Active Tuberculosis

Article Author:
Talha Jilani
Article Author (Archived):
Akshay Avula
Article Editor:
Abdul Siddiqui
8/14/2019 6:17:34 PM
PubMed Link:
Active Tuberculosis


Active tuberculosis is a condition in which the body’s immune system is unable to fight off or defend against the Mycobacterium tuberculosis bacterium. This inability causes an infection of the lungs, which is the most common presentation, or other parts of the body (tuberculosis is a multisystemic disease). Apart from the respiratory system, the organ systems most commonly affected include the gastrointestinal system, the musculoskeletal system, the lymphoreticular system, and the reproductive system, as well as the skin, and the liver.

Most individuals infected with tuberculosis do not show symptoms, which is known as latent tuberculosis. However, around 5% to 10% of patients with latent infections progress to active disease, which is a serious concern. If untreated, half of those with the active disease die.

The World Health Organization estimates that, annually, around 8 million people develop active tuberculosis globally, and nearly 2 million people die from the disease. Of every 10 people infected with M. tuberculosis, one may develop an active infection sometime in their lifetime. After infection, the risk of developing active tuberculosis is highest in the first year, but the active disease usually occurs many years later in most patients.

The World Health Organization (WHO) reported in 2017 that the estimated global incidence rate for tuberculosis has decreased by 1.5% each year since 2000. However, despite these substantial gains and drastic global efforts to eradicate tuberculosis, the disease still accounts for significant morbidity and mortality worldwide. Developing countries like India, Pakistan, the Philippines, China, South Africa, Indonesia, and Nigeria experience the highest morbidity and mortality rates. When combined, these countries accounted for 64% of all tuberculosis-related deaths in 2016, according to the WHO.[1][2][3]


Infection with Mycobacterium tuberculosis (alcohol and acid-fast bacillus) causes active tuberculosis. It is classified under the M. tuberculosis complex group, which includes 4 other mycobacteria that can cause active tuberculosis: M. canettii, M. microti, M. bovis, and M. africanum.[4][5][6]

M. tuberculosis is an obligate-aerobic, nonmotile, non-spore-forming, catalase-negative, and facultative intracellular bacteria. The high lipid content of M. tuberculosis gives it many unique clinical characteristics. These include resistance to several antibiotics and ability to survive in many extreme conditions. It also takes a long time to divide (around 16 to 20 hours), a significantly slower rate compared to other bacteria, which usually takes less than an hour.

The organism has a poor reaction to Gram stain and thus, is not classified as gram-positive or gram-negative. However, sometimes weakly positive cells are observed on Gram stain, referred to as “ghost cells.” As M. tuberculosis retains some stains even after being treated with solutions containing acids, hence it is considered an acid-fast bacillus. The Ziehl-Neelsen stain and the Kinyoun stain are most commonly used to identify M. tuberculosis. The test dyes the acid-fast bacilli bright red which makes it distinct against a blue background.

Humans are the only known population in which M. tuberculosis naturally lives and reproduces. The organism is spread primarily as an airborne aerosol from an individual in the infectious stage of tuberculosis although transdermal and gastrointestinal (GI) transmission is also possible.


Tuberculosis has a global distribution, and over two billion people (around 30% of the world's population) are suspected to be infected with M. tuberculosis. In 2003, the global incidence of tuberculosis reached its peak but has been declining slowly ever since. Most new cases of the disease in 2016 were reported from Asia (around 45%), followed by Africa (around 25%). The WHO reported in 2016 that approximately 10.4 million people became infected with tuberculosis, of which approximately 1.7 million died.[7][8][9]

Although present globally, the epidemiology of tuberculosis varies significantly depending on the region.

  • India, sub-Saharan Africa, Micronesia, and the islands of Southeast Asia had the highest rates (100 per 100,000 people or higher)
  • China, Eastern Europe, Central, and South America, and northern Africa had intermediate rates (26 to 100 cases per 100,000 people)
  • The United States, Canada, Japan, Western Europe, and Australia recorded the lowest rates (less than 25 cases per 100,000 people)

Although about 90% to 95% of the people infected with M. tuberculosis do not develop active disease and remain asymptomatic, around 5% to 10% of those infected develop the disease. In 2012, this amounted to around 8.6 million cases of active tuberculosis worldwide. In the United States, tuberculosis is commonly seen among the immigrant population. Whereas infections with non-tuberculous mycobacteria are not uncommon in the US especially among the susceptible and immunocompromised patients, many times the clinical differentiation among M. tuberculosis and nontuberculous mycobacterium becomes challenging as they possess similar clinical and pathophysiologic mechanisms. Nevertheless, it is important to distinguish among tuberculosis and non-tuberculous mycobacteria as the management are drastically different for both[10]

