Oral swab PCR as an alternative to sputum-based methods for diagnosis of pulmonary tuberculosis

Abstract

<bold>Background</bold>: Oral swab PCR (OSP) has been proposed as an alternative to sputum-based TB diagnosis of tuberculosis because it uses a non-invasive, convenient sample. Sputum can be difficult to obtain and handle, and an alternative sample could enable faster and less expensive PCR detection of <italic>Mycobacterium tuberculosis</italic> (MTB) bacilli in patient samples. OSP may also be an effective test for exposure to either MTB or non-tuberculous mycobacteria (NTM). The latter are environmentally transmitted and some species are opportunistic pathogens of humans. MTB and NTM bacilli may adhere to the oral epithelium, where they can be collected on a buccal swab. <bold>Methods</bold>: Three swabs each were collected from 20 HIV-negative subjects with active, (GeneXpert-confirmed) pulmonary tuberculosis, and from 55 healthy, unexposed controls. To detect MTB, the oral swab samples were tested using an in-house polymerase chain reaction (PCR) protocol targeting the IS6110 insertion element, which is unique to the MTB complex. To detect NTM, select samples were tested using PCR protocols specific to certain species (<italic>Mycobacterium avium</italic> complex, <italic>Mycobacterium abscessus</italic>, and <italic>Mycobacterium kansasii</italic>) and for the <italic>Mycobacterium</italic> genus. <bold>Results</bold>: 44/60 (73.3%) swabs collected from case subjects were positive for MTB DNA by OSP. 18/20 (90%) case subjects yielded positive results (at least 2 positive swabs). 100% of control samples were negative. 15/15 (100%) and 6/6 (100%) swab samples tested negative for specific species of NTM, and for the <italic>Mycobacterium</italic> genus, respectively. <bold>Conclusions</bold>: OSP appears promising as a simpler and more uniform alternative to sputum testing for pulmonary tuberculosis. Because OSP uses an easy, non-invasive sampling method that does not require active TB symptoms, it could potentially be used as an active case finding tool. The NTM results are a preliminary step toward improved assessment of NTM exposure using OSP, however further optimization is needed.