Interpretation of repeated tuberculin tests. Boosting, conversion, and reversion

How a different look at latency can help to develop novel diagnostics and vaccines against tuberculosis

Mycobacterium tuberculosis is one of the most successful human pathogens. It kills every year approximately 1.5 - 2 million people, and at present a third of the human population is estimated to be infected. Fortunately, only a relatively small proportion of the infected individuals will progress to active disease, and most will maintain a latent infection. Although a latent infection is clinically silent and not contagious, it can reactivate to cause highly contagious pulmonary tuberculosis, the most prevalent form of the disease in adults. Therefore, a thorough understanding of latency and reactivation may help to develop novel control strategies against tuberculosis. The most widely held view is that the mycobacteria are imprisoned in granulomatous structures during latency, where they can survive in a non-replicating, dormant form until reactivation occurs. However, there is no hard data to sustain that the reactivating mycobacteria are indeed those that laid dormant within the granulomas. In this review an alternative model, based on evidence from early studies, as well as recent reports is presented, in which the latent mycobacteria reside outside granulomas, within non-macrophage cell types throughout the infected body. Potential implications for new diagnostic and vaccine design are discussed.

Heparin-binding-hemagglutinin-induced IFN-gamma release as a diagnostic tool for latent tuberculosis

BACKGROUND

The detection of latent tuberculosis infection (LTBI) is a major component of tuberculosis (TB) control strategies. In addition to the tuberculosis skin test (TST), novel blood tests, based on in vitro release of IFN-gamma in response to Mycobacterium tuberculosis-specific antigens ESAT-6 and CFP-10 (IGRAs), are used for TB diagnosis. However, neither IGRAs nor the TST can separate acute TB from LTBI, and there is concern that responses in IGRAs may decline with time after infection. We have therefore evaluated the potential of the novel antigen heparin-binding hemagglutinin (HBHA) for in vitro detection of LTBI.

METHODOLOGY AND PRINCIPAL FINDINGS

HBHA was compared to purified protein derivative (PPD) and ESAT-6 in IGRAs on lymphocytes drawn from 205 individuals living in Belgium, a country with low TB prevalence, where BCG vaccination is not routinely used. Among these subjects, 89 had active TB, 65 had LTBI, based on well-standardized TST reactions and 51 were negative controls. HBHA was significantly more sensitive than ESAT-6 and more specific than PPD for the detection of LTBI. PPD-based tests yielded 90.00% sensitivity and 70.00% specificity for the detection of LTBI, whereas the sensitivity and specificity for the ESAT-6-based tests were 40.74% and 90.91%, and those for the HBHA-based tests were 92.06% and 93.88%, respectively. The QuantiFERON-TB Gold In-Tube (QFT-IT) test applied on 20 LTBI subjects yielded 50% sensitivity. The HBHA IGRA was not influenced by prior BCG vaccination, and, in contrast to the QFT-IT test, remote (>2 years) infections were detected as well as recent (<2 years) infections by the HBHA-specific test.

CONCLUSIONS

The use of ESAT-6- and CFP-10-based IGRAs may underestimate the incidence of LTBI, whereas the use of HBHA may combine the operational advantages of IGRAs with high sensitivity and specificity for latent infection.

Nosocomial Mycobacterium tuberculosis transmission among healthcare students in a high incidence region, in Vitória, State of Espírito Santo

This open comparative study for evaluating hypersensitivity to tuberculin among medical students (n=441), nursing students (n=178) and economics students (n=230) in Vitória, State of Espírito Santo, had the aim of assessing whether the prevalence of positive tuberculin tests among healthcare students could be used as a sentinel event for nosocomial transmission in localities with high endemicity. There was a significant change in the frequency of purified protein derivative reactivity in the nursing students (20. 3%) and medical students (18. 4%), in comparison with the economics students (6%) (p <0. 001). As expected, the medical and nursing students had more knowledge about tuberculosis than did the economics students (p <0. 001). Our data suggest that the incidence of Mycobacterium tuberculosis infection among nursing and medical students in our region, which has high endemicity of tuberculosis, does not differ from what is found in low-incidence countries. These data reinforce the need for implementing biosafety programs for this target population.

QuantiFERON®-TB Gold test in the identification of latent tuberculosis infection in immigrants

BACKGROUND

The identification and treatment of latent tuberculosis infection (LTBI) among immigrants are an effective strategy for TB control in developed countries. A new test for LTBI identification that uses more specific antigens of Mycobacterium tuberculosis is now commercially available under the brand name of QuantiFERON-TB Gold test.

OBJECTIVE

To compare QuantiFERON-TB Gold test to tuberculin skin testing (TST) for the detection of LTBI among immigrants from high endemic TB areas.

PATIENTS AND METHODS

Undocumented immigrants attending a district medical center were enrolled if they originated from high endemic TB areas, the time of arrival in Italy was < or = 5 years, had neither active TB disease nor known immunodeficiency status. The TST was applied according to standards and QuantiFERON-TB Gold test was performed following the manufacturer's instructions.

RESULTS

Hundred subjects were included in the comparative analysis. TST was positive in 44% of subjects; 15% had a positive QuantiFERON-TB Gold test result. The total agreement between TST and QuantiFERON-TB Gold test was 71%, for a kappa statistics of 0.37; agreement was 100% for TST negative results, but only 34% for TST positive ones. In the multivariate logistic regression analysis, previous BCG vaccination was independently associated with a lower chance of disagreement between the tests.

CONCLUSION

The prevalence of LTBI among immigrants was lower when determined by QuantiFERON-TB Gold; this may be a consequence of more specific MTB antigens used. Our results suggest that QuantiFERON-TB Gold may be used as confirmatory test for TST positive immigrants candidate to preventive therapy.

T-cell assays for the diagnosis of latent tuberculosis infection: moving the research agenda forward

For nearly a century, the tuberculin skin test was the only tool available for the detection of latent tuberculosis infection. A recent breakthrough has been the development of T-cell-based interferon-gamma release assays. Current evidence suggests interferon-gamma release assays have higher specificity than the tuberculin skin test, better correlation with surrogate markers of exposure to Mycobacterium tuberculosis in low-incidence settings, and less cross-reactivity as a result of BCG vaccination compared with the tuberculin skin test. The body of literature supporting the use of interferon-gamma release assays has rapidly expanded. However, several unresolved and unexplained issues remain. To address these issues, a group of experts met in Geneva, Switzerland, in March, 2006, to discuss the research evidence on T-cell-based assays, their clinical usefulness, limitations, and directions for future research, with a specific focus on resource-limited and high HIV prevalence settings. On the basis of 2 days of discussions, a comprehensive research agenda was generated, which will propel the field forward by stimulating focused high-impact research and encourage the investment of resources needed to tackle priority research questions, especially in resource-limited settings. Ultimately, if adequately financed, the research findings will inform appropriate use of novel latent tuberculosis infection diagnostics in global tuberculosis control.

