BCG vaccination to prevent tuberculosis in health care workers: a decision analysis

BCG and New Preventive Tuberculosis Vaccines: Implications for Healthcare Workers

Healthcare workers (HCWs) are at high risk of Mycobacterium tuberculosis (Mtb) infection and tuberculosis disease, but also play a crucial role in implementing healthcare. Preexposure tuberculosis vaccination, including revaccination with BCG, might benefit Mtb-uninfected HCWs, but most HCWs in tuberculosis-endemic countries are already sensitized to mycobacteria. A new postexposure tuberculosis vaccine offers greatest potential for protection, in the setting of repeated occupational Mtb exposure. Novel strategies for induction of mycobacteria-specific resident memory T cells in the lung by aerosol administration, or induction of T cells with inherent propensity for residing in mucosal sites, such as CD1-restricted T cells and mucosa-associated innate T cells, should be explored. The need for improved protection of HCWs against tuberculosis disease is clear. However, health systems in tuberculosis-endemic countries would need significantly improved occupational health structures to implement a screening and vaccination strategy for HCWs.

Agreement of decision analyses and subsequent clinical studies in infectious diseases

PURPOSE

Decision analysis techniques can compare management strategies when there are insufficient data from clinical studies to guide decision making. We compared the outcomes of decision analyses and subsequent clinical studies in the infectious disease literature to assess the validity of the conclusions of the decision analyses.

METHODS

A search strategy to identify decision analyses in infectious disease topics published from 1990 to 2005 was developed and performed using PubMed. Abstracts of all identified articles were reviewed, and infectious disease-related decision analyses were retained. Subsequent clinical trials and observational studies that corresponded to these decision analyses were identified using prespecified search strategies. Clinical studies were considered a match for the decision analysis if they assessed the same patient population, intervention, and outcome. Agreement or disagreement between the conclusions of the decision analysis and clinical study were determined by author review.

RESULTS

The initial PubMed search yielded 318 references. Forty decision analyses pertaining to 29 infectious disease topics were identified. Of the 40, 16 (40%) from 13 infectious disease topics had matching clinical studies. In 12 of 16 (75%), conclusions of at least 1 clinical study agreed with those of the decision analysis. Three of the 4 decision analyses in which conclusions disagreed were from the same topic (management of febrile children).

CONCLUSIONS

There was substantial agreement between the conclusions of decision analyses and clinical studies in infectious diseases, supporting the validity of decision analysis and its utility in guiding management decisions.

Kinetic analysis of Mycobacterium tuberculosis-specific cytokine production by PBMC in adults after BCG vaccination

Although bacille Calmette-Guerin (BCG) has been used worldwide as the only vaccine for tuberculosis, its protective efficacy in human adults is controversial. To investigate human immunological responses to Mycobacterium tuberculosis after BCG vaccination, we analyzed IFN-gamma and IL-10 production by peripheral blood mononuclear cells (PBMC) from health-care workers five times throughout the year after BCG vaccination. Of 449 health-care workers, 36 (8.0%) were negative by the tuberculin skin test, and of these, 20 were vaccinated with BCG. Because all the subjects had received BCG vaccination as infants, the present vaccination was considered to be a revaccination. The cytokine responses of the vaccinated and control tuberculin skin-test-positive subjects (n = 6) were followed at 0, 2, 4, and 8 weeks and at 12 months. The mean IFN-gamma production by PBMC when cultured with purified protein derivative (PPD) gradually increased, reached a peak at week 8, and then declined until 12 months, with four exceptions who showed no IFN-gamma elevation. The IFN-gamma level of the vaccinated group at week 0 was significantly lower than that of the controls. The mean IL-10 production in response to PPD reached a peak at week 2, and then declined to its lowest point at week 8. These results indicate that the BCG vaccine can induce a type I cytokine response to M. tuberculosis in most tuberculin skin-test-negative adults at week 8, suggesting the immunological efficacy of vaccination.

Dual skin testing for latent tuberculosis infection: a decision analysis

BACKGROUND

Recent data indicate that 10- to 14-mm Mycobacterium tuberculosis purified protein derivative (PPD) reactions are often due to prior infections with nontuberculous mycobacteria. Therefore, use of a 10-mm cutpoint to define latent tuberculosis infection (LTBI) results in false-positive diagnoses and unnecessary treatment for LTBI. A second skin test, Mycobacterium avium sensitin (MAS), has been shown to accurately identify false-positive PPD results.

OBJECTIVE

To compare the costs and accuracy of a single skin-test strategy (SST) with PPD alone with a dual skin-test strategy (DST) where 10- to 14-mm PPD results are also tested with MAS.

METHODS

A decision analytic model was developed to evaluate the two strategies. The model accounted for the costs of skin testing, the costs of LTBI treatment, the costs of undetected LTBI, and the sensitivity and specificity of each strategy.

RESULTS

We estimated that DST saved US dollars 3 per subject tested compared to SST. Savings were due to a reduction in false-positive PPD results and consequent reduction in unnecessary treatment for LTBI of >60%. The DST strategy was associated with a minimal increase in undetected LTBI (6% vs 7%). Results were stable for a broad range of parameter values.

CONCLUSIONS

DST is a promising approach to improving the specificity of LTBI testing when a 10-mm PPD cutpoint is used and would reduce costs and unnecessary drug treatment.