Comparative geographic concentrations of 4 sexually transmitted infections

Abstract

Objectives: We measured and compared the concentration of primary and secondary syphilis, gonorrhea, chlamydial infection, and genital herpes in a large county with urban, suburban, and rural settings.

Methods: We geocoded sexually transmitted infections reported to King County, Washington health department in 2000-2001 to census tract of residence. We used a model-based approach to measure concentration with Lorenz curves and Gini coefficients.

Results: Syphilis exhibited the highest level of concentration (estimated Gini coefficient = 0.68, 95% confidence interval [CI] = 0.64, 0.78), followed by gonorrhea (estimated Gini coefficient=0.57; 95% CI=0.54, 0.60), chlamydial infection (estimated Gini coefficient = 0.45; 95% CI = 0.40, 0.43), and herpes (estimated Gini coefficient=0.26; 95% CI=0.22, 0.29).

Conclusions: Geographically targeted interventions may be most appropriate for syphilis and gonorrhea. For less-concentrated infections, control strategies must reach a wider portion of the population.

FIGURE 1—

Lorenz curves for reported cases of 4 sexually transmitted infections in King County, Washington, 2000–2001.

FIGURE 2—

Lorenz curves and confidence bands for (a) primary and secondary syphilis, (b) gonorrhea, (c) chlamydial infection, and (d) initial episodes of genital herpes, King County, Washington, 2000–2001.

FIGURE 3—

Census tracts that account for 50% of estimated cases of (a) primary and secondary syphilis, (b) gonorrhea, (c) chlamydial infection, and (d) initial episodes of genital herpes, after tracts were arranged in descending order by estimated rate, King County, Washington, 2000–2001.…Note. Twenty-one census tracts (of 373 total) in eastern King County are not shown. None of these census tracts accounted for the first 50% of estimated sexually transmitted infection cases when tracts were arranged in descending order by estimated rate.

FIGURE 3—

Census tracts that account for 50% of estimated cases of (a) primary and secondary syphilis, (b) gonorrhea, (c) chlamydial infection, and (d) initial episodes of genital herpes, after tracts were arranged in descending order by estimated rate, King County, Washington, 2000–2001.…Note. Twenty-one census tracts (of 373 total) in eastern King County are not shown. None of these census tracts accounted for the first 50% of estimated sexually transmitted infection cases when tracts were arranged in descending order by estimated rate.

FIGURE 3—

Census tracts that account for 50% of estimated cases of (a) primary and secondary syphilis, (b) gonorrhea, (c) chlamydial infection, and (d) initial episodes of genital herpes, after tracts were arranged in descending order by estimated rate, King County, Washington, 2000–2001.…Note. Twenty-one census tracts (of 373 total) in eastern King County are not shown. None of these census tracts accounted for the first 50% of estimated sexually transmitted infection cases when tracts were arranged in descending order by estimated rate.

FIGURE 3—

Census tracts that account for 50% of estimated cases of (a) primary and secondary syphilis, (b) gonorrhea, (c) chlamydial infection, and (d) initial episodes of genital herpes, after tracts were arranged in descending order by estimated rate, King County, Washington, 2000–2001.…Note. Twenty-one census tracts (of 373 total) in eastern King County are not shown. None of these census tracts accounted for the first 50% of estimated sexually transmitted infection cases when tracts were arranged in descending order by estimated rate.