McGill researchers pursue faster, better TB test

Front-line health workers in developing settings stand to benefit

Michael Bourguignon | Tuberculosis is a rampant occupational hazard among health-care workers in poorer countries and it's a problem the world can ill afford to ignore, say two McGill researchers who are investigating a new and improved method of diagnosing the disease.

Dr. Madhukar Pai, above, is working with Dr. Dick Menzies of the Montreal Chest Institute to investigate the use of a modern, more reliable diagnostic test for tuberculosis.

Dick Menzies, director of the respiratory epidemiology unit at the Montreal Chest Institute, and Madhukar Pai, a researcher in the Department of Epidemiology, Biostatistics and Occupational Health, have discovered that more than half of all health-care workers in the developing world are carriers of the tuberculosis virus.

Their review of 51 published studies revealed that 54 percent of health-care workers in those countries have latent tuberculosis — meaning they carry the virus responsible for the disease but have no symptoms. The findings were published in the December edition of the Public Library of Science's PLoS Medicine journal.

"Hospitals, particularly in poor countries, have proven to be important sites of disease transmission because they are congregated environments," said Dr. Pai, citing the risk of patients infecting health-care workers who then infect members of the community at large. "Unknown cases are the ones that end up causing the biggest problem in terms of transmission. Someone sitting in an emergency room and coughing could have TB and not know it."

The study, co-authored by researchers in the Unites States and India, also indicates health-care workers are at greater risk of contracting tuberculosis because of their exposure to infected patients. Tuberculosis infects two billion people worldwide. The study examined the prevalence and risk factors of TB among health-care workers in India, South Africa, Peru and other developing countries.

"If you go to almost any poor country and talk to a doctor or a nurse, they've resigned themselves to the idea that they will eventually become infected with tuberculosis. In their minds, it's inevitable," said Dr. Pai.

Compounding the problem is the outdated mode of testing currently used to diagnose the disease. The tuberculine skin test, which involves injecting tuberculosis-related antigens into the patient and gauging the body's reaction over a period of time, is a century-old diagnostic tool with known limitations in accuracy and reliability.

Bringing testing into the new millennium

Dr. Pai, Dr. Menzies and their team have just received a three-year, $250,000 grant from the Canadian Institutes of Health Research to investigate the feasibility of replacing the skin test with a newer blood test that is considered simpler to administer and more reliable.

Although the new test has been developed over the past 10 years, "we are concerned that we don't have all the information we need about it," said Dr. Pai. "At the end of the study, we hope to come up with definitive data so Canadian hospitals and health agencies can finally abandon the century-old skin test." The study will involve 450 health-care workers from the McGill University Hospital Centre and 675 from the Mahatma Gandhi Institute in Sevagram, India.

One of the advantages of a blood test is that it's "a one-off test," said Dr. Menzies, who has been a consultant to national TB programs in the Dominican Republic, Guyana and Ecuador, and whose multi-disciplinary clinical service at the Montreal Chest Institute works closely with Immigration Canada to screen newly arrived immigrants at high risk for TB. "With the skin test, the patient has to come back after a few days to get the reading, and there could be infections or other adverse reactions."

Even with improved testing, tuberculosis will continue to be a global concern that requires a global solution, the researchers say.

"We live in a global community where we're all connected. No country can afford to say that this is not our problem," said Dr. Pai.