TB is an infectious disease caused by the bacillus Mycobacterium tuberculosis. It is primarily an infection of the lungs, but any organ system is susceptible, so its manifestations may be varied. Effective therapy and methods of control and prevention of tuberculosis have been developed, but the disease remains a major cause of mortality and morbidity throughout the world. The treatment of tuberculosis has been complicated by the emergence of drug-resistant organisms, including multiple-drug-resistant tuberculosis, especially in those with HIV infection.
Mycobacterium tuberculosis is transmitted by airborne droplet nuclei produced when an individual with active disease coughs, speaks, or sneezes. When inhaled, the droplet nuclei reach the alveoli of the lung. In susceptible individuals the organisms may then multiply and spread through lymphatics to the lymph nodes, and through the bloodstream to other sites such as the lung apices, bone marrow, kidneys, and meninges.
The development of acquired immunity in 2 to 10 weeks results in a halt to bacterial multiplication. Lesions heal and the individual remains asymptomatic. Such an individual is said to have tuberculous infection without disease, and will show a positive tuberculin test. The risk of developing active disease with clinical symptoms and positive cultures for the tubercle bacillus diminishes with time and may never occur, but is a lifelong risk. Only 5% of individuals with tuberculous infection progress to active disease. Progression occurs mainly in the first 2 years after infection; household contacts and the newly infected are thus at risk.
Many of the symptoms of tuberculosis, whether pulmonary disease or extrapulmonary disease, are nonspecific. Fatigue or tiredness, weight loss, fever, and loss of appetite may be present for months. A fever of unknown origin may be the sole indication of tuberculosis, or an individual may have an acute influenza-like illness. Erythema nodosum, a skin lesion, is occasionally associated with the disease.
The lung is the most common location for a focus of infection to flare into active disease with the acceleration of the growth of organisms. There may be complaints of cough, which can produce sputum containing mucus, pus- and, rarely, blood. Listening to the lungs may disclose rales or crackles and signs of pleural effusion (the escape of fluid into the lungs) or consolidation if present. In many, especially those with small infiltration, the physical examination of the chest reveals no abnormalities.
Mycobacterium avium-intracellulare (MAI)
Atypical mycobacterial infections are infections caused by a species of mycobacterium other than Mycobacterium tuberculosis, the causative bacteria of pulmonary TB and extrapulmonary TB such as cutaneous TB.
Atypical mycobacteria may cause many different types of infections such as septic arthritis, abscesses and skin and bone infection. They may also affect the lungs, gastrointestinal tract, lymphatic system and other parts of the body.
Skin infection tends to result in crusted nodules.
• Also known as MAC (Mycobacterium avium complex)
• Most common non-tuberculous mycobacterial infection associated with AIDS
• Symptoms include fever, swollen lymph nodes, diarrhea, fatigue, weight loss and shortness of breath
• May develop into pulmonary MAC
What is a chest infection?
Lower respiratory tract infection (LRTI), pneumonia and pleurisy are all infections of the lung. The bronchi are series of branching tubes, which carry air from the main windpipe (trachea) to the lung tissues. Here, oxygen gets absorbed into the bloodstream. Each lung is completely surrounded by two thin layers of lining called the pleura and is subdivided into smaller parts, called lobes. Infection can occur at any point sometimes at all points along the route from windpipe to the lung tissues. When it is in the larger bronchi, it is called bronchitis. When it involves the smallest tubes and the tissues surrounding them it is called bronchopneumonia. When a whole segment (lobe) of lung is infected this is called lobar pneumonia. If the lining of the lung also becomes infected, pleurisy has occurred. Cough, fever, chest pain and breathlessness are the typical symptoms of these conditions, but not all of them need occur together and there may be only one or two of them.
How does a chest infection occur?
There are many germs (or microbes) that may cause lung infections. The two most important types are viruses and bacteria. Most commonly, the infecting germ is inhaled, and multiplies in the lining of the bronchi, spreading the infection further down the tubes, or into the tissues themselves. The spreading infection may not be caused by the germ, which is inhaled, but by growth of other germs already present in the lungs in small numbers. This is called secondary infection, and occurs because the conditions are right for a germ, which is usually harmless to cause problems. Sometimes the infection comes as part of a generalized infection, which affects the whole body. A common example of this is pneumonia as a complication of influenza.
Why does a chest infection occur?
Lung infections are so common, and occur for so many different reasons, that it is not always possible to say why a particular infection occurred. The presence of other diseases increase the risk of developing these infections. People with other lung diseases – such as asthma, chronic bronchitis, lung cancer and cystic fibrosis – are all more prone to lung infections. Also, people whose resistance is generally low – such as those with chronic disease such as heart failure, diabetes or cancer – are more likely to develop any of these infections. The elderly, especially those who cannot move around normally (for example, because of bad arthritis or a stroke), are very susceptible to infections. This is why influenza can be such a dangerous infection in the elderly. People who smoke regularly are much more likely to suffer from repeated infections than non-smokers are. This is because cigarette smoke damages the lining of the bronchi, reducing the resistance of the lungs to infection. Some of the less common lung infections may come from the environment in which we live or work. Legionnaires’ disease a type of pneumonia caused by bacteria found in certain water supplies is an important example. Psittacosis is another type of lung infection due to a germ, which has been transferred from certain domestic birds (especially budgerigars).
Treatment involved for a chest infection:
The most effective weapons available for treating bacterial lung infections are antibiotics. However, viruses do not respond to antibiotic treatment, so the body’s own defenses are the main way of fighting virus infections. It is important to drink plenty of fluids if you have an infection. This helps to reduce fever and prevent dehydration. Anti-viral drugs increasingly are becoming available, but presently are effective only against a few of the many kinds of viruses responsible for respiratory infections. For infections caused by bacteria (these are the majority) the right antibiotic will help the body to overcome the infection. Some bacteria do not respond to certain antibiotics, and it is not always easy to be sure of choosing the right antibiotic in the early stages of an infection. Antibiotics are usually given as tablets or medicine, but for more severe infections they may need to be given by injection. Some people tend to stop taking antibiotics as soon as they feel better. This is not good practice. Yoou should always complete the full course prescribed by the doctor, as this may avoid a relapse. Occasionally, when the infection is severe, particularly with pneumonia, oxygen can be life saving. Pneumonia and pleurisy can be very painful conditions, and painkilling treatment may need to be given.