The contacts of a person who is infectious for tuberculosis (TB) need to be investigated and possibly treated. The time when the person first became infectious may be impossible to know with certainty, so some rough guidelines have been established.
Parameters:
(1) symptomatic, consistent with TB (cough, night sweats, etc.)
(2) objective evidence of infection (cavity lesion on chest X-ray, positive AFB smear on sputum)
(3) date of symptoms onset
(4) date of first objective finding
Symptomatic
Objective Finding
Minimum Time for Being Infectious
no
no
4 weeks before date diagnosed
no
yes
3 months before first objective finding
yes
no
3 months before onset of symptoms OR 3 months before first objective finding, whichever is longer
yes
yes
3 months before onset of symptoms OR 3 months before first objective finding, whichever is longer
date to start based on symptoms =
= (date of symptom onset) - 90 days
date to start based on objective findings =
= (date of first objective finding) - 90 days
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