Young adults have the highest rates of active tuberculosis globally, but in developed countries, older individuals experience the highest rates of disease. People of all age groups are at risk of progressing to active disease. Those at increased risk include:

  • Patients also infected with HIV are 20 to 30 times more likely to develop active tuberculosis.
  • People with other conditions that suppress the immune system are also at a higher risk of progressing to active disease. This group includes people on immunosuppressive agents such as long-term corticosteroids.
  • People with chronic lung diseases.
  • The use of tobacco products also increases the risk of progressing to active disease and death.
  • Malnutrition indicates a higher risk of progressing to active disease, making tuberculosis one of the principal illnesses of poverty.
  • Patients who have diabetes also have an increased risk of progressing to active tuberculosis and experience worse treatment outcomes.
  • The use of alcohol (greater than 40 g per day) also increases risk.


Inhaling the aerosolized droplets from an infected person is the principal mechanism through which tuberculosis spreads. Although tuberculosis most commonly causes a lung infection, it is a multisystemic disease and can present as variable pathologic findings. Subsequent deposition of the organism in the lungs can lead to a few possible outcomes, including:

  • The immediate clearance of the organism from the body
  • Primary disease: The immediate onset of active disease in the individual
  • Latent infection
  • Reactivation disease: The onset of active disease many years after a period of latent infection

The body’s ability to effectively restrict or eliminate the infective inoculum is dependent on the immune status of the individual, genetics, and whether exposure to the organism is primary or secondary. M. tuberculosis also possesses several virulence factors that make its elimination difficult for alveolar macrophages. These factors include the high mycolic acid content found in the bacterium’s outer capsule, which makes phagocytosis difficult for alveolar macrophages. Other constituents of the bacterium’s cell wall such as the cord factor could directly damage the alveolar macrophages. Several studies have demonstrated that M. tuberculosis also inhibits the formation of an effective phagolysosome, which limits and sometimes even prevents the elimination of the organisms. Other virulence factors include catalase-peroxidase, which helps resist the oxidative response of the host cell, and lipoarabinomannan, which helps induce cytokines and resist host oxidative stress.[11][12]

Individuals who fail to eliminate the mycobacterium after the first contact develop primary tuberculosis. The primary disease develops in approximately 5% to 10% of exposed individuals, and of these, roughly half develop active tuberculosis within the first 2 to 3 years after infection.

The tubercle bacilli induce infection of the lungs after they are transported in droplets small enough to reach the alveolar space (around 5 to 10 microns). If the infection is not eliminated by the innate defense system of the host, the bacilli could proliferate inside alveolar macrophages, which could migrate away from the lungs and enter other tissues.

Macrophages in the lungs produce chemokines and cytokines that attract other phagocytic cells, including neutrophils, monocytes, and other alveolar macrophages, which produce a nodular granulomatous structure known as a tubercle. If the continuous bacterial replication is not inhibited, the enlarging tubercle and bacilli could enter local draining lymph nodes. This causes lymphadenopathy, which is a characteristic manifestation of primary tuberculosis. A Ghon complex can develop if the lesion produced by the extension of the tubercle spreads into the lung parenchyma and lymph node. Bacteremia could also be seen in the initial infection.

The tubercle bacilli will proliferate until an effective cell-mediated immune response develops. This usually takes about 2 to 10 weeks following initial infection in more than 90% of infected individuals. In the lungs, failure to mount an effective cell-mediated immune response and tissue repair could lead to extensive damage. Tumor necrosis factor-alpha, nitrogen intermediates, reactive oxygen, and the constituents of cytotoxic cells (perforin, granzymes) whose function it is to eliminate M. tuberculosis could also contribute to the collateral damage of the host and the development of caseating necrosis. Therefore, much of the tuberculosis pathology results from the infected host's immune response to the tubercle bacilli.

Unchecked bacterial growth could lead to the hematogenous spread of bacilli and eventually disseminated tuberculosis. "Military tuberculosis" is the term for disseminated disease with lesions resembling millet seeds. The bacilli can also spread mechanically via erosion of the caseating lesions into the airways, at which time the host becomes infectious to other individuals. In the absence of treatment, the mortality rate is around 80%. The remaining patients could develop a chronic disease or recover. Chronic tuberculosis is characterized by recurrent episodes of healing by fibrotic changes surrounding the lesions and tissue breakdown. The complete spontaneous eradication of the tubercle bacilli is rare.

