THE lung infection tuberculosis poses a major global health threat. To raise awareness, the Journal of the American Medical Association published a special theme issue on the disease recently. “It will take the will and resources of the entire world to eradicate this global problem,” JAMA Editor in Chief Dr Catherine DeAngelis and Managing Deputy Editor Annette Flanagin wrote in an editorial.
The largest number of cases occurs in the South-East Asia region, which accounts for 33% of incident cases globally. However, the estimated incidence per capita in the sub-Saharan Africa is nearly twice that of South-East Asia at 350 cases per 100,000 population1.
Tuberculosis is often referred to as TB. Tuberculosis is caused by the bacteria called Mycobacterium tuberculosis. TB usually occurs as pneumonia in the lungs; however, it can also occur in the following organs: brain, back, knees, lymph nodes and bones.
Infection and transmission
Like the common cold, TB spreads through the air. Only people who are sick with TB in their lungs are infectious. When infectious people cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air. A person needs only to inhale a small number of these to be infected.
Left untreated, each person with active TB will infect on average between 10 and 15 people every year. But people infected with TB bacilli will not necessarily become sick.
The immune system “walls off” the TB bacilli which, protected by a thick waxy coat, can lie dormant for years. When someone’s immune system is weakened, the chances of becoming sick are greater1.
Usually, after a week or more of taking effective medication, most patients with TB disease will stop spreading germs. A doctor will test the patient and then decide when the patient is no longer contagious. Most TB patients live at home and can continue their normal activities as long as they are taking their TB medicine.
Screening and diagnosis
The recommended Mantoux skin test uses a needle to place a standard dose of tuberculin just under the surface of the skin. The multi puncture or “tine” test uses multiple tines (pins) dipped in tuberculin. This test is not considered as accurate as the Mantoux test because the quantity of the tuberculin administered cannot be precisely controlled. The Mantoux test should be used for screening and diagnosis2.
Many people are vaccinated against tuberculosis using the BCG (Bacillus Calmette Guerin) vaccine. BCG can cause a positive skin test, especially if it has been recently administered. There is no reliable method of distinguishing tuberculin reactions caused by vaccination with BCG from those caused by natural mycobacterial infections.
The TB skin test is typically performed by injecting a small amount of tuberculin under the superficial layers of the skin. The test is then read 48 to 72 hours later. A positive skin test results in a raised bump (induration) at the point of administration.
The size of the induration determines whether the skin test is considered significant. The American Thoracic Society (ATS) and the CDC recommend different sizes of induration, called cut points, to be used for different populations, depending on whether the individual is at high risk.
A positive (now called “significant”) reaction indicates infection with TB. It is important to understand that there is a difference between being infected with TB and having TB disease.
Someone who is infected with TB has the TB germs, or bacteria, in their body. The body’s defences are protecting them from the germs, and they are not sick.
Someone with TB disease is sick and may be able to spread the disease to other people. A person with a significant skin test needs to see a doctor to determine what further tests and treatment may be necessary. Chest x-rays, sputum tests and other tests are used to determine whether the positive reaction is associated with TB disease.
A false positive result, especially after repeated tests, can also occur from exposure to “atypical” mycobacteria, which cause different patterns of infection and disease. These non-tuberculous forms of mycobacteria are most often found in patients who are HIV positive, although they infrequently cause disease in non-HIV infected individuals.
A person recently infected with TB may not react to the TB skin test. This is also true of elderly, debilitated and immunocompromised patients. In the case of patients who fit into these categories and who are suspected to be infected with tuberculosis, other tests including a chest x-ray or a skin test at a later date may be used to determine the presence or absence of TB infection and disease.
Individuals with TB symptoms should receive medical attention immediately. TB symptoms include: prolonged cough, night sweats, unexplained weight loss, loss of appetite, weakness, fever/chills and occasionally coughing up blood.
Up until only 50 years ago, there were no medicines to cure TB. Now, strains that are resistant to a single drug have been documented in every country surveyed; what is more, strains of TB resistant to all major anti-TB drugs have emerged.
Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their medicines regularly for the required period because they start to feel better; or because doctors and health workers prescribe the wrong treatment regimens.
A particularly dangerous form of drug-resistant TB is multidrug-resistant TB (MDR-TB), which is defined as the disease caused by TB bacilli resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs. Rates of MDR-TB are high in some countries, and threaten TB control efforts.
From a public health perspective, poor supervision or incomplete treatment of TB is worse than no treatment at all. When people fail to complete standard treatment regimens, or are given the wrong treatment regimen, they may remain infectious. The bacilli in their lungs may develop resistance to anti-TB medicines. People they infect will have the same drug-resistant strain.
While drug-resistant TB is generally treatable, it requires extensive chemotherapy (up to two years of treatment) that is often prohibitively expensive (often more than 100 times more expensive than treatment of drug-susceptible TB), and is also more toxic to patients.
1. WHO (World Health Organization) – Tuberculosis Fact Sheet
2. American Thoracic Society and Centers for Disease Control and Prevention. Targeted Tuberculin Testing and Treatment of Latent Tuberculosis Infection. American Journal of Respiratory and Critical Care Medicine. Vol. 161(4), April 2000.
n Diong Swee Hoon is a pharmacist. For more information, e-mail email@example.com. The information provided is for educational purposes only and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.