TORONTO (FRONTLINE MEDICAL NEWS) – U.S.-based pulmonary and infectious disease specialists prefer interferon-gamma release assays (IGRA) over tuberculin skin tests (TST) for the diagnosis of latent TB infection, but may not fully understand how to use and interpret the test results, according to survey results presented at the CHEST annual meeting.

Adam G. Green, MD, conducted the research while he was a fellow in pulmonology/critical care at Montefiore Medical Center in New York. Dr. Green told attendees that about one-third of the world’s population are infected with TB and about 15 million of those live in the United States. Two-thirds of U.S. cases are seen in foreign-born individuals and are clustered in four states—New, York, California, Florida, and Texas.

“Epidemiological models have indicated that in order to eliminate the threat of TB in the United States, it will require a strategy of targeting latent tuberculosis infection specifically among foreign-born individuals,” he said during his presentation. “This highlights the need for us practitioners on the front line to have sound knowledge of identification, screening, and management of latent TB infection, especially given the multiple modalities for diagnosis.”

Among 304 clinicians who responded to an invitation to an online questionnaire, 78% said they preferred to use IGRA over TST and 91% said they had a “good understanding” of how to use and interpret IGRA. However, when queried further on how to best use and interpret IGRAs according to current guidelines, their answers to 11 knowledge-based questions told a somewhat different story, said Dr. Green, who is an intensivist at Cooper University Health Care in Camden, N.J.

While 96% knew IGRAs are not helpful in monitoring response to TB treatment, 20% erroneously thought that a positive IGRA predicts latent TB infection reactivation in the future.

Most respondents correctly answered two “fundamental” questions on cross-reactivity of IGRAs with Mycobacterium avium complex and bacilli Calmette-Guérin (BCG) vaccination (84% and 96%, respectively). “While 80% sounds good, I think we’re talking about ID and pulmonary docs at the best institutions across the United States, so I would have expected much higher,” Dr. Green said.

Only one-third of respondents knew that the T-SPOT.TB test , an IGRA, had the highest sensitivity for identifying those with latent TB infection. And only about half were able to appropriately identify the need to initiate therapy for latent TB in a scenario in which the patient was at “high risk for latent tuberculosis with a positive tuberculin skin test and a negative interferon-gamma release assay.”

Fellows comprised 42.5% of respondents and the remainder were attendings of varying levels of seniority. About half of respondents were pulmonologists and the other half infectious disease specialists. The majority (91%) were practicing or training in university hospitals.

One major limitation of the study, said Dr. Green, is the low response rate. “I would have liked 3,000 responses,” he said, rather than just over 300.

To disseminate the questionnaire, he contacted pulmonary and infectious disease academic program directors and coordinators and asked them to forward the survey invitation to their full-time faculty and fellows. Dr. Green also acknowledged that his project missed those physicians not working in academic centers.

“I would like to think that the reason people didn’t do as well as I had hoped is because of the conflicting literature out there and using not necessarily the guidelines but rather their current knowledge on what was most recently published,” said Dr. Green. “But maybe there is a true misunderstanding.”

The authors reported there were no product or funding disclosures relevant to this study.


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