February 21, 2017
2 min read

Smear-negative youth screened for TB reveal low risk of transmission in schools

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Researchers in Italy found that the Mycobactrium tuberculosis transmission rate in school settings from smear-negative index cases were very low, particularly in those aged younger than 5 years, according to findings published in The Pediatric Infectious Disease Journal.

“It is known that children with tuberculosis are less contagious than adults … but few data are available in literature about the M. tuberculosis transmission rate when the index case is a child,” Paola Piccini, MD, from the department of health sciences at the University of Florence, Anne Meyer Children’s University Hospital in Italy, and colleagues wrote. “The aim of the present study was to evaluate the risk of M. tuberculosis transmission from pediatric index cases with active pulmonary TB to school pupils.”

Researchers retrospectively collected data from four Public Health Services in the Tuscany region between January 2007 and December 2014. They performed systematic tuberculosis (TB) screenings on students who had both daily (Group A) and sporadic (Group B) exposure to index cases soon after contact and repeated after 8 to 12 weeks. During this period, school pupils aged younger than 5 years were prescribed isoniazid prophylaxis. In children aged older than 5 years, investigators carried out tuberculin skin tests (TSTs), interferon-gamma release assay (IGRA), and chest radiograph on both index cases and each contact.

They separated each index case, assigning smear-positive children to Group I, smear-negative/culture-positive children to Group II and smear/culture-negative children to Group III. They collected data on age, school attended, TST, IGRA and chest radiograph results. For each contact case, they also collected data on Bacillus CalmetteGuérin (BCG) vaccination and risk factors for TB, such as immigration or adoption; and for each index case, they collected additional data on detection of M. tuberculosis by smear or gastric aspirate microscopy and/or culture.

Among students in close contact with Group I index cases, transmission rate for school classmates without risk factors for TB was 21.6%, whereas the transmission rate was 0% among contacts of Group II and III index cases. Out of 20 index cases and 816 contacts, researchers discovered 38 cases of latent TB and two cases of active TB. They found 36 cases with latent TB and no case of active TB in contacts of Group one index cases; two cases with latent TB and one case of active TB in contacts of Group II index cases; and one case of active TB in contacts of Group III index cases. Index cases in Group I and their contacts were mainly adolescents aged 11 to 18 years, whereas index cases in Group II and III and their own cases were young children aged 0 to 13 years.

“Further studies are necessary to elucidate contagiousness of smear-negative children with TB in the community and, if our data are confirmed, school contacts of smear-negative index case could be screened only by clinical evaluation and TST (or IGRAs in BCG vaccinated children), avoiding routine use of chest radiographs in children younger than the age of five as well,” Piccini and colleagues wrote. “There could be a rationale for avoiding isoniazid prophylaxis in school contacts of an index case with negative smear or gastric aspirates microscopic results.” by Savannah Demko

Disclosure:  Infectious Diseases in Children was unable to confirm any relevant financial disclosures at the time of publication.