title: TST positivity in household contacts of tuberculosis patients: a case-contact study in Malawi.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: LSTM, Liverpool School of Tropical Medicine, Liverpool, UK. J.hector@solidarmed.ch.
authors.forename: Jonas
authors.identifier: 0000-0003-3643-7952
authors.initials: J
authors.lastname: Hector
authors.affiliation: Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.|Section of Paediatrics and Imperial College-Wellcome Trust Centre for Global Health Research, Department of Medicine, Imperial College London, London, UK.
authors.forename: Suzanne T
authors.initials: ST
authors.lastname: Anderson
authors.affiliation: Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Gertrude
authors.initials: G
authors.lastname: Banda
authors.affiliation: Department of Microbiology, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Mercy
authors.initials: M
authors.lastname: Kamdolozi
authors.affiliation: LSTM, Liverpool School of Tropical Medicine, Liverpool, UK.
authors.forename: Laura F
authors.initials: LF
authors.lastname: Jefferys
authors.affiliation: Department of Microbiology, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Doris
authors.initials: D
authors.lastname: Shani
authors.affiliation: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Garton
authors.affiliation: Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Agnes
authors.initials: A
authors.lastname: Mwale
authors.affiliation: Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Annie
authors.initials: A
authors.lastname: Jobe
authors.affiliation: Institute of Infection and Global Health, University of Liverpool, Liverpool, UK.
authors.forename: Geraint R
authors.initials: GR
authors.lastname: Davies
authors.affiliation: Malawi Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.|School of Medicine, University of St Andrews, Scotland, UK.
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Sloan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D058491:Bacterial Load; D002648:Child; D002675:Child, Preschool; D003710:Demography; D005192:Family Health; D005260:Female; D006801:Humans; D008295:Malawi; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009169:Mycobacterium tuberculosis; D011203:Poverty; D012307:Risk Factors; D013183:Sputum / Q000382:microbiology; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000635:transmission; D055815:Young Adult
keywords: Contact screening; HIV status; Lipid body; Malawi; Tuberculosis; Tuberculosis skin test; White blood cell count