The primary tuberculosis infection is usually located in the middle portion of the lungs and is referred to as the ghon focus. The Ghon focus usually enters a state of latency in most individuals, known as latent tuberculosis. If there is immunosuppression in the host, latent tuberculosis is capable of being reactivated.

Most individuals who develop tuberculosis do so after an extended latency period, often many years after the initial primary infection. This is known as reactivation disease or secondary tuberculosis. Individuals with latent infection but no underlying medical problems have a 5% to 10% risk of developing secondary tuberculosis in their lifetime. The location of the lesions of secondary tuberculosis is usually at the lung apices, and unlike primary disease, tends to be localized. A small number of people could also develop secondary tuberculosis after getting reinfected with M. tuberculosis. Secondary tuberculosis can be differentiated from primary progressive tuberculosis by the presence of cavitation and the location of the lesion.


The diagnostic histopathological hallmark of tuberculosis is a granuloma. The differentiating features of a tuberculosis granuloma include the presence of multinucleated giant cells and caseous necrosis demonstrable through a region of central eosinophilia.

History and Physical

The classic symptoms of active pulmonary tuberculosis include a chronic cough associated with hemoptysis, weight loss, and night sweats. Many patients also experience fever, chest pains, and weakness. 

When taking the history of a patient with the above symptoms, inquiry in detail about the following factors should be done as well, as they increase the likelihood that the patient could have an active tuberculosis infection:

  • History of HIV infection
  • History of prior tuberculosis treatment
  • History of a positive purified protein derivative of the tuberculin test result
  • Emigration from or travel to an area where tuberculosis is endemic

The presentation of secondary tuberculosis is different from that of primary progressive disease as the hypersensitivity and tissue reaction are more severe in secondary tuberculosis, and cavities are usually observed in the upper portion of the lungs.

The active disease could also result in pulmonary or systemic dissemination of tubercles, and this could manifest as miliary tuberculosis, which resembles millet-shaped lesions on radiographic images of the chest. Tuberculosis could also spread into the bowel, spine (Pott disease), or central nervous system (tubercular meningitis).


Screening Tests    

The Mantoux Test

The Mantoux test consists of injecting the individual with a dose of purified protein derivative and observing the skin for induration. This method is the traditional screening test for exposure to tuberculosis. The patient’s overall risk of exposure is taken into consideration when interpreting the result. Patients are then classified into three groups based on the size of the induration and the risk of exposure. These 3 groups include: 

  • Low risk: These patients have a minimal probability of exposure to tuberculosis. The Mantoux test is only considered positive if there is a significant induration of 15 mm or higher following the intradermal injection of purified protein derivative. People in this group include those with no history of travel to a tuberculosis-endemic region, no history of military service, no contact with a patient with a chronic cough, no history of steroid use, no known occupational exposure, are negative for HIV, and are not a resident of a tuberculosis-endemic country.
  • Intermediate risk: These patients have an intermediate probability of exposure to tuberculosis. Their test results are considered positive if the measured induration is greater than 10 mm. People in this group include those who are residents of tuberculosis-endemic countries such as Asia, Latin America, and Africa, residents or workers of shelters, those who reside in overcrowded vicinities, and medical personnel.
  • High risk: These patients have a significant probability of exposure to tuberculosis. Their test results are considered positive if the measured induration is greater than 5 mm. People in this group include those who are immunocompromised and cannot mount a sufficient immune response to the purified protein derivative test (HIV-positive patients, those on chronic steroids), patients with frequent exposure to those with persistent cough, and patients with evidence of a prior tuberculosis infection, such as a healed scar seen on X-ray.

A positive Mantoux test indicates exposure to tuberculosis or latent tuberculosis. However, this test lacks specificity, and patients require subsequent visits to interpret the result and a chest x-ray for confirmation of the disease. Although the test is considered relatively sensitive, it may give false-positive results if the patient has been administered the BCG vaccine. The Mantoux test should never be regarded as a confirmatory test.[13][14][15]

Interferon Release Assays

This is a far more specific screening test that is just as sensitive as the Mantoux test. It qualitatively assesses the level of inflammatory cytokines such as interferon-gamma. The advantage of this test, especially in those inoculated with the BCG vaccine, is that the test requires only a single blood draw, which negates the need for repeat visits by the patient to interpret results. Furthermore, additional investigations such as HIV screening could be performed on the same drawn sample of blood, after consent. Some disadvantages of this method include its high cost and the need for technical expertise to perform the test.

