TB is one of the oldest diseases known to humanity and remains the leading infectious cause of death in the world.

Once known as consumption, the disease now recognized as tuberculosis, or TB, is caused by an infection with the Mycobacterium tuberculosis complex of organisms. Included in this group of organisms are mammalian tubercle bacilli such as M. tuberculosis, M. bovis, and M. africanum. These bacteria are capable of attacking any part of the human body; however, the most common site of infection is the lung. Mycobacteria organisms are highly aerobic and tend to migrate into the apex of the lung, where oxygen tensions are higher. TB is one of the oldest diseases known to humanity, dating back by some estimates to possibly 4000 BC. Once the leading cause of death in the United States, although this is no longer the case, TB still remains the leading infectious cause of death in the world; approximately 3 million people die annually.¹

M. tuberculosis is transmitted by tiny airborne particles of 1 to 5 µm in diameter, and it is believed that when only one to five bacteria migrate into a terminal alveolus, infection can result.² According to the World Health Organization (WHO), one third of the population of the world is infected with the tubercle bacillus. Of these vast numbers of infected individuals, only about 4% of the current population in the United States has been shown to be infected. This equates to less than 10 cases per 100,000 people. In the year 2000, the total number of reported cases in this country was 16,377.³

Once a serious threat to the population of the United States, tuberculosis was nearly eliminated. However, in the early 1990s, there was a dramatic resurgence of the disease. A large number of these new cases were identified in New York City. It became the popular belief that the major source of infection came from immigrants of developing countries. This led to a closer scrutiny of immigration practices, as well as a major undertaking to curtail the transmission of the disease by improving hospital and correctional facilities, directly observing patient treatment, and educating the public and medical community on how to identify the disease.⁴

A critical element in the prevention of disease progression lies with the treatment of individuals with latent tuberculosis infection. This can be particularly problematic among immigrants from areas throughout the world possessing high rates of TB. The most important time factor appears to be within the first 5 years of immigrating. Those recently infected, intravenous drug users, and individuals infected with the human immunodeficiency virus (HIV) are at a particularly high risk for having latent TB.⁵

At-risk Populations
A primary source of individuals at a significantly increased risk for developing active TB can be found in correctional facilities. Many of these inmates come from low-income populations, are members of racial and ethnic communities, and have been homeless. Large numbers of these individuals are also intravenous drug users, many infected with HIV.⁶ These risk factors combined with a limited access to adequate health care put this population at significant threat for the expansion of this disease.

The problem is seen in both long-term and short-term correctional facilities, and thus it is important that both have TB infection-control programs in place. Three primary components must be present for these programs to be effective: screening, to help identify those who have active disease or those infected with M. tuberculosis; containment, to help prevent the transmission of the disease and the treatment of those who are infected; and assessment, to monitor and evaluate both the screening and containment activities of the program. Screening protocols have been developed and recommended by the Centers for Disease Control and Prevention (CDC) in Atlanta.⁶

It is believed that in the homeless population within the United States, the chance of TB infection may be 20 times greater than that in the rest of the population. Like inmates, homeless individuals are prone to high rates of substance abuse, increased rates of HIV infection, and reduced access to health care. These factors are all associated with an increased risk of developing TB. A computer simulation model was developed to examine the effects of TB-control strategies in the homeless population. The results revealed that improved access and effectiveness of treatment programs and vaccination of HIV-negative homeless people could significantly reduce mortality and morbidity associated with TB.⁷

More than 3,000 cases of TB among foreign-born individuals were reported in California in 1995. The largest numbers of these individuals immigrated from Mexico, the Philippines, Vietnam, and China. Most were in the United States less than 1 year, and likely were infected prior to coming to this country.⁸

Control and Treatment
The control of tuberculosis in the United States relies heavily on rapid diagnosis and treatment, particularly among immigrant and refugee populations. Since 1977, guidelines have been available for screening foreign-born individuals for TB in their countries and upon arrival in the United States. According to these guidelines, which were revised in 1990,⁹ immigrants and refugees are required to have chest radiographs performed, and if the results give any indication of active TB infection, sputum smears must be obtained; these are then examined for the presence of acid-fast bacilli. An individual’s visa status is dependent on the results of this testing.⁸

The ability to control TB within the foreign-born population is critical to the eventual elimination of the disease in the United States. The question of strict border screening frequently has been raised as a means to block entry to those harboring the infection. Should all foreign-born individuals entering the United States undergo mandatory screening? Would this type of screening program be cost-effective?

It is generally agreed that focus be placed on the TB screening of the foreign-born, immigrant population and not on mandatory screening of nonimmigrants. It is in the immigrant population that the yield resulting from screening programs is most favorable. To screen and monitor nonimmigrant groups would divert valuable, limited resources from the already proven beneficial programs for the control of TB for foreign-born immigrants. The required screening of nonimmigrants might actually worsen the TB epidemic.¹⁰

Significant health and financial benefits can be gained by a program of screening immigrants from developing nations across the globe for latent tuberculosis infection. One such model predicted that over a 1-year period such a program has the potential of eliminating up to 10,000 cases of active tuberculosis infection, at a savings of up to $90 million.¹¹

Perhaps the primary elements responsible for increased risk of tuberculosis infection in the immigrant population are poverty and HIV. Failure to address these issues appropriately may lead to substantial financial hardships, as well as unfair treatment to those seeking to make their homes in this country. As the United States and other industrialized nations work at eliminating this disease, the importance of working together on developing appropriate strategies cannot be overemphasized. Worldwide education programs aimed at understanding and recognizing this disease, the proper drugs used for treatment, and systematic follow-up monitoring of those suspected of being infected with tuberculosis may help stop a disease that was once on the verge of elimination.

Preventive care may play an important role with tuberculosis, as it does with most medical issues. Those considered at high risk for tuberculosis infection should undergo an initial tuberculin skin test. This will help to raise the level of alertness among health care providers and identify the need for preventive therapy. Those who test negative but are at an increased risk of exposure should be tested on a regular basis. Individuals who test positive to the tuberculin skin test should have a chest radiograph performed to evaluate for clinically active TB and/or the presence of old lesions. Follow-up skin testing and chest radiographs of those who have tested positive are usually unnecessary. These individuals should, however, be encouraged to seek medical care if symptoms should develop.¹²

Although the tuberculin skin testing method is most popular, there are limits to its effectiveness due to frequent false-negative results. This is particularly problematic in immunocompromised patients such as those with HIV. For these cases, use of the Mantoux test is preferred. This involves the injection of purified protein derivative intracutaneously. Those with symptoms of frequent cough, fever, and hemoptysis should also undergo chest radiography. This is recommended even if the skin testing is negative.

Summary
A resurgence of tuberculosis cases was experienced in the early 1990s. Although this was controlled fairly successfully, there is still an increased risk of contracting and spreading this disease among recent immigrants, the homeless population, and individuals infected with HIV. Failure to follow appropriate screening and treatment protocols may ultimately result in the untimely return of an age-old enemy.

Paul Nuccio, RRT, FAARC, is the director of respiratory care at Boston’s Brigham and Women’s Hospital.

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