Using GIS technology to identify areas of tuberculosis transmission and incidence

Abstract

BACKGROUND: Currently in the U.S. it is recommended that tuberculosis screening and treatment programs be targeted at high-risk populations. While a strategy of targeted testing and treatment of persons most likely to develop tuberculosis is attractive, it is uncertain how best to accomplish this goal. In this study we seek to identify geographical areas where on-going tuberculosis transmission is occurring by linking Geographic Information Systems (GIS) technology with molecular surveillance. METHODS: This cross-sectional analysis was performed on data collected on persons newly diagnosed with culture positive tuberculosis at the Tarrant County Health Department (TCHD) between January 1, 1993 and December 31, 2000. Clinical isolates were molecularly characterized using IS6110-based RFLP analysis and spoligotyping methods to identify patients infected with the same strain. Residential addresses at the time of diagnosis of tuberculosis were geocoded and mapped according to strain characterization. Generalized estimating equations (GEE) analysis models were used to identify risk factors involved in clustering. RESULTS: Evaluation of the spatial distribution of cases within zip-code boundaries identified distinct areas of geographical distribution of same strain disease. We identified these geographical areas as having increased likelihood of on-going transmission. Based on this evidence we plan to perform geographically based screening and treatment programs. CONCLUSION: Using GIS analysis combined with molecular epidemiological surveillance may be an effective method for identifying instances of local transmission. These methods can be used to enhance targeted screening and control efforts, with the goal of interruption of disease transmission and ultimately incidence reduction.

Figure 1

Derivation of study population, Tarrant County, Texas 1993 – 2000

Figure 2

Average incidence of Tuberculosis by zip code Tarrant County, Texas (1993 – 2000). Specific zip codes of interest are labeled in green.

Figure 3

Percent of patients genotypically cluster by zip code Tarrant County, Texas (1993 – 2000). Percent genotypically clustered cases = number of genotypically clustered cases/ total number of cases × 100

Figure 4

Three-dimensional analysis using Inverse Distance Weighting Interpolation, Tarrant County, Texas (1993 – 2000). Inverse power: w(d)= 1/d^p with p = 1. Zip code 1 consists of 264.89 acres.