Description

Tuberculosis (TB) is a contagious disease. Like the common cold, it spreads through the air. Only people who are sick with TB in their lungs are infectious. Tuberculosis (TB) is a potentially fatal contagious disease that can affect almost any part of the body but is mainly an infection of the lungs. It is caused by a bacterial microorganism, the tubercle bacillus or Mycobacterium tuberculosis. Although TB can be treated, cured, and can be prevented if persons at risk take certain drugs, scientists have never come close to wiping it out. Few diseases have caused so much distressing illness for centuries and claimed so many lives. There is also a group of organisms referred to as atypical tuberculosis. These involve other types of bacteria that are in the Mycobacterium family. Often, these organisms do not cause disease and are referred to a "colonizers," because they simply live alongside other bacteria in our bodies without causing damage. At times, these bacteria can cause an infection that is sometimes clinically like typical tuberculosis. When these atypical mycobacteria cause infection, they are often very difficult to cure. Often, drug therapy for these organisms must be administered for one and a half to two years and requires multiple medications.
1. Ninety five percent of tuberculosis (TB) cases occur in developing countries where co-infection with human immunodeficiency virus (HIV) is also common.
2. Between 19 and 43 % of the world’s population is infected with M.tuberculosis. In the United States, although the rate of TB infection has declined, 15 million people are infected with M. tuberculosis (2).
3. TB kills more people than any other infectious disease, including malaria and acquired immune deficiency syndrome (AIDS). Each year, more than 3 million people die and 8 million people develop disease (1).
4. High-risk groups are considered people living in urban areas, institutions (prisons, nursing homes), homeless, minorities, immigrants, drug users, people with immunosuppression or HIV, healthcare workers and others in close contact with infected individuals.
5. 8 to 10% of those infected with HIV develop TB.
6. Incidence in USA: Overall 7.4/100,0000. In high-risk groups: 32-100/100,000.

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 disease will infect on average between 10 and 15 people every year. But people infected with TB bacilli will not necessarily become sick with the disease. 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 greater.
a. Someone in the world is newly infected with TB bacilli every second.
b. Overall, one-third of the world's population is currently infected with the TB bacillus.
c. 5-10% of people who are infected with TB bacilli (but who are not infected with HIV) become sick or infectious at some time during their life. People with HIV and TB infection are much more likely to develop TB.

Global and regional incidence
The World Health Organization (WHO) estimates that the largest number of new TB cases in 2005 occurred in the South-East Asia Region, which accounted for 34% of incident cases globally. However, the estimated incidence rate in sub-Saharan Africa is nearly twice that of the South-East Asia Region, at nearly 350 cases per 100 000 population.
Tuberculosis spread much more widely in Europe when the industrial revolution began in the late nineteenth century. The disease became widespread somewhat later in the United States, because the movement of the population to large cities made overcrowded housing so common. When streptomycin, the first antibiotic effective against M. tuberculosis, was discovered in the early 1940s, the infection began to come under control. Although other more effective anti-tuberculosis drugs were developed in the following decades, the number of cases of TB in the United States began to rise again in the mid-1980s. This upsurge was in part again a result of overcrowding and unsanitary conditions in the poor areas of large cities, prisons, and homeless shelters. Infected visitors and immigrants to the United States also contributed to the resurgence of TB. An additional factor is the AIDS epidemic. AIDS patients are much more likely to develop tuberculosis because of their weakened immune systems. There still are an estimated 8 to 10 million new cases of TB each year worldwide, causing roughly 3 million deaths.
It is estimated that 1.6 million deaths resulted from TB in 2005. Both the highest number of deaths and the highest mortality per capita are in the Africa Region. The TB epidemic in Africa grew rapidly during the 1990s, but this growth has been slowing each year, and incidence rates now appear to have stabilized or begun to fall.
In 2005, estimated per capita TB incidence was stable or falling in all six WHO regions. However, the slow decline in incidence rates per capita is offset by population growth. Consequently, the number of new cases arising each year is still increasing globally and in the WHO regions of Africa, the Eastern Mediterranean and South-East Asia.

