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Title: TST positivity in household contacts of tuberculosis patients: a case-contact study in Malawi.
Authors: Hector, J
Anderson, ST
Banda, G
Kamdolozi, M
Jefferys, LF
Shani, D
Garton, NJ
Mwale, A
Jobe, A
Davies, GR
Sloan, DJ
First Published: 11-Apr-2017
Publisher: BMC (part of Springer Nature)
Citation: BMC Infectious Diseases, 2017, 17:259
Abstract: BACKGROUND: Screening household contacts of active tuberculosis (TB) patients is recommended for TB control. Due to resource constraints this rarely occurs in lower income countries. Demographic and clinical features of index cases may influence the likelihood of onwards TB transmission. It has also been proposed that accumulation of intracellular lipid bodies within M. tuberculosis cells may also enhance bacterial transmissibility. This study explored whether clinical and bacteriological observations recorded at baseline in TB cases in Malawi could help identify those with the highest risk of onwards transmission, to prioritise contact tracing. METHODS: In this case-contact study, data on clinical presentation, sputum bacterial load and the percentage of lipid body positive acid-fast bacilli (%LB + AFB) on sputum smears were recorded in adults with sputum smear and culture positive pulmonary TB before initiation of therapy. The Tuberculin Skin Test (TST) was used to detect infection with M. tuberculosis amongst household contacts under the age of 15 years. TST positivity of the child contacts was related to characteristics of the index case. RESULTS: Thirty four index cases brought 56 contacts (median: 1, range: 1-4 contacts each). 37 (66%) of contacts had a positive TST. Cavities or a high percentage of lung affected on index patient CXRs were associated with TST positivity. Multivariate analysis of non-radiological factors showed that male sex, HIV-negative status and raised peripheral blood white blood count (WBC) in index patients were also independent risk factors of TST positivity. Lower %LB + AFB counts were associated with TST positivity on univariate analysis only. CONCLUSION: TST positivity is common amongst household contacts of sputum smear positive adult TB patients in Malawi. Contact tracing in this high risk population could be guided by prioritising index cases with CXR cavities and extensive radiological disease or, in the absence of CXRs, those who are HIV-negative with a raised WBC.
DOI Link: 10.1186/s12879-017-2348-2
eISSN: 1471-2334
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © the authors, 2017. This is an open-access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Description: The datasets of the study is available from the corresponding author on reasonable request.
Appears in Collections:Published Articles, Dept. of Infection, Immunity and Inflammation

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