Longitudinal assessment of an ELISPOT test for Mycobacterium tuberculosis infection

BACKGROUND

Very little longitudinal information is available regarding the performance of T cell-based tests for Mycobacterium tuberculosis infection. To address this deficiency, we conducted a longitudinal assessment of the enzyme-linked immunosorbent spot test (ELISPOT) test in comparison to the standard tuberculin skin test (TST).

METHODS AND FINDINGS

In tuberculosis (TB) contacts we repeated ELISPOT tests 3 mo (n = 341) and 18 mo (n = 210) after recruitment and TSTs at 18 mo (n = 130). We evaluated factors for association with conversion and reversion and investigated suspected cases of TB. Of 207 ELISPOT-negative contacts, 51 (24.6%) had 3-mo ELISPOT conversion, which was associated with a positive recruitment TST (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.0-5.0, p = 0.048) and negatively associated with bacillus Calmette-Guérin (BCG) vaccination (OR 0.5, 95% CI 0.2-1.0, p = 0.06). Of 134 contacts, 54 (40.2%) underwent 3-mo ELISPOT reversion, which was less likely in those with a positive recruitment TST (OR 0.3, 95% CI 0.1-0.8, p = 0.014). Between 3 and 18 mo, 35/132 (26.5%) contacts underwent ELISPOT conversion and 28/78 (35.9%) underwent ELISPOT reversion. Of the 210 contacts with complete results, 73 (34.8%) were ELISPOT negative at all three time points; 36 (17.1%) were positive at all three time points. Between recruitment and 18 mo, 20 (27%) contacts had ELISPOT conversion; 37 (50%) had TST conversion, which was associated with a positive recruitment ELISPOT (OR 7.2, 95% CI 1.4-37.1, p = 0.019); 18 (32.7%) underwent ELISPOT reversion; and five (8.9%) underwent TST reversion. Results in 13 contacts diagnosed as having TB were mixed, but suggested higher TST sensitivity.

CONCLUSIONS

Both ELISPOT conversion and reversion occur after M. tuberculosis exposure. Rapid ELISPOT reversion may reflect M. tuberculosis clearance or transition into dormancy and may contribute to the relatively low reported ELISPOT conversion rate. Therefore, a negative ELISPOT test for M. tuberculosis infection should be interpreted with caution.

Serial testing for tuberculosis: can we make sense of T cell assay conversions and reversions?

The authors discuss a new study, which they say is a valuable addition to the existing literature on the performance of interferon gamma release assays in serial testing for TB infection.

Value of the Tuberculin Skin Test in Screening for Tuberculosis in Dialysis Patients

BACKGROUND

Hemodialysis patients are at high risk for tuberculosis, and a tuberculin skin test (TST) is not usually helpful in detecting tuberculosis infection because of anergic reactions. Prophylactic therapy against tuberculosis in dialysis patients is important to enhance transplantation success. Herein we evaluated the value of TST in screening for tuberculosis and analyzed any compounding factors that might affect the results of the test in hemodialysis patients in an endemic area of Turkey.

METHODS

A total of 187 (96 female, 91 male) patients were screened using a 2-step TST. Test results were compared with clinical, radiologic, and laboratory data.

RESULTS

None of the patients had active tuberculosis during the study and 55% had been vaccinated against tuberculosis. After the first purified protein derivative (PPD) test, 55.1% of the patients showed a positive reaction, ultimately reaching a total of 68.4% following the second test. Cumulative positive TST results were significantly correlated with male gender (P=.001, r=.352), previous tuberculosis history (P=.013, r=.183) positively, whereas with the ferritin level (P=.001, r=-.233) negatively; but there were no significant relationships between TST results and other data.

CONCLUSIONS

Impairment of delayed-type hypersensitivity reaction is frequent in dialysis patients, but we observed high rates of positivity with the two-step TST which could be attributed to tuberculosis being endemic in Turkey. Further comparative studies with more specific diagnostic methods will be helpful to evaluate the importance of TST positivity in identifying tuberculosis-infected HD patients.

The prognosis of latent tuberculosis: can disease be predicted?

In humans, Mycobacterium tuberculosis persists for long periods in a clinically latent state, creating a huge reservoir of 'silent' tuberculosis (TB) (roughly one-third of the global population) from which new cases continually arise. A prognostic marker for active TB would enable targeted treatment of the small fraction of infected individuals who are most at risk of developing contagious TB, contributing greatly to TB control efforts. Here, we propose that TB-specific interferon-gamma release assays might be useful for identifying individuals with progressive infections who are likely to develop the disease. This might provide an unprecedented advantage for TB control, namely targeted preventive therapy for individuals who are most at risk of developing active contagious TB.

Chemotherapy and diagnosis of tuberculosis

Since after the first streptomycin 1944 trials, anti-tuberculous chemotherapy research has been focused upon establishing drug combination regimens capable of overcoming drug resistance and amenable to ambulatory treatment in resource strapped countries. The first milestone being the 1959 Madras trial comparing home and sanatorium treatment in South India. Subsequently, the MRC trials led Fox and Mitchison to indicate rifampicin, isoniazid and pyrazinamide as the first line drugs for short course, 6 month, regimens and the 1982 Hong Kong Chest Service trials established intermittent therapy as the ambulatory treatment standard for directly observed therapy (DOT). The rising of the HIV epidemic at the beginning of the 1980s has refuelled tuberculosis spread in Africa and Asia and contributed to the expansion of drug-resistant tuberculosis worldwide making the development of new drugs and drug regimens for ambulatory treatment a top priority. Led by biotechnological advances, molecular biology has been brought into TB laboratory diagnosis for the highly sensitive and specific rapid identification of Mycobacterium tuberculosis in biological samples. The field of immunological diagnosis of TB infection, dominated since the early 1900s by the intradermal tuberculin reaction has been put back in motion by the discovery of M. tuberculosis-specific proteins and peptides, now employed in blood tests of high sensitivity and specificity for the diagnosis of latent TB which may help with the identification of contacts at higher risk of active disease and the eradication of epidemic cases.

The presence of a booster phenomenon among contacts of active pulmonary tuberculosis cases: a retrospective cohort

Background

Assuming a higher risk of latent tuberculosis (TB) infection in the population of Rio de Janeiro, Brazil, in October of 1998 the TB Control Program of Clementino Fraga Filho Hospital (CFFH) routinely started to recommend a two-step tuberculin skin test (TST) in contacts of pulmonary TB cases in order to distinguish a boosting reaction due to a recall of delayed hypersensitivity previously established by infection with Mycobacterium tuberculosis (M.tb) or BCG vaccination from a tuberculin conversion. The aim of this study was to assess the prevalence of boosted tuberculin skin tests among contacts of individuals with active pulmonary tuberculosis (TB).

