Article Text

  1. S Paranjothy1,
  2. M Eisenhut2,
  3. M Lilley3,
  4. I Abubaker3,
  5. S Bracebridge4,
  6. J Howard3,
  7. K Lack3,
  8. S Thomas4,
  9. R Mulla2,
  10. D Chalkley5,
  11. M McEvoy3
  1. 1Cardiff University, Cardiff, Wales, UK
  2. 2Luton and Dunstable Hospital NHS Foundation Trust, Luton, Bedfordshire, UK
  3. 3Bedfordshire and Hertfordshire Health Protection Unit, Bedford, Bedfordshire, UK
  4. 4Health Protection Agency Regional Epidemiology Unit, Cambridge, Cambridgeshire, UK
  5. 5Luton Primary Care Trust, Luton, Bedfordshire, UK


Objectives To establish source case and risk factors for infection with Mycobacterium tuberculosis in young children during an incident of extensive transmission of mycobacterium tuberculosis in a Junior School.

Methods Following the diagnosis of pulmonary tuberculosis in a 9-year old boy (the index case) with a right upper lobe consolidation and Mycobacterium tuberculosis grown from a smear-negative sputum, we detected a high rate of infection in his family and class contacts. This led to screening of all pupils (n = 200) and staff (n = 108) of a UK junior school for M. tuberculosis infection using a gamma interferon release assay and chest x-rays.

Results Altogether, 85 (42%) pupils of the junior school had a reactive gamma interferon release assay indicating infection with M. tuberculosis. The infection rate in the class of the index case was significantly higher (79%) than the infection rate among the other pupils at the school (35%) (p<0.01). Children without previous BCG vaccination had a significantly higher risk of being infected (OR 6.34, 95% CI 1.79 to 22.52, p<0.01). None of the adult contacts screened had pulmonary tuberculosis. Genetic finger printing revealed that the strain of M. tuberculosis matched a strain of a family contact of the index case (and the most likely source for this school outbreak) encountered six years previously.

Conclusions Smear-negative sputum and lack of cavitating disease on a chest x-ray do not exclude significant risk of transmission of infection from a patient with pulmonary tuberculosis. BCG immunisation was associated with a lower risk of infection.

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