Tehran University Medical Journal

Historically, tuberculosis has been the leading cause of death throughout human history. Tuberculosis infection (TB) causes by Mycobacterium tuberculosis that is very dangerous and can affect any parts of the body, especially lungs. Tuberculosis infection still remains a serious threat to human public health due to its contagious nature, capability to stay latent form in host for indefinite time and then appear as active disease. It is estimated that one third of world’s population, nearly 2 billion persons are infected with Mycobacterium tuberculosis. Transmission occurs among people through inhalation of infected droplets. Lungs and especially alveolar macrophage are primary sites of infection. Mycobacterium tuberculosis bacilli by preventing fusion of phagosome with lysosome can remain alive inside the macrophages. Such situation defined as latent infection. In fact, persons with latent tuberculosis infection (LTBI) are only infected with M. tuberculosis without any sign of infectious. Latent infection in compared with active infection is not contagious, but in about 10-5 percent of people will develop active tuberculosis especially in elderly and people who use immunosuppressive drugs. Pulmonary TB is an active form of tuberculosis infection in which bacteria can spread among people by infected droplets. So identifying and treating people with latent TB infection can significantly reduce the progression of latent form to active infection. The tuberculin skin test (TST) is the most widely used test in worldwide that is applied to determine a person who is infected with M. tuberculosis. TST provide valubale information for diagnosis LTBI however its specificity can be reduced by bacillus Calmette-Guérin (BCG) vaccination and infected with non-tuberculous mycobacteria (NTM). In TST test host hypersensitivity responses to Purified protein derivative (PPD) from mycobacterium are evaluated. TST positive reaction indicates the presence of high risk for acquiring TB infection or progression of latent tuberculosis to active form. Previous studies indicated that there is correlation between TST response and subsequent risk of active TB. Experimental evidence has shown that treatment of latent infection in the basis of positive TST reduces the risk of active TB. Although TST is far from gold standard but it's low cost and simplicity make it a suitable laboratory test especially in developing country.
 

The members of Mycobacterium tuberculosis complex (MTBC) known as causative agents of human tuberculosis. Tuberculosis infection is one of the most important occupational risks for healthcare workers (HCWs) in most countries, such as Iran. In general, there are two types of tuberculosis, they include: latent infection and active TB. Latent tuberculosis infection (LTBI) means: a patient is infected with Mycobacterium tuberculosis but, the patient does not have active tuberculosis, clinical symptoms and radiological findings. According to studies, TB infection from patients to health care workers, depending on geographic region and economic situation is two to five times more than general population. The lowest incidence and the highest rates of LTBI prevalence among HCWs were 7% in Mashhad and 82.8% in Zahedan respectively. The risk factor acquisition of TB infection was a significant relationship with certain hospital wards (lung disease unit, laboratory, etc.), Increasing age and duration of employment. And results of this study show that TB is a significant problem among HCWs in Iran. Infection control and personal protective measures with training programs to patients and HCW is required to reduce the occupational risk of TB. Early detection of Mycobacterium tuberculosis and prevention treatment in people with latent TB are key elements in control of tuberculosis. Until now, different methods for detection of latent tuberculosis infection has been introduced that are not gold standard none of them. However, the most important methods, tuberculin skin test and the tests that based on measuring the production of interferon gamma are recommended, but each one of them has advantages and disadvantages. However, in all the articles of the tuberculin skin test is used for screening and early diagnosis of latent tuberculosis infection. So, the aim of this study was to Incidence and prevalence of latent tuberculosis infection in health care workers and risk factors, advantages and disadvantages of each method for diagnosis of latent tuberculosis infection and evaluate different strategies for reducing the incidence of latent tuberculosis infection in health care workers.