Tuberculosis (TB)

A serious respiratory disease spread from person to person through the air. Children usually contract tuberculosis (TB) from close contact with a diseased adult. Because infants and young children do not have very strong immune systems, they are susceptible to TB, as are those with impaired immune systems.

Once known as “consumption,” “scrofula,” or “wasting,” this disease is less common today in the United States, but it infects half of the rest of the world’s people. TB usually affects the lungs, although it can also affect other parts of the body (such as the brain, kidneys, or spine). It was once the leading cause of death in the United States.

Children with TB infection but not the disease have the bacteria that causes the infection within their bodies, but the germs are inactive. They cannot spread the bacteria to others, but they may develop TB later on. Because of this, they are often treated to prevent them from developing the disease.

In 1993 the World Health Organization (WHO) declared a “global TB emergency” because of the massive TB epidemic that was spreading around the world. In its 1996 report on TB, the WHO concluded that worldwide, the disease is the leading killer of women and the leading killer of HIV positive patients. (Among those with HIV, one in 10 per year will develop active TB.) TB kills more adults than all other infectious diseases combined and leaves more orphaned children than any other infectious disease. In 1995 more people died of TB than in any other year in history. If current trends continue, at least 30 million people will die from TB in the next 10 years. For every person who died in 1995 of the Ebola virus, more than 12,000 people died of TB.

About eight million new cases of TB occur each year; the number of cases reported in the United States has increased each year since 1985. In 1993 there were 215,313 cases reported in this country. Between 10 to 15 million Americans are infected with the TB germ; these people may develop TB sometime in the future. In industrialized countries the steady drop in TB began to level off in the mid-1980s and then began to increase. This may be due in part to immigration from countries with a high rate of TB.

Treatment
Of most concern is the fact that cases of TB resistant to more than one drug have been reported in 17 states in the United States since 1989. Because of this, it is essential to treat TB patients with a recommended four-drug regimen of isoniazid, rifampin, pyrazinamide, and ethambutol, or streptomycin, since it is less likely that bacteria can become quickly resistant to multiple drugs at the same time.

Cause
TB is caused by three species of mycobacteria: Mycobacterium tuberculosis, M. bovis, and M. africanuum. Once inhaled, the bacteria settle in the lungs and grow; from here, they can travel through the blood to other parts of the body (such as the kidney, spine, or brain). TB in the lungs or throat is mildly infectious, but the bacteria in other parts of the body are not usually contagious.

TB bacteria are sprayed into the air when a child with the disease of the lungs or throat coughs or sneezes. People with active TB are most likely to spread it to those they spend time with every day (such as family members or coworkers). Infectiousness is directly related to the number of bacilli expelled into the air. Patients are more likely to be infectious if they have TB in the lungs or larynx, have a cavity in the lung, and cough a lot. Infectiousness is also related to not covering the mouth when coughing and not receiving adequate treatment.

While TB is infectious, it is not highly infectious and is not nearly as contagious as MEASLES or WHOOPING COUGH. Letting fresh air blow through a room will eradicate most of the infectious germs exhaled by a sick patient every day. The bacteria are also sensitive to ultraviolet rays, which means that infection rarely occurs outside in daylight. Indeed, only half of the people who live with an infected patient will contract the disease themselves.

People with TB are most likely to transmit the disease before it has been diagnosed and treated, and at least 12 weeks must pass before a person who has been exposed to the disease will test positive. Infectiousness seems to decrease quickly once treatment begins; those who have been treated for two to three weeks, whose symptoms have improved, and who have three consecutive negative sputum tests can be considered “noninfectious.”

Most people who breathe in the bacteria and become infected are able to fight off the disease; the bacteria become inactive, but they remain alive in the body and can become active later. This is called TB infection. People with TB infection have no symptoms, do not feel sick, and cannot spread the disease. However, they usually have a positive skin test for TB and they can develop the disease later in life if they do not receive preventive treatment. Many people who have the infection never develop the disease, however. In these people, the bacteria remain inactive for a lifetime

Symptoms
The illness does not cause symptoms at first. TB growing in the lungs may cause a bad cough that lasts longer than two weeks and pain in the chest. The patient may cough up blood or phlegm from the lungs. Other symptoms include fatigue or weakness, weight loss, appetite loss, chills, and fever.

Diagnosis
A tuberculin skin test determines if a person has the TB organism, but it cannot identify those with active disease. For this skin test, a small amount of fluid (tuberculin) is injected under the skin in the lower part of the arm. Two or three days later a health-care worker looks for a reaction on the arm.

