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Is stool a good specimen for diagnosing pulmonary tuberculosis in a high resource setting?

D B Folkvardsen(1) V N Dahl(1,2) T Lillebaek(1,3)

1:International Reference Laboratory of Mycobacteriology, Statens Serum Institut, Copenhagen, Denmark; 2:Department of Infectious Diseases, Aarhus University Hospital, Aarhus, Denmark; 3:Global Health Section, Department of Public Health, University of Copenhagen, Denmark

Sputum sampling for M. tuberculosis (Mtb) may be challenging in clinical practice. Because sputum is swallowed, acid-fast bacteria may potentially be detected in stool, providing an easily accessible specimen, especially in low-resource settings.

To investigate stool as a useful alternative to respiratory specimens in a resource rich tuberculosis (TB) low-burden setting, we examined one year of diagnostic specimens sent for mycobacteria investigations in Denmark. Of 14,966 specimens sent to the International Reference Laboratory of Mycobacteriology in Denmark during 2022, 306 were stool specimens received from 147 unique patients. In total, four of these from two different patients were Mtb culture positive. Both patients also had Mtb culture positive pulmonary specimens. In addition, eight of 136 (5.9%) stool culture negative patients had a culture positive respiratory specimen, two with non-tuberculous mycobacteria and six with Mtb (4.4%), respectively. The other 128 stool negative patients had no positive specimens. Of these, 47 only had stool sent for examination. Of 182 Mtb-PCR tested stool specimens, only three (1.6%) were positive, all also culture confirmed.

In conclusion, we found no added value of examining stool specimen from patients with pulmonary TB (PTB). All patients identified through stool also had positive respiratory specimens. In addition, some Mtb positive patients identified through respiratory specimens had positive stool samples. Thus, we discourage screening for PTB through stool specimens or examining stool specimens only, as this potentially leads to missed diagnoses of PTB, and advocate that the use of stool sampling for PTB is highly questionable in our setting.

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