Presenter: Katherine Ngo, MPH
Authors: Katherine Ngo MPH, Biru Yang MPH PhD,
Monica Slentz BS, Lu-Yu Hwang MD, M. Aaron
Sayegh PhD MPH
Presented to: 2011 Annual CSTE Conference
June 12 -16, 2011

• Houston has the highest rate of infection in the entire state of Texas.
1
• In 2008, Houston was ranked 14 th in the nation for diagnosis of HIV infection.
2
• In 2008, Houston’s estimated rate of diagnosis of HIV infection was 28.9 per 100,000 population.
2 http://searchsalf.blogspot.com/2009/09/hiv-cartoon-3-search-id-pwen42.html

in Houston/Harris Co., TX 1999-2007
1600
1400
1200
1433 1444
1423 1417
1206
1193
1159
1145 1147
1000
800
600
400
200
0
1999 2000 2001 2002 2003 2004 2005 2006 2007
HIV Diagnosis Year

(Per Capita Income)
Source: the ESRI 2009 Sourcebook America dataset

(Percent Black in Houston)
Source: the ESRI 2009 Sourcebook America dataset

• Why were zip codes not used?
– Zip code boundaries do not define social differences
– Census tracts created as a proxy for neighborhoods 3

• What are social determinants of health?
– World Health Organization Definition:
• The social determinants of health are the conditions in which people are born, grow, live, work and age, including the health system. These circumstances are shaped by the distribution of money, power and resources at global, national and local levels, which are themselves influenced by policy choices. The social determinants of health are mostly responsible for health inequities - the unfair and avoidable differences in health status seen within and between countries.

• In 2010, the Houston Department of Health and Human
Services (HDHHS) initiated a project to enhance HIV surveillance data collected across its jurisdiction. The project involves the geocoding and linking of HIV diagnoses information to social determinants of health
(SDH) data.

• Increased use of geocoding in HIV surveillance programs will provide a better understanding of local disease distribution and epidemiology and can provide more cost effective HIV surveillance, delivery of services, and better evaluation of current prevention activities. Once the HIV surveillance data are geocoded, the data can be linked with other data.
• GIS analyses will allow the user(s) to assess current activities to prevent HIV infection, to identify new venues or activities for engaging hard to reach high-risk populations, and to target the allocation of local resources.

• To determine the social determinants of health associated with HIV diagnosis in
Houston/Harris County.

• Data Sources: ehanced HIV/AIDS Reporting System
(eHARS), 2000 US Census
• Time frame: 2008 and 2009
• 525/754 census tracts
• Unit of Analysis: Census Tracts
• Geocoded Addresses of HIV cases newly diagnosed in
2008 and 2009 to the census tract level.
• Six social determinants of health (SDH) variables selected for study through literature review and focus group discussions
• SDH variables linked to census tracts

Outcome: Number of HIV cases per census tract
Geographic level: census tract
• % of population in extreme poverty
• % African American (Institutional segregation)
• % of linguistically isolated households
• % without high school education
• % residential stability (% of population living in the same house over a 5-year period)
• % unemployed or not participating in workforce

– Correlation analysis detected significant associations between the SDH variables and the number of new
HIV diagnoses in a census tract.
– Logistic and Linear Regression http://www.cadalyst.com/management/cad-cartoon-5379

Social Determinants of Health Variables
Percent below extreme poverty
Percent of persons over 25 years old without HS
Percent of persons over 16 years old who are in the labor force and unemployed
Percent of linguistically isolated households
Length of stay-percent of persons 5 years or older resided in the same house for the past 5 years
Percent of African American in the 2000 Census aOR
0.892
1.016
1.021
0.914
1.013
0.972
95% CI
(0.832-0.957)*
(0.994-1.038)
(0.983-1.061)
(0.874-0.956)*
(1.000-1.027)
(0.960-0.983)*

Social Determinants of Health Variables
Intercept
Percent below extreme poverty
Percent of persons over 25 years old without HS
Percent of persons over 16 years old who are in the labor force and unemployed
Percent of linguistically isolated households
Length of stay-percent of persons 5 years or older resided in the same house for the past 5 years
Percent of African American in the 2000 Census
Parameter
Estimate
6.01
0.12
-0.02
-0.10
0.05
-0.07
0.07
P-Value
<.0001
0.0084
0.4546
0.0159
0.1087
<.0001
<.0000

• Preliminary Data Analysis
• Small sample size
– Data for only 2 years
• Limited to 2000 Census

• First study of its kind
• Collaboration between bureaus
• Hypothesis generating

• These results indicate a significant linear relationship between the number of people newly diagnosed with
HIV, poverty and the racial ethnic composition of a census tract.
• The results of this study are consistent with the findings of previous studies on health disparities.
• Future analysis will determine if these associations represent successful outreach or service gaps.

• Houston Department of Health and Human
Services
• Biru Yang MPH PhD, Monica Slentz BS, M. Aaron
Sayegh PhD MPH
– Bureau of Epidemiology
– Bureau of Community Health Statistics
– Bureau of HIV/STD Prevention
• The University of Texas School of Public Health
– Lu-Yu Hwang MD

1.
http://www.dshs.state.tx.us/hivstd/reports/default.shtm
2.
http://www.cdc.gov/hiv/surveillance/resources/reports/2008report/pdf/2008SurveillanceReport.pdf
3.
Krieger N, Waterman PD, Chen JT, Soobader MJ, Subramanian SV, Carson R: Zip code caveat:
Bias due to spati-temporal mismatches between zip codes and U.S. census-defined geographic areas -- The Public Health Disparities Geocoding Project. Am J Public Health 2002, 92:1100-
1102.
4.
Krieger N, Chen JT, Waterman PD, Rehkopf DH, Subramanian SV (2005) Painting a truer picture of US socioeconomic and racial/ethnic health inequalities: The Public Health Disparities
Geocoding Project. Am J Public Health 95: 312 –323.
5.
http://www.who.int/social_determinants/en/
6.
http://www.cdc.gov/mmwr/pdf/other/su6001.pdf
7.
www.cdc.gov/mmwr/PDF/wk/mm6021.pdf

Katherine Ngo, MPH
Epidemiologist
Bureau of Epidemiology
Houston Department of Health and Human Services
Tel: 832-393-5080
E-mail: Katherine.ngo@houstontx.gov

• Katherine Ngo
– Recent graduate of the University of Texas
School of Public Health. Graduating with an
MPH
– Received Bachelor’s degree from the
University of Texas at Austin
– Began interning at the Houston Department of
Health and Human Services in 2008 doing foodborne surveillance