Tuberculosis or TB is a potentially fatal infectious disease caused by Mycobacterium tuberculosis, commonly afflicting the lungs. It is thought that one-third of the world population is infected with the bacteria, although their immune systems keep the infection at bay and symptoms never manifest. These are known as latent infections, which have a 10% chance of progressing to full-fledged active disease. Half of those whose infections become active diseases will die from them. Those with latent infections are not contagious and do not spread the disease. Historically referred to as "consumption," the disease causes a great deal of weight loss in those who contract it. Symptoms vary widely based on the area infected, as it is possible for the bacteria to infect the lungs, bones, lymphatic system, central nervous system, and the genitourinary system. Seeing as lung infection is the most prevalent (accounting for 90% of cases), infections are grouped into two categories: pulmonary and extrapulmonary. A blood test or 'tuberculin skin test' may be conducted to determine if someone has a latent tuberculosis infection.
A vaccination is available which decreases the risk of contracting the bacteria by 20%, while it decreases the risk of latent infections progressing into active disease by as much as 66%. New infections arise in approximately 1% of the world's population each year, and the number of new cases has been declining since 2000. 95% of annual deaths from the condition occur in developing countries. The disease has afflicted both human and animal since antiquity, with evidence of tubercular decay, found in 17,000 North American bisons and the spines of Egyptian mummies dating back as far as 3000 BC. One study suggests the incidence of tuberculosis may have contributed to pre-industrial vampire folklore, citing bioarcheological and biocultural evidence. For example, after one family member's seemingly mysterious demise from what we now know to be tuberculosis, the other family members would have contracted the contagious disease - this would be construed as the original member ‘draining the life from other family members.'
Robert Koch eventually won the Nobel Prize in physiology or medicine for his 1882 discovery of the bacillus causing tuberculosis. Albert Calmette and Camille Guerin later developed the first vaccine against TB using an attenuated bovine strain of the disease, however, it was not widely implemented until after WWII.
TB became a massive public health concern in the 19th and 20th centuries as it became more prevalent among the urban poor. It remains closely linked with malnutrition and overcrowding, making it far more common in poverty stricken areas of the world. Although an exceptional number of people have been infected with TB, the incidence of even latent infections remains small in the United States, Europe, and Australia.
Causes of Tuberculosis
TB is spread when someone with an active infection speaks, coughs, sneezes, laughs or sings. Tiny germ-containing droplets are released into the surrounding air.
TB bacteria grow and divide at a remarkably slow rate, taking between 16 and 20 hours. Most other bacteria take less than an hour to do so. This is why it is difficult to catch TB despite the fact that it is contagious. One must spend a great deal of time in the company of someone who has TB in order to catch it themselves. For this reason, transmission is easiest between friends, family, and co-workers.
After transmission, the immune system may well keep the bacteria in check, allowing it to exist in the body ‘latently.' People infected with latent TB will not spread the disease to others, however, the bacteria may one day become ‘active' and progress to full-fledged infection. If an individual's immune system becomes compromised, by contracting HIV for example, they are at high risk for developing an active infection from the latent TB in their body. 35% of HIV deaths were the result of a latent TB infection becoming active.
The very act of admitting an infectious TB patient to a hospital places health care staff and other patients at risk for developing infection themselves. Seeing as hospitals are hubs of immunocompromised individuals, the admittance of a TB-infected person is especially risky because the immune systems of those around them are weaker, and thereby more susceptible to acquiring a case of active TB.
If bacteria gain access to the bloodstream from a wound or area in which tissue is damaged, this can lead to a severe condition known as miliary TB. Tiny white foci of infection known as tubercles disseminate throughout the body; this form has a high fatality rate with 30% of those infected succumbing to the disease.
Symptoms of Tuberculosis
If a person is infected with latent TB, they will exhibit no symptoms. Skin and blood tests can determine if someone has a latent TB infection. If and when someone develops an active TB infection they may experience:
- A cough lasting more than 3 weeks
- Loss of appetite
- Chest pain
- Coughing up blood
- Feeling tired all the time
- Nail clubbing
- Night sweats
- Weight loss
Symptoms will depend in part on the area of the body that the bacteria infects. Although 90% of cases involve the lungs, it is possible for TB to infect other systems and areas in the body, engendering different symptoms when it does so.
Treatment of Tuberculosis
An unusual chemical composition and structure make tuberculosis more difficult to effectively treat with antibiotics. If the drug cannot enter the cell wall, it is rendered ineffective. However, potent antibiotics do display some efficacy but must be administered for a prolonged period in order to be effective. Active TB is usually treated with a host of antibiotics in order to reduce the risk of the bacteria becoming antibiotic-resistant. The World Health Organization recommends directly observing patients while taking their antibiotics. It is critical patients do not miss rounds of antibiotics, as this gives bacteria the opportunity to feasibly acquire antibiotic-resistance, which can become a public health concern should they infect others.
Antibiotics used to treat tuberculosis:
- Rifampin (Rifadin, Rimactane)
- Ethambutol (Myambutol)
Risk Factors of Tuberculosis
Anything that compromises the immune system will place someone at a higher risk of developing TB. Therefore malnutrition, immunosuppressant drugs (such as those taken for psoriasis, Crohn's disease, colitis, post-transplant surgeries, etc), HIV and other conditions that engender an immunosuppressed state can lay the ground for tuberculosis infection. This includes those with the following conditions:
- Diabetes mellitus
- Severe kidney disease
- Low body weight
- Organ transplants
- Head and neck cancer
- Regular substance abusers
- Infants and children with underdeveloped immune systems
Prevention of Tuberculosis in Hospitals
Prevention hinges on the vaccination of infants, diligent detection of existing infections and implementing appropriate treatment. The BCG vaccine is available and widely used. In areas where TB is uncommon, such as Canada, the UK and the United States, the vaccine is only administered to high-risk groups.
In hospitals, administrative control is the most effective means of tuberculosis prevention. This is carried out in three sectors: patients, contacts, and staff. The hospitalization of TB patients should be minimized, in effect, they should be treated as outpatients or discharged to TB hospitals. 95% of TB patients are discharged within 4 days of a positive microbiology report. Those who have made contact with TB patients, such as health care providers, are not a great risk for infection unless they spent 3 or more weeks in prolonged contact, in which case they should undergo chest x-rays. Hospital staff who must intubate TB positive patients should be provided with respirator masks. Engineering controls are another point of prevention. Hospitals with central AC systems should be equipped with negative pressure isolation rooms.