A paired comparison of tuberculin skin test results in health care workers using 5 TU and 10 TU tuberculin

Tuberculin skin test and QuantiFERON-Gold In Tube assay for diagnosis of latent TB infection among household contacts of pulmonary TB patients in high TB burden setting

BACKGROUND

World Health Organization (WHO) recommends systematic screening of high-risk populations, including household contacts (HHCs) of adult pulmonary tuberculosis (TB) patients, as a key strategy for elimination of TB. QuantiFERON-TB Gold In-Tube (QFT-GIT) assay and tuberculin skin test (TST) are two commonly used tools for the detection of latent tuberculosis infection (LTBI) but may yield differential results, affecting eligibility for TB preventive therapy.

MATERIALS AND METHODS

A prospective cohort study of adult pulmonary TB patients and their HHCs were recruited in 2 cities of India, Pune and Chennai. HHCs underwent QFT-GIT (QIAGEN) and TST (PPD SPAN 2TU/5TU). A positive QFT-GIT was defined as value ≥0.35 IU/ml and a positive TST as an induration of ≥5 mm. A secondary outcome of TST induration ≥10mm was explored. Proportion positive by either or both assays, discordant positives and negatives were calculated; test concordance was assessed using percentage agreement and kappa statistics; and risk factors for concordance and discordance including age categories were assessed using logistic regression. Sensitivity and specificity was estimated by latent class model.

RESULTS

Of 1048 HHCs enrolled, 869 [median (IQR) age: 27 years (15-40)] had both TST and QFT-GIT results available and prevalence of LTBI by QFT-GIT was 54% [95% CI (51, 57)], by TST was 55% [95% CI (52, 58)], by either test was 74% [95% CI (71, 77) and by both tests was 35% [95% CI (31, 38)]. Discordance of TST+/QFT-GIT- was 21% while TST-/QFT-GIT+ was 26%. Poor to fair agreement occurred with TST 5mm or 10mm cutoff (60 and 61% agreement with kappa value of 0.20 and 0.25 respectively). Test agreement varied by age, TST strength and induration cut-off. In multivariate analysis, span PPD was a risk factor for QFT-GIT+ and TST- while absence of BCG scar was for TST+ and QFT-GIT-. Being employed and exposure to TB case outside the household case were associated with positivity by both the tests. Sensitivity of TST and QFT-GIT to diagnose LTBI was 77% and 69%. Probability of having LTBI was >90% when both tests were positive irrespective of exposure gradient.

CONCLUSION

Prevalence of LTBI among HHCs of adult pulmonary TB patients in India is very high and varies by test type, age, and exposure gradient. In our high TB burden setting, a strategy to treat all HHCs or a targeted strategy whereby an exposure index is used should be assessed in future preventive therapy and vaccine studies as HHCs have several factors that place them at high risk for progression to TB disease.

Tuberculosis and biologics in rheumatology: A special situation

India has a huge patient burden of rheumatic diseases (RDs) including rheumatoid arthritis. The use of biologics has transformed the treatment paradigm for RD; however, biologic treatment-related infections (especially tuberculosis [TB]) are an area of potential concern for TB-endemic nations like India. Anti-tumor necrosis factor (TNF) therapy impairs the physiological TNF-mediated signaling and may cause reactivation and dissemination of latent TB infection (LTBI). Careful screening is, thus, crucial in RD patients who are about to commence anti-TNF treatment. To date, there is no consensus available for the screening, evaluation and treatment of LTBI as well as on the drug dosage and duration regimen (monotherapy or combination therapy) in the Indian population. An evidence-based algorithm for LTBI screening and management in RD patients undergoing biologic disease-modifying anti-rheumatic drug therapy is suggested in this review for Indian rheumatologists. The proposed algorithm guides physicians through a step-wise screening approach, including medical history, tuberculin skin test, interferon gamma release assay, chest radiograph and management of LTBI with isoniazid therapy or its combination with rifampicin. Further, the provided algorithm can aid the national bodies (such as National TB Control Program) in formulating recommendations for LTBI in this high-risk population.

Diagnosis of latent tuberculosis: Can we do better?