HIV and TB
HIV and TB form a lethal combination, each speeding the other's progress. HIV weakens the immune system. Someone who is HIV-positive and infected with TB bacilli is many times more likely to become sick with TB than someone infected with TB bacilli who is HIV-negative. TB is a leading cause of death among people who are HIV-positive. In Africa, HIV is the single most important factor contributing to the increase in incidence of TB since 1990.
WHO and its international partners have formed the TB/HIV Working Group, which develops global policy on the control of HIV-related TB and advises on how those fighting against TB and HIV can work together to tackle this lethal combination. The interim policy on collaborative TB/HIV activities describes steps to create mechanisms of collaboration between TB and HIV/AIDS programmes, to reduce the burden of TB among people and reducing the burden of HIV among TB patients.

Drug-resistant TB

Until 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, because doctors and health workers prescribe the wrong treatment regimens, or because the drug supply is unreliable. 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, especially in the former Soviet Union, and threaten TB control efforts.
While drug-resistant TB is generally treatable, it requires extensive chemotherapy (up to two years of treatment) with second-line anti-TB drugs which are more costly than first-line drugs, and which produce adverse drug reactions that are more severe, though manageable. Quality-assured second-line anti-TB drugs are available at reduced prices for projects approved by the Green Light Committee.
The emergence of extensively drug-resistant (XDR) TB, particularly in settings where many TB patients are also infected with HIV, poses a serious threat to TB control, and confirms the urgent need to strengthen basic TB control and to apply the new WHO guidelines for the programmatic management of drug-resistant TB.

High-risk populations
1. THE ELDERLY. Tuberculosis is more common in elderly persons. More than one-fourth of the nearly 23,000 cases of TB reported in the United States in 1995 developed in people above age 65. Many elderly patients developed the infection some years ago when the disease was more widespread. There are additional reasons for the vulnerability of older people: those living in nursing homes and similar facilities are in close contact with others who may be infected. The aging process itself may weaken the body's immune system, which is then less able to ward off the tubercle bacillus. Finally, bacteria that have lain dormant for some time in elderly persons may be reactivated and cause illness.
2. RACIAL AND ETHNIC GROUPS. TB also is more common in blacks, who are more likely to live under conditions that promote infection. As the end of the century approaches, two-thirds of all cases of TB in the United States affect African Americans, Hispanics, Asians, and persons from the Pacific Islands. Another one-fourth of cases affect persons born outside the United States. As of 1992, the risk of TB was still increasing in all these groups.
3. LIFESTYLE FACTORS. The high risk of TB in AIDS patients extends to those infected by human immunodeficiency virus (HIV) who have not yet developed clinical signs of AIDS. Alcoholics and intravenous drug abusers are also at increased risk of contracting tuberculosis. Until the economic and social factors that influence the spread of tubercular infection are remedied, there is no real possibility of completely eliminating the disease.
4. Alcoholism
5. Homelessness
6. Crowded living conditions
7. Diseases that weaken the immune system
8. Migration from a country with a high number of cases
9. Health-care workers

DIAGNOSIS
Clinical
1. Systemic symptoms of tuberculosis include anorexia, weight loss, weakness, night sweats, fatigability, malaise and fever.
2. Pulmonary TB presents with cough progressing from non- productive to productive and rarely, hemoptysis and dyspnea.
3. The majority of pulmonary TB infections in those with normal immune function are clinically and radiographically undetectable. A positive TB skin test is often the only indication of infection.
4. These latent infections, without active disease, are not infectious and the organism cannot be transmitted.
5. 10% of individuals with latent infection, if untreated, will develop active TB.

