Latent TB: The case for vigilance

The US Preventive Services Task Force (USPSTF) recently released draft recommendations on screening for tuberculosis (TB).¹ The USPSTF continues to recommend screening for latent TB infection (LTBI) in those at high risk.

Why is this important? Up to one-quarter of the world’s population has been infected with TB, according to World Health Organization (WHO) estimates. In 2021, active TB was diagnosed in 10.6 million people, and it caused 1.6 million deaths.² Worldwide, TB is still a major cause of mortality: It is the 13th leading cause of death and is the leading cause of infectious disease mortality in non-COVID years.

Although the rate of active TB in the United States has been declining for decades (from 30.7/100,000 in 1960 to 2.4/100,000 in 2021), 7882 cases were reported in 2021, and an estimated 13 million people in the United States have LTBI.³ If not treated, 5% to 10% of LTBI cases will progress to active TB. This risk is higher in those with certain medical conditions.³ People born outside the United States currently account for 71.4% of reported TB cases in the United States.³

To reduce the morbidity and mortality of TB, the Centers for Disease Control and Prevention (CDC), WHO, and USPSTF all recommend screening for and treating LTBI. An effective approach to TB control also includes early detection and completion of treatment for active TB, as well as testing contacts of active TB cases.

Who should be screened? Those at high risk for LTBI include those who were born in, or who have resided in, countries with high rates of TB (eg, Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia); those who have lived in a correctional facility or homeless shelter; household and other close contacts of active TB cases; and health care workers who provide care to patients with TB.

Some chronic medical conditions can increase risk for progression to active TB in those with LTBI. Patients who should be tested for LTBI as part of their routine care include those who are HIV positive; are receiving immunosuppressive therapy (chemotherapy, biological immune suppressants); have received an organ transplant; have silicosis; use illicit injected drugs; and/or have had a gastrectomy or jejunoileal bypass.

In addition, local communities may have populations or geographic regions in which TB rates are high. Family physicians can obtain this information from their state or local health departments.

There are 2 screening tests for LTBI: TB blood tests (interferon-gamma release assays [IGRAs]) and the Mantoux tuberculin skin test (TST). Two TB blood tests are available in the United States: QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB test (T-Spot).

There are advantages and disadvantages to both types of tests. A TST requires accurate administration and interpretation and 2 clinic visits, 48 to 72 hours apart. The cutoff on a positive test (5, 10, or 15 mm) depends on the patient’s age and risk.⁴ An IGRA should be processed within 8 to 32 hours and is more expensive. However, a major advantage is that it is more specific, because it is unaffected by previous vaccination with bacille Calmette-Guérin or by most nontuberculous mycobacteria infections.

To rule out active TB ... If a TB screening test is positive, the recommended work-up is to ask about TB symptoms and perform a chest x-ray to rule out active pulmonary TB. Sputum collection for acid-fast smear and culture should be ordered for anyone with a suspicious chest x-ray, respiratory symptoms consistent with TB, or HIV infection.

Treatment for LTBI markedly reduces the risk for active TB. There are 4 options:

• Isoniazid (INH) plus rifapentine (RPT) once per week for 3 months.
• Rifampin (RIF) daily for 4 months.
• INH plus RIF daily for 3 months.
• INH daily for 6 or 9 months.

Details about the variables to consider in choosing a regimen are described on the CDC website.^4,5

Know your resources. Local and state public health departments should have TB control programs and are sources of information on TB diagnosis and treatment; they also can assist with follow-up of TB contacts.⁶ Although LTBI is a reportable condition only in young children, any suspicion of community spread of active TB should be reported to the public health department.

The US Preventive Services Task Force (USPSTF) recently released draft recommendations on screening for tuberculosis (TB).¹ The USPSTF continues to recommend screening for latent TB infection (LTBI) in those at high risk.

Why is this important? Up to one-quarter of the world’s population has been infected with TB, according to World Health Organization (WHO) estimates. In 2021, active TB was diagnosed in 10.6 million people, and it caused 1.6 million deaths.² Worldwide, TB is still a major cause of mortality: It is the 13th leading cause of death and is the leading cause of infectious disease mortality in non-COVID years.

Although the rate of active TB in the United States has been declining for decades (from 30.7/100,000 in 1960 to 2.4/100,000 in 2021), 7882 cases were reported in 2021, and an estimated 13 million people in the United States have LTBI.³ If not treated, 5% to 10% of LTBI cases will progress to active TB. This risk is higher in those with certain medical conditions.³ People born outside the United States currently account for 71.4% of reported TB cases in the United States.³

To reduce the morbidity and mortality of TB, the Centers for Disease Control and Prevention (CDC), WHO, and USPSTF all recommend screening for and treating LTBI. An effective approach to TB control also includes early detection and completion of treatment for active TB, as well as testing contacts of active TB cases.

Who should be screened? Those at high risk for LTBI include those who were born in, or who have resided in, countries with high rates of TB (eg, Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia); those who have lived in a correctional facility or homeless shelter; household and other close contacts of active TB cases; and health care workers who provide care to patients with TB.

Some chronic medical conditions can increase risk for progression to active TB in those with LTBI. Patients who should be tested for LTBI as part of their routine care include those who are HIV positive; are receiving immunosuppressive therapy (chemotherapy, biological immune suppressants); have received an organ transplant; have silicosis; use illicit injected drugs; and/or have had a gastrectomy or jejunoileal bypass.

