Tuberculosis Series: Epidemiology and Prevention

The World Health Organization’s 2019 Global Tuberculosis Report estimates that approximately 10 million people contract tuberculosis around the world each year. Of those 10 million new infections, around 90% arise from only 30 countries. In the US, the CDC reports that just over 9,000 cases were diagnosed in 2018, a .7% decrease from 2017.

Of those US diagnoses, around 30% of people were born in the US. In the US, individuals who are at greater risk of a new TB infection as well as latent TB include ethnic minorities, especially those who recently migrated, people with limited access to healthcare, incarcerated individuals, the homeless, and anyone who is immune compromised especially those previously diagnosed with HIV infection.

It is important to regularly screen patients from these backgrounds as early treatment can prevent lifelong disability. If detected and treated with antibiotics early, TB infection will never progress to tuberculosis disease and can not be transmitted further. Once TB disease does develop, antibiotic treatment is also used to combat the infection and stop progression, but the damaging impact is typically lifelong.

TB Case Study: Non-U.S.-Born Patients

A 24 year old Vietnamese woman who worked as a waitress in small restaurant presented to an Urgent Care with back pain. She had no significant history and was discharged after an  evaluation and then  given Ibuprofen for a muscle strain. She returned again with worsening back pain a week or so later and an x-ray and eventual CT of her spine revealed several lytic lesions and complete liquefaction of T11. She was transferred to the regional trauma center for neurosurgery and orthopedics surgery to stabilize her spine. Bone biopsy and culture revealed TB osteomyelitis although she had no evidence of new or old TB in her lungs. She was treated with four drugs for a year, and her spine required operative orthopedic stabilization, but she has subsequently done well.

Similarly a 63 year old Latinex woman had a long history of mixed connective tissue disease had been screened LTBI positive years before but her compliance with therapy was never assured. She presented with bruising and epistaxis to the ED and was noted to have very low platelets. After a full work-up it became clear she had Idiopathic Thrombocytopenic Purpura and was treated with 50 mg of Prednisone to control her thrombocytopenia, after several days on therapy she developed a cough, two to three days later she was admitted to the ICU for intubation with milliary TB. Unfortunately she died after 2 weeks of respiratory failure from milliary TB.

In both cases high risk populations reactivated their latent tuberculosis because they were not screened or screened and failed to comply with LTBI treatment. There are many other examples of scenarios where chemotherapy for cancers, TNF inhibitors for autoimmune disorders, and high dose steroids trigger reactivation in settings where a second communicable disease only complicates an already difficult situation. In some cases becomes debilitating.

Populations with Increased Susceptibility to TB Disease

In the United States, populations that are at greatest risk for acquiring a new tuberculosis infection primarily involve people with limited access to healthcare. This includes homeless and incarcerated individuals, as their living situation typically involves many people in close contact. Remember, pulmonary or extrapulmonary TB disease only manifests in times of immunocompromise, but a person can become infected and develop latent infection at any time. Persons of African American descent are disproportionately susceptible to acquiring a new infection as well as receiving a late diagnosis. Hospital workers and family members who work and live close to already infected individuals are additional populations that should be regularly screened for TB. The good news is, due to increased screening and public awareness of TB, overall rates of LTBI and TB disease have been decreasing among all groups in the US.

Persons diagnosed with HIV and LTBI are at a significantly increased risk of developing TB disease if they do not take their antiretroviral medications as prescribed. Globally, TB disease is the leading cause of death among HIV infected people. HIV, the virus that causes AIDS, is deadly because of how severely it can cause a person to become immunocompromised. TB, a bacteria that lies in wait for the immunocompromised, is much more likely to progress to TB disease in a person with HIV/AIDS. All patients with a new diagnosis of HIV should be screened for TB, as well as patients with risk factors for HIV who have not been diagnosed with the disease.

Case Study

A 29 year-old, asymptomatic, male recently tested positive for HIV after exposure to the virus from unprotected sex. He has no pertinent medical history did move to the United States from rural Mexico with his family at age 10. He does not smoke or use alcohol, and has no history of IVDU. At a follow up appointment, labs were ordered and his CD4 count was found to be 350 with a viral load of 12,000. Additionally, his TB blood test taken during initial labs resulted as positive. 

While this patient is not experiencing symptoms associated with active TB infection at this time, his positive QuantiFERON-TB Gold test indicates he was infected with M. tuberculosis in the past and likely has LTBI. HIV, as well as any other potentially immunocompromising condition, significantly increases the likelihood of LTBI transitioning to disseminated TB.

Prevention

Most people in the US will not be exposed to TB in their daily lives. Incarceration, prolonged hospitalization, healthcare workers, homelessness, and international travel, however, can increase a person’s risk and certain precautions should be employed when staying in a high risk area. If a person is regularly in close contact with someone who has a known, active TB infection, environmental precautions should be used (like N95 masks or PAPRs).

The BCG (Bacille Calmette-Guerin) vaccine has been developed for high risk TB exposed populations but is not used often in the United States. Current reasons for administration in the US include:

• A child with a negative TB test who is regularly exposed to an adult who is untreated for some reason or has an infection caused by a strain resistant to isoniazid and rifampin.
• A healthcare worker who is frequently exposed to patients that are infected with resistant strains, especially if previous healthcare workers have become infected after exposure and infection control precautions have been unsuccessful.

Many people who were not born in the US have received the BCG Vaccine in their lifetime. A history of vaccination can lead to false positive results when screening with the TB skin test, but would not test positive with the TB blood test (IGRA).

There is no way to know that someone has a LTBI without screening and chest Xray or sputum sample as this is an asymptomatic period of the disease. Therefore, the main form of prevention of TB disease is frequent and appropriate screening. Primary care physicians must be astute in their assessment of risk factors that a patient may have experienced in their life to know who to screen. A positive skin and blood test indicates a person has been infected with Mycobacterium tuberculosis. Chest Xray or sputum sample is required to determine if the person has LTBI or active infection.

Resources

Are You At Risk for TB?
TB Risk Screening tool from TB Free California.

Animated video demonstrating the transmission and pathogenesis of tuberculosis (TB). This video is used by CDC’s Division of Tuberculosis Elimination (DTBE) as part of the Interactive Core Curriculum: What the Clinician Should Know web-based training.