|
Tuberculosis (abbreviated as TB for tubercle bacillus or Tuberculosis) is a common and deadly infectious disease caused
by mycobacteria, mainly Mycobacterium tuberculosis. Tuberculosis most commonly attacks the lungs (as pulmonary TB) but can
also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, joints
and even the skin. Other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti, and Mycobacterium
microti can also cause tuberculosis, but these species do not usually infect healthy adults.
In the past, tuberculosis was called consumption, because it seemed to consume people from within, with a bloody cough,
fever, pallor, and long relentless wasting. Over one-third of the world's population has been exposed to the TB bacterium,
and new infections occur at a rate of one per second. Not everyone infected develops the full-blown disease; asymptomatic,
latent TB infection is most common. However, one in ten latent infections will progress to active TB disease, which, if left
untreated, kills more than half of its victims.
Tuberculosis spreads through airborne droplets when a person with the infection coughs, talks or sneezes. In general,
you need prolonged exposure to an infected person before becoming infected yourself. Even then, you may not develop symptoms
of the disease. Or, symptoms may not show up until many years later.
However, some patients - especially those with compromised immune systems - may progress directly from initial TB infection
to active tuberculosis. In another 10% of those with latent TB infection that has not been treated, the mycobacteria will
later be reactivated and begin to multiply - leading to active progressive tuberculosis disease.
Tuberculosis has plagued human beings for millennia and has been a leading cause of death for thousands of years.. Signs
of tubercular damage have been found in Egyptian mummies and in bones dating back at least 5,000 years. Today, despite advances
in treatment, TB is a global pandemic, fueled by the spread of HIV/AIDS, poverty, a lack of health services and the emergence
of drug-resistant strains of the bacterium that causes the disease.In the days before the discovery of antibiotics it was
called consumption, and those who contracted it were put into long-term hospitals called sanatoriums for the rest of their
lives. In the early 1900s, more than 80% of the U.S. population was infected with TB, and tuberculosis was the single most
common cause of death.
Although its incidence has decreased dramatically in the United States, the World Health Organization (WHO) estimates
that one-third of the world’s population is currently infected with M. tuberculosis and that a new person is infected
every second. Worldwide, TB is still the leading cause of death due to infection, killing about 2 million people a year.
In the U.S., there are now about 10 to 15 million people with latent TB infection. Active TB was thought to be under control
until a resurgence in new cases in the early 1990s. The majority of these new cases were among those living in overcrowded
or confined populations such as correctional facilities, nursing homes, and schools. The most vulnerable were those who were
medically underserved or had diseases and conditions that weakened their immune systems, such as: the homeless, alcoholics,
intravenous drug users, those with HIV or AIDS, and those with chronic kidney or liver diseases. Often these new cases were
multi-drug resistant (MDR), making them more difficult to treat. While the numbers of new cases of active TB have again declined
in the U.S. due to constant vigilance by the medical community, TB remains a significant national and global public health
concern.
How can I get tested for TB?
You should get tested for TB if
* You have spent time with a person known to have active TB disease or suspected to have active TB disease; or
* You have HIV infection or another condition that puts you at high risk for active TB disease; or
* You think you might have active TB disease; or
* You are from a country where active TB disease is very common (most countries in Latin America and the Caribbean,
Africa, Asia, Eastern Europe, and Russia); or
* You live somewhere in the United States that active TB disease is more common such as a homeless shelter, migrant
farm camp, prison or jail, and some nursing homes); or
* You inject illegal drugs.
Patients infected with both HIV and M. tuberculosis are a continuing concern. They have been shown to be at a significantly
increased risk of developing active TB and of dying from it. Extensively drug-resistant tuberculosis (XDR TB) is an emerging
concern. It is even more resistant and difficult to treat than MDR and has been recently defined by WHO and the Centers for
Disease Control and Prevention as M. Tuberculosis that is resistant to the drugs isoniazid and rifampin, to the drug class
fluoroquinolone, and to at least one of three injectable “second-line” drugs (amikacin, kanamycin, or
capreomycin). Although still relatively rare, cases of XDR TB are being closely monitored by the world medical community and
measures are being taken in hopes of limiting its spread.
Active tuberculosis will kill about two of every three people affected if left untreated. Treated tuberculosis has a mortality
rate of less than 5% (or less in developed countries where intensive supportive measures are available).
The standard "short" course treatment for tuberculosis (TB), if it is active, is isoniazid, rifampicin, pyrazinamide,
and ethambutol for two months, then isoniazid and rifampicin alone for a further four months. The patient is considered cured
at six months (although there is still a relapse rate of 2 to 3%). For latent tuberculosis, the standard treatment is six
to nine months of isoniazid alone.
Non-compliance
Patients who take their TB treatment in an irregular and unreliable way are at greatly increased risk of treatment failure,
relapse and the development of drug-resistant TB strains.
