The index case (source) was determined in 2009 when the same local health department received a hospital report indicating a 42-year-old woman, born in Italy, had previously worked as an assistant in one of the kindergartens at the school. She was diagnosed with cavitary lesions of both upper and lower lungs; sputum cultures were positive, but acid-fast bacilli (AFB) smears were negative. Both her son and father had been treated for TB in 1996 and 1999, but she was unaware of treatment with isoniazid. She noted a frequent cough during her time at the kindergarten, tested negative by TST, and had no chest x-ray. The cough had been treated with mucolytic and antimicrobial drugs (as for a bacterial infection) by her family physician. Traveling to southern Italy, when her illness progressed she consulted a respiratory physician, who advised immediate hospital care.
Gastric aspirate specimens from three children at the school were smear-positive for AFB, and specimens from nine children were culture-positive for M. tuberculosis. All isolates were susceptible to first-line drugs, except one which was moderately resistant to isoniazid. The specimens included gastric aspirates, a vertebral abscess, and a sputum specimen (from the index case). After direct nucleic acid amplification testing (NAAT) for M. tubercuolosis, DNA finger printing proved the strain from the woman matched the strains isolated from the children who had been exposed. Clinical and epidemiological data indicated she was the only source of infection.
The CDC study determined that late diagnosis and poor follow-up of the school assistant and her family caused the outbreak. Although most of the school staff tested positive with the TST, there are no requirements for testing school employees in Italy. Also notable is the fact that children do not usually transmit the disease because of their non-infectious state (no sputum is produced). They are AFB smear negative and do not cough, thus having a decreased likelihood of spreading infectious material.