Additional Information on Screening Tests

A positive result on a screening test indicates that the individual has had exposure to tuberculosis and has a high chance of developing active disease in the future. The incidence of tuberculosis in those patients who had a positive Mantoux test is around 2% to 10% without treatment.

Patients who have a positive screening test should have at least a basic diagnostic test like a chest X-ray performed. In certain cases, patients should have additional tests. Patients with negative diagnostic test results who do not meet the criteria for active disease should receive prophylaxis with isoniazid for latent disease if they meet the criteria.

Immunocompromised patients may show lower levels of induration to the purified protein derivative or a false-negative Mantoux because of cutaneous anergy.

When reviewing negative screening results for tuberculosis in HIV-positive patients, a high level of suspicion should be entertained. 

Confirmatory Tests

These tests are performed after positive screening tests, or after negative screening tests in patients with high suspicion of disease, to confirm active disease. Confirmatory tests include:

  • Chest x-ray, which can determine the presence of active disease in all positive screening tests
  • Culture
  • Acid-fast staining, or Ziehl-Neelsen stain
  • Nuclear amplification and gene-based tests

Nuclear amplification and gene-based tests represent a new generation of tools used for the diagnosis of tuberculosis. These tests enable the identification of the bacteria or bacteria particles by making use of DNA-based molecular techniques. These techniques are faster and allow accelerated diagnosis with high precision. Confirmation of the tuberculosis infection could be made in a few hours compared to the days or weeks it usually takes to wait for a standard culture. These tests are especially important among immunocompromised patients for whom there is a high rate of false-negative results. A few of the molecular-based tests such as DR-MTB and GeneXpert also allow for the identification of multiple-drug-resistant tuberculosis infections.

Treatment / Management

Patients with a possible tuberculosis infection should be isolated in a private room with negative pressure, either through a high-efficiency particulate air filter or by exhausting the air outside. The medical staff should always wear high-efficiency disposable masks to filter the tubercle bacillus. Isolation should continue until collected sputum smears are negative for three consecutive determinations, usually after approximately 2 to 4 weeks of treatment. Unfortunately, these measures are neither practical nor possible in developing countries where tuberculosis is a public health problem.[16][17][18]

The treatment of an active tuberculosis infection requires a combination of drugs. Monotherapy should never be used for the active disease to reduce the risk of the mycobacterium developing antibiotic resistance. First-line medications are the most commonly used regimens for active tuberculosis, including:    

  • Isoniazid: This is given with vitamin B6 to prevent neuropathies.
  • Rifamycin: Patients should have baseline and follow-up liver function tests done as rifamycin is hepatotoxic.
  • Ethambutol: Used only in children whose visual acuity can be determined and monitored (usually older than 6 years), as ethambutol can cause optic neuritis.
  • Pyrazinamide: Patients should have periodic liver function tests, chest X-rays, serum uric acids, and sputum cultures done at 2 to 3 months and at the completion of treatment.

The four-medication combination (isoniazid, rifampin, ethambutol, and pyrazinamide) is administered for 2 months, followed by a combination of isoniazid and rifampin for 4 months.

Directly observed therapy is recommended for patients receiving treatment. With this type of therapy, patients on the above regimens could be switched to 2 to 3 times per week dosing after completing an initial 2 weeks of daily dosing. Those taking medication 2 times per week must not miss any doses. Daily therapy should be prescribed for patients who are on self-administered medication. [19][20]

Patients diagnosed with active tuberculosis should have sputum analysis done for M. tuberculosis every week until sputum conversion is documented.

Second-line medications include: 

  • Injectable Aminoglycoside: Streptomycin, amikacin, and kanamycin.
  • Injectable polypeptides: Viomycin and capreomycin
  • Fluoroquinolones: Levofloxacin, gatifloxacin, ofloxacin, and moxifloxacin
  • Others: Para-aminosalicylic acid, ethionamide, cycloserine, prothionamide, terizidone, linezolid, and thioacetazone.

Third-line anti-tuberculosis medications are drugs with variable but unproven efficacy against the disease. They are the last resort for total drug-resistant tuberculosis infections and include:

  • Amoxicillin/clavulanic acid
  • Clarithromycin
  • Clofazimine
  • Linezolid
  • Imipenem/cilastatin

Multiple-drug-resistant tuberculosis infections are becoming increasingly common. A high-dose combination of the first-line and second-line drugs is being used to treat this condition. 

