Airborne Infection with Bacillus anthracis—from Mills to Mail

The lack of identified exposures in 2 of the 11 cases of bioterrorism-related inhalation anthrax in 2001 raised uncertainty about the infectious dose and transmission of Bacillus anthracis. We used the Wells-Riley mathematical model of airborne infection to estimate 1) the exposure concentrations in postal facilities where cases of inhalation anthrax occurred and 2) the risk for infection in various hypothetical scenarios of exposure to B. anthracis aerosolized from contaminated mail in residential settings. These models suggest that a small number of cases of inhalation anthrax can be expected when large numbers of persons are exposed to low concentrations of B. anthracis. The risk for inhalation anthrax is determined not only by bacillary virulence factors but also by infectious aerosol production and removal rates and by host factors

Making sense of agreement among interferon-gamma release assays and tuberculosis skin testing

BACKGROUND: Numerous studies of interferon-gamma release assays (IGRAs) and tuberculin skin testing (TST) to assess latent tuberculosis infection have been published without a framework to understand the extent to which these two tests should agree. Analyzing the causes of variability in agreement levels is crucial. METHODS: A mathematical model of agreement between dichotomous tests was used to understand variations in the level of agreement between IGRA and TST results. The effect of cut-off point selection on agreement was also explored using the model. Model-based predictions are illustrated using published literature. RESULTS: Analyses of IGRAs and TST that depart from model predictions are an indication that surrogates of prevalence of Mycobacterium tuberculosis infection may have been improperly measured or analyzed. For fixed prevalence, the extent of agreement between tests depends upon cut-off point selection. Changing cut-off points while holding prevalence constant may lead to increasing, decreasing or even no change in agreement. CONCLUSIONS: Researchers have recognized that experimental error, clinical risk and prevalence of non-tuberculous mycobacteria contribute to study-to-study variability. In the present study, we show that paradoxical findings in certain IGRA studies can be explained by the proposed mathematical model. Re-analysis of existing studies may lead to overlooked hypotheses. Future IGRA studies will require epidemiologically well-characterized populations. © 2008 The Union

HIV virologic response better with single-tablet once daily regimens compared to multiple-tablet daily regimens

Background: Single-tablet regimens are preferred prescription choices for HIV treatment, but there are limited outcomes data comparing single-tablet regimens to multiple-tablet regimens. Methods: We retrospectively assessed treatment-naïve patients at a single urban HIV clinic in the United States for viral load suppression at 6 and 12months after initiating either single-tablet or multiple-tablet regimens. Multivariate regression was performed to obtain relative risks and adjust for potential confounders. Results: Of 218 patients, 47% were on single-tablet regimens and 53% on multiple-tablet regimens; 77% of single-tablet regimen patients had undetectable viral load at 6months compared to 61% of multiple-tablet regimen patients (p=0.012). At 12months, 82% on single-tablet regimens and 66% on multiple-tablet regimens (p=0.019) had undetectable viral load. Relative risk of any detectable viral load was 1.6 (95% confidence interval: 1.1–2.5) for patients on multiple-tablet regimens compared to single-tablet regimens at 6months, and 2.2 (95% confidence interval: 1.2–4.0) at 12months. Conclusion: Single-tablet regimens may provide better virologic control than multiple-tablet regimens in urban HIV-infected persons