About ¼ of the world's population is infected with M. tuberculosis. The gold standard for diagnosis is cultural exam.

Nucleic Acid Amplification Tests (NAAT) are recommended in the initial diagnosis, allowing the early detection of tuberculosis (TB).

Its isolated positivity remains unclear, particularly in patients who do not report previous MTB infection.


To evaluate clinical, imaging and sociodemographic characteristics of individuals with positive NAAT, but negative AFB and cultural exams.


Retrospective analysis of bronchoscopies performed between 04/01/2007 and 12/31/2021. Inclusion criteria: positivity in any of the diagnostic methods.

2 groups were created (I: positive NAAT only; II: positivity in ?1 of the other diagnostic methods).


Results of 3019 bronchoscopies.

Group I (n=16):

Predominance of males (n=9; 56.3%). Average age: 70.06 years. Previous respiratory pathology: 5 (31.3%). Constitutional symptoms: 6 (37.5%). Suspected infection: 3 (18.8%). Cavitation: 2 (12.5%). History of smoking: 3 (18.8%). Under antibacillary drugs: 1 (6.25%). Previous diagnosis of TB: 6 (37.5%). 3 (18.8%) developed the disease. Statistically significant relationship (p=0.036) between previous infection and development of TB. Mean time between positive NAAT and development of TB: 4.4 years.

Group II: n=69.

Statistically significant differences between groups: age (p=0.006), previous MTB infection (p=0.034) and cavitation (p=0.032).


Patients from group I had higher age and history of MTB infection and developed the disease, on average, 4.4 years after NAAT result.

More robust studies are needed to establish which factors influence NAAT positivity, especially in the absence of previous TB.