Conversion rates of an interferon-γ release assay and the tuberculin skin test in the serial monitoring of healthcare workers

Serial testing of healthcare workers for latent tuberculosis infection and long-term follow up for development of active tuberculosis

Background

Healthcare workers (HCWs) are at high risk of tuberculosis (TB) infection due to occupational exposure. It is important to diagnose TB infections in HCWs to prevent nosocomial transmission, particularly among immunocompromised patients.

Objective

The aim of this study was to analyze the rate of tuberculin skin test (TST) conversion and to assess the incidence of active TB after the latent TB infection screenings in high-risk HCWs.

Methods

This retrospective cohort study involved 458 HCWs in TB-related departments between 2009 and 2013. All HCWs underwent a TST and a chest radiograph annually; an interferon-γ release assay (IGRA) was performed on the TST-converted subjects. TST-converted and IGRA-positive HCWs underwent treatment for latent TB infection.

Results

The TST conversion rate was 30.3% from 2009 to 2011 in two years, 7.4% from 2011 to 2012, and 17.4% from 2012 to 2013. Eleven subjects out of 42 TST converters (26%) were IGRA-positive; two of them developed into active pulmonary TB during the follow-up period.

Conclusions

There was significant discordance between TST conversion and IGRA results in high-risk HCWs, and active TB developed only in TST-converted and IGRA-positive HCWs. Therefore, the combined use of TST and IGRA for periodic monitoring of TB infections in high-risk HCWs may be useful.

The Prevalence and Risk Factors of Latent Tuberculosis Infection among Health Care Workers Working in a Tertiary Hospital in South Korea

Background

The risk of tuberculosis (TB) infection among health care workers (HCWs) is higher than as noted among workers in the general population. The prevalence and risk factors of TB infection among HCWs were assessed in a tertiary hospital in South Korea, resulting in a conclusion of an intermediate TB burden within the country.

Methods

This cross-sectional study enrolled HCWs who underwent a QuantiFERON-TB Gold In-Tube (QFT-GIT) test to detect the presence of a latent TB infection (LTBI), in patients admitted to a tertiary hospital in South Korea in 2017. The departments of the hospital were divided into TB-related and TB-unrelated departments, which were based on the risk of exposure to TB patients. In this sense, the risk factors for LTBI, including current working in the TB-related departments, were analyzed.

Results

In this case, a total of 499 HCWs (54 doctors, 365 nurses and 80 paramedical personnel) were enrolled in this study. The median age of the subjects was 31 years (range, 20–67 years), 428 (85.8%) were female, and 208 (41.7%) were working in the TB-related departments. The prevalence of LTBI was 15.8% based on the QFT-GIT. Additionally, the prevalence of experience of exposure to pre-treatment TB patents was higher among HCWs working in the TB-related departments, than among HCWs working in the TB-unrelated departments (78.8% vs. 61.9%, p<0.001). However, there was no significant difference in the prevalence of LTBI between the two groups (17.3% vs. 14.8%, p=0.458). On a review of the multivariate analysis, only the factor of age was independently associated with an increased risk of LTBI (p=0.006).

Conclusion

Broadly speaking, the factor of age was associated with an increased risk of LTBI among the HCWs in South Korea. However, those workers current working in the TB-related departments was not associated with an increased risk of LTBI.

Occupational Risk of Latent Tuberculosis Infection in Health Workers of 14 Military Hospitals

Tuberculosis (TB) is a known occupational risk to health workers. Identifying risk factors in health care settings is critical to the prevention of TB for health workers and patients. In 2014, we carried out a TB screening and survey for 902 health workers from 14 selected military hospitals to determine the prevalence rate of latent tuberculosis infection (LTBI) as well as occupational risk factors. Of all subjects, 19.5% reported having provided TB patient care for 1 year or more (176/902), and 26.9% (243/902) were positive for the tuberculin skin test (TST) (10 mm or more of induration). Additionally, 21.4% (52/243) of those who tested positive were also positive for the interferon-gamma release assay (IGRA). The proportion of LTBI in the study population was 5.8% (52/902). In a multivariate logistic regression analysis, providing TB patient care for one year or more was the only significant occupational risk factor (adjusted odds ratio [aOR], 2.27; 95% confidence interval [CI], 1.13-4.56). This study suggests that military health workers working with TB patients should be regularly examined by chest radiography, TST and IGRA to detect LTBI in the early stage and control nosocomial infection of TB.

