latent tuberculosis latent tuberculosis latent tuberculosis (ltb), also called latent tuberculosis infection (ltbi) is when a person is infected with mycobacterium tuberculosis, but does not have active tuberculosis. active tuberculosis can be contagious while latent tuberculosis is not, and it is therefore not possible to get tb from someone with latent tuberculosis. the main risk is that approximately 10% of these people (5% in the first two years after infection and 0.1% per year thereafter) will go on to develop active tuberculosis. this is particularly true, and there is added risk, in particular situations such as medication that suppresses the immune system or advancing age. latent tuberculosisother nameslatent tuberculosis infectionspecialtyinfectious disease the identification and treatment of people with latent tb is an important part of controlling this disease. various treatment regimens are in use for latent tuberculosis. they generally need to be taken for several months. transmission latent disease tb bacteria are spread only from a person with active tb disease ... in people who develop active tb of the lungs, also called pulmonary tb, the tb skin test will often be positive. in addition, they will show all the signs and symptoms of tb disease, and can pass the bacteria to others. so, if a person with tb of the lungs sneezes, coughs, talks, sings, or does anything that forces the bacteria into the air, other people nearby may breathe in tb bacteria. statistics show that approximately one-third of people exposed to pulmonary tb become infected with the bacteria, but only one in ten of these infected people develops active tb disease during their lifetimes.however, exposure to tuberculosis is very unlikely to happen when one is exposed for a few minutes in a store or in a few minutes social contact. "it usually takes prolonged exposure to someone with active tb disease for someone to become infected. after exposure, it usually takes 8 to 10 weeks before the tb test would show if someone had become infected."depending on ventilation and other factors, these tiny droplets can remain suspended in the air for several hours. should another person inhale them, he or she may become infected with tb. the probability of transmission will be related to the infectiousness of the person with tb, the environment where the exposure occurred, the duration of the exposure, and the susceptibility of the host.in fact, "it isn't easy to catch tb. you need consistent exposure to the contagious person for a long time. for that reason, you're more likely to catch tb from a relative than a stranger." if a person had latent tuberculosis, they do not have active/contagious tuberculosis. once exposed, people very often have latent tuberculosis. to convert to active tuberculosis, the bacteria must become active. in some countries like canada people have medical privacy or "confidentiality" and do not have to reveal their active tuberculosis case to family, friends, or co-workers; therefore, the person who gets latent tuberculosis may never know who had the active case of tuberculosis that caused the latent tuberculosis diagnosis for them. only by required testing (required in some jobs) or developing symptoms of active tuberculosis and visiting a medical doctor who does testing will a person know they have been exposed. because tuberculosis is not common in the united states, doctors may not suspect tuberculosis; therefore, they may not test. if a person has symptoms of tuberculosis, it is wise to be tested. persons with diabetes may have an 18% chance of converting to active tuberculosis. in fact, death from tuberculosis was greater in diabetic patients. persons with hiv and latent tuberculosis have a 10% chance of developing active tuberculosis every year. "hiv infection is the greatest known risk factor for the progression of latent m. tuberculosis infection to active tb. in many african countries, 30–60% of all new tb cases occur in people with hiv, and tb is the leading cause of death globally for hiv-infected people." reactivation once a person has been diagnosed with latent tuberculosis (ltbi) and a medical doctor confirms no active tuberculosis, the person should remain alert to symptoms of active tuberculosis for the remainder of their life. even after completing the full course of medication, there is no guarantee that the tuberculosis bacteria have all been killed."when a person develops active tb (disease), the symptoms (cough, fever, night sweats, weight loss etc.) may be mild for many months. this can lead to delays in seeking care, and results in transmission of the bacteria to others." tuberculosis does not always settle in the lungs. if the outbreak of tuberculosis is in the brain, organs, kidneys, joints, or others areas, the patient may have active tuberculosis for an extended period of time before discovering that they are active. "a person with tb disease may feel perfectly healthy or may only have a cough from time to time." however, these symptoms do not guarantee tuberculosis, and they may not exist at all, yet the patient may still have active tuberculosis. a person with symptoms listed may have active tuberculosis, and the person should immediately see a physician so that tuberculosis is not spread. if a person with the above symptoms does not see a physician, ignoring the symptoms can result in lung damage, eye damage, organ damage and eventually death. when tuberculosis settles in other organs (rather than lungs) or other parts of the body (such as the skeletal), symptoms may be different from when it settles in the lungs (such as the symptoms listed above). thus, without the cough or flu-like symptoms, a person can unwittingly have active tuberculosis. other symptoms include back pain, flank pain, pid symptoms, confusion, coma, difficulty swallowing, and many other symptoms that would be a part of other diseases. (please see the reference for more information on symptoms.) therefore, seeing a physician and asking for a tuberculosis test is absolutely necessary to rule out tuberculosis when a patient has symptoms without a diagnosis of disease. risk factors situations in which tuberculosis