Prof evaluates tuberculosis testing in prisons

Study finds blood testing to be more accurate than skin testing in identifying tuberculosis among Canadian inmates

Dr. Wendy Wobeser says skin tests for latent tuberculosis can be inaccurate.
Dr. Wendy Wobeser says skin tests for latent tuberculosis can be inaccurate.

There’s a more efficient way to treat tuberculosis in Canadian prisons, according to a review conducted by a Queen’s professor.

Dr. Wendy Wobeser, a medical professor and infectious diseases specialist, was invited by Correctional Service Canada (CSC) to evaluate the effectiveness of Interferon Gamma Release Assays (IGRA) blood testing in identifying latent tuberculosis (TB) among inmates.

Correctional Services currently uses skin testing as the standard method to check for TB.

According to Wobeser, nine per cent of Canadian inmates have latent TB infections, compared to three per cent of the general Canadian population.

People with latent TB aren’t infectious and don’t exhibit symptoms of the airborne disease.

If untreated, latent TB can develop into active TB over time. Symptoms of this typically include fatigue, chills and unexplained weight loss. Wobeser said TB is an important concern in prison systems around the world.

“CSC already has a screening program in place for tuberculosis,” Wobeser said.

“But we wanted to see what the impact of using [IGRA blood tests] would be in terms of increasing the efficiency and effectiveness of the program.”

Wobeser said skin tests take 48 to 72 hours and require two separate appointments to complete. IGRA blood tests get taken directly to the laboratory in order to increase the odds of accuracy.

Skin tests are problematic because they can’t always differentiate between a TB infection and Bacille Calmette Guerin (BCG), a vaccine used to prevent tuberculosis.

Results from Wobeser’s study show that the number of infected inmates is far less than the number indicated by the skin tests.

Wobeser worked with Paxton Back, MD ’13 and medical resident Ilan Schwartz to look at 100 inmates from Kingston’s Millhaven Institute, a maximum security prison for adult men. The 100 inmates had tested positive for latent tuberculosis infection through skin test methods.

They collectively determined that only 30 inmates tested positive under IGRA blood testing.

According to the findings, 70 of 100 inmates would have been put on twice-weekly treatment plan for nine months to cure infections they didn’t have. Treatment requires visits to healthcare clinics.

Though skin tests involve putting the burden of treatment on people who might not even have TB, there’s a small chance that IGRA tests could miss someone who’s TB positive, Wobeser said.

IGRA tests have only been used to confirm infections found in skin tests, adding that it would require further study to “expand beyond that application.”

“In the future, there is potential that it will replace the skin test altogether,” she said. “But I’m not advocating that at this time.”

Correctional Services director general of clinical services Kate Jackson said Wobeser’s review is just one of many factors CSC will take into account when determining its policy on TB.

The CSC organized the Wobeser’s review with the aim of introducing the IGRA test into their routine TB screening.

But Jackson said they can’t fully implement Wobeser’s findings because they aren’t definitive.

“We have to take into consideration more than just this one study,” she said. “Even the results of the test don’t suggest that you only use IGRA.”

Jackson said the CSC is also hesitant to integrate IGRA testing because it isn’t available everywhere in Canada and the CSC wants nation-wide consistency.

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