Diagnosis and Treatment of Latent Tuberculosis Infection in Healthcare Workers

Tuberculosis (TB) is one of the most important occupational risks for healthcare workers (HCWs) in South Korea. Many policies regarding the control and prevention of TB in healthcare settings recommend that HCWs are tested for latent tuberculosis infection (LTBI) in addition to active TB. Moreover, the Korean Tuberculosis Prevention Act also recommends that HCWs receive regular testing for LTBI. However, there are no specific or detailed guidelines for dealing with LTBI in HCWs. Herein, we discuss the diagnosis and treatment of LTBI in HCWs and focus particularly on the baseline screening of hired HCWs, routine follow-up, and contact investigation.

Comparison of the interferon-gamma release assay with the traditional methods for detecting Mycobacterium tuberculosis infection in children

The purpose of the article is to compare the whole blood interferon-γ release assay (IGRA) with the traditional methods for detecting Mycobacterium tuberculosis (MTB) infection in children. Fifteen childhood patients with tuberculosis and 15 healthy children were recruited. Sputa samples and venous blood were collected, and according to different procedures, IGRA, sputum smear, colloidal gold assay (CGA), fluorescence quantitation polymerase chain reaction (FQ-PCR), and tuberculosis skin test (TST) were, respectively, performed. Thirty healthy children vaccinated with Bacillus Calmette-Guérin (BCG) were also recruited, and the comparative test was carried out between IGRA and TST. In all of 15 childhood patients with TB, the positive rates were 86.7%, 20.0%, 26.7%, 40%, and 66.7% in IGRA, sputum smear, CGA, FQ-PCR, and TST, respectively. In the children vaccinated with BCG, the positive rate of IGRA was significantly lower than that of TST (6.7% vs 76.7%). From high to low, the specificities of the five methods were sputum smear (100%), IGRA (86.7%), FQ-PCR (86.7%), TST (40%), and CGA (26.7%). Although the specificities of sputum smear and FQ-PCR were more than or equal to that of IGRA, the relative sensitivities limited their applications in populations of children. IGRA is a sensitive and specific method, and could be taken as a first choice for detecting MTB infection in populations of children.

IGRA-positive patients and interferon-gamma/interleukin-2 signatures: can the Fluorospot assay provide further information?

A goal of testing for latent tuberculosis (TB) infection is to identify individuals who are at increased risk for the development of active TB. No laboratory tool is currently available to distinguish between individuals in the process of progressing from latent TB infection towards active disease and those who are not. Determination of the interferon-gamma and interleukin-2 T cell signature might provide an additional and rapid tool to evaluate treatment necessity and clinical management of a patient. Here, we present three cases of interferon-gamma release assay-positive patients with differing interferon-gamma and interleukin-2 signatures when analyzed by the Fluorospot assay.

Impact of cytotoxic and targeted antineoplastic drugs on the validity of the mitogen-induced interferon-gamma release assay for latent tuberculosis infection: results of a prospective trial at a comprehensive cancer center

Abstract The T-SPOT.TB test (TS.TB), an interferon-gamma (IFN-γ) release assay (IGRA), is superior in diagnosing latent tuberculosis infection compared with the conventional tuberculin skin test (TST). However, whether cytotoxic chemotherapy and treatment with new-generation antineoplastic monoclonal antibodies affects the TS.TB is not certain. We evaluated the feasibility of using the TS.TB in this population. Sixteen cancer patients at high risk for tuberculosis exposure were prospectively evaluated with the TST and TS.TB. Blood samples were obtained 7.5 ± 89.3 days after the most recent cycle of antineoplastic therapy. Six patients (38%) were febrile within 24 h of blood sampling; high-dose corticosteroid therapy and profound treatment-induced neutropenia were present in 1 patient each. In all patients, TS.TB showed no evidence of latent tuberculosis infection. A robust mitogen-induced IFN-γ response was seen in samples from 14 patients (88%) despite therapy with high-dose corticosteroids, cyclophosphamide, fludarabine, gemtuzumab ozogamicin, and alemtuzumab. The presence of fever or profound neutropenia did not negatively impact mitogen response by peripheral lymphocytes. The 2 patients whose peripheral blood lymphocytes (> 500 cells/ml) failed to generate a cytokine response to ex vivo mitogen stimulation had refractory advanced cancer. Unlike the TST, a negative TS.TB provided interpretable results even in cancer patients undergoing new-generation immunosuppressive therapy.