Laboratory
1. The gold standard for identifying M. tuberculosis infection without disease is the skin test with tuberculin purified protein derivative (PPD).
2. A 5-unit dose of PPD is 0.1 ml (1 mg) and should be applied intradermally.
3. Result interpretation at 48 to 72 hours by measuring the size of induration (2)
4. 5 mm - positive (in persons with HIV infection, immunosuppression, in close contact with infectious case or with radiological findings consistent with TB).
5. 10 mm - positive (in persons with risk factors: foreign born, IV drug use, low income, long term care facilities residents, medical conditions with risk of infection and age less than 4 years.
6. 15 mm - positive (in older than 4 years of age and no risk factors)(3)
7. Identification of organisms is critical in the diagnosis of tuberculosis.
8. Clinical specimens for detection of organisms may include sputum, bronchial washings, urine, blood, cerebrospinal fluid, tissue and other body fluids (2).
9. Acid-fast bacilli (AFB) in stained smears is evidence of Mycobacteria presence; easy and fast; is quantitative and can estimate degree of infectiousness: negative in up to 20% which does not rule out disease.
10. Culture: 4-6 weeks on solid media or 2 weeks on Bactec broth system.
At least 3 morning sputum samples (or other body fluid) are needed for AFB stain and culture.
11. Presumptive diagnosis is made through identification of AFB in smears and the diagnosis is confirmed when possible through isolation of the organism on culture
12. Polymerase chain reaction (PCR) is a rapid technique which allows for direct dentification of M. tuberculosis in clinical specimens.
13. Drug susceptibility tests of the infecting organism should be performed in order to determine resistance and the most effective treatment.

TREATMENT
• Therapy should always include multiple agents. It is best managed by and expert who works with the public health department. Directly Observed Therapy (DOT) is the most effective way to assure compliance.
• Isoniazid (INH) should be included in all treatment regimens except in cases of significant resistance to the drug.
• Rifampin (RMP) is the second major line of therapy.
• Isoniazid and Rifampin are bactericidal to both rapidly and slow growing TB organisms.
• Both pyrazinamide (PZA) and ethambutol are essential components of four-drug regimen therapy (Isoniazid, Rifampin, PZA, and Ethambutol) for resistant cases.
• Nine months of treatment with INH and RMP is effective for most cases of drug sensitive tuberculosis.
• Available second-line agents are more toxic and/or less efficacious (5).

FOLLOW-UP
• DOT (directly observed therapy): twice-weekly therapy (standard)
• Sputum for AFB: monthly
• CXR: at 3 months and at completion of therapy
• Not infectious if…clinical response after 2-3 weeks therapy and 3 negative AFB smears.

VACCINATION
• Bacillus of Calmette and Guerin (BCG) vaccine.
• Prevents progression to clinical disease not an infection.
• Not routinely used in the US or other industrialized nations due to the relatively low risk of infection in these areas.
• 60-80% effective in reducing the incidence of TB in children.
• May be useful in areas with high prevalence of TB infection.
• Administer only if tuberculin-negative.
• May be indicated for tuberculin-negative close contacts of a TB infected person who is untreated or ineffectively treated for pulmonary tuberculosis or who is infected with a drug resistant strain (4,5,6).

PREVENTION

1. TB prevention and control plans must be established in all health care settings and regularly evaluated for effectiveness
2. TB screening programs (PPDs) for all health care workers
3. Health care worker training and education
4. Use of preventive therapy (Isoniazid) to treat latent infection
5. Report suspected tuberculosis cases to the local health department
6. Use airborne isolation: until 2 (-) AFB smears from expectorated sputum. See policy for further instructions for discontinuing isolation.
7. Minimal air quality standard is 6-air exchanges/ hour (In 1 hour all droplet nuclei are removed from the air).
8. Identify and treat infectious cases to decrease transmission.
9. Reduce or eliminate conditions increasing the spread of infection (i.e. over crowding).
10. Educate the public regarding transmission, control methods and the importance of early diagnosis and treatment.
11. Adherence to prescribed therapy for tuberculosis should be emphasized and enforced (i.e. DOT) (4).
12. Quarantine is NOT necessary in most cases.
13. TB testing (PPD) of all close contacts. Chest x-rays should be performed on all with positive screening tests.
14. 3 months preventive treatment is recommended for close contacts who are skin test negative. Skin test should be repeated after 3 months to determine the need for further therapy (4).