An Italian study found that transmission of smear-negative TB among schoolchildren was rare, reports Healio.

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 Calmette–Guérin (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.