Comparable specificity of 2 commercial tuberculin reagents in persons at low risk for tuberculous infection

Screening for Latent Tuberculosis Infection in Adults: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force

Importance

Latent tuberculosis infection (LTBI) can progress to active tuberculosis disease, causing morbidity and mortality.

Objective

To review the evidence on benefits and harms of screening for and treatment of LTBI in adults to inform the US Preventive Services Task Force (USPSTF).

Data Sources

PubMed/MEDLINE, Cochrane Library, and trial registries through December 3, 2021; references; experts; literature surveillance through January 20, 2023.

Study Selection

English-language studies of LTBI screening, LTBI treatment, or accuracy of the tuberculin skin test (TST) or interferon-gamma release assays (IGRAs). Studies of LTBI screening and treatment for public health surveillance or disease management were excluded.

Data Extraction and Synthesis

Dual review of abstracts, full-text articles, and study quality; qualitative synthesis of findings; meta-analyses conducted when a sufficient number of similar studies were available.

Main Outcomes and Measures

Screening test accuracy; development of active tuberculosis disease, transmission, quality of life, mortality, and harms.

Results

A total of 113 publications were included (112 studies; N = 69 009). No studies directly evaluated the benefits and harms of screening. Pooled estimates for sensitivity of the TST were 0.80 (95% CI, 0.74-0.87) at the 5-mm induration threshold, 0.81 (95% CI, 0.76-0.87) at the 10-mm threshold, and 0.60 (95% CI, 0.46-0.74) at the 15-mm threshold. Pooled estimates for sensitivity of IGRA tests ranged from 0.81 (95% CI, 0.79-0.84) to 0.90 (95% CI, 0.87-0.92). Pooled estimates for specificity of screening tests ranged from 0.95 to 0.99. For treatment of LTBI, a large (n = 27 830), good-quality randomized clinical trial found a relative risk (RR) for progression to active tuberculosis at 5 years of 0.35 (95% CI, 0.24-0.52) for 24 weeks of isoniazid compared with placebo (number needed to treat, 112) and an increase in hepatotoxicity (RR, 4.59 [95% CI, 2.03-10.39]; number needed to harm, 279). A previously published meta-analysis reported that multiple regimens were efficacious compared with placebo or no treatment. Meta-analysis found greater risk for hepatotoxicity with isoniazid than with rifampin (pooled RR, 4.22 [95% CI, 2.21-8.06]; n = 7339).

Conclusions and Relevance

No studies directly evaluated the benefits and harms of screening for LTBI compared with no screening. TST and IGRAs were moderately sensitive and highly specific. Treatment of LTBI with recommended regimens reduced the risk of progression to active tuberculosis. Isoniazid was associated with higher rates of hepatotoxicity than placebo or rifampin.

Skin tests for the detection of Mycobacterial infections: achievements, current perspectives, and implications for other diseases

Immunological and molecular advances have modernized diagnostic testing for many diseases. Although interferon gamma-release and polymerase chain reaction assays have been developed to detect Mycobacterium tuberculosis (Mtb) infection, purified protein derivative (PPD)-based tuberculin skin testing (TST) remains the most widely used method. Indeed, the TST is a simple and cost-effective tool that can be easily applied for widespread screening for Mtb infection. However, the lack of specificity has been a limitation of these tests, and, more recently, supply issues have arisen. Building upon the skin tests that historically have been used within TB and leprosy control programs, we discuss recent developments using modern technologies for improving mycobacterial skin testing as well as practical advantages inherent to the technique. Furthermore, we outline how this knowledge could be applied to develop similar tests that could benefit diagnostic strategies for other infections. KEY POINTS: • Skin testing provides a significantly cheaper alternative to most modern technologies. • Skin tests provide a lab-independent diagnostic strategy that can be widely administered. • Diseases for which T cell responses are more robust or durable than antibody responses are accessible for skin testing.

The single recombinant M. tuberculosis protein DPPD provides enhanced performance of skin testing among HIV-infected tuberculosis patients

Diagnostic testing for M. tuberculosis infection has advanced with QuantiFERON and GeneXpert, but simple cost-effective alternatives for widespread TB screening has remained elusive and purified protein derivative (PPD)-based tuberculin skin testing (TST) remains the most widely used method. PPD-based tests have reduced performance, however, in BCG vaccinees and in individuals with immune deficiencies. We compared the performance of skin testing with the recombinant DPPD protein against that of a standard PPD-based skin test. Our data indicates similar performance of DPPD and PPD (r² = 0.7689) among HIV-negative, active TB patients, all of whom presented greater than 10 mm induration following administration. In contrast to results demonstrating that PPD induced indurations greater than 5 mm (i.e., the recommended threshold for positive results in this population) in only half (19 of 38) of the HIV positive TB patients, 89.5% (34 of 38) of these participants developed indurations greater than 5 mm when challenged with DPPD. Importantly, none of the patients that were positive following PPD administration were negative following DPPD administration, indicating markedly improved sensitivity of DPPD among HIV-infected individuals. Our data indicate that DPPD has superior performance in skin testing than the current TST standard.