Methods

Retrospective cohort of TB contacts ≥ 12 years old who were evaluated between October 1^st, 1998 and October 31^st 2001. Contacts with an initial TST ≤ 4 mm were considered negative and had a second TST applied after 7–14 days. Boosting reaction was defined as a second TST ≥ 10 mm with an increase in induration ≥ 6 mm related to the first TST. All contacts with either a positive initial or repeat TST had a chest x-ray to rule out active TB disease, and initially positive contacts were offered isoniazid preventive therapy. Contacts that boosted did not receive treatment for latent TB infection and were followed for 24 months to monitor the development of TB. Statistical analysis of dichotomous variables was performed using Chi-square test. Differences were considered significant at a p < 0.05.

Results

Fifty four percent (572/1060) of contacts had an initial negative TST and 79% of them (455/572) had a second TST. Boosting was identified in 6% (28/455). The mean age of contacts with a boosting reaction was 42.3 ± 21.1 and with no boosting was 28.7 ± 21.7 (p = 0.01). Fifty percent (14/28) of individuals whose test boosted met criteria for TST conversion on the second TST (increase in induration ≥ 10 mm). None of the 28 contacts whose reaction boosted developed TB disease within two years following the TST.

Conclusion

The low number of contacts with boosting and the difficulty in distinguishing boosting from TST conversion in the second TST suggests that the strategy of two-step TST testing among contacts of active TB cases may not be useful. However, this conclusion must be taken with caution because of the small number of subjects followed.

Comparison of Two Interferon-γ Assays and Tuberculin Skin Test for Tracing Tuberculosis Contacts

BACKGROUND

The tuberculin skin test (TST) has low specificity. QuantiFERON-TB Gold (QFT-G) and T-SPOT.TB are based on interferon (IFN)-gamma responses to Mycobacterium tuberculosis-specific antigens. A novel in-tube format of QFT-G (QFT-GIT) offers logistical advantages.

OBJECTIVE

To compare TST, QFT-GIT, and T-SPOT.TB in bacillus Calmette-Guérin unvaccinated contacts and correlate results with measures of recent exposure.

METHODS

When a supermarket employee with smear-positive tuberculosis had infected most close contacts, a contact investigation among more than 20,000 customers was performed. We recruited subjects randomly on the day of TST administration (n = 469) and subjects with TST of more than 0 mm on the day of TST reading (n = 316). QFT-GIT and T-SPOT.TB were performed. Demographic data and measures of exposure were collected. TST results were analyzed at a cutoff of 10 or 15 mm. Blood tests were interpreted following the manufacturers' criteria and by varying cutoff levels.

RESULTS

Among 785 study participants, TST results were associated with age, whereas positive IFN-gamma responses were significantly associated with cumulative shopping time, most markedly for QFT-GIT. Among participants with a TST of 15 mm or greater, sensitivity of QFT-GIT and T-SPOT.TB was 42.2 and 51.3%, respectively. Interassay agreement was 89.6% (kappa = 0.59). By varying cutoff values, agreement between the IFN-gamma assays was optimal at 93.6% (kappa = 0.71) using a cutoff of 0.20 IU/ml for QFT-GIT and 13 spots for T-SPOT.TB.

CONCLUSIONS

Blood test results were associated with exposure, whereas the TST was not. A possible lack of sensitivity of IFN-gamma assays in detecting individuals with TST of 15 mm or greater, despite negative bacillus Calmette-Guérin vaccination status, warrants further investigation into alternative cutoff values.

Transmission network analysis to complement routine tuberculosis contact investigations

OBJECTIVE

We examined the feasibility and value of network analysis to complement routine tuberculosis (TB) contact investigation procedures during an outbreak.

METHODS

We reviewed hospital, health department, and jail records and interviewed TB patients. Mycobacterium tuberculosis isolates were genotyped. We evaluated contacts of TB patients for latent TB infection (LTBI) and TB, and analyzed routine contact investigation data, including tuberculin skin test (TST) results. Outcomes included number of contacts identified, number of contacts evaluated, and their TST status. We used network analysis visualizations and metrics (reach, degree, betweenness) to characterize the outbreak.

RESULTS

secondary TB patients and more than 1200 contacts. Genotyping detected a 21-band pattern of a strain W variant. No HIV-infected patients were diagnosed. Contacts prioritized by network analysis were more likely to have LTBI than nonprioritized contacts (odds ratio=7.8; 95% confidence interval=1.6, 36.6). Network visualizations and metrics highlighted patients central to sustaining the outbreak and helped prioritize contacts for evaluation.

CONCLUSIONS

A network-informed approach to TB contact investigations provided a novel means to examine large quantities of data and helped focus TB control.

Nursing and Community Rates of Mycobacterium tuberculosis Infection among Students in Harare, Zimbabwe

BACKGROUND

African hospitals have experienced major increases in admissions for tuberculosis, but they are ill-equipped to prevent institutional transmission. We compared institutional rates and community rates of tuberculin skin test (TST) conversion in Harare, Zimbabwe.

METHODS

We conducted a cohort study of TST conversion 6, 12, and 18 months into training among 159 nursing and 195 polytechnic school students in Harare. Students had negative TST results (induration diameter, < or =9 mm) with 2-step testing at the start of training.

RESULTS

Nursing students experienced 19.3 TST conversions (increase in induration diameter, > or =10 mm) per 100 person-years (95% confidence interval [CI], 14.2-26.2 conversions per 100 person-years), and polytechnic school students experienced 6.0 (95% CI, 3.5-10.4) conversions per 100 person-years. The rate of difference was 13.2 conversions (95% CI, 6.5-20.0) per 100 person-years. With a more stringent definition of conversion (increase in the induration diameter of > or =10 mm to at least 15 mm), which is likely to increase specificity but decrease sensitivity, conversion rates were 12.5 and 2.8 conversions per 100 person-years in nursing and polytechnic school students, respectively (rate difference, 9.7 conversions per 100 person-years; 95% CI, 4.5-14.8 conversions per 100 person-years). Nursing students reportedly nursed 20,868 inpatients with tuberculosis during 315 person-years of training.

CONCLUSIONS

Both groups had high TST conversion rates, but the extremely high rates among nursing students imply high occupational exposure to Mycobacterium tuberculosis. Intense exposure to inpatients with tuberculosis was reported during training. Better prevention, surveillance, and management of institutional M. tuberculosis transmission need to be supported as part of the international response to the severe human immunodeficiency virus infection epidemic and health care worker crisis in Africa.

Using ELISPOT to expose false positive skin test conversion in tuberculosis contacts

Background

Repeat tuberculin skin tests may be false positive due to boosting of waned immunity to past mycobacterial exposure. We evaluated whether an ELISPOT test could identify tuberculosis (TB) contacts with boosting of immunity to non-tuberculous mycobacterial exposure.

