Tuberculosis (TB) is an airborne disease caused by Mycobacterium tuberculosis. Although it typically infects the lungs, it can attack other organs including the spine, brain, and kidney (1). TB infections take on one of two forms; latent or active. In the latent form, TB bacteria in the body is suppressed by the immune system. Hence it is asymptomatic and incapable of spreading between individuals. However, infected individuals can progress to active TB disease months to years later (2). In the active form, it is symptomatic and highly contagious. Both forms are detectable by routine TB monitoring and with a properly executed monitoring programs outbreaks can be mitigated. Healthcare employees are a high-risk population that is susceptible to TB because of the exposure to unsuspected or undiagnosed TB infected patients. (3). In 1994, Centers for Disease Control and Prevention (CDC) published guidelines on infection control policies and practices that are intended to reduce the risk of transmission of TB in healthcare facilities which was recently updated in 2019 (4). According to the new policy, annual TB testing of healthcare personnel is not recommended unless there is a known exposure or ongoing transmission at a healthcare facility. However, any existing employees with untreated latent TB infection should receive an annual TB testing. Additionally, it is highly recommended to consider using annual TB screening for specific groups at increased occupational risk for TB exposure (e.g., pulmonologists or respiratory therapists) or in particular settings, if a transmission has occurred in the past (e.g., emergency departments). Prior studies have reported that strict maintenance of the CDC policy has helped in reducing the infection of TB among healthcare workers (3, 5). Clearly, the TB testing policy adopted by a health system affects the program maintenance cost.
Currently, two widely adopted testing procedures exist; the first and oldest test is the Mantoux tuberculin skin test (TST). This test involves an injection of 0.1 mL of liquid containing 5 tuberculin units into the top layer of the forearm. Once injected, the test is read 48–72 hours later by a trained clinician, usually a registered nurse (RN), and the outcome is interpreted using a ruler to measure the diameter of possible induration of the area. If no induration occurs, then the test is reported negative; whereas if the diameter of the indurated area exceeds 10 mm, then the test is considered positive. In the case of a negative test result, the second step of testing is administered, which is similar to the first step. Whereas, in case of positive reading, further testing is performed to evaluate for TB disease, which includes a physical examination and an X-Ray. If for any reason the patient does not return in the stipulated timeframe to have the test read, the testing must be repeated from the first step. Although used predominantly, TSTs are not perfect and various factors may produce a false-positive result. Infection with nontuberculous mycobacterium is one example. In the case of patients that have previously received the Bacille Calmette-Guerin (BCG) vaccine, TSTs could record a false-positive result (6). Finally, clinician interpretation of the TST is subjective and requires manual measurement that may influence reporting, especially in borderline cases. Despite being a 2 step, 2-day process with limitations, TSTs are still adopted by the majority of health systems as the preferred method of testing among employees.
The other testing procedure are whole-blood Interferon-Gamma Release Assays (IGRAs). IGRAs are quicker and do not require multiple visits to the facility. Instead of injecting a patient and waiting 48–72 hours for an immune response, 1 to 3 vials of blood are drawn from the patient and sent to the lab for automated testing. Two IGRAs are available in the US: the QuantiFERON-TB Gold In-Tube test (QFT-GIT) and the T-SPOT.TB test (T-Spot). QFT-GIT test involves the collection of three tubes of blood (a positive control, a negative control, and a test) that are sent to a laboratory, and they are tested within 16 hours of collection. In the lab the concentration of interferon gamma (IFN-g) is measured. The T-Spot test differs from the QFT-GIT in that it only requires one tube of blood to be drawn and measures the number of IFN-g producing cells. IGRAs have a few advantages over the TSTs: they require only a single visit for a blood draw, results can be available in less than 24 hours, and prior BCG vaccination does not cause a false-positive IGRA test result. However, the IGRAs are costlier than the TSTs. On average IGRA supply costs are $30–38 higher than a TST (7). Additionally, the blood testing must be completed within a time frame and some facilities do not have the in-house capability to test the sample. Both TST and IGRA tests require the patient’s skin to be punctured with a needle.
Under the new CDC mandate, the cost incurred by a health system for maintaining a TB testing will reduce as it does not require all existing employees to undergo annual TB testing. However, it is still essential to conduct a cost analysis as TB screening is a time-consuming process and results in loss of employee's productive working hours. While prior research has focused on comparing the effectiveness of a TST to IGRA for detecting TB, very few have investigated the overall system costs of these processes (8, 9). For example, a TST requires a minimum of three (with the potential for five) visits to the facility, compared to a single visit with IGRAs. Hence it is crucial to identify which screening process should be recommended for an employee who requires testing based on the direct cost and indirect costs of testing.
The studies that have evaluated the cost of TB testing for a health system have considered only the direct cost associated with the testing procedure (10). TB testing incurs a direct cost like all laboratory testing; these direct costs include the material cost, procedure cost, and resource cost. However, the healthcare organization will incur an additional indirect cost resulting from an employee's absence from the workplace during testing. A microscopic view indicates that the indirect cost depends on four factors: time taken to travel to the facility, the time spent in the facility, missed employee work hours and the hourly wage or salary of the employee. Although a few studies have considered the indirect costs, to our knowledge, none of the studies have examined all the indirect costs discussed above (11).
Additionally, most of the cost comparison studies to date have focused on analyzing the cost of maintaining a TST and IGRA separately (12). Hence the conclusion was focused on recommending which specific TB testing method should a health system adopt. However, a more integrated approach of understanding how to blend the two testing methods may identify the ideal maintenance costs for the required TB testing program. This study was designed to explore whether a switching point exists in the selection of the most economical TB testing method in a large healthcare system.