False-positive tuberculin skin test results among health care workers

Diagnosis and treatment of latent tuberculosis infection: an update

It is estimated that more than two billion people have latent M. tuberculosis infection, and this population serves as an important reservoir for future tuberculosis cases. Prevalence estimates are limited by difficulties in diagnosing the infection, including the lack of an ideal test, and an incomplete understanding of latency. Current tests include the tuberculin skin test and two interferon-γ release assays: QuantiFERON Gold In-Tube and T-SPOT.TB. This update focuses on recent publications regarding the ability of these tests to predict tuberculosis disease, their reproducibility over serial tests, and discordance between tests. We also discuss recent advances in the treatment of latent M. tuberculosis infection, including the three-month regimen of once-weekly rifapentine plus isoniazid, and prolonged isoniazid therapy for HIV-infected persons living in high-tuberculosis-incidence settings. We provide an update on the tolerability of the three-month regimen.

Tuberculosis screening among health sciences students in Saudi Arabia in 2010

BACKGROUND AND OBJECTIVES

Tuberculosis (TB) is a major health threat in both developed and developing nations. The aim of this study was to determine the prevalence of reactivity to the Mantoux test or tuberculin skin test (TST) among health sciences students after an open case of TB infection was detected in one of the students.

DESIGN AND SETTING

A cross-sectional screening survey among students of the Health Sciences College for Girls in Jeddah conducted in June 2010.

SUBJECTS AND METHODS

Students were screened using a standardized TST, and the bacillus Calmette-Guérin (BCG) scars were later inspected.

RESULTS

Of 320 students, only 296 (92.5%) participated in the survey. Thirty-five (12%) had a positive test reactivity (≥10 mm). Seventy-six (25.7%) students had no BCG vaccination scar.

CONCLUSIONS

The prevalence of a positive TST was high among students when considered as a primary diagnostic method for latent Mycobacterium tuberculosis infection. Strengthening infection control measures is recommended during students' health care training.

Differences in tuberculin reactivity as determined in a veterans administration employee health screening program

In response to a difference in pricing, the San Diego Veterans Administration Medical Center changed its tuberculin preparation from Tubersol to Aplisol in the fall of 2006. Following the change, an increased number of employee skin test conversions was noted. Employee tuberculin skin test converters from 2006 were screened with the QuantiFERON Gold (QFT-G) gamma interferon release assay. Those employees who tested negative by QFT-G were asked to repeat their skin test with both Tubersol and Aplisol tuberculin preparations. Of the new purified protein derivative converters, 12 of 14 returned for repeat testing with QFT-G, and the assay was negative for 83% (10/12), positive for 8% (1/12), and indeterminate for 8% (1/12) of the individuals. Nine of the individuals who were QFT-G negative agreed to repeat skin testing with both tuberculin preparations, and 7/8 (87.5%) demonstrated reactivity with the Aplisol preparation, while 0/8 (0%) reacted to the Tubersol preparation. A change from Tubersol to Aplisol resulted in elevated tuberculin skin test conversion rates that may be due to false-positive reactions. The differences in skin test reactivity between preparations support CDC guidelines that recommend that institutions should not change tuberculin preparations, as doing so may falsely increase the number of positive reactions.

Increase in tuberculin skin test converters among health care workers after a change from Tubersol to Aplisol

BACKGROUND

Comparability of the 2 commercially available tuberculin skin testing (TST) preparations, Aplisol (Parkdale Pharmaceuticals, Inc, Rochester, MI) and Tubersol (Aventis Pasteur, Inc, Swiftwater, PA), remains uncertain, particularly in groups that undergo repeated testing, such as health care workers.

METHODS

Data from the annual tuberculosis screening program for health care workers at the Kennedy Krieger Institute in Baltimore, Maryland, were analyzed. Conversion rates during 1997-2003 in workers screened with Tubersol (n = 8897 screenings) were compared with 1203 workers who underwent screening with Aplisol in 2004. Repeat testing with Tubersol was examined in those who converted in 2004 with Aplisol.