Methodology/Principal Findings

We conducted tuberculin and ELISPOT tests in 1665 TB contacts: 799 were tuberculin test negative and were offered a repeat test after three months. Those with tuberculin test conversion had an ELISPOT, chest X-ray and sputum analysis if appropriate. We compared converters with non-converters, assessed the probability of each of four combinations of ELISPOT results over the two time points and estimated boosting with adjustment for ELISPOT sensitivity and specificity. 704 (72%) contacts had a repeat tuberculin test; 176 (25%) had test conversion, which increased with exposure to a case (p = 0.002), increasing age (p = 0.0006) and BCG scar (p = 0.06). 114 tuberculin test converters had ELISPOT results: 16(14%) were recruitment positive/follow-up positive, 9 (8%) positive/negative, 34 (30%) negative/positive, and 55 (48%) were negative/negative. There was a significant non-linear effect of age for ELISPOT results in skin test converters (p = 0.038). Estimates of boosting ranged from 32%–41% of skin test converters with increasing age. Three converters were diagnosed with TB, two had ELISPOT results: both were positive, including one at recruitment.

Conclusions/Significance

We estimate that approximately one third of tuberculin skin test conversion in Gambian TB case contacts is due to boosting of immunity to non-tuberculous mycobacterial exposure. Further longitudinal studies are required to confirm whether ELISPOT can reliably identify case contacts with tuberculin test conversion that would benefit most from prophylactic treatment.

QuantiFERON-TB Gold: state of the art for the diagnosis of tuberculosis infection?

Tuberculosis (TB) remains a major threat to global health. The recently launched Global Plan to Stop Tuberculosis 2006-2015 highlights the need for accurate, simple and low-cost diagnostic tests for the detection of TB infection. For the first time in decades, new diagnostic tools have emerged that may facilitate this goal. The discovery of Mycobacterium tuberculosis-specific immunodominant antigens has led to the development of interferon gamma-release assays that have been shown to have high sensitivity and specificity for TB disease. This review focuses on the QuantiFERON-TB Gold tests and addresses the potential strengths and limitations of the current assays, summarizes the available evidence for their use and identifies areas of future research and development. Although representing an advance in TB diagnostics, with the potential to have a significant impact on global TB control, many issues remain unanswered. The cost of the tests and laboratory requirements may limit their use in developing countries. Most importantly, additional studies are needed in TB-endemic regions, particularly in high-risk persons such as children and individuals who are also co-infected with HIV.

Tuberculosis among health-care workers in low- and middle-income countries: a systematic review

BACKGROUND

The risk of transmission of Mycobacterium tuberculosis from patients to health-care workers (HCWs) is a neglected problem in many low- and middle-income countries (LMICs). Most health-care facilities in these countries lack resources to prevent nosocomial transmission of tuberculosis (TB).

METHODS AND FINDINGS

We conducted a systematic review to summarize the evidence on the incidence and prevalence of latent TB infection (LTBI) and disease among HCWs in LMICs, and to evaluate the impact of various preventive strategies that have been attempted. To identify relevant studies, we searched electronic databases and journals, and contacted experts in the field. We identified 42 articles, consisting of 51 studies, and extracted data on incidence, prevalence, and risk factors for LTBI and disease among HCWs. The prevalence of LTBI among HCWs was, on average, 54% (range 33% to 79%). Estimates of the annual risk of LTBI ranged from 0.5% to 14.3%, and the annual incidence of TB disease in HCWs ranged from 69 to 5,780 per 100,000. The attributable risk for TB disease in HCWs, compared to the risk in the general population, ranged from 25 to 5,361 per 100,000 per year. A higher risk of acquiring TB disease was associated with certain work locations (inpatient TB facility, laboratory, internal medicine, and emergency facilities) and occupational categories (radiology technicians, patient attendants, nurses, ward attendants, paramedics, and clinical officers).

CONCLUSIONS

In summary, our review demonstrates that TB is a significant occupational problem among HCWs in LMICs. Available evidence reinforces the need to design and implement simple, effective, and affordable TB infection-control programs in health-care facilities in these countries.

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.

Childhood tuberculosis diagnosed and managed as asthma: case report

The worldwide incidence of tuberculosis (TB) has been increasing. Although its diagnosis is well established in adults, in children it is difficult due to its particular aspects. We report a 3 years and 8 month-old infant who experienced chronic wheezing, classified as moderate-to-severe asthma, had recurrent pneumonia, and was not responsive to management with beta adrenergic agents. Chest X-rays (CXR) showed heterogeneous condensation in medium lobe and the chest computerized-tomography scan (CCT) a heterogeneous increase in pulmonary transparency, like condensation in the same lobe. After four months of treatment with anti tuberculosis agents, a significant improvement in symptoms, normal CXR, absence of pulmonary medium lobe condensation, and persistence fibro-atelectatic band in lingula were observed.

A novel fusion protein-based indirect enzyme-linked immunosorbent assay for the detection of bovine tuberculosis

Enzyme-linked immunosorbent assay (ELISA) for diagnosis of bovine tuberculosis has been widely explored over the years. Three Mycobacterium bovis-specific antigen genes, namely, mpb70, mpb83, and esat-6 were recombined in tandem by spliced overlap extension technology and expressed in Escherichia coli to obtain the fusion protein (rM70-83-E6). Western blot analysis showed that rM70-83-E6 can specifically react with bovine tuberculosis-positive sera but not those from cattle infected with other bovine diseases such as bovine paratuberculosis. An indirect ELISA (iELISA) method was established with rM70-83-E6 as the diagnostic antigen. The diagnostic criteria were determined using 150 serum samples from healthy cattle. Analyses of 85 serum samples from cattle with bovine tuberculosis and 100 serum samples from healthy cattle demonstrated that the sensitivity of the iELISA was 69.4% (59/85) and the specificity was 96.0% (96/100). Moreover, 46 out of 67 purified protein derivative (PPD) skin test-positive samples were also positive by iELISA, giving a positive coincidence of 68.7%, while all 50 PPD skin test-negative samples were negative by iELISA, giving a negative coincidence of 100%. The total coincidence between iELISA and the PPD skin test was 82.1%. This study demonstrated that iELISA using rM70-83-E6 antigen is simple, sensitive and easy to perform and can be used to analysis of a large number of samples for serodiagnosis of bovine tubercuiosis.

Dynamic Antigen-specific T-Cell Responses after Point-Source Exposure toMycobacterium tuberculosis

RATIONALE

The kinetics of Mycobacterium tuberculosis-specific Th1-type T-cell responses after M. tuberculosis infection are likely to be important in determining clinical outcome.

OBJECTIVE

To investigate the kinetics of T-cell responses, in the context of a point-source school tuberculosis outbreak, in three groups of contacts who differed by preventive treatment status and tuberculin skin test (TST) results: 38 treated TST-positive students, 11 untreated TST-positive staff, and 14 untreated students with negative or borderline TST results.

METHODS

We used the ex vivo IFN-gamma enzyme-linked immunospot assay (ELISpot) to track T cells specific for two region of difference 1 (RD1) antigens, early secretory antigenic target 6 and culture filtrate protein 10, for 18 mo after cessation of tuberculosis exposure.

MAIN RESULTS

The treated TST-positive students had an average 68% decline in frequencies of RD1-specific IFN-gamma-secreting T cells per year (p < 0.0001) and 6 of 38 students had no detectable RD1-specific T cells by 18 mo. No change in frequencies of these cells was observed in the untreated TST-positive staff (p = 0.38) and none were ELISpot-negative at 18 mo. Of the 14 untreated students, 7 were persistently ELISpot-positive (all of whom had borderline TST results), and 7 became ELISpot-negative (all but one had negative TST results) during follow-up.

