spatial clusters of hiv infection by mode of transmission in texas
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Spatial clusters of people living with HIV/AIDS by risk
of transmission in Texas
Sonia Arbona PhDPraveen R. Pannala, MD, MPHSharon K. Melville, MD, MPH
May 26, 2009
Background
The areas of higher concentrations of people living with HIV/AIDS in Texas are the major metropolitan areas and the cities in their periphery (Texas DSHS, 2010)
Beyond this general pattern there is a need to identify clusters that can be targeted for public health interventions
Study Purpose
The analysis aims to identify spatial clusters within the known general distribution of HIV/AIDS cases in Texas
Spatial clusters characterized by:
Methods Statistics
The SaTScan software implemented the Spatial Scan Statistics (Kulldorff 1997, Kulldorff et al. 2009):
Methods Statistics (Cont’d)
Statistics for each cluster are based on a Monte Carlo simulation:
• likelihood ratio, which indicates the probability of a cluster being real, and its corresponding p value
• relative risk estimate (RR = incidence proportioninside the cluster/incidence proportion outside the cluster)
Cases aggregated by zip codes are the units of observation
Methods Sample
The analysis included 46,301 people living with HIV/AIDS in Texas as of December 31, 2008 by HIV transmission risk:
The 46,301 persons excluded institutionalized individuals and those without a residential zip code at time of report
Results Number and location of clusters
7
Nineteen clusters identified
18,173 (39.2%) of the cases included in the spatial clusters
Major metropolitan areas have more than one cluster
Results Cluster Statistics
Table 1. Spatial clusters of HIV/AIDS in Texas by HIV mode of transmission in 2008
Mode of Transmission
Cluster LocationObserved
casesExpected
casesRelative risk
estimateLog-likelihood
ratioP value
IDU
1 Houston 1196 358.4 3.98 674.95 0.0012 Fort Worth 108 8.15 13.49 180.09 0.0013 Dallas 182 39.31 4.75 138.1 0.0014 El Paso 30 4.4 6.84 32.02 0.0015 Dallas 29 5.54 5.26 24.61 0.0016 Waco 35 8.54 4.12 22.97 0.001
MSM
1 Dallas 4681 837.95 6.53 4501.07 0.0012 Houston 4514 1132.83 4.57 3086.00 0.0013 Austin 1585 711.75 2.30 410.11 0.0014 San Antonio 390 70.93 5.56 347.54 0.0015 El Paso 166 51.39 3.24 80.28 0.001
MSM/IDU
1 Houston 358 64.78 6.13 333.79 0.0012 Dallas 262 69.62 4.03 161.25 0.0013 Austin 198 53.40 3.90 118.44 0.0014 Fort Worth 57 15.33 3.77 33.46 0.001
HRT
1 Houston 3858 1173.57 4.68 2353.98 0.0012 Dallas 299 68.11 4.49 214.09 0.0013 Dallas 179 61.59 2.94 74.25 0.0014 Fort Worth 46 14.28 3.23 22.14 0.001
Results Demographic Characteristics
9
clustered
notclustered
38.9%
61.1%
Figure 2
Results Spatial Clusters in Dallas – Fort Worth
Results Spatial Clusters in Central Texas
Results Spatial Clusters in Houston
12
Comments and Future Directions
Bibliography
Kulldorff M (1997) A spatial scan statistic. Communications in Statistics 26:1481-1496
Kulldorff M and Information Management Services, Inc. (2009) SaTScanTM v8.0: Software for the spatial and space-time scan statistics. http://www.satscan.org/
Texas Department of State Health Services (2010) 2008 HIV/STD Program Annual Report. Publication Number 13-10667