Part II: TB screening prior to long term care admission: time to choose wisely

I’m happy that my initial post sparked a discussion about the existing policy across Ontario that every new patient admitted to long-term care has a chest x-ray done within 90 days of admission.

I was shown this study from 2013 in the Canadian Journal of Public Health that detailed a TB outbreak in an Ontario long-term care home from 2010-2011, which is believed to be the only published report of a TB outbreak in a long-term care home in Canada. I would encourage anyone with an interest in this topic to read the study as it is quite interesting.

The index case for the outbreak was a 40-year old health care worker who presented with symptoms in April 2010. She had previously had a negative TST in 2007. Three residents developed active TB, diagnosed in July 2010, October 2010 and January 2011, respectively.

There were a number of issues identified that may have contributed to the outbreak. Baseline TST results were only available for 40% of staff members, while 96.5% of residents had a documented TST. The TST in residents is of limited use, however, as prevalence of latent TB infection (LTBI) in residents >65 years old in long-term care facilities in Canada may approach 20-30%. The residents with active TB also presented with subtle changes of weight loss and chronic cough which likely delayed a prompt diagnosis.

The recommendations made following this outbreak included (among other recommendations): mandatory baseline and annual TST for staff and volunteers, and to suspect TB in any resident with fever, cough > 3 weeks, unexplained weight loss, hemoptysis, lack of appetite, or night sweats.

Both recommendations are completely reasonable, and would potentially serve to reduce the risk of a future outbreak.

But here’s the recommendation that is completely out of thin air: “Baseline posterior-anterior and lateral chest X-ray for new residents”. 

There was no suggestion from the case report that the 3 active TB residents may have had active TB at the time of admission that would have been picked up on chest x-ray. One of the residents most likely had LTBI that activated at some unknown time. Given that 20-30% of the residents have LTBI, we cannot predict which of those patients will go on to develop active TB, nor can we reasonably or safely treat all of the LTBI patients with INH (recall from the case report that one of the active TB patients died of INH hepatitis).

As I mentioned in the first post, insisting on a chest x-ray of asymptomatic patients at the time of admission is completely arbitrary. If the patient is asymptomatic, they are just as likely to have asymptomatic active TB 6 months into their admission as they do at the time of admission. But we don’t insist on another chest x-ray at 3 months, 6 months, or 12 months. Wouldn’t their LTBI be just as likely activate at those time points?

I would argue that one of the most harmful aspects of the current screening program is that it creates a false sense of reassurance for physicians who may assume that their residents are low risk for TB because of their normal chest x-ray.

We need a change in the legislation and policy. Change the screening criteria to the following: at least one lifetime chest x-ray, and a completed set of screening questions to rule out any symptoms of TB at the time of admission. Part of the education around this change in protocol would raise awareness to physicians and staff about the high prevalence of LTBI, and the importance of being vigilant to look for subtle signs of active TB in residents. This heightened awareness would serve to reduce the risk of further outbreaks more than any chest x-ray screening program could ever achieve.

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