Overview of TB
Tuberculosis or TB is an infectious disease caused by the bacteria, Mycobacterium tuberculosis. According to global tuberculosis report given by the World Health Organisation or WHO, TB is the most causes the highest infectious disease-related mortality rate worldwide. It is the ninth leading cause of death worldwide. In 2016, there were an estimated 1.3 million TB deaths among HIV-negative people (down from 1.7 million in 2000). In 2016 out of all the people who fell ill with TB around 90% were adults. 56% of people are living in five countries (India, Indonesia, China, the Philippines, and Pakistan). An estimated 10.4 million people suffered from TB in 2016.
The TB bacterium usually spreads from one person to another through tiny droplets released into the air during coughing and sneezing. These bacteria usually infect the lungs, but can also infect other parts of the body as well, such as the brain, the kidneys or the spine. The source of TB in people with active pulmonary infection. When a person with active pulmonary TB disease coughs, talks, sneezes, sings or laughs, they spread TB. It is a potentially a severe infection which can be cured with the right antibiotics.
You may have to visit a doctor if you have unexplained weight loss, persistent cough, drenching night sweats and unexplained fever. A physician can confirm if you have TB or not by doing specific tests. The symptoms may vary from person to person and are divided into latent and active TB depending on the symptoms expressed in the individuals.
Latent TB infection
- In some individuals, after entry into the body, the TB bacteria become inactive, and the patient does not experience any symptoms. However, if their immune system becomes weakened at a later stage of life, then they may develop active disease.
- It can develop within the first few weeks or may take up to years after the TB bacterium enters the body. This condition can spread from one person to another.
- People diagnosed with HIV or AIDS and people who use alcohol and IV drug abusers are at higher risk of TB infections. Other risk factors include end-stage kidney disease, diabetes, malnourishment and certain cancers. Risk of TB is high when you travel to regions (countries like sub-Saharan Africa, India, and Mexico) where TB rates are high.
- In recent years, many drug-resistant strains of TB have emerged. It occurs when an antibiotic fails to kill all the bacteria and the surviving bacteria become more resistant to the drug. Some TB bacteria have developed resistance to isoniazid and rifampin (most common drugs used in the treatment of tuberculosis).
Causes of TB (Tuberculosis)
Tuberculosis is an infectious disease caused by the bacteria, Mycobacterium tuberculosis also called tubercle bacilli. It can spread from one person to another person through the microscopic droplets released into the air from an infected individual (active TB). These bacteria are intracellular aerobic, slow growing parasites. They have a unique cell wall which protects it from the body’s defense mechanisms.
The bacteria primarily infect the lungs, but it can spread via blood or lymphatic systems to most organs such as kidneys, and bones (especially those organs that have rich oxygen supply). They can retain certain dyes like fuchsin, a reddish dye even after an acid rinse. The bacteria infect tissue and causes necrosis. These areas have a dry, soft and cheesy appearance.
In patients with HIV infection, the immune system is weak, thus making it more difficult for the body to fight the tubercle bacilli. There are higher chances of progression of the latent infection to active infection in these people.
Few patients are resistant to the two most potent TB drugs (isoniazid and rifampin) and are known to have Multi-drug resistant tuberculosis. This resistance of mycobacteria develops in cases where the patient does not take proper treatment or failure of treatment is seen.
In rare cases, few patients are resistant to rifampin and isoniazid, plus any fluoroquinolone along with at least one of the three second-line drugs such as kanamycin, amikacin, or capreomycin. These patients are known to have XDR tuberculosis (Extensively-drug resistant)
Signs And Symptoms of TB
It is responsible for 85% of TB infections. The classical clinical symptoms and signs of pulmonary TB may include the following
- Night Sweats
- Unexplained fever, chronic cough
- Decrease or loss of appetite, unexplained loss of weight
- Hemoptysis (coughing up bloody sputum), shortness of breath
- Chest pain
- Swollen lymph nodes and fatigue
- In elderly patients, pneumonitis (the infection that inflames the air sacs in lungs) can be seen
Extra Pulmonary Tuberculosis
Extra Pulmonary Tuberculosis symptoms occur when tuberculosis affects areas other than lungs (non-specific areas)
- Pleural effusions(fluid in lungs) and empyema (collection of pus in pleural cavity of lungs) are seen in pleural TB,
- Pain in spine, back stiffness and paralysis is possible in TB (also termed Pott’s disease).