Latent tuberculosis infection (LTBI) is often diagnosed by the tuberculin skin test (TST). The latter has several limitations with regard to its sensitivity and specificity. It may be positive in people with prior bacille Calmette-Guérin (BCG) vaccination or exposure to nontuberculous mycobacteria. False negative TST results frequently occur in patients with impaired T-cell function. Therefore TST results have to be interpreted taking into consideration the pretest risk of TB infection or reactivation. Recently, interferon gamma release assays (IGRA) were introduced for the diagnosis of LTBI. These include the T-SPOT-TB and the QuantiFERON^®-TB Gold tests.These tests measure interferon gamma released in response to T-cell stimulation by specific Mycobacterium tuberculosis antigens. These tests have been shown to be more specific than the TST as they are not affected by BCG vaccination. Their sensitivity was similar to that of the TST and in some studies they correlated better with the degree of exposure. In immune-compromised patients their sensitivity was better than that of the TST. IGRA tests were shown to have better predictive value for the development of active disease among individuals with LTBI. These tests are expensive. Their most cost-effective utilization is as confirmatory tests in patients with positive TST results, particularly in areas with high rates of BCG vaccination.

Six Mantoux tuberculin skin tests with 1, 2, 5, 10, 20, and 50 units in a healthy male without side-effects - is skin reaction a linear function of tuberculin dose?

BACKGROUND

Tuberculosis remains a serious disease worldwide. Anti-tuberculosis campaigners many times face negative tuberculin skin tests after Bacille Calmette Guérin vaccination. Increasing tuberculin units might be a solution. However, is skin reaction a linear function of tuberculin dose? Are there any side-effects when higher tuberculin doses are administered?

CASE PRESENTATION

Six simultaneous Mantoux tuberculin skin tests, using 1, 2, 5, 10, 20, and 50 tuberculin units (88 altogether) of purified protein derivative RT23 per 0.1 mL were applied in a healthy male Greek 35-years-old, with known natural Mycobacterium tuberculosis primary infection since five years. Skin indurations 72 hours later were 15, 22, 23, 19, 23, and 27 mm respectively.

CONCLUSION

No linear relation between tuberculin dose and skin reaction observed; skin reaction increased as tuberculin dose increased but with a decreasing rate, especially after 2 TUs, which seem correctly defined for detection of natural infection. No side-effects occurred.

Diagnosis of latent tuberculosis infection: The potential role of new technologies

Tuberculosis (TB) is a major cause of morbidity and mortality worldwide. TB control programmes need improvement in the diagnosis of latent TB infection. The tuberculin skin test (TST) is far from a 'gold' standard as it often gives false results. Interferon-gamma assays are newly available tests to detect latent TB infection, but they are currently not routinely used. They are based on immune responses to purified protein derivative (PPD) or to region of difference 1 (RD1) specific antigens. Assays based on RD-1 specific antigens perform better than both PPD based assays and TST. They correlate with TB exposure and are less likely to give false results in non-tuberculous mycobacterial disease, Bacille Calmette-Guerin (BCG) vaccination and immunosuppression. More accurate diagnosis of latent TB infection with RD-1 specific antigen based interferon-gamma assays may allow targeting of chemoprophylaxis to reduce the burden of active TB while decreasing wastage of health care resources due to false results associated with TST. However, further research and development is required to verify that new tests can predict the risk of later development of active TB and to make it feasible to perform these tests in a reproducible fashion at low cost, particularly in developing countries.

Use of lidocaine-prilocaine patch for the mantoux test: Influence on pain and reading

A formulation of a eutectic mixture of lidocaine-prilocaine (EMLA) changes basal skin perfusion. Its use for alleviating pain associated with the Mantoux test may modify the recruitment of sensitised lymphocytes and then the response to tuberculin test. Twenty-four healthy BCG-vaccinated volunteers (26.7+/-4.1 years) received on each forearm an intradermal injection of 10IU tuberculin, one of the forearms being randomly pre-treated for 1h with EMLA-patch 5%. Pain associated with the Mantoux test was evaluated using a visual analogue scale. The transversal diameter of the induration was read at 72h. Subjects with 6mm difference between diameters (i.e. twice the usual variation for a Mantoux test) were recorded. Results were compared using a paired t-test. When using lidocaine-prilocaine prior to the test, a three-fold decrease in pain was noted (p<0.0001). Reading of the test were not affected by the lidocaine-prilocaine application (p=0.26). Four subjects had 6mm or more difference between their two tests, two of them having an induration greater than 15mm with lidocaine-prilocaine. Lidocaine-prilocaine reduces significantly pain associated with the Mantoux test but does not normally affect the test reading. However, when the induration is more than 15mm, a control without lidocaine-prilocaine has to be considered.