The Prevalence of Latent Tuberculosis Infection in the United States

RATIONALE

Individuals with latent tuberculosis infection (LTBI) represent a reservoir of infection, many of whom will progress to tuberculosis (TB) disease. A central pillar of TB control in the United States is reducing this reservoir through targeted testing and treatment.

OBJECTIVES

To estimate the prevalence of LTBI in the United States using the tuberculin skin test (TST) and an IFN-γ release assay.

METHODS

We used nationally representative data from the 2011-2012 National Health and Nutrition Examination Survey (n = 6,083 aged ≥6 yr). LTBI was measured by both the TST and QuantiFERON-TB Gold In-Tube test (QFT-GIT). Weighted population, prevalence, and multiple logistic regression were used.

MEASUREMENTS AND MAIN RESULTS

The estimated prevalence of LTBI in 2011-2012 was 4.4% as measured by the TST and 4.8% by QFT-GIT, corresponding to 12,398,000 and 13,628,000 individuals, respectively. Prevalence declined slightly since 2000 among the U.S. born but remained constant among the foreign born. Earlier birth cohorts consistently had higher prevalence than more recent ones. Higher risk groups included the foreign born, close contact with a case of TB disease, and certain racial/ethnic groups.

CONCLUSIONS

After years of decline, the prevalence of LTBI remained relatively constant between 2000 and 2011. A large reservoir of 12.4 million still exists, with foreign-born persons representing an increasingly larger proportion of this reservoir (73%). Estimates and risk factors for LTBI were generally similar between the TST and QFT-GIT. The updated estimates of LTBI and associated risk groups can help improve targeted testing and treatment in the United States.

Tuberculosis Infection in Early Childhood and the Association with HIV-exposure in HIV-uninfected Children in Rural Uganda

BACKGROUND

In high tuberculosis (TB) burden countries, a significant proportion of the latent TB reservoir is established by the age 5 years. There are critical knowledge gaps in our understanding of the age-specific prevalence of TB infection and the influence of HIV exposure on TB infection in the first 5 years of life among HIV-uninfected children in sub-Saharan Africa.

METHODS

We measured TB infection with the Quantiferon Gold-in-Tube (QFT) and tuberculin skin tests (TST) in 447 children ≤60 months and their 284 HIV-infected and IV-uninfected mothers in rural Uganda.

RESULTS

The overall prevalence of TB infection in children ≤60 months by TST was 24% (95% confidence intervals [CI]: 19.9-27.9). The prevalence of TST positivity was highest among children in their first year of life (36%; 95% CI: 26.0-45.9) and declined with age to 19% at 36-60 months of age, χ test for trend P = 0.014. In contrast, 4% (95% CI: 1.9-5.87%) of children had a positive QFT, and there was no trend detected with age, P = 0.576. QFT positivity was detected as early as 5 months. HIV-exposed uninfected children had significantly higher odds of TB infection by QFT (odds ratio [OR]: 21.2; P = 0.008; 95% CI: 2.2-204.7) or positive TST or QFT (OR, 2.4; P = 0.020; 95% CI: 1.2-5.1) compared with HIV-unexposed uninfected children, adjusting for age, BCG vaccination and a positive maternal TST or QFT.

CONCLUSIONS

An appreciable prevalence of TB infection was detected in early childhood. HIV-exposed uninfected children have a higher risk for TB infection compared with children born to HIV-uninfected mothers.

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.

Purified protein derivatives of tuberculin--past, present, and future

The tuberculin skin test, which involves monitoring the immune reaction to an injection of purified protein derivative (PPD), has been the most widely used method for detecting infection with Mycobacterium tuberculosis since its development in 1930s. Until recently, the molecular composition of PPD was unknown. This thwarted the discovery of improved skin testing reagents and drastically hindered efforts to define the mechanism of action. Proteomic evaluation of PPD combined with a detailed analysis in the guinea pig model of tuberculosis led to further definition of the molecular composition of PPD. This communication reviews the history and current status of PPD, in addition to describing candidate next-generation PPD reagents, based on the use of an individual protein or protein cocktails.

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.

Cost-effectiveness of alternative strategies for tuberculosis screening before kindergarten entry

OBJECTIVE

We undertook a decision analysis to evaluate the economic and health effects and incremental cost-effectiveness of using targeted tuberculin skin testing, compared with universal screening or no screening, before kindergarten.

METHODS

We constructed a decision tree to determine the costs and clinical outcomes of using targeted testing compared with universal screening or no screening. Baseline estimates for input parameters were taken from the medical literature and from California health jurisdiction data. Sensitivity analyses were performed to determine plausible ranges of associated outcomes and costs. We surveyed California health jurisdictions to determine the prevalence of mandatory universal tuberculin skin testing.

