String test: a potentially useful tool in the diagnosis of pulmonary tuberculosis in Brazilian children and adolescents

This study investigated the potential use of the String Test (ST) for the diagnosis of pulmonary tuberculosis (PTB) in children and adolescents. This is a case series of patients aged 4-15 years presenting with clinically presumed PTB and submitted to ST in three pediatric TB referral centers in Brazil, between November 2017 and July 2020. The ST was performed in the morning, after 4-12 h of fasting, followed by ingestion of the capsule by the patient, which was attached to the patient’s malar region. The material was collected for simultaneous smear microscopy (acid-fast bacilli - AFB), culture and the molecular investigation by the GeneXpert MTB/RIF(®). Thirty-three patients with presumed PTB were included and ST was performed in 26 (78.8%) of them and 7 (21.2%) patients could not swallow the cord. The diagnosis of PTB was established in 11 (42.3%) of the 26 patients who underwent the ST. The diagnosis of PTB was confirmed (by culture or GeneXpert MTB/RIF(®)) in 5 patients, 4 of whom were also positive by the ST. Two of them showed positivity by the GeneXpert MTB/RIF(®) only in the ST sample. Two other patients had a positive ST following the induced sputum test (AFB, GeneXpert MTB/RIF(®), and positive culture in both specimens). Thus, ST was positive in 36.4% of the patients in whom PTB was diagnosed. ST could be a useful test for diagnosing PTB in children and adolescents.