Tuberculosis Diagnosis

  • Diagnosis

    Tuberculosis (TB) is a contagious bacterial infection that most frequently affects the lungs. In addition, TB involves other areas of the body, such as the lymph nodes, genitourinary tract, bones, joints, the membranes covering the brain (meninges), and the membranes covering the digestive organs (peritoneum).

    Transmission of TB usually occurs as a result of prolonged contact with an infected person. Most people who are exposed to TB do not develop an active infection. Older people and those with HIV or cancer are more likely to develop an active infection. People with a history of TB exposure have about a 10% lifetime risk of developing the active disease. People with HIV and a history of TB exposure have about a 10% yearly risk of developing the active disease.

    Tuberculosis infection can be either active or latent. Tuberculosis can exist as a latent infection, usually in the lungs. If you have a latent infection, you will not feel ill, and in most cases will not be contagious to others. If your immune system becomes compromised, the latent infection may become active, and you will feel ill and become contagious.

    Tuberculosis is caused by airborne bacteria spread most commonly from person to person by inhaling contaminated droplets of coughs and sneezes. Mycobacterium tuberculosis is the bacterium that most commonly causes TB. Air becomes contaminated when a person with active tuberculosis coughs out the bacteria, which may then remain in the air for several hours. Once inhlaled by another person, the infection will usually gravitate towards the base of the lungs. There, the bacteria multiply slowly and spread to nearby lymph nodes (a sort of drainage system for the body). If the bacteria spread from the lymph nodes to the blood, the infection may then travel to other organs in the body.

    Other closely related organisms, such as Mycobacterium bovis (transmitted in unpasturized milk in developing countries) and Mycobacterium africanum, can cause the disease; however, they are less common, especially in the United States. Casual, one-time exposure to TB bacteria rarely causes an infection. Rather, one must experience prolonged exposure to an individual with an active infection (for example, living with an infected family member, or working in close proximity to someone with an active infection) in order for transmission to occur.

    In the early stages, you may have very mild, coldlike symptoms—a cough or a general feeling of malaise—or no symptoms at all. At this stage, you may not even know that you have TB unless a skin test or chest x-ray are performed.

    If TB persists beyond the initial stages, you may experience mild cough, fever, night sweats, poor appetite, and problems gaining weight Table 01. In many cases, your immune system will fight off TB in its preliminary stages, and you will have no further symptoms. If, however, your body is unable to fight the infection efficiently (as often happens with immune-compromised or elderly individuals), further symptoms will appear. These additional symptoms include difficulty breathing, chest pain, and a cough that may produce discolored mucus (which may be bloody or blood-streaked).

    TB can affect many different areas in the body, such as the bones, skin, and heart, causing an array of symptoms Table 01.

    Table 1.  Common Symptoms of TB

    GENERAL SYMPTOMS
    Fever
    Night sweats
    Loss of appetite
    Malaise
    Fatigue
    Weight loss
    Lung-specific symptoms
    Chronic cough
    Spitting up blood or blood-streaked sputum
    Chest pain
    Shortness of breath
    OTHER SYMPTOMS
    Lymph nodes
    Swollen glands at the sides and base of the neck.
    Bones and joints
    Pain and swelling of a joint, such as the knee or hip; hunchback-type of curvature of the spine; damage to bones of the spine.
    Genitals and urinary tract
    Pain in the lower back and side; frequent urination; pain on urination or bloody urine; a slowly enlarging mass in the testes or prostate for men, or in the fallopian tubes or uterus for women.
    Skin
    A red, hardened rash, usually on the arms or legs.
    Nervous system
    Headache or stiffness of the neck (may indicate tuberculous meningitis); a tumor-like mass in the brain.
    Heart
    Prominent neck veins; shortness of breath, dizziness, headache.
    Adrenal glands
    Dizziness and symptoms of Addison's disease (weakness, darkening of the skin).

    Patients with AIDS and others with a weakened immune system have an increased risk of contracting TB Table 02. AIDS prevents the immune system from fighting off such infections as TB. Alcoholism and homelessness (due to malnutrition, overcrowding, and close contact with others with active TB) are also associated with weakened immune response, and thus create an additional risk for contracting TB.

    TB is more common in the elderly. Aging diminishes the efficacy of the immune system, making elderly individuals more susceptible to TB infection. In addition, since older adults are more likely to have contracted TB during their lifetimes, when the disease was more common, they are more likely to have the dormant bacteria in their bodies. These bacteria may reactivate, for example, as a consequence of ill health when the immune system is weakened. Older adults who live in chronic care facilities in close contact with other individuals with TB are at additional risk of contracting the disease.

