title: The distribution of the prevalence of ocular chlamydial infection in communities where trachoma is disappearing.
abstract: Mathematical models predict that the prevalence of infection in different communities where an infectious disease is disappearing should approach a geometric distribution. Trachoma programs offer an opportunity to test this hypothesis, as the World Health Organization (WHO) has targeted trachoma to be eliminated as a public health concern by the year 2020. We assess the distribution of the community prevalence of childhood ocular chlamydia infection from periodic, cross-sectional surveys in two areas of Ethiopia. These surveys were taken in a controlled setting, where infection was documented to be disappearing over time. For both sets of surveys, the geometric distribution had the most parsimonious fit of the distributions tested, and goodness-of-fit testing was consistent with the prevalence of each community being drawn from a geometric distribution. When infection is disappearing, the single sufficient parameter describing a geometric distribution captures much of the distributional information found from examining every community. The relatively heavy tail of the geometric suggests that the presence of an occasional high-prevalence community is to be expected, and does not necessarily reflect a transmission hot spot or program failure. A single cross-sectional survey can reveal which direction a program is heading. A geometric distribution of the prevalence of infection across communities may be an encouraging sign, consistent with a disease on its way to eradication.
authors.affiliation: F.I Proctor Foundation, San Francisco, CA, USA; Department of Ophthalmology, San Francisco, CA, USA; Department of Epidemiology & Biostatistics, University of California, San Francisco, CA, USA. Electronic address: tom.lietman@ucsf.edu.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Lietman
authors.affiliation: The Carter Center, Atlanta, GA, USA.
authors.forename: Teshome
authors.initials: T
authors.lastname: Gebre
authors.affiliation: Programme National de Lutte Contre la Cecité, Niamey, Niger.
authors.forename: Amza
authors.initials: A
authors.lastname: Abdou
authors.affiliation: F.I Proctor Foundation, San Francisco, CA, USA; Department of Ophthalmology, San Francisco, CA, USA; Department of Epidemiology & Biostatistics, University of California, San Francisco, CA, USA; The Carter Center, Atlanta, GA, USA; Programme National de Lutte Contre la Cecité, Niamey, Niger; NIH Fogarty International Center, Bethesda, MD, USA; Berhan Health, Addis Ababa, Ethiopia.
authors.forename: Wondu
authors.initials: W
authors.lastname: Alemayehu
authors.affiliation: The Carter Center, Atlanta, GA, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Emerson
authors.affiliation: F.I Proctor Foundation, San Francisco, CA, USA; NIH Fogarty International Center, Bethesda, MD, USA.
authors.forename: Seth
authors.initials: S
authors.lastname: Blumberg
authors.affiliation: F.I Proctor Foundation, San Francisco, CA, USA; Department of Ophthalmology, San Francisco, CA, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Keenan
authors.affiliation: F.I Proctor Foundation, San Francisco, CA, USA; Department of Ophthalmology, San Francisco, CA, USA; Department of Epidemiology & Biostatistics, University of California, San Francisco, CA, USA.
authors.forename: Travis C
authors.initials: TC
authors.lastname: Porco
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D017963:Azithromycin / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D002690:Chlamydia Infections / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D005002:Ethiopia / Q000453:epidemiology; D015818:Eye Infections, Bacterial / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D008962:Models, Theoretical; D015995:Prevalence; D014141:Trachoma / Q000188:drug therapy* / Q000453:epidemiology*
chemical_list: D000900:Anti-Bacterial Agents; D017963:Azithromycin
keywords: Eradication; Geometric distribution; Mass drug administration; Trachoma; Transmission model