People infected with TB bacilli will not necessarily become sick with the disease. The immune system "walls off" the TB bacilli which, protected by a thick waxy coat, can lie dormant for years.The spread of TB bacteria depends on factors such as the number and concentration of infectious people in any one place together with the presence of people with a higher risk of being infected (such as those with HIV/AIDS). The risk of becoming infected increases with the longer the time that a previously uninfected person spends in the same room as the infectious case. The risk of spread increases where there is a high concentration of TB bacteria, such as can occur in closed environments like overcrowded houses, hospitals or prisons. The risk will be further increased if ventilation is poor. The risk of spread will be reduced and eventually eliminated if infectious patients receive proper treatment. Diagnosis
Successful diagnosis of XDR-TB depends on the patients access to quality health-care services. If TB bacteria are found in the sputum, the diagnosis of TB can be made in a day or two, but this finding will not be able to distinguish between drug-susceptible and drug-resistant TB. To evaluate drug susceptibility, the bacteria need to be cultivated and tested in a suitable laboratory. Final diagnosis in this way for TB, and especially for XDR-TB, may take from 6 to 16 weeks.The original method used to test for MDR-TB and XDR-TB was the Drug Susceptibility Testing (DST).
History
XDR-TB is defined as TB that has developed resistance to at least rifampicin and isoniazid (resistance to these first line anti-TB drugs defines Multi-drug-resistant tuberculosis, or MDR-TB), as well as to any member of the quinolone family and at least one of the following second-line anti-TB injectable drugs: kanamycin, capreomycin, or amikacin. This definition of XDR-TB was agreed by the World Health Organization (WHO) Global Task Force on XDR-TB in October 2006. The earlier definition of XDR-TB as MDR-TB that is also resistant to three or more of the six classes of second-line drugs, is no longer used, but may be referred to in older publications. South African epidemic
XDR-TB was first widely publicised following the report of an outbreak in South Africa in 2006. 53 patients in a rural hospital in Tugela Ferry were found to have XDR-TB of whom 52 died. The median survival from sputum specimen collection to death was only 16 days and that the majority of patients had never previously received treatment for tuberculosis suggesting that they had been newly infected by XDR-TB strains, and that resistance did not develop during treatment. This was the first epidemic for which the acronym XDR-TB was used, and although TB strains that fulfill the current definition have been identified retrospectively, this was the largest group of linked cases ever found. Since the initial report in September 2006, cases have now been reported in most provinces in South Africa. As of 16 March 2007, there were 314 cases reported, with 215 deaths.