| Tuberculosis infection The natural history of TB infection is usually followed by an immune response and latency after exposure. In about 5-10% of cases, the latent period progresses to an active infection.The organism that causes TB infection is Mycobacterium tuberculosis. This organism is pictured in the photograph to the right as observed when stained with acridine orange stain. Infection occurs when a susceptible person inhales droplet nuclei containing Mycobacterium tuberculosis and the organism reaches the alveoli of the lungs.About 2-12 weeks after infection, the immune system limits multiplication of additional bacteria and the immunological test becomes positive.Latent tuberculosis infection (LTBI) is the stage when the viable organism remains in the body, and the patient has no symptoms and is non-infectious.Most infected persons do not experience clinical illness and are noninfectious. About 5-10% of persons infected with Mycobacterium tuberculosis who are not treated will develop TB during their lifetime. The risk for progression is highest during the first several years after infection.TB infects the lungs most often; however, it can infect almost any organ in the body, including bones and joints. | View Page |
| How tuberculosis is spread The Mycobacterium tuberculosis organism is spread through infectious droplet nuclei.When a person infected with pulmonary tuberculosis coughs, sneezes, shouts, or sings, the infectious particles are expelled into the air.The risk of infection is related to both concentration of infectious droplet nuclei and duration of exposure. | View Page |
| High Risk Infection Groups The following persons are at higher risk for exposure to and infection from Mycobacterium tuberculosis: Frequent travelers to tuberculosis endemic areas; Residents and employees of high-risk congregate settings such as correctional facilities, long-term care facilities, and homeless shelters; Healthcare workers who serve high-risk patients or have unprotected exposure; Medically underserved and low-income populations; Infants, children, and adolescents exposed to adults in high-risk categories. | View Page |
| High Risk Progression Groups The following persons are at high risk for progression from LTBI to TB disease: Persons infected with HIV Persons infected with Mycobacterium tuberculosis within the past two years Persons with untreated or inadequately treated TB disease Infants and children <4 years of age Persons with chronic medical conditions or immunocompromising conditions | View Page |
| Matching Facts | View Page |
| LTBI Testing Introduction It is important to identify and treat persons with LTBI to prevent progression to active disease. Currently there are two tests available to identify LTBI.The tuberculin skin test (TST) is performed on the inner arm.The Blood Assay for Mycobacterium tuberculosis (BAMT) is performed on a blood specimen. | View Page |
| False Positive TST reactions A false positive reaction is a TST induration >5 millimeters even though the person is not infected with Mycobacterium tuberculosis. Some causes are:
previous BCG vaccination,infection with nontuberculosis mycobacteria,incorrect TST administration or interpretation. | View Page |
| TST False Negative Reactions A false negative reaction is no induration after a TST even if the person is infected with Mycobacterium tuberculosis. Some causes of this are: weakened immune system,recent, old or overwhelming TB infection,immature immune system (<6 months of age),some viral illnesses,recent live-virus vaccinations,incorrect TST administration or interpretation. | View Page |
| Blood Assay for Mycobacterium tuberculosis (BAMT) The BAMT is a blood test that can detect LTBI.The BAMT has the advantage of no false positive results due to previous BCG vaccination or infection with nontuberculosis mycobacteria.The BAMT was approved by the FDA in 2005. | View Page |
| The two step TST has no false positive reactions due to infection with nontuberculosis mycobacteria or BCG vaccination. | View Page |
| Which of the following secondary barriers are recommended for microbiology laboratories that work with Biosafety level 3 agents (e.g., Mycobacterium tuberculosis)? | View Page |
| Biosafety Level 3 Biosafety level (BSL) 3 practices, safety equipment, and facility design and construction are applicable to microbiology laboratories that work with indigenous or exotic agents with a potential for respiratory transmission, and which may cause serious and potentially lethal infection. If the laboratory is propagating and manipulating cultures for M. tuberculosis, BSL 3 practices, containment equipment, and facilities are required. Nonaerosol-producing manipulations can be performed using BSL 2 practices, containment equipment, and facilities. At biosafety level 3, laboratory manipulations should be performed in a Class l or Class ll biosafety cabinet (BSC) or other physical containment device. Secondary barriers include controlled access to the laboratory and ventilation requirements that minimize the release of infectious aerosols from the laboratory. Secondary barriers should include self-closing double-door access and negative airflow into the laboratory. Exhausted air must not be recirculated. | View Page |