Tuberculosis (TB) is a bacterial infection primarily caused by Mycobacterium tuberculosis, a slow-growing bacterium. While it most commonly affects the lungs, it can also impact other parts of the body, including the kidneys, spine, and brain. Accurately and promptly identifying TB is important for effective treatment and to prevent the infection from spreading to others.
Recognizing Potential Symptoms
Individuals should seek medical evaluation for TB if they experience a persistent cough lasting three weeks or longer, which may sometimes produce blood or sputum. Chest pain, particularly when breathing or coughing, can also be a symptom. Other signs include unexplained fever and night sweats.
Unintentional weight loss and a general feeling of fatigue or malaise are additional indicators that could suggest a TB infection. It is important to remember that these symptoms are not unique to tuberculosis and can be associated with many other conditions. Therefore, proper medical diagnosis through specific testing is necessary to determine the actual cause.
Initial Screening Tests
Initial screening for tuberculosis involves tests that detect the body’s immune response to the TB bacteria. The Tuberculin Skin Test (TST), also known as the Mantoux test, involves injecting a small amount of tuberculin purified protein derivative (PPD) under the skin. A healthcare professional then measures the induration (a raised, hardened area) 48 to 72 hours later. A positive result indicates exposure to TB bacteria, but it does not differentiate between active disease and latent infection.
Another common screening method involves Interferon-Gamma Release Assays (IGRAs), such as the QuantiFERON-TB Gold Plus or the T-SPOT.TB test. These blood tests measure the amount of interferon-gamma released by white blood cells after they are exposed to specific TB antigens in a test tube. Like the TST, a positive IGRA signifies prior exposure to Mycobacterium tuberculosis. These screening tests identify individuals who have been infected, but they cannot definitively confirm active, contagious tuberculosis disease.
Confirmatory Diagnostic Methods
When initial screening tests are positive or symptoms suggest tuberculosis, confirmatory diagnostic methods identify active disease. Sputum smear microscopy is a rapid technique where a sample of mucus coughed up from the lungs is examined under a microscope for acid-fast bacilli (AFB). The presence of these bacteria can quickly indicate active TB, allowing for immediate isolation and treatment.
Sputum culture is the “gold standard” for diagnosing active pulmonary tuberculosis. This involves growing the Mycobacterium tuberculosis bacteria from a sputum sample in a laboratory, a process that can take several weeks due to the slow growth rate of the organism. Once grown, the bacteria can also be tested for drug susceptibility, which helps guide antibiotic treatment regimen. Chest X-rays are also used to look for characteristic abnormalities in the lungs, such as infiltrates, cavities, or pleural effusions, which indicate active disease.
Advanced molecular tests, such as Nucleic Acid Amplification Tests (NAATs), offer rapid detection of TB bacteria by identifying their genetic material (DNA or RNA) from patient samples. These tests, like Xpert MTB/RIF, provide results within hours and can also detect resistance to rifampicin, a common TB drug. Other imaging techniques, such as CT scans, may be used in complex cases or when TB affects areas outside the lungs for more detailed anatomical information.
Distinguishing Latent from Active Tuberculosis
Understanding the difference between latent TB infection (LTBI) and active TB disease is important for patient management and public health. In latent TB, individuals carry Mycobacterium tuberculosis but do not experience any symptoms. Their immune system contains the bacteria, preventing active disease, and they are not contagious. Diagnosis of LTBI relies on a positive TST or IGRA, a normal chest X-ray, and no signs of active disease.
In contrast, active TB occurs when the bacteria multiply and cause symptoms. Individuals with active TB are contagious, especially if the disease is in the lungs or throat, and can transmit bacteria to others through coughing or sneezing. The distinction is made by combining initial screening tests with confirmatory methods like sputum cultures and chest X-rays. Treating LTBI can prevent progression to active disease, while active TB requires prompt, multi-drug treatment to cure the illness and halt transmission.
Importance of Early and Accurate Diagnosis
Early and accurate diagnosis of tuberculosis is important. It allows for prompt treatment, which can prevent the disease from progressing and causing severe health complications. Identifying active cases quickly also reduces transmission. This timely intervention contributes to better patient outcomes and helps control TB spread within communities.