In addition, local communities may have populations or geographic regions in which TB rates are high. Family physicians can obtain this information from their state or local health departments.

There are 2 screening tests for LTBI: TB blood tests (interferon-gamma release assays [IGRAs]) and the Mantoux tuberculin skin test (TST). Two TB blood tests are available in the United States: QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB test (T-Spot).

There are advantages and disadvantages to both types of tests. A TST requires accurate administration and interpretation and 2 clinic visits, 48 to 72 hours apart. The cutoff on a positive test (5, 10, or 15 mm) depends on the patient’s age and risk.⁴ An IGRA should be processed within 8 to 32 hours and is more expensive. However, a major advantage is that it is more specific, because it is unaffected by previous vaccination with bacille Calmette-Guérin or by most nontuberculous mycobacteria infections.

To rule out active TB ... If a TB screening test is positive, the recommended work-up is to ask about TB symptoms and perform a chest x-ray to rule out active pulmonary TB. Sputum collection for acid-fast smear and culture should be ordered for anyone with a suspicious chest x-ray, respiratory symptoms consistent with TB, or HIV infection.

Treatment for LTBI markedly reduces the risk for active TB. There are 4 options:

• Isoniazid (INH) plus rifapentine (RPT) once per week for 3 months.
• Rifampin (RIF) daily for 4 months.
• INH plus RIF daily for 3 months.
• INH daily for 6 or 9 months.

Details about the variables to consider in choosing a regimen are described on the CDC website.^4,5

Know your resources. Local and state public health departments should have TB control programs and are sources of information on TB diagnosis and treatment; they also can assist with follow-up of TB contacts.⁶ Although LTBI is a reportable condition only in young children, any suspicion of community spread of active TB should be reported to the public health department.

The US Preventive Services Task Force (USPSTF) recently released draft recommendations on screening for tuberculosis (TB).¹ The USPSTF continues to recommend screening for latent TB infection (LTBI) in those at high risk.

Why is this important? Up to one-quarter of the world’s population has been infected with TB, according to World Health Organization (WHO) estimates. In 2021, active TB was diagnosed in 10.6 million people, and it caused 1.6 million deaths.² Worldwide, TB is still a major cause of mortality: It is the 13th leading cause of death and is the leading cause of infectious disease mortality in non-COVID years.

Although the rate of active TB in the United States has been declining for decades (from 30.7/100,000 in 1960 to 2.4/100,000 in 2021), 7882 cases were reported in 2021, and an estimated 13 million people in the United States have LTBI.³ If not treated, 5% to 10% of LTBI cases will progress to active TB. This risk is higher in those with certain medical conditions.³ People born outside the United States currently account for 71.4% of reported TB cases in the United States.³

To reduce the morbidity and mortality of TB, the Centers for Disease Control and Prevention (CDC), WHO, and USPSTF all recommend screening for and treating LTBI. An effective approach to TB control also includes early detection and completion of treatment for active TB, as well as testing contacts of active TB cases.

Who should be screened? Those at high risk for LTBI include those who were born in, or who have resided in, countries with high rates of TB (eg, Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia); those who have lived in a correctional facility or homeless shelter; household and other close contacts of active TB cases; and health care workers who provide care to patients with TB.

Some chronic medical conditions can increase risk for progression to active TB in those with LTBI. Patients who should be tested for LTBI as part of their routine care include those who are HIV positive; are receiving immunosuppressive therapy (chemotherapy, biological immune suppressants); have received an organ transplant; have silicosis; use illicit injected drugs; and/or have had a gastrectomy or jejunoileal bypass.

In addition, local communities may have populations or geographic regions in which TB rates are high. Family physicians can obtain this information from their state or local health departments.

There are 2 screening tests for LTBI: TB blood tests (interferon-gamma release assays [IGRAs]) and the Mantoux tuberculin skin test (TST). Two TB blood tests are available in the United States: QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB test (T-Spot).

There are advantages and disadvantages to both types of tests. A TST requires accurate administration and interpretation and 2 clinic visits, 48 to 72 hours apart. The cutoff on a positive test (5, 10, or 15 mm) depends on the patient’s age and risk.⁴ An IGRA should be processed within 8 to 32 hours and is more expensive. However, a major advantage is that it is more specific, because it is unaffected by previous vaccination with bacille Calmette-Guérin or by most nontuberculous mycobacteria infections.

To rule out active TB ... If a TB screening test is positive, the recommended work-up is to ask about TB symptoms and perform a chest x-ray to rule out active pulmonary TB. Sputum collection for acid-fast smear and culture should be ordered for anyone with a suspicious chest x-ray, respiratory symptoms consistent with TB, or HIV infection.

Treatment for LTBI markedly reduces the risk for active TB. There are 4 options:

• Isoniazid (INH) plus rifapentine (RPT) once per week for 3 months.
• Rifampin (RIF) daily for 4 months.
• INH plus RIF daily for 3 months.
• INH daily for 6 or 9 months.

Details about the variables to consider in choosing a regimen are described on the CDC website.^4,5

Know your resources. Local and state public health departments should have TB control programs and are sources of information on TB diagnosis and treatment; they also can assist with follow-up of TB contacts.⁶ Although LTBI is a reportable condition only in young children, any suspicion of community spread of active TB should be reported to the public health department.