RESULTS

In our base-case scenario, the cost to prevent an additional case of tuberculosis by using targeted testing, compared with no screening, was $524,897. The cost to prevent an additional case by using universal screening, compared with targeted testing, was $671,398. The incremental cost of preventing a case through screening remained above $100,000 unless the prevalence of tuberculin skin testing positivity increased to >10%. More than 51% of children entering kindergarten in California live where tuberculin skin testing is mandatory.

CONCLUSIONS

The cost to prevent a case of tuberculosis by using either universal screening or targeted testing of kindergarteners is high. If targeted testing replaced universal tuberculin skin testing in California, then $1.27 million savings per year would be generated for more cost-effective strategies to prevent tuberculosis. Improving the positive predictive value of the risk factor tool or applying it to groups with higher prevalence of latent tuberculosis would make its use more cost-effective. Universal tuberculin skin testing should be discontinued, and targeted testing should be considered only when the prevalence of risk factor positivity and the prevalence of tuberculin skin testing positivity among risk factor-positive individuals are high enough to meet acceptable thresholds for cost-effectiveness.

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.

Diagnosis of latent Mycobacterium tuberculosis infection: is the demise of the Mantoux test imminent?

Tuberculosis is responsible for more then 2 million deaths worldwide each year and vies with HIV as the world's most fatal infectious disease. In many developing countries, attempts to control the spread of infection rely solely on identification and treatment of those with active disease, ignoring subclinical infection. However, in developed countries, large efforts are also expended to identify and give prophylactic drugs to people with latent tuberculosis infection. Until recently, the 100-year-old tuberculin skin test (Mantoux) has been the only available diagnostic test for latent tuberculosis infection, despite its many well-known limitations. Advances in scientific knowledge have led to the development of tests for tuberculosis that measure the production of interferon-gamma by T-cells stimulated in vitro with Mycobacterium tuberculosis-specific antigens. These interferon-gamma tests are highly specific and unaffected by prior Bacille Calmette-Guérin vaccination or immune reactivity to most atypical mycobacteria. They are more sensitive than the tuberculin skin test in detecting people with active tuberculosis, and their results correlate more closely with M. tuberculosis exposure risk factors than the tuberculin skin test in people likely to have latent tuberculosis infection. Science has caught up with one of the oldest diagnostic tests still in use worldwide, and the adoption of new, tuberculosis-specific interferon-gamma-based tests should move us one step closer to better control of this insidious pathogen.

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.

Specific detection of tuberculosis infection: an interferon-gamma-based assay using new antigens

The tuberculin skin test for immunologic diagnosis of Mycobacterium tuberculosis infection has many limitations, including being confounded by bacillus Calmette-Guérin (BCG) vaccination or exposure to nontuberculous mycobacteria. M. tuberculosis-specific antigens that are absent from BCG and most nontuberculous mycobacteria have been identified. We examined the use of two of these antigens, CFP-10 and ESAT-6, in a whole blood IFN-gamma assay as a diagnostic test for tuberculosis in BCG-vaccinated individuals. Because of the lack of an accurate standard with which to compare new tests for M. tuberculosis infection, specificity of the whole blood IFN-gamma assay was estimated on the basis of data from people with no identified risk for M. tuberculosis exposure (216 BCG-vaccinated Japanese adults) and sensitivity was estimated on the basis of data from 118 patients with culture-confirmed M. tuberculosis infection who had received less than 1 week of treatment. Using a combination of CFP-10 and ESAT-6 responses, the specificity of the test for the low-risk group was 98.1% and the sensitivity for patients with M. tuberculosis infection was 89.0%. The results demonstrate that the whole blood IFN-gamma assay using CFP-10 and ESAT-6 was highly specific and sensitive for M. tuberculosis infection and was unaffected by BCG vaccination status.

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.

Comparison testing of current (PPD-S1) and proposed (PPD-S2) reference tuberculin standards

Since 1951, the tuberculin PPD-S1 has been used to standardize commercial PPD reagents and perform special tuberculin surveys. PPD-S1 is now in short supply and a new standard (PPD-S2) has been manufactured. To determine if PPD-S2 is equivalent and can replace PPD-S1, we conducted a double-blind clinical trial. Between May 14 and October 28, 1997, 69 subjects with a history of culture-proven tuberculosis (TB patients) and 1,189 subjects with a very low risk for TB infection were enrolled, received four skin tests (with PPD-S1, PPD-S2, and one each of the commercially available PPDs), and had reactions measured by two trained observers. Among the TB patients, we found statistically indistinguishable immunogenicity (mean reaction size +/- standard deviation): 15.6 +/- 6.6 mm for PPD-S1 and 14.8 +/- 5.6 mm for PPD-S2. Among low-risk subjects, the tests had equally high specificities (PPD-S1, 98.7% and PPD-S2, 98. 5%), using a 10-mm cutoff. The number of discordant (negative versus positive) interpretations for PPD-S2, assuming that low-risk subjects who had a >/= 10 mm reaction to PPD-S1 were truly infected, was low (0.5%) and indistinguishable from the rate of discordant interpretations of the same test when read by two different observers (0.8%). The study results indicate that PPD-S2 is qualified to be used as the new U.S. reference standard for PPD tuberculin.