Majority (>80%) of Tuberculosis cases in United States are due to reactivation of latent tuberculosis. Latent tuberculosis is a stage of tuberculosis infection where the there is not symptom indicating the disease, but the patients act as reservoirs of tuberculosis bacteria, Mycobacterium tuberculosis. But, if these latent cases of tuberculosis are detected early, they can be cured completely only by following a course of drugs. Therefore, in United Stated it is recommended to screen for latent tuberculosis cases.
Screening is recommended only for population subgroups with a high prevalence of latent tuberculosis infection or those with a high likelihood of progression from latent tuberculosis infection to active disease.
Direct detection of the bacteria in latent patients is very difficult because the number of bacteria is very low. Therefore, the commonly used method is the “Tuberculin Test”, which looks for the immune reaction which occurs only in infected persons. This test has a high sensitivity, but its specificity is very low.
Screening for latent tuberculosis using tuberculin test has been done in year 1999 and 2000. The test has revealed that 4.5% of people who underwent the test had tuberculosis. Of these positive patients only 5% has developed tuberculosis later in their life. Considering the above difficulties, two other tests methods have come into play. They are,
1. QuantiFERON–TB Gold (QFT) (Cellestis)
2. T-SPOT.TB test (Oxford Immunotec)
The disease is possible to cure completely only if the patients takes the course of antibiotics continuously for 9 months. Since this is a very long period, the patient compliance is as low as 50%.
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