TB disease - treatment and infection

Question

Background: I'm currently performing research in mathematical biology, specifically on the treatment dynamics of HIV and TB co-infection.

Question: Can a person infected with TB disease, who are undergoing treatment for it, infect a person with no history of TB bacteria in their body?

Reformulation: In other words, is there a similar analogue for TB as for HIV, wherein an HIV+ person undergoing treatment for HIV will have a lowered viral load and thus have negligible chances of infecting a person with no history of HIV?

Please note that my model does not incorporate latent TB because it would become too complicated to analyze. I am focusing only on TB disease because only it is infectious.

Thanks for any help.

Answer 1

First there is one major difference between HIV and TB: As long as the TB bacteria are still susceptible to treatment (which is developing into a major problem in some regions of the world) there is a effective treatment which can eradicate the infection. For HIV this is not possible. Here we can only lower the viral load (sometimes under the detection limit), but when the treatment is stopped, the virus will return.

Then it seems that patients under treatment of a drug susceptible TB are infectious for a longer time than previously thought. Until now they have been isolated at the beginning of the treatment (typically around the first two weeks) until three consecutive sputum samples had been negative. Then they were released from isolation and thought to be non-infectious. At this point they are not cured, the treatment has to go on for several weeks.

Now there is newer research indicating that patients can still be infectious although they are under treatment and have negative sputum samples. It seems here that the currently used detection method is not sensitive enough. See these references for more information:

• How Many Sputum Culture Results Do We Need To Monitor Multidrug-Resistant-Tuberculosis (MDR-TB) Patients during Treatment?
• High incidence of tuberculosis, low sensitivity of current diagnostic scheme and prolonged culture positivity in four colombian prisons. A cohort study.
• Prolonged infectiousness of tuberculosis patients in a directly observed therapy short-course program with standardized therapy.

Answer 2

I think its a bit difficult to compare HIV and TB this way because TB is transmitted mainly through respiratory droplets whilst HIV is mainly through contamination of blood products/sex, etc but not via the respiratory route. As far as I know, there's still a likelihood of TB transmission from a treated patient to an untreated patient. TB is quite complex, treated patients can still undergo reactivation later in life and still infect other people-the mechanisms are not fully understood. Treated patients can also develop drug resistance and then relapse which will make them again highly infectious.