Tuberculin response in BCG vaccinated schoolchildren and the estimation of annual risk of infection in Hong Kong

Evaluation of Treatment Indications, Tuberculin Skin Test, and Bacillus Calmette-Guerin Vaccination Scars in the Cases of Latent Tuberculosis Infection Treatment

OBJECTIVES

The aim of our study was to evaluate the latent tuberculosis infection (LTBI) treatment application and to investigate if there is change between tuberculin skin test (TST) results according to bacillus Calmette-Guerin (BCG) scar numbers after LTBI treatment with isoniazid (INH).

MATERIAL AND METHODS

Data were collected from the LTBI treatment files from the dispensary of 2006. The results were statistically evaluated.

RESULTS

Latent tuberculosis infection was administered to 253 cases in 2006. The male/female case rate was 51/49. The age of most patients was under 15 years out of 14 cases. The mean age was 8.92±6.87 years (range, 0-84 years). One case had liver function test abnormality and INH was stopped in the first month of treatment. The completion rate of LTBI treatment was 95%. BCG vaccination rate was 93%. Active tuberculosis did not develop during the LTBI treatment in our study. Of all the cases, 221 scar numbers and TST were full. Of all cases 221 the scar numbers and TST value were full.TST of the 221 cases according to BCG vaccine scar numbers and indications were compared pre- and post-treatment with INH. Indications for LTBI treatment in these cases were close contact with smear-positive active pulmonary tuberculosis cases (n=77, 35%), TST-positive children aged <15 years (n=138, 62%), and the other (n=6, 3%) immunosuppressed patient cases. After treatment with INH, TST values decreased in the TST-positive children aged <15 years with one and 2 scars, with a statistically significant this result were found statistically significant (p<0.05).

CONCLUSION

The age of patients in most cases with LTBI treatment was under 15 years. The treatment completion rate and BCG vaccination rate were high. One case had liver function test abnormality. Active tuberculosis did not develop during the LTBI treatment. In the group with TST-positive children aged <15 years with one and 2 BCG vaccine scars, the decrease between pre- and post-treatment TST results showed a statistically significant difference.

Poor agreement between diagnostic tests for latent tuberculosis infection among HIV-infected persons in Hong Kong

BACKGROUND AND OBJECTIVE

The tuberculin skin test (TST), T-Spot.TB (T-Spot) and QuantiFERON-TB Gold-In Tube (QFT) were compared in diagnosing latent tuberculosis infection (LTBI) among human immunodeficiency virus (HIV)-infected persons.

METHODS

Human immunodeficiency virus-infected persons without previous history of tuberculosis or LTBI were simultaneously tested by TST, T-Spot and QFT annually and followed up for tuberculosis.

RESULTS

Among 110 HIV-infected subjects with 85% previous TST screening coverage, 75% on anti-retroviral therapy, well-preserved median CD4 count (414/μL) and low median viral load (<75/μL), baseline TST, T-Spot and QFT were positive in 5.5%, 5.6% and 4.9%, respectively, with almost complete discordance of positive results. Among 91 (83%), 66 (60%) and 26 (24%) subjects successfully undergoing the first, second and third annual retesting, TST, T-Spot and QFT were, respectively, positive in 11/123 (8.9%), 13/173 (7.5%) and 21/182 (11.5%) on retesting, with similar discordance of positive results. There was no significant association with the concurrent CD4 count or viral load. Conversion occurred in 11/123 (8.9%), 8/160 (5.0%) and 18/168 (10.7%) of TST, T-Spot and QFT, respectively, and none was associated with changes in CD4 count or viral load. More than half of the positive T-SPOT and QFT results reverted to negative on follow-up. None of these tests picked up the single case of culture-confirmed tuberculosis observed after 798 person-years of follow-up.

CONCLUSION

Major discordance in positive results, high reversion rates and low tuberculosis incidence among test-positive subjects cast serious doubt on the utility of the currently available LTBI tests in the annual screening of HIV-infected persons in an intermediate tuberculosis burden area.