There are variety of reasons why patients fail to take their medication. The symptoms of TB commonly resolve within a
few weeks of starting TB treatment and many patients then lose motivation to continue taking their medication. Regular follow-up
is important to check on compliance and to identify any problems patients are having problems with their medication. Patients
need to be told of the importance of taking their tablets regularly, and the importance of completing treatment, because of
the risk of relapse or drug-resistance developing otherwise.
One of the main complaints is the bulkiness of the tablets. The main offender is PZA (the tablets being the size of horse
tablets). PZA syrup may be offered as a substitute, or if the size of the tablets is truly an issue and liquid preparations
are not available, then PZA can be omitted altogether. If PZA is omitted, the patient should be warned that this results in
a significant increase in the duration of treatment (details of regimens omitting PZA are given below).
The other complaint is that the medicines must be taken on an empty stomach to facilitate absorption. This can be difficult
for patients to follow (for example, shift workers who take their meals at irregular times) and may mean the patient waking
up an hour earlier than usual everyday just to take medication. Taking the medicines with food also helps ease the nausea
that many patients feel when taking the medicines on an empty stomach. The effect of food on the absorption of INH is not
clear: two studies have shown reduced absorption with food but one study showed no difference.
It is possible to test urine for isoniazid and rifampicin levels in order to check for compliance. The interpretation
of urine analysis is based on the fact that isoniazid has a longer half-life than rifampicin.
What if I have a positive test for TB?
If you have a positive reaction to the TB skin test or the QFT-G, your doctor or nurse may do other tests to see if you
have active TB disease. These tests usually include a chest x-ray. It may also include a test of the phlegm you cough up.
Because the TB bacteria may be found somewhere other than your lungs, your doctor or nurse may check your blood or urine,
or do other tests. If you have active TB disease, you will need to take medicine to treat the disease.
What if I have been vaccinated with BCG?
BCG is a vaccine for TB. This vaccine is not widely used in the United States, but it is often given to infants and small
children in other countries where TB is common. BCG vaccine does not always protect people from getting TB.
If you were vaccinated with BCG, you may have a positive reaction to a TB skin test. This reaction may be due to the
BCG vaccine itself or due to infection with the TB bacteria. Your positive reaction probably means you have been infected
with TB bacteria if
* You recently spent time with a person who has active TB disease; or
* You are from an area of the world where active TB disease is very common (such as most countries in Latin America
and the Caribbean, Africa, Asia, Eastern Europe, and Russia); or
* You spend time where TB disease is common (homeless shelters, migrant farm camps, drug-treatment centers, health
care clinics, jails, prisons).
If I have latent TB infection, how can I keep from developing active TB disease?
Many people who have latent TB infection never develop active TB disease. But some people who have latent TB infection
are more likely to develop active TB disease than others. These people are at high risk for active TB disease. They include
* people with HIV infection
* people who became infected with TB bacteria in the last 2 years
* babies and young children
* people who inject illegal drugs
* people who are sick with other diseases that weaken the immune system
* elderly people
* people who were not treated correctly for TB in the past
If you have latent TB infection (a positive TB skin test reaction or positive QFT-G) and you are in one of these high-risk
groups, you need to take medicine to keep from developing active TB disease. This is called treatment for latent TB infection.
There are several treatment options. You and your health care provider must decide which treatment is best for you.
The medicine usually taken for the treatment of latent TB infection is called isoniazid (INH). INH kills the TB bacteria
that are in the body. If you take your medicine as instructed by your doctor or nurse, it can keep you from developing active
TB disease. Children and people with HIV infection may need to take INH for a longer time.
Because there are less bacteria in a person with latent TB infection, treatment is much easier. Usually, only one drug
is needed to treat latent TB infection. A person with active TB disease has a large amount of TB bacteria in the body. Several
drugs are needed to treat active TB disease.
Sometimes people are given treatment for latent TB infection even if their skin test reaction is not positive. This is
often done with infants, children, and HIV-infected people who have recently spent time with someone with active TB disease.
This is because they are at very high risk of developing active TB disease soon after they become infected with TB bacteria.
It is important that you take all the pills as prescribed. If you start taking INH, you will need to see your doctor or
nurse on a regular schedule. He or she will check on how you are doing. Some people have serious side effects from INH. If
you have any of the following side effects, call your doctor or nurse right away:
* no appetite
* nausea
* vomiting
* yellowish skin or eyes
* fever for 3 or more days
* abdominal pain
* tingling in the fingers and toes
Warning: Drinking alcoholic beverages (wine, beer, and liquor) while taking INH can be dangerous. Check with your doctor
or nurse for more information.
People who have latent TB infection need to know the symptoms of active TB disease. If they develop symptoms of active
TB disease, they should see a doctor right away.
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.
World TB Day is March 24, 2008. http://www.stoptb.org/events/world_tb_day/2008/
|
