Tuberculosis screening programme using the QuantiFERON®-TB Gold test and chest computed tomography for healthcare workers accidentally exposed to patients with tuberculosis
Introduction
Healthcare-associated transmission of tuberculosis (TB) is a serious issue.1, 2 Healthcare workers (HCWs) have been reported to show a high incidence of TB, which was probably transmitted by accidental exposure to patients with TB.3, 4, 5, 6 In turn, this creates a risk for the patients receiving care from these HCWs. Periodical or pre-employment screenings of all HCWs, in addition to as-needed screenings of HCWs accidentally exposed to patients with TB, are important.3
Tuberculosis infection may be active or latent (LTBI); the former presents symptoms or other indications of disease, whereas the latter is silent. The diagnosis of active TB is straightforward: signs and symptoms, or chest radiograph findings are confirmed by culture or polymerase chain reaction tests. However, the diagnosis of LTBI is not as simple. This is suspected as a result of an enhanced reaction to the tuberculin skin test (TST), but there is no procedure for confirming diagnosis. The classification of TB determines the regimen of the treatment required. Active disease is treated with multiple antituberculosis drugs, whereas LTBI is treated with isoniazid (INH) monotherapy.
The treatment scheme stated above has been widely acknowledged and used. Nevertheless, there is a risk of undertreatment due to insufficient sensitivity of chest radiographs for detecting active TB; patients may be diagnosed as having LTBI and treated only by INH. There is also a risk of overtreatment due to the insufficient specificity of TST for detecting LTBI; a positive TST can be either due to bacille Calmette–Guérin (BCG) vaccination or infection with non-tuberculous mycobacteria. As a result, patients who have not been exposed to TB may be treated by INH. This is especially relevant to the countries with a high BCG vaccination rate such as Japan (96.5%).7 The addition of chest computed tomography (CT) will increase the sensitivity of TB disease detection, and replacement of the TST with the QuantiFERON®-TB Gold (QFT-G) will increase the specificity in detecting LTBI, thus enabling more precise treatment. We therefore integrated chest CTs and the QFT-G test into our TB screening programme for HCWs. First, contacts were tested using the QFT-G test; those who tested negative were excluded. Positive contacts were investigated by CT and classified as having active, latent or old TB. Finally, those with active TB were treated with a multidrug regimen [INH, rifampicin (REF), ethambutol (EB), and pyrazinamide (PZA)], whereas those with LTBI were treated with INH monotherapy. We retrospectively investigated the utility, safety, and feasibility of this programme that has been conducted at the Saitama Medical University Hospital (SMUH) for five years.
Section snippets
Infection Control Subcommittee for Tuberculosis (ICST)
The SMUH is a 712-bed general hospital for patients with acute or subacute illnesses. It does not have a ward dedicated to patients with TB. The ICST was organised in April 2005 by members of the Infection Control Team with experts on TB control, and has been responsible for the TB screening programme.
Traced contacts
The TB screening programme has been active from April 2005 to the present. The programme is conducted by the ICST: once every two years, targeting HCWs who have worked in an infectious disease
TB screening programme
Between April 2005 and April 2010, 11 patients who had not been diagnosed with active TB on admission were later found to have the disease. The ICST conducted the TB screening programme for HCWs in the infectious disease ward twice, and an additional 11 times for HCWs who could have had accidental exposures (Table I). A total of 512 close contacts and high risk contacts underwent screening; 34 (6.64%) had a positive QFT-G test, and 478 (93.36%) were negative. Of the 34 QFT-G positives, four had
Discussion
The combination of the QFT-G test and chest CT is widely used in the clinical practice of TB diagnosis. However, there are no reported TB screening procedures that integrate both the QFT-G and chest CT in the healthcare setting. This prompted us to design the procedures reported in the current study.
The QFT-G test has greater specificity than the TST in detecting current or past history of exposure to M. tuberculosis; thus, we obtained chest CT scans of all contacts with positive QFT-G test
Conflict of interest statement
None declared.
Funding source
This study was performed using research funds of the Saitama Medical University.
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