T-Spot.TB outperforms tuberculin skin test in predicting development of active tuberculosis among household contacts

BACKGROUND AND OBJECTIVE

In Hong Kong, neonatal Bacillus Calmette-Guerin (BCG) vaccination is practiced with 99% coverage. This study was to compare the performance of T-Spot.TB and tuberculin skin test (TST) in predicting tuberculosis (TB) among household contacts.

METHODS

From 1 March 2006 to 31 July 2010, 1049 asymptomatic household contacts of smear-positive patients were simultaneously tested with T-Spot.TB and TST, and then followed for up to 5 years for development of TB. Attending clinicians and subjects were blinded to the results of T-Spot.TB.

RESULTS

T-Spot.TB gave a significantly higher positive rate (32.7% vs 22.1%) and better association with exposure time than TST at the 15 mm cut-off. Agreement between T-Spot.TB and TST using cut-offs of 5, 10 and 15 mm were relatively poor (kappa 0.25-0.41) irrespective of presence or absence of BCG scar. Only T-Spot.TB positivity was negatively associated with BCG scar. Both T-Spot.TB (incidence rate ratio between test-positive and test-negative subjects, IRR: 8.2) and TST (IRR: 4.1, 6.1 and 2.8, using cut-offs of 5 mm, 10 mm and 15 mm, respectively) helped to predict TB. Using a TST cut-off of 15 mm, 56% of future TB cases and 62.5% of bacteriologically confirmed cases were missed. Lowering the TST cut-off to 10 mm or 5 mm could achieve sensitivity comparable with that of T-Spot.TB, but at the expense of lower specificities, with more positive tests (thus requiring treatment) per case of TB predicted.

CONCLUSIONS

T-Spot.TB outperformed TST in predicting TB among household contacts in a high-income area with widespread BCG vaccination coverage.

[The tuberculosis control program in Pelotas/RS, Brazil: home contact investigations]

The aim of this study is to evaluate the investigation actions of home contacts of tuberculosis (TB) index cases in the Tuberculosis Control Program (TCP) of Pelotas/RS - Brazil. This cross-sectional descriptive study was based on data from the records of index cases. The sample consisted of 163 contacts of 68 subjects with pulmonary TB in treatment in the TCP between June and August, 2009. These contacts were predominantly female, over 10 years of age and the daughters of index cases. The requested examination was a chest radiography and bacilloscopy. Active TB was found in 1.8 % of contacts. Results show that assistance for TB patients in Pelotas-Brazil, which is centralized in a single specialized service, hinders the investigation of home contacts. Primary care is required to narrow the gap between professionals and the family, and facilitate early diagnosis and interruption of the TB transmission chain in a timely manner.

In silico analysis and experimental validation of Mycobacterium tuberculosis -specific proteins and peptides of Mycobacterium tuberculosis for immunological diagnosis and vaccine development

Comparative analyses of the Mycobacterium tuberculosis genome with the genomes of other mycobacteria have led to the identification of several genomic regions of difference (RDs) between M. tuberculosis and M. bovis BCG. The identification of immunodominant and HLA-promiscuous antigens and peptides encoded by these RDs could be useful for diagnosis and the development of new vaccines against tuberculosis. The analysis of RD proteins and peptides by in silico methods (using computational programs to predict major and HLA-promiscuous antigenic proteins and peptides) and experimental validations (using peripheral blood mononuclear cells and sera from tuberculosis patients and BCG-vaccinated healthy subjects to assess antigen-specific cellular and humoral immune responses in vitro) identified several major antigens and peptides. To evaluate the in vivo potentials, the genes of immunodominant antigens were cloned and expressed in DNA vaccine vectors. Immunizations of experimental animals with the recombinant constructs induced antigen-specific cellular responses. Further experiments showed that each of these proteins had several T and B cell epitopes scattered throughout their sequence, which confirmed their strong immunogenicity. In conclusion, the bioinformatics-based in silico identification of promiscuous antigens and peptides of M. tuberculosis is a useful approach to identify new candidates important for diagnosis and vaccine applications.

A strong tuberculin reaction in primary school children predicts tuberculosis in adolescence

BACKGROUND

In Hong Kong, neonatal bacillus Calmette-Guerin vaccination coverage has been around 99% since 1970. Children younger than 14 years of age appear to have a relatively low risk of tuberculosis (TB), but the risk of TB increases rapidly after 15 years of age to a secondary peak in young adulthood.

