Public-use data 

files are released in 2-year cycles for U.S. estimates and can be grouped across cycles. Data was 

aggregated over these 6 years (1999–2004), which allowed for adequate sample size to make 

estimates for LAC (10). 

Sample base weights were calculated to account for the differential probabilities of selection. 

Adjustment to base weights to account for nonresponse was done separately for the LAC sample 

and the U.S. sample. Weights for the U.S. sample were post-stratified to the population control 

totals for the United States at the midpoint of each survey cycle. Weights for the LAC sample 

were post-stratified to the midpoint of the 1999–2004 population control totals for LAC (11). 

Standard errors of the percentages were estimated using Taylor Series Linearization in SUDAAN 

version 10.0 (RTI, Research Triangle Park, N.C.), a method that incorporates the sample weights 

and sample design. Ninety-five percent confidence intervals were estimated by using the exact 

binomial method (12). Differences in prevalence between the United States and LAC were 

evaluated by examining p-values calculated using a univariate t-statistic obtained from the 

combined standard errors between the two samples. All differences reported are statistically 

significant (p < 0.5) unless otherwise indicated.

Because 69% of the unweighted LAC sample was Mexican-American persons and there were 

relatively small numbers of non-Hispanic white and non-Hispanic black persons in the LAC 

sample, race and ethnicity specific estimates were only calculated for Mexican-American persons. 

About the authors

Deanna Kruszon-Moran, Kathryn Porter, Geraldine McQuillan, and Rosemarie Hirsch are with 

the Centers for Disease Control and Prevention’s National Center for Health Statistics (NCHS), 

Division of Health and Nutrition Examination Surveys. Veena Goud Billioux is with NCHS’ 

Division of Vital Statistics. Dr. Robert Kim-Farley is Director of the Division of Communicable 

Disease Control and Prevention of the Los Angeles County Department of Public Health. 

Acknowledgments

Leyla Mohadjer, Ph.D.; Jill Montaquila, Ph.D.; and Sylvia Dohrmann, M.S. of Westat for 

developing the Los Angeles County Weights.
NCHS Data Brief ■ No. 90 ■ April 2012

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immunity levels in the United States population: Has the threshold of viral elimination been 

reached? Clin Infect Dis 43:S146–50. 2006.

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positive counts estimated from survey data. Surv Methodol 24:193–201. 1998. 
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Suggested citation

Kruszon-Moran D, Porter KS, McQuillan G, 

Goud Billioux V, Kim-Farley R, Hirsch R. 

Infectious disease prevalence in Los Angeles 

County–A comparison to national estimates, 

1999–2004. NCHS data brief, no 90. 

Hyattsville, MD: National Center for Health 

Statistics. 2012.

Copyright information

All material appearing in this report is in 

the public domain and may be reproduced 

or copied without permission; citation as to 

source, however, is appreciated.

National Center for Health 

Statistics

Edward J. Sondik, Ph.D., Director

Jennifer H. Madans, Ph.D., Associate 

Director for Science

Division of Health and Nutrition

Examination Surveys

Clifford L. Johnson, M.S.P.H., Director

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