Also, lack of money may deter people from finishing treatment. This can have serious consequences. The bacteria will then be able to mutate and develop resistance to the drugs. People can then pass this resistant TB onto others, and treatment can become difficult or ineffective. This long period of treatment is needed to kill all M. tuberculosis in the body.
Resistance can also occur when patients are treated with too few drugs or the wrong ones.
The Center for Disease Control has reported numerous MDR-TB outbreaks in prisons and hospitals. Usually a second line of TB drugs are needed, many of which can cause serious side effects. Therapy can last from 18 months to 2 years, during which the patient should be taking at least 3 drugs to which the TB is susceptible. Diagnosis in HIV-infected people is difficult. Often they produce symptoms similar to TB but will not react positively with the tuberculin skin test because their immune systems are suppressed.