CONCLUSIONS

The decrease in M. tuberculosis-specific T cells and their disappearance in a proportion of treated students likely reflect declining antigenic and bacterial load in vivo induced by antibiotic treatment. The observed disappearance of M. tuberculosis-specific T cells in the untreated TST-negative contacts suggests that an acute resolving infection may occur in some contacts.

Safety of ESAT-6

A recombinant dimer of the Mycobacterium tuberculosis (MTb) 6 kDa early secreted antigenic target (ESAT-6) was produced in Lactococcus lactis. Pharmacodynamic and safety studies were carried out in guinea pigs, rats, mice and dogs with intradermal (id), subcutaneous (sc) and intravenous (iv) administration of the antigen. In contrast to tuberculin purified protein derivative (PPD) the recombinant dimer (rdESAT-6) was able to discriminate MTb infection from BCG vaccination in vivo. In guinea pigs sensitized by infection with MTb, 1 microg rdESAT-6 gave a mean delayed-type hypersensitivity (DTH) response of 22 mm, a significantly stronger reaction than in animals sensitised by the environmental mycobacteria M. kansasii, M. szulgai and M. marinum. rdESAT-6 proved to be a safe tuberculin reagent in a dose range of 1-1000 microg with no or only minor local reactions.

Risk of tuberculin conversion among healthcare workers and the adoption of preventive measures

BACKGROUND

In industrialised countries, occupational tuberculosis among healthcare workers (HCWs) is re-emerging as an important public health issue. To prevent and control tuberculosis transmission, several institutions have issued and implemented recommendations and practice guidelines.

OBJECTIVES

To estimate the annual rate of tuberculosis infection (ARTI; per 100 person-years) among HCWs in Turin, the capital of the Piedmont region of Italy, to identify factors associated with variations in the ARTI and to evaluate the efficacy of the regional guidelines to prevent and control tuberculosis.

METHODS

The study was conducted between 1997 and 2004 on a cohort of HCWs. The tuberculosis infection was diagnosed through tuberculin skin testing (TST) conversion and defined as an induration increase of at least 10 mm from a previous negative TST. The ARTI and the hazard ratio for each at-risk subgroup, categorised according to working activities and settings, was estimated using exponential survival models. The efficacy of the regional guidelines was estimated by stratifying the analysis according to the moment of the implementation of the guidelines (before/after).

RESULTS

The 2182 study participants were drawn from the dynamic cohort. The overall adjusted ARTI was 1.6 (95% CI: 1.3 to 1.9)/100 person-years. Different workplaces (eg, administrative and infectious diseases inpatient services) and occupations (eg, clerical and medical workers) were associated with significantly different ARTIs, ranging between 0.62 and 2.62 and between 0.61 and 1.71, respectively, whereas the TST conversion risk differed by about 16-68% and 30-60%, respectively. The implementation of the guidelines coincided with overall ARTI reductions of 1.3/100 person-years, and concurrently the variations between ARTIs of different occupations and workplaces disappeared.

CONCLUSIONS

The occupational risk categories for targeting the surveillance and prevention of tuberculosis transmission among HCWs were identified, and the introduction of preventive measures was observed to be effective in decreasing the overall risk of tuberculosis infection among HCWs.

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.

Tuberculin skin test conversion and reactivity rates among adults with and without human immunodeficiency virus in urban settings in Ethiopia

To investigate whether low CD4+ T-cell counts in healthy and human immunodeficiency virus (HIV)-infected Ethiopians influence tuberculosis (TB) immunological memory, tuberculin skin test (TST) conversion and reactivity rates were investigated among adults with and without HIV infection in urban settings in Ethiopia. Reaction to the TST was analyzed with purified protein derivative by the Mantoux technique. A total of 1,286 individuals with TST results of > or = 5-mm (n = 851) and < or = 4-mm (n = 435) induration diameters were included. Individuals with < or = 4-mm induration sizes were followed up for 21.4 +/- 9.5 months (mean +/- standard deviation) to observe skin test conversion. The overall TST reactivity (> or = 5-mm induration diameter) was 66.2% (n = 851). Reactivity was significantly lower among HIV-positive persons (40.5%) than among HIV-negative persons (68.7%) (P < 0.001). Of the above persons, 32 incident TB patients were checked for their TST status 13.05 +/- 11.1 months before diagnosis and reactivity was found among 22 (68.7%) of them. Of the TST-negative persons with 0- to 4-mm indurations who were followed up for 3 years, the conversion rate to positivity was 17.9/100 person-years of observation (PYO) (14.4/100 PYO and 18.3/100 PYO in HIV-positive and -negative persons, respectively). Despite lower absolute CD4+ T-cell numbers in Ethiopians, higher TST conversion and reactivity rates show the presence of a higher rate of latent TB infection and/or transmission. The lower TST positivity rate before a diagnosis of TB disease showed the lower sensitivity of the test. This indicates the need for other sensitive and specific diagnostic and screening methods to detect TB infection, particularly among HIV-positive persons, so that they can be given prophylactic isoniazid therapy.

Serial testing of health care workers for tuberculosis using interferon-gamma assay

RATIONALE

Although interferon-gamma (IFN-gamma) assays are promising alternatives to the tuberculin skin test (TST), their serial testing performance is unknown.

OBJECTIVE

To compare TST and IFN-gamma conversions and reversions in healthcare workers.

METHODS

We prospectively followed-up 216 medical and nursing students in India who underwent baseline and repeat testing (after 18 mo) with TST and QuantiFERON-TB Gold In-Tube (QFT). TST conversions were defined as reactions greater than or equal to 10 mm, with increments of 6 or 10 mm over baseline. QFT conversions were defined as baseline IFN-gamma less than 0.35 and follow-up IFN-gamma greater than or equal to 0.35 or 0.70 IU/ml. QFT reversions were defined as baseline IFN-gamma greater than or equal to 0.35 and follow-up IFN-gamma less than 0.35 IU/ml.

RESULTS

Of the 216 participants, 48 (22%) were TST-positive, and 38 (18%) were QFT-positive at baseline. Among 147 participants with concordant baseline negative results, TST conversions occurred in 14 (9.5%; 95% confidence interval [CI] = 5.3-15.5) using the 6 mm increment definition, and 6 (4.1%; 95% CI = 1.5-8.7) using the 10 mm increment definition. QFT conversions occurred in 17/147 participants (11.6%; 95% CI = 6.9-17.9) using the definition of IFN-gamma greater than or equal to 0.35 IU/ml, and 11/147 participants (7.5%; 95% CI = 3.8-13.0) using IFN-gamma greater than or equal to 0.70 IU/ml. Agreement between TST (10 mm increment) and QFT conversions (>or= 0.70 IU/ml) was 96% (kappa = 0.70). QFT reversions occurred in 2/28 participants (7%) with baseline concordant positive results, as compared with 7/10 participants (70%) with baseline discordant results (p < 0.001).