- Persistent headaches, mental changes, and coma are seen in TB meningitis.
- TB arthritis: Most commonly affected are the hips and knees and mostly it is pain in a single joint.
- Flank pain, dysuria (pain while urinating), increased frequency of urination, masses or lumps (granulomas) in the kidney are seen in genitourinary TB.
- Multiple small nodules were widespread in organs that resemble millet seeds in miliary tuberculosis.
- Difficulty in swallowing, abdominal pain, malabsorption, non-healing ulcers, diarrhea (may or may not contain blood) is seen in gastrointestinal TB.
- Rarely TB can infect the areas that surround your heart. It may cause fluid accumulation around the heart and inflammation. This condition can be fatal and may lead to death. It is known as cardiac tamponade.
Risk Factors of TB (Tuberculosis)
The risk of TB increases when a patient has a weakened immune system. Many risk factors are associated with TB such as
- Children and the elderly with weakened immune systems (especially those with a positive TB skin test)
- Patients with HIV infection and diabetes
- Drug abusers (especially IV drug abuse whose immune system is weak have a higher risk when exposed to TB bacteria)
- Visitors and immigrants from areas known to have high incidence of TB (Africa, Russia, Eastern Europe, Asia, Latin America and Caribbean Islands)
- Transplant patients
- Patients with kidney diseases
- People undergoing immunosuppressive therapy such as CHEMOTHERAPY
- Malnutrition and silicosis
- Tobacco usage
- Some drugs that are used to treat rheumatoid arthritis, psoriasis and, Crohn’s disease.
- In countries where poverty and overcrowding is high
Diagnosis of TB
Tuberculosis can be diagnosed by the following tests
The skin test is known as the Mantoux tuberculin skin test (or) the tuberculin skin test (or) TST. This skin test can be done to determine if you are carrying the tubercle bacteria. In this test, 0.1 mL of PPD (purified protein derivative or tuberculin – an extract made from killed mycobacteria) is injected under the top layer of your skin. If there is a welt or induration observed after 2-3 days on your skin, you may be positive. This test does not determine whether you have an active infection but it can tell whether you have been exposed to TB previously or not.
However, the test is not always correct. People who have recently received the BCG vaccine may test positive. Some patients respond to the test even if they don’t have active TB and others don’t respond to the test even if they have TB.
Chest X-ray: If your physician finds that your PPD test is positive, then he may recommend you to have a chest x-ray done. If small spots are observed in your lungs in the chest x-ray, then it may indicate an active TB infection. When your body tries to isolate tubercle bacteria, these spots in the lungs may appear on an x-ray.
Sputum is extracted from deep inside your lungs to check for TB bacteria. If your sputum test is positive, then it indicates that you have an active TB infection and the treatment must be started immediately. Precautionary measures like wearing a special mask, avoiding public areas must be taken to prevent the spread of TB bacteria to others.
The growth of mycobacteria from sputum culture or tissue biopsy culture is the definitive diagnosis of active tuberculosis. The mycobacteria are slow growing bacteria, hence it may take weeks for them to grow on the specialized media.
IGRA (interferon-gamma release assays): These tests can measure the immune response to Mycobacterium tuberculosis.
People with positive symptoms, positive sputum smear, or positive cultures are considered infected with TB and contagious (active TB).
Treatment of TB
If you are diagnosed with TB you may have to take one or more medications for six to nine months depending on the type of infection. The treatment for TB depends on,
- The type of TB infection and
- Drug sensitivity of the mycobacteria
First-line drugs used are isoniazid (INH), rifampin (RIF), ethambutol (EMB), and pyrazinamide. You’ll be contagious for about two to three weeks into your course of treatment if you’re diagnosed with pulmonary TB. The CDC offers a guide for the basic treatment schedules for active TB (drug-susceptible TB organisms) as follows :
a) In the Initial Phase
Preferred regimen is daily isoniazid, rifampin, pyrazinamide and ethambutol for 56 doses (8 weeks) ,
Alternative regimens are daily isoniazid, rifampin, pyrazinamide and ethambutol for 14 doses (2 weeks), then twice weekly for 12 doses (6 weeks).
b) In the continuation phase
|Preferred regimen is
Daily isoniazid and rifampin for 126 doses (18 weeks) or
Twice-weekly isoniazid and rifampin for 36 doses (18 weeks)
|Alternative regimens are :
Twice weekly isoniazid and rifampin for 36 doses (18 weeks).