RESULTS

Annual TST conversion rates ranged from 0.3% to 0.9% between 1997 and 2003 using Tubersol. After switching to Aplisol in 2004, the TST conversion rate significantly increased to 2% (P < .001). Among 24 health care workers who were converters with Aplisol in 2004, only 6 of 23 (26%) were converters on repeat testing with Tubersol (1 declined retesting). None of the apparent converters (n = 24) had radiographic evidence of Mycobacterium tuberculosis infection, and there was no epidemiologic evidence of transmission. Reclassification based on Tubersol testing in 2004 resulted in conversion rates comparable with previous years.

CONCLUSION

We conclude that the change from Tubersol to Aplisol resulted in falsely elevated conversion rates. Our results support the guidelines from the Centers for Disease Control and Prevention recommendations that 1 product should be used consistently in populations undergoing periodic testing.

Occupational Medicine Forum

The Occupational Medicine Forum is prepared by the ACOEM Occupational and Environmental Medical Practice Committee and does not necessarily represent an official ACOEM position. The Forum is intended for health professionals and is not intended to provide medical or legal advice, including illness prevention, diagnosis or treatment, or regulatory compliance. Such advice should be obtained directly from a physician and/or attorney.

American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America: Controlling Tuberculosis in the United States

During 1993-2003, incidence of tuberculosis (TB) in the United States decreased 44% and is now occurring at a historic low level (14,874 cases in 2003). The Advisory Council for the Elimination of Tuberculosis has called for a renewed commitment to eliminating TB in the United States, and the Institute of Medicine has published a detailed plan for achieving that goal. In this statement, the American Thoracic Society (ATS), Centers for Disease Control and Prevention (CDC), and the Infectious Diseases Society of America (IDSA) propose recommendations to improve the control and prevention of TB in the United States and to progress toward its elimination. This statement is one in a series issued periodically by the sponsoring organizations to guide the diagnosis, treatment, control, and prevention of TB. This statement supersedes the previous statement by ATS and CDC, which was also supported by IDSA and the American Academy of Pediatrics (AAP). This statement was drafted, after an evidence-based review of the subject, by a panel of representatives of the three sponsoring organizations. AAP, the National Tuberculosis Controllers Association, and the Canadian Thoracic Society were also represented on the panel. This statement integrates recent scientific advances with current epidemiologic data, other recent guidelines from this series, and other sources into a coherent and practical approach to the control of TB in the United States. Although drafted to apply to TB-control activities in the United States, this statement might be of use in other countries in which persons with TB generally have access to medical and public health services and resources necessary to make a precise diagnosis of the disease; achieve curative medical treatment; and otherwise provide substantial science-based protection of the population against TB. This statement is aimed at all persons who advocate, plan, and work at controlling and preventing TB in the United States, including persons who formulate public health policy and make decisions about allocation of resources for disease control and health maintenance and directors and staff members of state, county, and local public health agencies throughout the United States charged with control of TB. The audience also includes the full range of medical practitioners, organizations, and institutions involved in the health care of persons in the United States who are at risk for TB.

Tuberculosis prevention and control in long-term-care facilities for older adults

In the United States, older adults comprise 22% of cases of tuberculous disease but only 12% of the population. Most cases of tuberculosis (TB) occur in community dwellers, but attack rates are highest among frail residents of long-term-care facilities. The detection and treatment of latent TB infection and TB disease can pose special challenges in older adults. Rapid recognition of possible disease, diagnosis, and implementation of airborne precautions are essential to prevent spread. It is the intent of this evidence-based guideline to assist healthcare providers in the prevention and control of TB, specifically in skilled nursing facilities for the elderly.