CONCLUSIONS

IFN-gamma assay shows promise for serial testing, but repeat results need to be interpreted carefully. To meaningfully interpret serial results, the optimal thresholds to distinguish new infections from nonspecific variations must be determined.

High rate of negative results of tuberculin and QuantiFERON tests among individuals with a history of positive skin test results

OBJECTIVES

To evaluate individuals at high risk for tuberculosis exposure who had a history of a positive tuberculin skin test (TST) result in order to determine the prevalence of unsuspected negative TST results. To confirm these findings with the QuantiFERON-TB test (QFT), an in vitro whole-blood assay that measures tuberculin-induced secretion of interferon-gamma.

METHODS

This survey was conducted from November 2001 through December 2003 at 3 sites where TST screening is regularly done. Detailed histories and reviews of medical records were performed. TSTs were placed and read by 2 experienced healthcare workers, and blood was drawn for QFT. Any subject with a negative result of an initial TST during the study (induration diameter, <10 mm) underwent a second TST and a second QFT. The TST-negative group comprised individuals for whom both TSTs had an induration diameter of <10 mm. The confirmed-negative group comprised individuals for whom both TSTs yielded no detectable induration and results of both QFTs were negative.

RESULTS

A total of 67 immunocompetent subjects with positive results of a previous TST were enrolled in the study. Of 56 subjects who completed the TST protocol, 25 (44.6%; 95% confidence interval [CI], 31.6%-57.6%) were TST negative (P<.001). Of 31 subjects who completed the TST protocol and the QFT protocol, 8 (25.8%; 95% CI, 10.4%-41.2%) were confirmed negative (P<.005).

CONCLUSIONS

A significant proportion of subjects with positive results of a previous TST were TST negative in this study, and a subset of these were confirmed negative. These individuals' TST status may have reverted or may never have been positive. It will be important in future studies to determine whether such individuals lack immunity to tuberculosis and whether they should be considered for reentry into tuberculosis screening programs.

The importance of two-step tuberculin skin testing for newly employed healthcare workers

At the time of hire, 4059 of 6522 healthcare workers required a 2-step tuberculin skin test; 114 workers (2.8%) demonstrated a boosted reaction after the second step. Boosted reactions were significantly associated with male sex and older age. A verbal history of previous tuberculin skin test results was not a reliable indicator of baseline tuberculin skin test status at the time of hire.

Transtracheal Open Ventilation in Acute Respiratory Failure Secondary to Severe Chronic Obstructive Pulmonary Disease Exacerbation

RATIONALE

Patients who fail noninvasive ventilation are generally intubated and are then subjected to complications of invasive mechanical ventilation. With transtracheal open ventilation, ventilator support is delivered through an uncuffed small bore minitracheostomy tube, which eliminates pooling of secretions above the cuff and thus reduces the risk of tracheobronchial microbial colonization.

OBJECTIVE

To compare transtracheal open ventilation (treatment group) with conventional invasive ventilation (control group) in patients with exacerbation of chronic obstructive pulmonary disease who initially failed noninvasive ventilation.

METHODS

Patients were randomized to receive trans-tracheal open ventilation (n=19) or conventional invasive ventilation (n=20).

MEASUREMENTS AND MAIN RESULTS

There was no difference in arterial blood gases after 1 and 30 h between the two groups. Two patients receiving transtracheal open ventilation and 13 undergoing conventional ventilation had complications (p<0.0001). Compared with conventional ventilation, transtracheal open ventilation significantly decreased both the duration of mechanical ventilation (7.6+/-4.7 vs. 18.6+/-10.6 d, p<0.0001) and length of stay in the intensive care unit (10.2+/-4.5 vs. 21.3+/-9.7 d, p<0.0001).

CONCLUSIONS

Transtracheal open ventilation was as effective as conventional ventilation in maintaining adequate gas exchange and reducing complications, duration of mechanical ventilation, and intensive care unit length of stay.

Prevalence and incidence of Mycobacterium tuberculosis infection in nursing students in Vitória, Espírito Santo

This prospective study evaluated the incidence of Mycobacterium tuberculosis infection among nursing students at the Federal University of Espírito Santo, using the purified protein derivative test. In parallel, we evaluated whether knowledge on tuberculosis transmission mechanisms had any impact on nursing students' attitudes in relation to the risk of tuberculosis infection. The incidence of tuberculin conversion was 10.5% per year (p=0.035, 95% CI = 3.63-17.43), whereas the expected conversion rate in the overall population in Brazil is 0.5% per year. These results indicate nursing students as a group at risk for TB infection. Among the risk factors studied only the use of NIOSH95 masks was associated with protection against infection (RR=0.2). Furthermore there was no statistical difference among students that PPD converted and those who remained negative regarding disease knowledge and the existence of adequate facilities for patient hospitalization. Our data reinforces the need for implementing special biosafety programs targeting this professional group.

The Value of Serum Antilipoarabinomannan Antibody Detection in the Diagnosis of Latent Tuberculosis in Hemodialysis Patients

BACKGROUND

The risk for tuberculosis (TB) reactivation in hemodialysis (HD) patients is increased, and screening for latent TB is recommended. The tuberculin skin test (TST) is inaccurate because of the high incidence of anergy in skin testing in HD patients and its inability to differentiate latent from eradicated TB infection. In this study, use of serum antilipoarabinomannan (anti-LAM) antibody detection for the diagnosis of latent TB in a dialysis population was evaluated.

METHODS

Seventy-four HD patients never treated for TB composed the first group. Forty-eight healthy volunteers never treated for TB served as controls. Twenty-one TST-positive renal transplant candidates on dialysis therapy who had completed preventive anti-TB treatment formed a third group. The TST (using the Mantoux method) and anti-LAM test (using an immunochromatographic assay) were performed in all subjects participating in the study.

RESULTS

In the first group, a strong association was detected between results of the TST and anti-LAM test (P < 0.0001, chi-square test). A similar association was found in the second group. In the group of HD patients treated for TB, a positive TST result and negative anti-LAM test result was a constant finding.

CONCLUSION

The association between the TST and anti-LAM test in HD patients suggests that the anti-LAM test could be a useful tool for diagnosing latent TB. The absence of anti-LAM antibodies in anti-TB-treated HD patients suggests that immune response to lipoarabinomannan lacks long-lasting memory. A negative anti-LAM test result might reflect the absence of latent TB, even in patients with a positive TST result.

Number of negative acid-fast smears needed to adequately assess infectivity of patients with pulmonary tuberculosis

STUDY OBJECTIVES

To investigate the relationship between the number of negative acid-fast bacilli (AFB) smear results and infectivity of pulmonary tuberculosis (TB).

DESIGN

Retrospective analysis.

