PUBLIC HEALTH

Public Health Update

Addressing Latent TB Infections to Eliminate TB

LETICIA GARCIA CASTILLO, MSN, RN, PHN MAGGIE PARK, MD

Background

Tuberculosis (TB) has affected humans for centuries, and yet it is still one of the leading causes of death due to infectious disease in the world. TB is caused by the bacterium Mycobacterium tuberculosis. Infection occurs when a person inhales droplet nuclei containing tubercle bacilli that reach the alveoli of the lungs. There, the bacilli multiply and may spread through the bloodstream to more distant tissues and organs. In some people, the tubercle bacilli overcome the immune system and multiply further, resulting in progression to active TB disease. In most people, macrophages ingest and encapsulate the bacilli forming a granuloma, that keeps the bacilli contained and under control. At this point, a latent TB infection (LTBI) has been established and may be detected by a tuberculin skin test or an interferon-gamma release assay (IGRA).

Persons with LTBI are infected with M.tuberculosis, but they do not have TB disease. They usually have a positive TST or IGRA, but they have a normal chest x-ray and are not symptomatic nor infectious. Individuals with LTBI and no risk factors have a 5%-10% lifetime risk of progressing to active disease. Risk factors, such as immunosuppression or diabetes, significantly increase that risk of progression. A person can live with LTBI for years or decades before it progresses to active disease.

LTBI is the primary cause of TB disease in California. In 2021, California reported 1,750 new active TB cases. Of those, 87% were from LTBI progressing to active disease, 10% from recent transmission and 3% from importation (being sick at arrival). It is estimated that more than 2 million Californians have LTBI. Of those, only an estimated 20% are aware of the diagnosis and only 12% get treated for LTBI.

LTBI treatment stops TB infection from progressing to disease. It is also much less costly to test and treat an individual with LTBI than for TB disease. So why aren’t more people with LTBI getting treated? San Joaquin County Public Health Services (PHS) hopes to better understand the issue.

What PHS is doing

In 2021, San Joaquin County (SJC) reported 41 new active TB cases, a case rate of 5.2 per 100,000. The county TB rate has typically been slightly higher than the state rate. SJC also a history of large concurrent multiyear TB outbreaks. In 2020, SJC’s TB death rate was 17.4%, compared to 10.7% for California (figure 1).

Traditionally, PHS TB Control has focused on case management of active TB patients, contact investigations and outbreak management. In May of this year, the program started a new project focused on LTBI. Public health nurses and communicable disease investigators began making phone calls to SJC residents who had a positive IGRA in the past 12 months. There were 1900 positive IGRA lab reports received in 2021. The goal was to get a better idea

about the treatment status of these individuals and provide education to those that may have not started treatment.

To date, over 500 calls have been made and 367 clients have answered the call. Of those 367 clients, 204 (37%) had not started LTBI treatment (figure 2). Surprisingly, most of them stated that the reason they had not started treatment was because the ordering provider had not informed them of the positive results even though for many it had been several months since the test was completed. PHS provided these clients with education on TB and advised them to follow up with the ordering provider for treatment. Most clients stated they were interested in LTBI treatment and would follow up with their provider.

PHS is working closely with the CDPH TB Control Branch to conduct more outreach and education to our community providers. Addressing LTBI is a priority to disrupt TB transmission. We must find and treat LTBI to prevent progression to disease. Primary care providers, civil surgeons, and community health clinics play a key role in the elimination of TB because they often provide care to populations at risk.

Recommendations for Community Providers

PHS asks that community providers evaluate and treat LTBI using the following 4 steps:

Step 1: Identify patients at risk for TB infection. Use the California TB Risk Assessment to identify patients for LTBI testing. TB risk factors for infection include birth, travel, or residence in a country with an elevated TB rate, immunosuppression, and being a close contact to someone with infectious TB.

Step 2: Test patients for TB infection. An IGRA is preferred over TST for non-U.S.-born persons >2years old.

Step 3: Evaluate for active TB disease. If the IGRA is positive, evaluate for active disease with a TB symptom screen, physical exam, and chest x-ray. Do not treat for LTBI until TB disease is excluded.

Step 4: Treat for LTBI. Use a short-course LTBI treatment regimen whenever possible. Preferred short course regimens: Isoniazid and Rifapentine weekly x 12 weeks OR Rifampin daily x 4 months. If a rifamycin-based regimen is not an option (due to drug resistance or intolerance), use Isoniazid daily x 9 months.

Resources for Healthcare Providers

Latent Tuberculosis Infection Guidance for Preventing Tuberculosis in California https://ctca.org/wp-content/uploads/LTBI-Guidelines-62019-Revision-FINAL.pdf CDC Latent Tuberculosis Infection Resources https://www.cdc.gov/tb/publications/ltbi/ltbiresources.htm PHS no longer has a public health clinic and does not provide treatment.

For TB questions, call San Joaquin County TB Control at (209) 468-3828.

San Joaquin Medical Society 3031 W. March Lane, Suite 222W Stockton, California 95219-6568

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