Clinical and epidemiological characteristics of individuals resistant to M. tuberculosis infection in a longitudinal TB household contact study in Kampala, Uganda

Ningning Ma, Sarah Zalwango, La Shaunda L. Malone, Mary Nsereko, Eddie M. Wampande, Bonnie A. Thiel, Brenda Okware, Robert P. Igo, Moses L. Joloba, Ezekiel Mupere, Harriet Mayanja-Kizza, W. H. Boom, Catherine M. Stein

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34 Scopus citations

Abstract

Background: Despite sustained exposure to a person with pulmonary tuberculosis (TB), some M. tuberculosis (Mtb) exposed individuals maintain a negative tuberculin skin test (TST). Our objective was to characterize these persistently negative TST (PTST-) individuals and compare them to TST converters (TSTC) and individuals who are TST positive at study enrollment.Methods: During a TB household contact study in Kampala, Uganda, PTST-, TSTC, and TST + individuals were identified. PTST- individuals maintained a negative TST over a 2 year observation period despite prolonged exposure to an infectious tuberculosis (TB) case. Epidemiological and clinical characteristics were compared, a risk score developed by another group to capture risk for Mtb infection was computed, and an ordinal regression was performed.Results: When analyzed independently, epidemiological risk factors increased in prevalence from PTST- to TSTC to TST+. An ordinal regression model suggested age (p < 0.01), number of windows (p < 0.01) and people (p = 0.07) in the home, and sleeping in the same room (p < 0.01) were associated with PTST- and TSTC. As these factors do not exist in isolation, we examined a risk score, which reflects an accumulation of risk factors. This compound exposure score did not differ significantly between PTST-, TSTC, and TST+, except for the 5-15 age group (p = 0.009).Conclusions: Though many individual factors differed across all three groups, an exposure risk score reflecting a collection of risk factors did not differ for PTST-, TSTC and TST + young children and adults. This is the first study to rigorously characterize the epidemiologic risk profile of individuals with persistently negative TSTs despite close exposure to a person with TB. Additional studies are needed to characterize possible epidemiologic and host factors associated with this phenotype.

Original languageEnglish
Article number352
JournalBMC Infectious Diseases
Volume14
Issue number1
DOIs
StatePublished - Jun 27 2014

Keywords

  • Exposure
  • Household characteristics
  • Latent Mtb infection
  • PPD test
  • Transmission risk factors

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