METHODS

We followed prospectively 19,383 students who were 6 to 10 years of age participating in the 1999/2000 bacillus Calmette-Guerin revaccination program by cross-matching with the territory-wide TB registry until December 31, 2010, using the identity card number as a unique identifier.

RESULTS

After 214,753 person-years of follow-up, 44 active TB cases (22 culture-confirmed) were detected for an overall incidence of 20.5/100,000 person-years. The incidence differed significantly by baseline tuberculin reaction sizes (13.0, 18.8, 22.5, 280.4 per 100,000 person-years for reaction size of 0-4, 5-9, 10-14, and ≥15 mm, respectively, P < 0.001). Consistent results were observed for culture-confirmed cases and after adjustment for gender and baseline age. For those with tuberculin reaction size ≥15 mm, the incidence of TB was significantly higher beyond the age of 15 years than for those less than 15 years (608.1 vs. 37.5 per 100,000 person-years, P < 0.001). Although older baseline age was associated with larger tuberculin reaction sizes, it did not independently predict subsequent development of disease.

CONCLUSION

Strong tuberculin reactions in primary school children predicted TB in adolescents after an initial quiescent period. Endogenous reactivation, possibly related to changes in host immunity, might account for the upsurge of TB in adolescence.

Tuberculin Reactivity in School Age Children; Five-year Follow-up in Iran

OBJECTIVE

Tuberculosis (TB) is an important infectious disease worldwide. Tuberculin skin test (TST) is the standard test for diagnosis of tuberculosis infection; Bacillus Calmette-Guerin (BCG) vaccination at birth has effects on this test. The aim of this study was to determine the prevalence of positive TST cases among 7- to 11-year-old primary school children and also to follow test-positive individuals for a five-year period.

METHODS

TST was performed on 10.184 children aged 7-11 years sampled by cluster random method in Kermanshah, West Iran. Those who had a positive test result (i.e. an induration of ≥15 mm following 72 hours of injecting 0.1 ml of 5 tuberculin units of purified protein derivative from Mycobacterium tuberculosis) were followed for five years to determine the presence of active TB. Also tuberculin positive rates at cut-off points of 10 mm and ≥15 mm for boys and girls and at different ages were derived and compared using the chi-squared test.

FINDINGS

Of 10.184 studied subjects, 830 (8.15%) cases showed positive TST. This rate was 8.7% in boys and 7.8% in girls (P=0.1). A significant linear trend was found between the tuberculin positive rates and age at all cut-off points (P<0.001). No active TB was detected during 5-year follow-up.

CONCLUSION

The rate of positive TST cases in primary school children in Kermanshah, Iran was 8.15% with no new cases of active tuberculosis detection within five-year follow-up.

Immunogenicity of neonatal BCG vaccination in children entering primary school

This study has been designed to evaluate the immunogenicity of neonatal BCG-vaccination in children at the age of 7 to 8 years, by skin test using Purified Protein Derivative (PPD), as BCG vaccination at birth is a part of routine program of immunization in our country, Iran; we decided to study its efficacy and also tried to determine if there is any correlation between PPD-test results and BCG scar size. This is a comparative study on 150 children (94 males and 56 females) at the age of 7 to 8 years, who possess neonatal-BCG scar. They were chosen from several primary schools in Tabriz-Iran, by simple random sampling and tested with 0.1 mL of 5-unit-PPD solution (a product of Iran Institute of Razi); then observations recorded. The average diameter of BCG scars were 7.03 mm in girls, 5.45 mm in boys and 6.05 for all. The diameter of induration area resulted from PPD-test after 72 h was less than 5 mm in 95.33% and 5-9 mm in 4.66% of studied children; there was no case with induration area of 10 mm or more at all. Every child who developed an induration area of 5 mm or more by PPD test, had a BCG scar with the diameter of 5 mm or more. There was a statistically meaningful direct correlation between sizes of neonatal-BCG scar and diameter of induration area after PPD-test (r = 0.21 and p = 0.008). This study shows that reactivity to PPD test (and probably immunity against tuberculosis) decreases as age increases; therefore it seems to be necessary to repeat BCG-vaccination in children at the age of entering primary school.