Differential Diagnosis

  • Actinomycosis
  • Histoplasmosis
  • Blastomycosis
  • Cat scratch disease
  • Aspergillosis
  • Lung abscess
  • Nocardiosis
  • Lung cancer

Toxicity and Side Effect Management

Side effects of anti-tuberculous drugs include:


Liver injury (nausea, fatigue, vomiting, malaise, abdominal pain), nausea, rash, numbness, and tingling in extremities, headache


Jaundice, red/orange discoloration of the urine and other secretions of the body, arthralgias, fever


Visual dysfunction which includes blurring or decreased vision, and blindness, liver injury, headache, nausea


nausea, painful or swollen joints, liver injury

Regular monitoring of liver function tests is essential, and in the case of elevated liver enzymes, depending on the severity, the medications should be discontinued. Second or third-line drugs can be used instead.


The mortality rate for those with an active tuberculosis infection who do not receive adequate treatment is around 50%. Those at an increased risk for worse outcomes and possible death include:

  • Young children (especially infants) and elderly patients
  • Those who have a delay or do not receive proper treatment
  • Patients who display an extensive spread of the disease on radiologic imaging
  • Patients who have a severe respiratory compromise
  • Those who are taking drugs or suffer from a disease that causes immunosuppression


Complications from active tuberculosis are frequently seen in patients with the risk factors mentioned above. Patients who do not receive proper or complete treatment for active disease are also at a higher risk of developing complications. Some complications caused by active disease include:

  • Acute respiratory distress syndrome
  • Extensive destruction of the lung
  • Empyema
  • Pneumothorax
  • Disseminated tuberculosis infection (including tubercular meningitis)
  • Bronchiectasis
  • Fibrothorax
  • Aspergilloma
  • Hemoptysis

Postoperative and Rehabilitation Care

All patients with TB need long-term follow up. This is to ensure that the disease is resolving and that the patient is compliant. Because the treatment is long term, compliance with drug therapy can be low and hence, the pharmacist may be involved in direct observation therapy.


  • Infectious disease 
  • Thoracic surgeon if the patient develops complications
  • Pulmonologist

Deterrence and Patient Education

The patient should be educated about compliance, as tuberculosis requires long term treatment. If non-compliance is a concern, "directly observed therapy" should be implemented as it is known to have better outcomes in patients, having difficulty adhering to the medication regimen.

Educating the patient about potential side effects of treatment is of utmost importance. They should be counselled about monitoring, which should be done at least once per month, to ensure there are no signs of toxicity, such as liver injury. Signs of liver injury must also be discussed which include loss of appetite, vomiting, dark-colored urine, jaundice, abdominal pain, or fatigue. The patient needs to immediately stop taking the medication if any of these signs develop and should notify their healthcare provider.

Post-partum women are at an increased risk for side effects.

Enhancing Healthcare Team Outcomes

TB is a serious infection with the potential to spread. Whenever a case of tuberculosis is identified, the public health department must be notified. Untreated tuberculosis carries a mortality rate of more than 50%. More important, it can lead to devastating complications. Thus, the treatment of tuberculosis involves an interprofessional team approach that includes the pulmonologist, an infectious disease expert, a thoracic surgeon, and a public health nurse or clinician. Besides treatment, patient education is vital. The nurse and pharmacist should educate patients on the BCG vaccine, especially in children. The pharmacist is critical for direct observation therapy and ensuring compliance to treatment, and reporting back to the physicians, nurse practitioner, or physician assistant managing the patient if compliance is lacking. Further, since patients are treated as outpatients, the pharmacist is in a position, to note the presence of any adverse effects of drug therapy which also needs to be reported. The social worker should be involved to ensure that the patient has adequate financial resources for treatment. The patient needs close follow up with serial monitoring by the clinicians to ensure that the treatment is working. The patient should be urged not to get pregnant while on therapy, but if pregnancy does happen, the obstetrician and the infectious disease expert should be involved in the care.

The radiologist should be involved as regular imaging studies are required to determine the response to treatment. Only through open communication between the team members can the morbidity and mortality rates of tuberculosis be reduced. [21][22][23](Level V)


The treatment of tuberculosis is slow and full resolution can take months. Despite adequate therapy, recurrence rates vary from 2-12%. The recurrences usually occur with the first 12 months of therapy and may be due to reinfection or low compliance with drug therapy. Poor prognostic markers for the infection include immunocompromised state, extrapulmonary involvement, advanced aged, and a history of prior infection. More important, complications of tuberculosis are also common and may include fibrothorax, collapsed lung, empyema, and massive hemoptysis. [2][24](Level V)


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