Culturing stool specimens has no added value in diagnosing pulmonary tuberculosis

Patients with pulmonary tuberculosis (PTB) may face challenges in providing sputum specimens for diagnosis. Mycobacterium tuberculosis (Mtb) is potentially present in the stool due to swallowed sputum. Therefore easy-to-obtain stool could be used as an alternative to sputum sampling. However, the evidence for using stool specimens for PTB diagnosis is sparse, especially in resource-rich settings. In this study, spanning two years, the results of 562 stool specimens were evaluated alongside those of respiratory specimens sent to the International Reference Laboratory of Mycobacteriology in Denmark. Despite the potential advantages of stool culture, only five out of 19 patients with PTB had Mtb culture-positive stool, all of whom also had positive respiratory specimens. Conversely, relying solely on stool specimens could lead to missed diagnoses of PTB. While stool analysis may offer additional value in specific settings or populations, such as those unable to produce sputum, this study discourages its general use for PTB testing in resource-rich, TB low-incidence settings like Denmark. Instead, we advocate for prospective trials in specific subpopulations to elucidate the role of stool as a complementary diagnostic tool for PTB. The study underscores the importance of tailoring diagnostic approaches based on the setting and patient characteristics.