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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.
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