By Carol A. Kemper, MD, FIDSA
Medical Director, Infection Prevention, El Camino Hospital, Palo Alto Medical Foundation
SOURCE: Ku JH, Fischer H, Qian LX, et al. Latent tuberculosis infection testing practices in a large U.S. integrated healthcare system. Clin Infect Dis 2024;78:1304-1312.
Screening for latent tuberculosis (TB) infection (LTBI) in persons at risk is woefully lax in our country — and yet, reactivation TB is such an eminently preventable disease.
I recently saw in consultation an 80-plus-year-old chronically ill Filipino woman with suspected active pulmonary TB. She had received regular medical care at a large multispecialty clinic and at a nearby tertiary care facility for more than 20 years — and she had never been screened for TB.
Data for 2023 for our county in Northern California indicate that a whopping 97% of cases of active TB occurred in those born outside the United States, although 64% of them had lived in the United States for more than 10 years. All of these individuals were born in either the Philippines, Vietnam, India, Mexico, or China — only 3% of active TB cases in our county were born in the United States. The mortality rate for patients receiving TB therapy was 8%, up from 6% in 2022, many of whom were elderly, chronically ill, and/or immunosuppressed.
The Kaiser Permanente (KP) database provided an excellent opportunity for these authors to examine risk factors for TB and rates of testing for LTBI. From 2008 to 2019, available data on risk factors for TB and testing for LTBI were collected in adults ≥ 18 years of age who had been members of the KP system for two or more years.
The authors also determined the number tested for LTBI who specifically met California Department of Public Health (CDPH) criteria for testing — including birth in or travel greater than one month to a country endemic for TB, exposure to active TB, and immunosuppression. Patients with a history of active TB were excluded.
During this 12-year surveillance period, nearly 4 million adults receiving care at Kaiser for two or more years and without a history of active TB were eligible for LTBI testing. Of these, 706,367 (18%) had been tested, including 82.6% with tuberculin skin test only, 11.4% with interferon gamma release assay (IGRA) only, and 6% with both purified-protein derivative and IGRA.
Of these, two-thirds were female, 45% were younger (ages 18-35 years), 22% were born in a country endemic for TB, and 5.7% received immunosuppressive therapy or were immunocompromised (IST/IC). Among those who were never tested for LTBI, 30% were foreign born and 1.4% received IST or were IC.
This means that among those 1,087,237 persons who were born in a country endemic for TB, only 14% were screened for LTBI, and of those 183,741 receiving IST, only 48% were screened for LTBI.
Among those who met CDPH criteria for screening, rates of LTBI positivity were 34% for close contacts to active TB, 22% for those born in a country endemic for TB, 18% for a history of travel greater than one month to a country endemic for TB, and 8% of those prior to first receiving immune suppressive therapy.
Thus, screening for LTBI was less likely to occur if you were born outside the United States in a country endemic for TB. It was more likely to occur in women, younger persons (ages 18-35 years), those with higher household income, those with a history of travel and/or exposure to TB, people with end-stage renal disease (where screening usually is a requirement for hemodialysis), and those with human immunodeficiency virus infection.
Based on these data, an estimated 935,000 people in Southern California met criteria for LTBI screening between 2008 and 2019 and were not screened, at least through the Kaiser system. Suppose 22% of them tested positive for LTBI, and the lifetime rate of reactivation TB is 5% to 10%. That suggests that 10,285 to 20,570 cases of active TB could occur in this group over their lifetimes. This figure completely aligns with the 9,615 cases of active TB reported in California in 2023.
While TB generally is no longer considered a fatal disease in the United States, 8% of those with active TB in our county died last year on therapy.
What is saddest about these data is that three-fourths of those diagnosed with TB are 65 years of age or older, many with chronic medical conditions, and often are the most difficult to treat for active TB. They could easily have received preventive therapy — if their primary care doctors had thought about it. Alarm bells should be ringing.
Screening for latent tuberculosis (TB) infection in persons at risk is woefully lax in our country — and yet, reactivation TB is such an eminently preventable disease.
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