However, given that most deaths from TB are preventable, the death toll from the disease is still unacceptably high and efforts to combat it must be accelerated. Worldwide the proportion of new cases with multidrug-resistant TB (MDR-TB) was 3. 5 in 2013 and has not changed compared with recent years. However, much higher levels of resistance and poor treatment outcomes are of major concern in some parts of the world. ?Of the estimated 9 million people who developed TB in 2013, more than half (56) were in the South-East Asia and Western Pacific Regions.
A further one quarter were in the African Region, which also had the highest rates of cases and deaths relative to population. India and China alone accounted for 24 and 11 of total cases, respectively. Definition ? Pulmonary tuberculosis is an infectious disease caused by Mycobacterium tuberculosis. In many cases, M tuberculosis becomes dormant before it progresses to active TB. It most commonly involves the lungs and is communicable in this form, but may affect almost any organ system including the lymph nodes, CNS, liver, bones, genitourinary tract, and gastrointestinal tract. Etiology ?
The development of TB requires infection by M tuberculosis and inadequate containment by the immune system. Patients infected with M tuberculosis who have no clinical, bacteriologic, or radiographic evidence of active TB are said to have latent TB infection. Active TB may occur from reactivation of previously latent infection or from progression of primary infection. ?Transmission of TB occurs from individuals infected with pulmonary (and rarely laryngeal) disease. Infection results from the inhalation of aerosolized droplets containing the bacterium.
The likelihood of transmission depends on the infectivity of the source case, the degree of exposure to the case (proximity, ventilation, and the length of exposure), and susceptibility of the person in contact with an infected case. HIV-infected individuals are at greater risk of reactivation as well as progression to primary TB. Other groups at increased risk for the development of active TB include persons with recent tuberculin skin test (TST) conversion, the homeless, injection drug users, cigarette smokers, and immunocompromised individuals. Pathophysiology ?
Infection with TB requires inhalation of droplet nuclei. Following deposition in the alveoli, M tuberculosis is engulfed by alveolar macrophages, but survives and multiplies within the macrophages. Proliferating bacilli kill macrophages and are released this event produces a response from the immune system. Exposure may lead to clearance of M tuberculosis, persistent latent infection, or progression to primary disease. ?Successful containment of TB is dependent on the cellular immune system, mediated primarily through T-helper cells (TH1 response).
T cells and macrophages form a granuloma with a center that contains necrotic material. M tuberculosis, and peripheral granulation tissue consisting primarily of macrophages and lymphocytes the granuloma serves to prevent further growth and spread of M tuberculosis. These individuals are noninfectious and have latent TB infection the majority of these patients will have a normal chest x-ray and be tuberculin skin test (TST)-positive. Active TB typically occurs through a process of reactivation. Approximately 10 of individuals with latent infection will progress to active disease over their lifetime.
The risk is greatest within the 2 years following initial acquisition of M tuberculosis. A number of conditions can alter this risk, particularly HIV infection, in which the annual risk of developing active TB is 8 to 10. Immunocompromised conditions and treatment with immunosuppressing medications, including systemic corticosteroids and TNF-alpha antagonists, also contribute to reactivation. Diagnostic Approach ? The diagnosis may be obvious in some cases but is frequently difficult. A high level of suspicion is important in evaluating a patient with risk factors. Diagnosis confirmation requires culturing of M tuberculosis. Delays in diagnosis and initiation of therapy are associated with transmission of disease and increased mortality.
If suspicion for disease is high, the patient should be isolated (at home or in a negative-pressure room in a hospital) until 5 days to 2 weeks of therapy has been completed. Active TB, confirmed or highly suspected, is a reportable condition to the local health authorities. Clinical history, Risk Factors, Symptoms ? The possibility of TB should be considered in any person with risk factors for TB exposure, who has suggestive symptoms (fever, malaise, pleuritic chest pain, cough longer than 2-3 weeks, night sweats, and weight loss, hemoptysis, psychological symptoms, clubbing, erythema nodosum) or CXR abnormalities.
1 / 3 Although the presence of upper lobe infiltrates is characteristic of the disease, atypical CXR presentation is common among children, and among HIV-infected and immunocompromised patients (including people with diabetes). TB tests are generally not needed for people with a low risk of infection with TB bacteria. ?Certain people should be tested for TB bacteria because they are more likely to get TB disease, including people who have spent time with someone who has TB disease people with HIV infection or another medical problem that weakens the immune system people who have symptoms of TB disease (fever, night sweats, cough, and weight loss).