Thrice-weekly isoniazid and rifampin for 54 doses (18 weeks).
Drug-Resistant And Multidrug-Resistant Tuberculosis
Treatment of drug-resistant and MDR TB can be difficult. Multiple approaches are recommended by the CDC in patients with MDR and XDR TB that involves variable treatment schedules and other anti-TB drugs. Treatment with six or more different medications may be needed, if you’re infected with a drug-resistant form of TB.
New drugs & treatment schedules that are approved by FDA are
- Bedaquiline (Sirturo) has been approved for treatment of MDR TB, and
- Research on moxifloxacin (with an antimicrobial drug), suggests it may help in treatment protocols.
Surgical resection of the diseased lung tissue is done in some patients when the lung destruction may be severe.
Loss of appetite, jaundice, nausea or vomiting, bruise formation (bleeding) and vision changes are few side effects of treatment of TB.
People taking TB medications should avoid high dose antibiotics that may harm the liver and must be aware of symptoms such as dark urine, loss of appetite, unexplained nausea or vomiting, jaundice, or yellowing of the skin or if the fever lasts longer than three days.
Prevention of TB
1) The entire course of medication: In patients with active TB, the most important step is to finish the entire course of medication. The TB bacteria may develop resistance to the most potent drugs (Ex: rifampin and isoniazid) if you stop the treatment early or skip the doses. The drug-resistant strains are more difficult to treat and may be fatal to the patient.
2) TB Test: If you live in areas where the prevalence of TB is high or if you have a suspicion that you might be affected with TB bacteria, then you have to test for TB. If you test positive, you may be advised by your health care professional to take medications.
3) Protect yourself and your family: Only active TB is highly contagious. In the case of active tuberculosis infection, you can take certain precautions to prevent the spread of TB to your family and friends.
- Cover your mouth with a tissue or napkin while coughing or talking to other people (to prevent the spread of bacteria in air),
- You can wear a mask to reduce the risk of transmission during the first 3 weeks of treatment.
- Proper ventilation of the rooms is necessary. TB bacteria can spread more easily in closed rooms and small spaces.
- During the first few weeks of active tuberculosis infection, avoid staying or sleeping in the same room with other people. Avoid going to public areas like workplaces, school, parks etc.
- Multi-drug resistant TB and extensive drug-resistant TB can be prevented by quickly diagnosing cases of suspected individuals in TB prevalent areas. The quick monitoring of patients, following recommended treatment guidelines, monitoring of the response of the patients to the treatment and making sure the treatment is completed can also prevent MDR and XDR TB.
- The infection control and occupational health care experts must be consulted to take precautionary measures to prevent the spread of TB (especially in crowded places like prisons, nursing homes, homeless shelters).
- Necessary environmental and administrative procedures must be taken to preventing the spread of TB. The risk of exposure to TB decreases once those precautions or procedures are implemented. Additional personal measures can also be taken that include using personal respiratory protective devices.
- Bacillus Calmette-Guerin (BCG) vaccine is given to infants to prevent severe forms of tuberculosis in areas where the prevalence of TB is high.
FAQ’s of TB
1) How can I prevent myself from getting tuberculosis?
Avoid close contact with known TB patients in crowded and enclosed environments like hospitals, clinics, prisons, or homeless shelters.
2) What should I do if I think I have been exposed to someone with TB disease?
If you think you have been exposed to someone with TB disease, you should contact your physician and inform them about your exposure and get a TB skin test or TB blood test done.
3) Can the TB vaccine (BCG) help prevent XDR TB?
The TB vaccine is called Bacille Calmette-Guérin (BCG), and it is used in many countries to prevent severe forms of TB in children. However, it is not proved to prevent TB completely in a person who has taken BCG vaccine.