Comparing Interferon- Release Assay with Tuberculin Skin Test Readings at 48-72 Hours and 144-168 Hours with Use of 2 Commercial Reagents

BACKGROUND

Despite widespread use, the tuberculin skin test (TST) has many limitations, including a requirement for a second visit between 48 and 72 hours. The goal of this study was to determine the reliability of a TST reading between 144 and 168 hours.

METHODS

Tuberculin antigen was applied into both forearms (Aplisol in one arm and Tubersol in the other, from single lots of each product) by the Mantoux method. Blood samples were obtained for interferon- gamma release assay. Subjects were seen at 48-72 hours for the initial (day 2) TST reading and returned at 144-168 hours for a second (day 7) reading.

RESULTS

A total of 116 subjects at increased risk for tuberculosis were studied; 25 (22%) had positive results at day 2 with Tubersol and 27 (23%) had positive results at day 2 with Aplisol. Overall agreement between Tubersol and Aplisol at day 2 was 93% (kappa = 0.80) and at day 7 was 94% (kappa = 0.76). Overall agreement between day 2 and day 7 was 89% for Tubersol and 86% for Aplisol. Discordant results between day 2 and day 7 occurred mostly in persons with a history of bacille Calmette-Guerin vaccination.

CONCLUSIONS

Subjects who fail to present at 48-72 hours for TST reading may still have a reliable TST reading at up to 168 hours. Aplisol and Tubersol reagents produce comparable results when compared with the interferon- gamma release assay.

A meta-analysis of the effect of Bacille Calmette Guérin vaccination on tuberculin skin test measurements

BACKGROUND

The accurate diagnosis of latent tuberculosis infection (LTBI) is an important component of any tuberculosis control programme and depends largely on tuberculin skin testing. The appropriate interpretation of skin test results requires knowledge of the possible confounding factors such as previous BCG vaccination. Uncertainty about the effect of BCG vaccination on tuberculin skin testing and the strength with which recommendations are made to individual patients regarding treatment of LTBI have identified a need to analyse the available data on the effect of BCG on skin testing. A meta-analysis of the evidence for the effect of BCG vaccination on tuberculin skin testing in subjects without active tuberculosis was therefore performed.

METHODS

Medline was searched for English language articles published from 1966 to 1999 using the key words "BCG vaccine", "tuberculin test/PPD", and "skin testing". Bibliographies of relevant articles were reviewed for additional studies that may have been missed in the Medline search. Articles were considered for inclusion in the meta-analysis if they had recorded tuberculin skin test results in subjects who had received BCG vaccination more than 5 years previously and had a concurrent control group. Only prospective studies were considered. The geographical location, number of participants, type of BCG vaccine used, type of tuberculin skin test performed, and the results of the tuberculin skin test were extracted.

RESULTS

The abstracts and titles of 980 articles were identified, 370 full text articles were reviewed, and 26 articles were included in the final analysis. Patients who had received BCG vaccination were more likely to have a positive skin test (5 TU PPD: relative risk (RR) 2.12 (95% confidence interval (CI)1.50 to 3.00); 2 TU RT23: 2.65 [corrected] (95% CI 1.83 to 3.85). The effect of BCG vaccination on PPD skin test results was less after 15 years. Positive skin tests with indurations of >15 mm are more likely to be the result of tuberculous infection than of BCG vaccination.

CONCLUSIONS

In subjects without active tuberculosis, immunisation with BCG significantly increases the likelihood of a positive tuberculin skin test. The interpretation of the skin test therefore needs to be made in the individual clinical context and with evaluation of other risk factors for infection. The size of the induration should also be considered when making recommendations for treatment of latent infection.

Evolution and current use of the tuberculin test

Since it was first introduced in the late 1800s, the tuberculin test has undergone continual refinement in its formulation, standardization, and dosage, as well as its interpretation and indications for use. New guidelines have replaced universal screening with targeted testing and rigid definitions of positivity with individualized criteria formulated from a Bayesian approach. This review summarizes the evolution of the test and provides information to help gauge its predictive value.