People from a country where TB disease is common (most countries in Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia) people who live or work somewhere in the United States where TB disease is more common (homeless shelters, prison or jails, or some nursing homes), and people who use illegal drugs. TB is also more prevalent in men than it is in women. ?Investigations for active infection include CXR, 3 sputum samples obtained for acid-fast bacilli (AFB), nucleic acid amplification testing (NAAT), CBC, and electrolytes (e. g. , sodium). ?
Stained smears should be made from sputum specimens to identify AFB, as this is the first bacteriologic evidence of infection and gives an estimate of how infectious the patient is. If AFBs are seen on smear, therapy should be started and the patient maintained in isolation. Patients with smear-negative disease may be infectious, although the risk of transmission is lower than in smear-positive disease. If the suspicion of TB is high, consideration should be given to starting antituberculous medications prior to laboratory confirmation. ?
Sputum culture supports the diagnosis of TB, is more sensitive than smear staining, facilitates identification of the mycobacterium species by nucleic acid hybridization or amplification, and evaluates drug sensitivity. CT of the chest, although not done routinely, may be of use to exclude other pathology for example, cancer. It is also recommended that all patients who have TB should be tested for HIV within 2 months of diagnosis. Susceptibility testing ? Drug resistance is a global issue initial testing is against first-line drugs (isoniazid, rifampin, pyrazinamide, ethambutol).
If there is documented resistance to isoniazid or rifampin, susceptibility testing against second-line drugs is performed. Screening ? It is recommended by the CDC that high-risk populations in the US are screened for latent infection, including HIV patients, IV drug users, healthcare workers who serve high-risk populations, and contacts of individuals with pulmonary TB. A tuberculin skin test or interferon gamma release assay are the standard method for identifying persons infected with the mycobacterium. Screening persons other than high-risk population places a burden on resources and is therefore not recommended.
Screening is only one aspect of controlling the disease it is recommended that priority should be given to completion of treatment of active disease and investigating contacts. Treatment Approach ? The main goals are to cure the patient and to prevent further transmission of TB to others. Therapy for TB requires a minimum of 6 months of treatment except for culture-negative pulmonary TB. The treating physician acts in a public health role as well and thus is responsible for ensuring that the patient successfully adheres to and completes treatment.
Treatment is initiated when TB is confirmed or strongly suspected and consists of an initial intensive phase and a subsequent continuation phase. While infectious, patients should remain isolated (at home or in an appropriate room in the hospital). The treating physician should discuss the case with the local public health department to learn specific local requirements and to initiate a contact investigation in a timely fashion. Prevention Vaccinations ? In countries where tuberculosis is more common, infants often are vaccinated with bacille Calmette- Guerin (BCG) vaccine because it can prevent severe tuberculosis in children.
The BCG vaccine isnt recommended for general use in the United States because it isnt very effective in adults. Dozens of new TB vaccines are in various stages of development and testing. Active TB, confirmed or highly suspected, is a reportable condition to the local health authorities in order to interrupt further TB transmission in the community. There are currently 15 vaccine candidates in clinical trials. Secondary Prevention ? Because of the infectious nature of the condition, patients should avoid new encounters with people who are not household members while they are infectious.
Household members should be promptly evaluated and treated if appropriate. The patient may need to be 2 / 3 isolated in the short term. After approximately 2 weeks of effective TB treatment, the patient is less infectious to others. ?If you have active TB, keep your germs to yourself. It generally takes a few weeks of treatment with TB medications before youre not contagious anymore. Follow these tips to help keep your friends and family from getting sick Stay home- dont go to work or school or sleep in a room with other people during the first few weeks of treatment for active tuberculosis. Ventilate the room- tuberculosis germs spread more easily in small closed spaces where air doesnt move.
If its not too cold outdoors, open the windows and use a fan to blow indoor air outside. Cover your mouth- use a tissue to cover your mouth anytime you laugh, sneeze or cough. Put the dirty tissue in a bag, seal it and throw it away. Wear a mask- wearing a surgical mask when youre around other people during the first three weeks of treatment may help lessen the risk of transmission. Finish your entire course of medication- this is the most important step you can take to protect yourself and others from tuberculosis.
When you stop treatment early or skip doses, TB bacteria have a chance to develop mutations that allow them to survive the most potent TB drugs. The resulting drug- resistant strains are much more deadly and difficult to treat. Prognosis ? Without treatment the mortality rate of TB exceeds 50 however, TB is a treatable disease. Risk factors for death include increased age, delay in diagnosis of TB, extent of radiographic involvement, the need for mechanical ventilation, ESRD, diabetes, and immunosuppressant. In general, patients with treated TB can expect to do well with minimal or no sequelae.
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