Tuberculosis and TB Testing Update

The Fraser Valley Travel Clinic offers TB testing for anyone.  Travellers benefit from having TB testing prior to and after returning from travel overseas. TB testing done this way can allow doctors to identify people who have been exposed to TB before symptoms occur. These individuals may be offered effective post-exposure treatment to prevent symptomatic TB.

Tuberculosis Update:

TB kills more than 2 million people per year.  TB is becoming more dangerous due to deterioration of health services in various world regions, the spread of HIV/AIDS and the emergence of multi drug-resistant TB.  Within the next 20 years, 1 billion new cases of TB will occur world-wide, 200 million will get sick and 35 million people will die from TB.

Infection and Transmission:

TB is contagious and is spread through the air like the common cold. Only people who are sick with pulmonary TB are infectious. When infectious people cough, sneeze, talk or spit they propel TB germs known as bacilli into the air.  Only a small number of these germs needs to be inhaled by someone else to get infected. Left untreated, each person with active TB will infect on average 10 to 15 people every year.  Not everyone infected with TB gets sick.  The immune system "walls off" the TB germs with a thick waxy coat. TB this way can lie dormant for years.  When someone's immune system weakens for any reason, the chances of the TB becoming "active" increases.

TB Stats:

World Infection Rate:  1 new case per person per second

This means 1% of the entire world's population become newly infected every year.

1 out of 3 humans on planet earth are infected with TB right now!


Until 50 years ago, there were no drugs to treat TB. Now the majority of TB cases can be treated effectively. Treatment however takes a minimum of 6 months and a combination of three drugs are used.  However, because of poor compliance, strains of TB resistant to all major anti-TB drugs have emerged. Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their drugs regularly for the required period because they start to feel better, inconsistent prescribing habits by health professionals or unreliable drug supply causing interruption of treatment.  Poorly supervised or incomplete treatment of TB is worse than no treatment at all. That is why there are extensive clinical practice guidelines physicians must follow.  People who develop multi drug-resistant TB, when infecting others, will also infect them with the same drug resistant strain. While drug-resistant TB is treatable, it requires extensive chemotherapy (up to two years of treatment) that is often prohibitively costly (often more than 100 times the cost of standard treatments) and often has more side-effects.

2-Step TB Testing (Taken from the Canadian Tuberculsosis Standards and Wikipedia):

A two-step  TB Test (TST) should be performed if subsequent TSTs will be conducted at regular intervals or following exposure to an infectious TB case, for instance among health care or correctional service workers . This is to reduce the chance of a false-positive TST conversion when the TST is repeated.

This concept is well explained on Wikipedia:

Some people who were previously infected with TB may have a negative reaction when tested years after infection, as the immune system response may gradually wane. This initial skin test, though negative, may stimulate (boost) the body's ability to react to tuberculin in future tests. Thus, a positive reaction to a subsequent test may be misinterpreted as a new infection, when in fact it is the result of the boosted reaction to an old infection.

Use two-step testing for initial skin testing of adults who will be retested periodically (e.g., health care workers). This ensures that any future positive tests can be interpreted as being caused by a new infection, rather than simply a reaction to an old infection.

Return to have first test read 4872 hours after injection

If first test is positive, consider the person infected.

If first test is negative, give second test 13 weeks after first injection

Return to have second test read 4872 hours after injection

If second test is positive, consider person previously infected

If second test is negative, consider person uninfected

A person who is diagnosed as "infected" on two-step testing is called a "tuberculin converter". The US recommendation, that prior BCG-vaccination be ignored, results in almost universal false diagnosis of tuberculosis infection in people who have had BCG (mostly foreign nationals).

TB testing is our most effective tool in the fight against TB.