DOTS is used with intermittent dosing (thrice weekly or 2HREZ/4HR3). Twice weekly dosing is effective but not recommended by the World Health Organization (WHO), because there is no margin for error (accidentally omitting one dose per week results in once weekly dosing, which is ineffective).Treatment with properly implemented DOTS has a success rate exceeding 95% and prevents the emergence of further multi-drug resistant strains of tuberculosis. Administering DOTS, decreases the possibilities of tuberculosis from recurring, resulting in a reduction in unsuccessful treatments. This is in part due to the fact that areas without the DOTS strategy generally provide lower standards of care. Areas with DOTS administration help lower the number of patients seeking help from other facilities where they are treated with unknown treatments resulting in unknown outcomes. However, if the DOTS program is not implemented or done so incorrectly positive results will be unlikely. For the program to work efficiently and accurately health providers must be fully engaged, links must be built between public and private practitioners, health services must be available to all, and global support is provided to countries trying to reach their TB prevention, and treatment aims. Some researchers suggest that, because the DOTS framework has been so successful in the treatment of tuberculosis in sub-Saharan Africa, DOTS should be expanded to non-communicable diseases such as diabetes mellitus, hypertension, and epilepsy. DOTS-Plus strategy
The WHO extended the DOTS programme in 1998 to include the treatment of MDR-TB (called "DOTS-Plus").
Isolates that are multi-resistant to any other combination of anti-TB drugs but not to INH and RMP are not classed as MDR-TB. As of Oct 2006, "Extensively drug-resistant tuberculosis" (XDR-TB) is defined as MDR-TB that is resistant to quinolones and also to any one of kanamycin, capreomycin, or amikacin. The old case definition of XDR-TB is MDR-TB that is also resistant to three or more of the six classes of second-line drugs. This definition should no longer be used, but is included here because many older publications refer to it. The principles of treatment for MDR-TB and for XDR-TB are the same. The main difference is that XDR-TB is associated with a much higher mortality rate than MDR-TB, because of a reduced number of effective treatment options. The epidemiology of XDR-TB is currently not well studied, but it is believed that XDR-TB does not transmit easily in healthy populations, but is capable of causing epidemics in populations which are already stricken by HIV and therefore more susceptible to TB infection. Epidemiology of drug-resistant TB
A 1997 survey of 35 countries found rates above 2% in about a third of the countries surveyed. The highest rates of drug-resistant TB were in the former USSR, the Baltic states, Argentina, India and China, and was associated with poor or failing national Tuberculosis Control programmes.