    Crowding and poor ventilation increase the likelihood of TB infection. Persons who live or work in nursing homes, hospitals, prisons, or other crowded, poorly ventilated institutions are at higher risk for exposure to TB. This is because the close proximity makes it more likely for these individuals to come in contact with air contaminated with the bacteria that cause the disease.

    Impoverished population groups and people living in developing countries have an increased risk for contracting TB. The combination of crowding, poor medical care, and consumption of unpasteurized milk (which may contain M. bovis, another causative agent) places individuals living in such situations at an increased risk for TB.

    Table 2.  TB Risk Factors

    AIDS
    Alcoholism
    Homelessness
    Old age
    Living or working in crowded conditions: (i.e., nursing homes, prison, hospitals, dormitories)
    Living in a developing country
    Drinking unpasturized milk

    Your doctor will take a history and perform a physical exam. Your doctor will ask you specific questions about your condition; for example, if you have a cough, the doctor will want to know when it started, or if it has been a dry or productive cough. Your doctor will also want to know if you have been exposed to a person with an active TB infection, and if you have any other symptoms that might indicate TB (i.e., fever, night sweats, fatigue, malaise, or weight loss). Your doctor will likely listen to your lungs with a stethoscope to check for abnormal breath sounds that could indicate an infection.

    A chest x-ray will often be the first sign of TB Figure 01. An abnormal chest x-ray will raise suspicion of the possibility of pulmonary TB. As the bacteria that cause TB multiply in the lungs, the body reacts by sending immune agents to the area, which in turn trigger inflammation and mucus production. This collection of substances eventually becomes thick enough to be visible on an x-ray, typically appearing as uneven white areas in the lung against the dark background.

    Click to enlarge: Chest X-ray of a Man With Tuberculosis

    Figure 01. Chest X-ray of a Man With Tuberculosis

    A skin test is necessary to help diagnose the disease. Once TB is suspected based on risk factors or symptoms, your doctor will perform a skin test to determine whether you have ever been exposed to the bacteria that cause the disease. For this test, the doctor will inject your arm with both protein from TB bacteria and a neutral substance for comparison. In two to three days, if the TB injection site is red and swollen compared to where the neutral substance was injected, then you have at some time been infected with the TB bacteria. A positive result, however, does not indicate whether or not your infection is active. Your infection will only be deemed active and contagious if you also have an abnormal chest x-ray, and have organisms in your sputum sample that cause TB.

    Your doctor will perform a laboratory test on samples of mucus from your lungs (called sputum) for the bacteria that cause TB. Three sputum specimens are required for this examination. These samples have to be taken in the morning when you wake up, as this is the time when you are likely to produce the most mucus. Laboratory results usually take three to six weeks; however, newer techniques, which are becoming more common, can accomplish the same task in about two to three weeks. If TB is suspected to have spread beyond the lungs, the laboratory will examine tissue or fluid from the affected area of the body.

    If you have active TB, your doctor will also want to test you for HIV, the virus that causes AIDS. This is because AIDS is a risk factor for TB.

    Ask your doctor about your need for skin testing if you live or work in an environment where TB risk is high, or if you travel to developing countries.

    Patients should be isolated for a few days in the early stages of drug treatment while they are still contagious to others. Patients with TB undergoing treatment do not need to be isolated for more than a few days, since the drugs work quickly to reduce infectiousness. However, those who cough and fail to take their medication need to be isolated for longer periods.

    Public health authorities and people who come in close contact with you must be alerted to new cases of TB. Since active TB is contagious and a public heath risk, health authorities and individuals who have come in close contact with the infected patient must be notified.

  • Prevention and Screening

    Ask your doctor about your need for skin testing if you live or work in an environment where TB risk is high, or if you travel to developing countries.

    Patients should be isolated for a few days in the early stages of drug treatment while they are still contagious to others. Patients with TB undergoing treatment do not need to be isolated for more than a few days, since the drugs work quickly to reduce infectiousness. However, those who cough and fail to take their medication need to be isolated for longer periods.

    Public health authorities and people who come in close contact with you must be alerted to new cases of TB. Since active TB is contagious and a public heath risk, health authorities and individuals who have come in close contact with the infected patient must be notified.

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