title: False-positive Xpert® MTB/RIF assays in previously treated patients: need for caution in interpreting results.
abstract: Xpert(®) MTB/RIF is the initial diagnostic test of choice for tuberculosis (TB). It is not known if false-positive results are more common in previously treated patients. We report four patients with successful treatment for TB up to 5 years previously who presented with respiratory tract infection and were Xpert-positive, but had negative TB cultures and clinical improvement without anti-tuberculosis treatment. We hypothesise that the Xpert results were false-positive due to the presence of dead Mycobacterium tuberculosis bacilli in lungs and sputum. Further work is required to determine the specificity of Xpert in previously treated patients.
authors.affiliation: <label>*</label>Division of Infectious Diseases and HIV Medicine, Department of Medicine, Groote Schuur Hospital, University of Cape Town, Cape Town, South Africa.
authors.forename: T H
authors.initials: TH
authors.lastname: Boyles
authors.affiliation: <label><sup>†</sup></label>Médecins Sans Frontières, Khayelitsha, Cape Town, South Africa.
authors.forename: J
authors.initials: J
authors.lastname: Hughes
authors.affiliation: <label><sup>†</sup></label>Médecins Sans Frontières, Khayelitsha, Cape Town, South Africa.
authors.forename: V
authors.initials: V
authors.lastname: Cox
authors.affiliation: <label><sup>‡</sup></label>Khayelitsha District Hospital, Khayelitsha, Cape Town, South Africa.
authors.forename: R
authors.initials: R
authors.lastname: Burton
authors.affiliation: <label><sup>§</sup></label>Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: G
authors.initials: G
authors.lastname: Meintjes
authors.affiliation: <label>*</label>Division of Infectious Diseases and HIV Medicine, Department of Medicine, Groote Schuur Hospital, University of Cape Town, Cape Town, South Africa.
authors.forename: M
authors.initials: M
authors.lastname: Mendelson
mesh_terms: D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008168:Lung / Q000382:microbiology; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D012141:Respiratory Tract Infections / Q000175:diagnosis* / Q000382:microbiology; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology; D014376:Tuberculosis / Q000175:diagnosis* / Q000382:microbiology