A positive reaction usually means that the person has been infected with the TB germ, but not
necessarily that they have an active infection. Other tests (chest X ray and sample of phlegm) are necessary to identify active disease.

People should be tested for TB if they have spent time with someone with infectious TB, have HIV, come from a country where TB is common (most countries in Latin America, the Caribbean, Africa, and Asia except for Japan). Others at high risk are those who inject drugs or who live in the United States where TB is common (homeless shelters, migrant farm camps, prisons, and some nursing homes).

Because it may take several weeks after infection for the immune system to react to the TB skin test, it may be necessary to be retested 10 to 12 weeks after the last exposure to TB. If the reaction to the second test is negative, there is probably no TB infection present.

The skin test is mandatory in some states and countries for immigrants and students from Africa, Asia, and Latin America, as well as for personnel in schools, hospitals, prisons, food handlers, group homes, child-care centers, and substance abuse centers. At the moment, screening of children entering kindergarten or day-care centers is not required in all school districts, but the government recommends that school children be tested for TB to ensure that all U.S. citizens are tested at least once in their lives.

A new test can now diagnose TB in a clinical lab much more quickly than in the past. The new test can confirm a TB diagnosis in just six hours, as opposed to the current two to six weeks required to confirm TB bacteria in culture. This new test is under consideration for approval by the U.S. Food and Drug Administration. The new test appears to have a low rate of false positives, which has been a problem with other tests in the past.

Treatment
Up to the 1700s it was thought that the touch of a king or queen would cure TB; today, scientists know that TB is cured by taking several drugs for up to nine months. If patients stop taking the drugs too soon, or if they do not take the drugs correctly, the TB organisms may become resistant. TB that is resistant to drugs is harder to treat.

Within a month after treatment begins, the patient should feel well, regain weight, and have no fever. Coughing should have slowed down, and there should be improvements on X ray. If the disease was severe, however, complete end of treatment may not occur for a year.

If there is no improvement within three months, a change in therapy may be needed. Relapses usually occur within six months after treatment ends and are usually due to patients who do not follow correct drug procedures.

When TB becomes active again in a patient who had been treated before, there is a very good chance that these bacteria will be drug-resistant. If the microorganism is resistant to standard drugs, it may be necessary to use more toxic drugs to treat the infection.

Prevention
Some people who have the TB germ but not active disease are more likely than others to develop an active case. These high-risk individuals include those with HIV infection, those who were recently exposed to someone with TB disease, and those with certain medical conditions.

For patients who have TB germs but not the active disease, physicians recommend taking isoniazid for up to 12 months. Infants and children who have spent time with someone who is infected are often given preventive therapy even if their skin test is negative.

There is a vaccine for TB disease that is used in many countries but is not widely used in the United States. Called BCG (Bacillus Calmette-Guérin), this vaccine does not completely prevent people from getting TB. Those who have been vaccinated with BCG can be given a tuberculin skin test; although the vaccine can cause a positive reaction to the test, it is more likely that a positive reaction is caused by TB infection if the reaction is large, the person was vaccinated a long time ago, the person has been around someone with TB disease, or the person is from a country where TB is common.

While there is some question as to how effective the BCG vaccine really is against adults, the World Health Organization recommends its use in newborns in developing countries, because it appears to offer some protection in children.

A relatively new TB vaccine from “naked” DNA might work better with less risk of infection than the current BCG vaccine. The traditional BCG vaccine is made from an altered, weakened form of the disease that infects cows. But in 1996 researchers reported that they had made a new vaccine out of a gene taken from the human version of TB. The use of use one gene (known as “naked DNA”) instead of the many genes contained in TB DNA, appears to be as effective as the earlier cow vaccine. However, trials in humans have not yet been done.

Unlike traditional vaccines, which stimulate the human body to produce disease-fighting antibodies, naked DNA vaccines are incorporated by the cells and the immune response begins there. There is also a lower risk of infection with this new vaccine. While this did not occur often with the old vaccine, it did happen in certain rare cases.

Scientists also have recently discovered that it is possible to transmit TB on an airplane. In the spring of 1994, a woman on an eight-and-a-half-hour United Airlines flight from Chicago to Honolulu infected four passengers sitting near her; all tested positive for the disease, but none have yet become ill. A few days later, the woman died from TB. Because this showed transmission is possible on airlines, the Centers for Disease Control and Prevention (CDC) recommended that when airlines learn that a passenger or crew member has traveled with the disease (especially on long flights) they should contact passengers and crew members and inform them. The CDC pointed out that only those passengers sitting near the woman were infected; others sitting farther away breathed air that passed through the plane’s filtration system.