METHODS AND SUBJECTS

We examined 122 index cases in Harris County, TX, reported in 1998 and 1999. All cases had only negative AFB smear results during the infectious period and were categorized in two groups: group A consisted of cases with only one or two sputum specimens collected and processed, and group B consisted of cases with at least three sputum specimens or at least one bronchoscopic specimen. Tuberculin skin test (TST) results of contacts were ascertained from the results of contact investigations performed by the City of Houston Department of Health and Human Services, Tuberculosis Control Division. Univariate and multivariate analyses were done to explore index case and contact attributes associated with tuberculosis (TB) transmission using positive TST results of contacts as a measure of recent transmission.

RESULTS

We found male gender and younger age of index cases along with Hispanic ethnicity of contacts to be independently associated with positive TST results, while younger contacts were less likely to be TST positive. Smear category of the index case (group A vs group B) was not independently associated with transmission. We also found that the first two sputum specimens in cases where three or more were performed yielded 90% of all positive culture results for Mycobacterium tuberculosis (MTB).

CONCLUSIONS

We conclude that two sputum specimens negative for AFB stain are adequate for both assessing infectivity and for isolating MTB from patients with pulmonary TB.

CD69 expression on CD4+ T lymphocytes after in vitro stimulation with tuberculin is an indicator of immune sensitization against Mycobacterium tuberculosis antigens

The expression of the CD69 antigen on CD4 T lymphocytes after in vitro stimulation with purified protein derivative (2 tuberculin units) was used to evaluate the tuberculin reactivities of 52 individuals from four experimental groups: Mycobacterium bovis BCG-vaccinated healthy individuals with a negative tuberculin skin test (TST) result (group A), BCG-vaccinated healthy individuals with a positive TST result (group B), patients with active tuberculosis (TB) before treatment (group C), and individuals with clinically inactive TB who had previously completed a prescribed course of chemotherapy (group D). The expression of CD69 on CD4 T lymphocytes was significantly higher in patients with active TB (16.2%+/-7.3%), individuals with clinically inactive TB (10.5%+/-7.4%), and healthy individuals with a positive TST result (15.5%+/-7.2%) than in healthy individuals with a negative TST result (3.8%+/-4.3%) (P<0.005). We confirmed the correlation between CD69 antigen expression on T lymphocytes after stimulation with tuberculin and the TST induration diameter (Spearman rho=0.783; P<0.001), an assay for gamma interferon (the Quantiferon-TB assay; Spearman rho=0.613; P<0.001), and the lymphocyte BLAST transformation test (Spearman rho=0.537; P<0.001). Our results demonstrate the usefulness of the determination of CD69 on CD4 T lymphocytes after in vitro stimulation with tuberculin as a rapid indicator of immune sensitization against Mycobacterium tuberculosis.

High risk of Mycobacterium tuberculosis infection during the Hajj pilgrimage

INTRODUCTION

Annually more than 2 million pilgrims from all over the world attend the Hajj in Saudi Arabia. Overcrowding during this pilgrimage leads to a high risk of transmission of airborne infectious diseases. Tuberculosis (TB) is common among hospitalized pilgrims, but the overall risk of acquiring Mycobacterium tuberculosis infection during this pilgrimage is not known. We conducted a prospective study to assess the risk of M. tuberculosis infection among Hajj pilgrims.

METHODS

We measured the immune response to TB antigens using a whole-blood assay (QuantiFERON TB assay) prior to departure and 3 months after return from the Hajj pilgrimage.

RESULTS

Of 357 paired assays, 149 pilgrims were negative prior to the Hajj and 15 (10%) of these had a significant rise in immune response to TB antigens.

CONCLUSIONS

Pilgrims may be at high risk of acquiring M. tuberculosis infection during the Hajj. This has significant public health implications for TB control in countries with large Muslim populations.

The utility and interpretation of tuberculin skin tests in the Middle East

Tuberculin skin test (TST) interpretation can be confounded by Bacillus Calmette-Guerin (BCG) vaccination and infection with nontuberculosis mycobacteria (NTM). However, a wealth of epidemiologic information has allowed the formulation of recommendations for reasonably informed interpretation of the TST in most clinical situations. In the Middle East, the TST remains a useful test. BCG vaccination is given at birth, which should have minimal effect on TST reactions in adolescents or adults. In countries of the Middle East with moderate to high incidence of active smear-positive pulmonary TB (>20 per 100,000 per year), a positive TST will almost always indicate true TB infection. However, in Middle East countries with very low incidence of active TB (<10 per 100,000 per year), a positive TST will more likely be false positive because BCG vaccination is still routinely given; until BCG vaccination is abandoned, the TST will be less useful in these countries. These findings are applicable to countries in other regions of the world, and the utility TST will also be increased where the likelihood of TB infection is higher and lowered where TB infection is unlikely, yet BCG vaccination is still given.

Influência do tamanho do frasco de tuberculina nos resultados da prova tuberculínica

INTRODUÇÃO: A solução de tuberculina é armazenada em frascos de diferentes tamanhos. Sua adsorção ao frasco pode influenciar o resultado da prova tuberculínica. OBJETIVO: Avaliar o efeito do tamanho do frasco de armazenamento da tuberculina nos resultados obtidos na prova tuberculínica. MÉTODO: Sessenta e três pacientes internados com diagnóstico de tuberculose ativa foram submetidos a duas provas tuberculínicas simultâneas, em ambos os antebraços. A técnica usada foi a de Mantoux e consistiu na aplicação de 0,1 ml de tuberculina armazenada em frascos de 5 ml ou de 1,5 ml, no antebraço direito e no antebraço esquerdo, de forma aleatória. A leitura da induração foi efetuada de forma cega por um único leitor treinado previamente. As leituras com diferenças de até 2 mm foram consideradas resultados concordantes. RESULTADOS: Vinte e um pacientes não tiveram induração e foram excluídos da análise. Entre os 42 pacientes restantes, a média dos diâmetros das indurações obtidas nas provas com tuberculina armazenada nos frascos grandes foi maior do que as obtidas com a armazenada em frascos pequenos. A concordância entre as leituras foi obtida em 40,5% delas (17/42), e a diferença foi negativa (frasco grande menor que frasco pequeno) em 16,7% (7/42) e positiva em 42,9% delas (18/42). CONCLUSÃO: O tamanho do frasco de armazenamento da tuberculina pode influenciar o resultado da prova tuberculínica. A adsorção da tuberculina à parede do frasco pode explicar o fenômeno. Os autores alertam para o impacto dessas variações nos estudos epidemiológicos e operacionais.

Validity of using tuberculin skin test erythema measurement for contact investigation during a tuberculosis outbreak in schoolchildren previously vaccinated with BCG

BACKGROUND

Few studies have examined the validity of administering tuberculosis control measures based on tuberculin skin test (TST) erythema measurement. The present study aimed to clarify the relationship between the erythema and the induration seen following TST and to evaluate the validity of diagnosing tuberculosis infection based on the erythema following TST in school-aged contacts who had been vaccinated with bacillus Calmette-Guérin (BCG) in infancy.

METHODS

A 56-month longitudinal study from January 1999 through September 2003 followed 566 junior high school students in Kochi City who were contacts of an infectious tuberculosis case. To evaluate the diagnostic accuracy of the erythema and induration following TST of the contacts, false-positive and false-negative TST results were noted.

