Background. At school there are special circumstances of living togeth
er and a particular susceptibility, which favour the emergence of tube
rculosis microepidemics. We report here the microepidemic ocurred at a
school among 9-year old children. Methods. After ruling out a possibl
e familiar source in a child with pulmonary tuberculosis, we detected
a case with high bacillar shedding in a female teacher and conducted a
tuberculin search among children and teachers, initially outlining th
e theoretical groups at risk. Tuberculin positive children underwent c
hest-X-ray and when abnormalities were found, children were derived to
the pediatrician for chemotherapy. All converters received secondary
chemoprophylaxis and all non-respondents primary chemoprophylaxis. Res
ults. The classroom where the teacher spent most of het time had a hig
her rate of converters (70%) than other classroom, where the index tea
cher spent only a partial time (40%; RR: 1.75; CI: 1.06-2.88) or the c
ollective of teachers (45.4%; RR: 1.45; CI: 0.94-2.23). Three addition
al cases of secondary disease were detected, all of them children. The
initial compliance with chemoprophylaxis was greater among (for) chil
dren (97.0%) than among teachers (41.6%). Among children there was one
case of tuberculin conversion compared with three cases among teacher
s. No additional cases were detected; also, an abnormal rate of reacto
rs outside the initially studied groups was also not detected. Conclus
ions. Our results somehow agree with those reported from other school
outbreaks. To note the anergy and lack of symptoms in the index case a
nd the suggestion to delineate the degree of spending hours together t
o identify groups with a higher theoretical risk of being infected. Th
us, an unnecessary expense of resources and a social alarm would be av
oided.