[Assessment of nurses' understanding of tuberculin testing at a general hospital]

BACKGROUND

The last ten years have seen a resurgence of tuberculosis, yet little information is available about the implementation of tuberculin testing and consistency in its use and interpretation.

OBJECTIVE

To evaluate knowledge of tuberculin testing among hospital nurses.

MATERIAL AND METHOD

A questionnaire on various aspects of the tuberculin test was administered to registered nurses assigned to various services of our university hospital. The questions were grouped by sections (techniques for administering the test, reading the results and interpreting them).

RESULTS

One hundred thirty-five nurses were surveyed; 127 (94%) answered all the questions. Overall, only 42% responded to 10 or more of the 14 items on the questionnaire. By sections, questions related to technique of administration, reading the tuberculin test result and interpreting it were answered correctly by 46%, 11% and 7% of the subjects, respectively. Only two variables were independently related to the number of correct responses: 1) working on a medical ward at the time of the survey or 2) administering the test more than once a week.

CONCLUSIONS

This study confirms that hospital nurses' understanding of tuberculin testing is unacceptable. A team of professionals skilled in tuberculin testing should be designated at every level of the health care system to assure the reliability of tests performed for clinical or research purposes.

Tuberculin test measurement: variability due to the time of reading

STUDY OBJECTIVES

It is recommended that the PPD Mantoux tuberculin test be read at 48 or 72 h. We have compared the measurements at these time points.

DESIGN

A 10-tuberculin unit (TU) PPD Mantoux test was administered to 116 healthy subjects (76.7% with bacillus Calmette-Guérin scars).

PARTICIPANTS

One hundred sixteen healthy adult volunteers were recruited (health service employees, 29 volunteers; general public, 87 volunteers).

RESULTS

The measurements made at 72 h were significantly higher than those made at 48 h (median, 9.4 vs 4.95 mm, respectively; p = 0.017). In those subjects with induration at either or both time points (n = 69), the readings taken at 72 h were on average 1.7 mm (95% confidence interval, 0.4 to 3.0 mm) larger than those at 48 h. Using an induration of > 15 mm diameter to define a positive result, there were more positive test results at 72 h (36) compared to 48 h (28), with the results from 10 subjects (8.5%) changing because of the time of measurement.

CONCLUSIONS

This study demonstrates that, in adults, the size of the 10-TU Mantoux reaction is significantly larger at 72 h compared to the reaction at 48 h. In clinical practice, tuberculin tests should be read at 72 h as negative tests at 48 h may be false results.

Repeat tuberculin testing in BCG-vaccinated subjects in the United Kingdom. The booster effect varies with the time of reading

The booster effect varies between populations, but has not been studied in the UK. The aim of this study was to investigate the effect of repeat tuberculin tests at 1 wk in BCG-vaccinated healthy subjects (all hospital employees) in the UK; we have assessed whether a booster effect is present 48 and 72 h after injection. Twenty-six subjects received two tuberculin tests (both 10 units) administered by the Mantoux technique-Tests 1 and 2. At Test 2 there was a significant increase in induration at 48 h (mean, 7.8 mm; p < 0.001), no difference at 72 h (mean, 0.2 mm; p = 0.93), and a reduction at 96 h (mean, -4.2 mm; p = 0.02). There were more positive results (> 15 mm induration) at Test 2 compared with Test 1 at 48 h (19 vs. 9, respectively; p = 0.002), but similar numbers at 72 h (11 vs. 10, respectively). These results show that repeat tuberculin testing in this BCG-vaccinated population caused a booster effect that varied with the time of measurement and was maximal at 48 h.