RESULTS

The natural logarithm of the erythematous response size was linearly related to the induration size. When the size of the erythematous response was used to determine the presence of tuberculosis infection, the proportion of infected children increased with increasing exposure to the index case. When the TST results in the contact investigation were interpreted together with the change in the size of the erythematous response from that observed at the regular school-entry checkup, false positive test results were avoidable among the students who had a large erythematous response after the contact investigation TST, but whose response was only slightly larger than their erythematous response following the school-entry TST. Among the students whose TST results were negative, 1.9% developed tuberculosis.

CONCLUSION

Both erythema and induration measurement were equally effective for identifying tuberculosis infection in schoolchildren vaccinated with BCG.

Influence of Bacille Calmette-Guerin Vaccination on Size of Tuberculin Skin Test Reaction: To What Size?

BACKGROUND

Previous bacillus Calmette-Guerin (BCG) vaccination can confound the results of a tuberculin skin test (TST). We sought to determine a cutoff diameter of TST induration beyond which the influence of BCG vaccination was negligible in evaluating potential Mycobacterium tuberculosis infection in a population of health care workers with a high vaccination rate and low incidence of tuberculosis.

METHODS

From 1991 through 1998, all new employees at the University Hospital of Lausanne, Switzerland, underwent a 2-step TST at entry visit. We also gathered information on demographic characteristics, along with factors commonly associated with tuberculin positivity, including previous BCG vaccination, history of latent M. tuberculosis infection, and predictors for M. tuberculosis infection.

RESULTS

Among the 5117 investigated subjects, we found that influence of BCG vaccination on TST results varied across categories of age (likelihood ratio test, 0.0001). Prior BCG vaccination had a strong influence on skin test results of <or=18 mm in diameter among persons <40 years old, compared with the influence of factors predictive of M. tuberculosis infection. Prior latent M. tuberculosis infection and travel or employment in a country in which tuberculosis is endemic also had significant influences.

CONCLUSIONS

Interpretation of TST reactions of <or=18 mm among BCG-vaccinated persons <40 years of age must be done with caution in areas with a low incidence of tuberculosis. In such a population, except for persons who have never been vaccinated, TST reactions of <or=18 mm are more likely to be the result of prior vaccination than infection and should not systematically lead to preventive treatment.

Revised Guidelines for the Diagnosis and Control of Tuberculosis

Despite major progress in the development of new strategies for diagnosing and treating tuberculosis, the disease still remains a major challenge for healthcare workers throughout the world. A number of causes are responsible for this threat but, unfortunately, many of these cannot be resolved easily because of cultural and social factors. Furthermore, not all countries throughout the world have enough financial resources to support educational and therapeutic programmes. The major challenges with tuberculosis are 2-fold: (i) to deal with the growing epidemic around the world (and especially in 'low-income' [developing] countries), and; (ii) to ensure correct use of antituberculosis medications in order to protect these drugs for future use. In 'high-income' countries, a major decline in the incidence of tuberculosis has been observed. Nevertheless, tuberculosis remains an important challenge in some risk groups, particularly the elderly patient, in these countries. The clinical and radiological presentations are often nonspecific, leading to delayed diagnosis and appropriate treatment, which often results in a large proportion of cases being discovered at autopsy only. Considering tuberculosis in the differential diagnosis remains the cornerstone of a fast and accurate diagnosis of this condition. Management of active tuberculosis in the elderly does not differ fundamentally from that in younger patients with respect to outcomes or adverse effects of treatment. However, empirical treatment perhaps may be considered more readily in the elderly patient. Elderly persons infected with tuberculosis at the beginning of the 20th century constitute a large reservoir of latent tuberculosis infection. Furthermore, these individuals are at increased risk of reactivation of this remote infection as their immunological status declines with aging. Compared with the past, modern guidelines are less reluctant to recommend use of tuberculin skin testing, treatment of latent tuberculosis infection in elderly persons, and prevention of transmission of tuberculosis in nursing homes.

Vaccination technique, PPD reaction and BCG scarring in a cohort of children born in Guinea-Bissau 2000-2002

The rates of positive tuberculin skin test (TST) reactions and BCG scarring after BCG vaccination vary between studies and populations. Tuberculin reactivity and BCG scarring may be related to better child survival in low-income countries. We therefore studied determinants for TST reaction and scarring in Guinea-Bissau. In a cohort of children born in suburban Bissau from March 2000 to July 2002, we assessed a Mantoux test with Purified protein derivative (PPD) (SSI, 2 T.U.) at 2 (2689 children), 6 (N=2148) and 12 months (N=1638) of age, and BCG scar was assessed at 2 (N=2698) and 6 months (N=2225) of age. In a subgroup of the children the vaccination technique was monitored by direct observation of post-vaccination wheal and route of administration. Three different types of BCG vaccine supplied by the local Extended Programme on Immunization were used. At 6 months of age the rate of PPD reactors (>1mm) after BCG vaccination was 25% and the rate of scarring was 89%. One BCG strain was associated with fewer PPD reactors (OR=0.54 (0.31-0.91)) and BCG scars (OR=0.13 (0.05-0.37)) and larger post-vaccination wheals produced more PPD reactions (OR 1.21 (95% CI 1.02-1.43)) and BCG scars (OR 1.66 (1.24-2.21)). In the multivariable analyses of BCG-vaccinated children assessed at 6 months of age, monitoring of vaccination technique and type of BCG vaccine were important. This was not changed by control for other determinants, including sex, season, vaccination place, birthplace, ethnic group, low birth weight, place of residence, education and civil status of mother. We reason that vaccination technique and BCG strain are important for PPD reaction and scarring in response to BCG vaccination. Considering that these responses are associated with better infant survival, the importance of monitoring vaccination technique and of different BCG strains should be evaluated with respect to infant mortality.

The influence of BCG immunisation on tuberculin reactivity and booster effect in adults in a country with a high prevalence of tuberculosis

The relationship of age and previous BCG vaccination with tuberculin skin test (TST) reactivity was investigated to assess the interpretation of TST results in the adult population of Turkey, where there is a high prevalence of tuberculosis and a routine BCG vaccination programme. The influences of age and BCG vaccine status on booster reaction were also evaluated. TST was applied (5 tuberculin units of purified protein derivative intradermally) to two healthy adult groups, namely 98 medical students and 187 elderly people in a retirement home. The TST was considered positive if an induration > or = 10 mm in diameter was produced. Subjects (41 elderly people and 39 students) with a reaction < 10 mm in diameter were retested 1 week later. There was no significant difference between the students (59.1%) and elderly subjects (58.8%) with respect to positive TST response. No influence of BCG scars on TST reactivity was observed in either group. The booster effect was seen more commonly in the elderly, but the presence of a BCG scar did not influence the booster effect in either group. It was concluded that a positive TST response and booster reaction in adults in high-prevalence countries may be caused by latent tuberculosis rather than previous vaccination.