may become reactivated are: if there is onset of a disease affecting the immune system (such as aids) or a disease whose treatment affects the immune system (such as chemotherapy in cancer or systemic steroids in asthma or enbrel, humira or orencia in rheumatoid arthritis); malnutrition (which may be the result of illness or injury affecting the digestive system, or of a prolonged period of not eating, or disturbance in food availability such as famine or residence in a refugee camp. concentration camp); degradation of the immune system due to aging. certain systemic diseases such as diabetes, and "other conditions: debilitating disease (especially haematological and some solid cancers), long-term steroids, end-stage renal disease, silicosis and gastrectomy/jejuno-ileal bypass all confer an increased risk. "elderly patients: latent tb may reactivate in elderly patients." young age. diagnosis there are two classes of tests commonly used to identify patients with latent tuberculosis: tuberculin skin tests and ifn-γ (interferon-gamma) tests. the skin tests currently include the following two: mantoux test heaf test ifn-γ tests include the following three: t-spot.tb quantiferon-tb gold quantiferon-tb gold in-tube tuberculin skin testing the tuberculin skin test (tst) in its first iteration, the mantoux test, was developed in 1908. tuberculin (also called purified protein derivative or ppd) is a standardised dead extract of cultured tb, injected into the skin to measure the person's immune response to the bacteria. so, if a person has been exposed to the bacteria previously, they should express an immune reaction to the injection, usually a mild swelling or redness around the site. there have been two primary methods of tst: the mantoux test, and the heaf test. the heaf test was discontinued in 2005 because the manufacturer deemed its production to be financially unsustainable, though it was previously preferred in the uk because it was felt to require less training to administer and involved less inter-observer variation in its interpretation than the mantoux test. the mantoux test was the preferred test in the us, and is now the most widely used tst globally. mantoux test see: mantoux test the mantoux test is now standardised by the who. 0.1 ml of tuberculin (100 units/ml), which delivers a dose of 5 units is given by intradermal injection into the surface of the lower forearm (subcutaneous injection results in false negatives). a waterproof ink mark is drawn around the injection site so as to avoid difficulty finding it later if the level of reaction is small. the test is read 48 to 72 hours later. the area of induration (not of erythema) is measured transversely across the forearm (left to right, not up and down) and recorded to the nearest millimetre. heaf test see:heaf test the heaf test was first described in 1951. the test uses a heaf gun with disposable single-use heads; each head has six needles arranged in a circle. there are standard heads and pediatric heads: the standard head is used on all patients aged 2 years and older; the pediatric head is for infants under the age of 2. for the standard head, the needles protrude 2 mm when the gun is actuated; for the pediatric heads, the needles protrude 1 mm. skin is cleaned with alcohol, then tuberculin (100,000 units/ml) is evenly smeared on the skin (about 0.1 ml); the gun is then applied to the skin and fired. the excess solution is then wiped off and a waterproof ink mark is drawn around the injection site. the test is read 2 to 7 days later. grade 0: no reaction, or induration of 3 or less puncture points; grade 1: induration of four or more puncture points; grade 2: induration of the six puncture points coalesce to form a circle; grade 3: induration of 5 mm; or more grade 4: induration of 10 mm or more, or ulceration the results of both tests are roughly equivalent as follows: heaf grade 0 & 1 ~ mantoux less than 5 mm; heaf grade 2 ~ mantoux 5–14 mm; heaf grade 3 & 4 ~ mantoux 15 or greater tuberculin conversion tuberculin conversion is said to occur if a patient who has previously had a negative tuberculin skin test develops a positive tuberculin skin test at a later test. it indicates a change from negative to positive, and usually signifies a new infection. boosting the phenomenon of boosting is one way of obtaining a false positive test result. theoretically, a person's ability to develop a reaction to the tst may decrease over time – for example, a person is infected with latent tb as a child, and is administered a tst as an adult. because there has been such a long time since the immune responses to tb has been necessary, that person might give a negative test result. if so, there is a fairly reasonable chance that the tst triggers a hypersensitivity in the person's immune system – in other words, the tst reminds the person's immune system about tb, and the body overreacts to what it perceives as a reinfection. in this case, when that subject is given the test again (as is standard procedure, see above) they may have a significantly greater reaction to the test, giving a very strong positive; this can be commonly misdiagnosed as tuberculin conversion. this can also be triggered by receiving the bcg vaccine, as opposed to a proper infection. although boosting can occur in any age group, the likelihood of the reaction increases with age. boosting is only likely to be relevant if an individual is beginning to undergo periodic tsts (health care workers, for example). in this case the standard procedure is called two-step testing. the individual is given their first test and in the event of a negative, given a second test in 1 to 3 weeks. this is done to combat boosting in situations where, had that person waited up to a year to get their next tst, they might still have a boosted reaction, and be misdiagnosed as a new infection. here there is a difference in us and uk guidelines; in the us testers are told to ignore the possibility of false positive due to the bcg vaccine, as the bcg is seen as having waning efficacy over time. therefore, the cdc urges that individuals be treated based on risk stratification regardless of bcg vaccination history, and