Kristian Rey M. Jalagat November 27, 2010

N103, B2

Pulmonary Tuberculosis (PTB)

Tuberculosis (TB) is an infectious disease that primarily affects the lung parenchyma. It

also may be transmitted to other parts of the body, including the meninges, kidneys, bones,

and lymph nodes. The primary infectious agent, Mycobacterium tuberculosis, is an acid-fast

aerobic rod that grows slowly and is sensitive to heat and ultraviolet light. Despite advances in

treatment, TB remains a major cause of illness and death worldwide, especially in Africa and

Asia. Every year, tuberculosis kills almost 2 million people. Since the 1980s, rates of TB have

increased, fueled by the HIV/AIDS epidemic and the emergence of drug-resistant strains of the

TB bacteria. Most cases of tuberculosis can be cured by taking a combination of medications

for several months or longer. It's important to complete your whole course of therapy.

Causes

Tuberculosis is caused by an organism called Mycobacterium tuberculosis. The bacteria

spread from person to person through microscopic droplets released into the air. This can

happen when someone with the untreated, active form of tuberculosis coughs, speaks,

sneezes, spits, laughs or sings. Rarely, a pregnant woman with active TB may pass the

bacteria to her unborn child. Although tuberculosis is contagious, it's not especially easy to

catch. You're much more likely to get tuberculosis from a family member or close co-worker

than from a stranger. Most people with active TB who've had appropriate drug treatment for at

least two weeks are no longer contagious.

Since the 1980s, the number of cases of tuberculosis has increased dramatically

because of the spread of HIV, the virus that causes AIDS. Tuberculosis and HIV have a deadly

relationship — each drives the progress of the other. Infection with HIV suppresses the

immune system, making it difficult for the body to control TB bacteria. As a result, people with

HIV are many times more likely to get TB and to progress from latent to active disease than

are people who aren't HIV-positive.

Another reason TB remains a major killer is the increase in drug-resistant strains of the

bacterium. Ever since the first antibiotics were used to fight TB 60 years ago, the germ has

developed the ability to survive attack, and that ability gets passed on to its descendants.

Drug-resistant strains of TB emerge when an antibiotic fails to kill all of the bacteria it targets.

The surviving bacteria become resistant to that particular drug and frequently other antibiotics

as well. Today, for each major TB medication, there's a TB strain that resists its treatment.

The major cause of TB drug resistance is inadequate treatment, either because the

wrong drugs are prescribed or because people don't take their entire course of medication.

Risk factors

Anyone can get tuberculosis, but certain factors increase your risk of the disease. These

factors include:

Lowered immunity. A healthy immune system can often successfully fight TB bacteria,

but your body can't mount an effective defense if your resistance is low. A number of

factors can weaken your immune system. Having a disease that suppresses immunity,

such as HIV/AIDS, diabetes, end-stage kidney disease, certain cancers or the lung

disease silicosis, can reduce your body's ability to protect itself. Your risk is also higher

if you take corticosteroids, certain arthritis medications, chemotherapy drugs or other

drugs that suppress the immune system.

Close contact with someone with infectious TB. In general, you must spend an

extended period of time with someone with untreated, active TB to become infected

yourself. You're more likely to catch the disease from a family member, roommate,

friend or close co-worker.

Country of origin. People from regions with high rates of TB — especially sub-Saharan

Africa, India, China, the islands of Southeast Asia and Micronesia, and parts of the

former Soviet Union — are more likely to develop TB. In the United States, more than

half the people with TB were born in a different country. Among these, the most

common countries of origin were Mexico, the Philippines, India and Vietnam.

Age. Older adults are at greater risk of TB because normal aging or illness may weaken

their immune systems. They're also more likely to live in nursing homes, where

outbreaks of TB can occur.

Substance abuse. Long-term drug or alcohol use weakens your immune system and

makes you more vulnerable to TB.

Malnutrition. A poor diet or one too low in calories puts you at greater risk of TB.

Lack of medical care. If you are on a low or fixed income, live in a remote area, have

recently immigrated to the United States or are homeless, you may lack access to the

medical care needed to diagnose and treat TB.

Living or working in a residential care facility. People who live or work in prisons,

immigration centers or nursing homes are all at risk of TB. That's because the risk of the

disease is higher anywhere there is overcrowding and poor ventilation.

Living in a refugee camp or shelter. Weakened by poor nutrition and ill health and

living in crowded, unsanitary conditions, refugees are at especially high risk of TB

infection.

Health care work. Regular contact with people who are ill increases your chances of

exposure to TB bacteria. Wearing a mask and frequent hand washing greatly reduce

your risk.

International travel. As people migrate and travel widely, they may expose others or

be exposed to TB bacteria.

Modes of Transmission

Airborne droplet method through coughing, singing or sneezing

Direct invasion through mucous membranes or breaks in the skin may occur, but

extremely rare

Bovine tuberculosis results from exposure to TB cattle, usually by ingestion of

unpasteurized milk or dairy products.

Classification

The current clinical classification system for tuberculosis (TB) is based on the pathogenesis of the disease

Classification System for TB

Class Type Description

0 No TB exposureNot infected

No history of exposureNegative reaction to tuberculin skin test

1 TB exposureNo evidence of infection

History of exposureNegative reaction to tuberculin skin testGhon complex

2 TB infectionNo disease

Positive reaction to tuberculin skin testNegative bacteriologic studies (if done)Fibrocaseous cavitary lesion (usually in upper lobe of lungs)

3 TB, clinically active M. tuberculosis cultured (if done)Clinical, bacteriologic, or radiographic evidence of current disease

4 TBNot clinically active

History of episode(s) of TBorAbnormal but stable radiographic findingsPositive reaction to the tuberculin skin testNegative bacteriologic studies (if done)andNo clinical or radiographic evidence of current disease

5 TB suspect Diagnosis pendingTB disease should be ruled in or out within 3 months