Modeling Clinician Detection Time of a Disease Outbreak Due to Inhalation Anthrax

1. Introduction • Goal: Develop a probabilistic model of the time for clinicians to detect a disease outbreak due to an outdoor release of anthrax spores in an assumed geographical region. • Assume that clinicians have access only to traditional clinical information. • Use the model to estimate an upper bound on the mean detection time of an anthrax outbreakby clinicians. • How might this be useful? • Planning for anthrax outbreaks • Assessing the usefulness of computer-based outbreak • detection algorithms Figure 1: The possible ways that were modeled for a clinician to diagnose inhalational anthrax in a patient. Model N: The total number of patients in an anthrax outbreak who are seen by clinicians. DT: The time to detect the anthrax outbreak Detection: The detection of the anthrax outbreak due to a patient being diagnosed with anthrax. ti: The time when the ith case with anthrax is seen by a clinician. wi: The probability that anthrax is diagnosed 4 hours after the ith anthrax patient is seen by a clinician. xi: The probability that anthrax is diagnosed 48 hours after the ith anthrax patient is seen by a clinician. vj: The probability that the jth patient with anthrax is not diagnosed as having anthrax. Si: The cases admitted in the interval (ti, ti+ 44]. • SensitivityAnalysis: • We used expert judgment to define confidence intervals for 11 of the key probabilities used in the model. • We explored the values of those 11 parameters that maximize the average expected time of detection of anthrax by clinicians. • Results: • Conclusions • The model yielded an expected detection time of an outbreak of anthrax due to an airborne release of anthrax spores as being 3 to 9 days, depending on the assumed release amount. • A sensitivity analysis resulted in an upper bound on the expected detection time of about 5 to 11 days, again depending on the assumed release amount. Modeling Clinician Detection Time of a Disease Outbreak Due to Inhalation Anthrax - • Methods • The Anthrax Outbreak Simulator [6] • The simulator assumes the population distribution of Allegheny County, Pennsylvania. • The incubation period is modeled with lognormal distributions, and varies based on the amount of spores inhaled. Greater airborne concentrations of anthrax lead to a shorter incubation periods • We used the simulator to generate data sets corresponding to simulated releases of anthrax of the following amounts: • 1.0, 0.5, 0.25, 0.13 and 0.02. • We created 100 data sets for each simulated release amount. Each data set has a unique release location. • MainAssumptions: • A patient is only seen by a health care provider (clinician) once (i.e., no return visits). • Each clinician diagnoses a given case of inhalational anthrax (IA) independent of his or her prior cases and independent of the activities of other clinicians. • KeyParameters Used in Modeling Clinician Detection Time: • Assume that each of the following probabilities is conditioned on a patient having IA. • P(IAseverity | Time) • P( XrayDone | IAseverity) • P( XRayResult| XRayDone, Time, IAseverity) • P(CultureDone | XRayResult, IAseverity) • P(CultureDone | MW, XRayResult, Time) • P(CulturePositive | CultureDone) • P(MW | XRayResult, Time) • MW: Widened mediastinum Christina Adamou, Gregory F. Cooper, Weng-Keen Wong (Oregon State University), John N. Dowling, William R. Hogan RODS Laboratory, Center of Biomedical Informatics University of Pittsburgh, Pittsburgh, Pennsylvania • References • Meselson M, Guillemin J, Hugh-Jones M, Langmuir A, Papova I, Shelokov A, Yampolskaya O. The Sverdlovsk anthrax outbreak of 1979. Science 1994;266:1202-1207. • Inglesby TV, O’Toole T, Henderson DA, Bartlett JG, Ascher MS, Eitzen E, et al. Anthrax as a biological weapon, 2002: Updated recommendations for management. JAMA 2002;287:2236-2252. • Brachman PS. Inhalation anthrax. Ann NY Acad Sci. 1980;353:83-93. • Penn CC, Klotz SA. Anthrax pneumonia Sem Resp Med 1997;12:28-30. • Jernigan JA, Stephens DS, Ashford DA, Omenaca C, Topiel MS, Galbraith M, et al. Bioterrorism-related inhalation anthrax: The first 10 cases reported in the United States. Emerg Infect Dis. 2001;7:933-944. • Hogan WR, Cooper GF, Wallstrom, GL., Wagner MM. The Bayesian aerosol release detector. In Proceedings of the National Syndromic Surveillance Conference [CD-ROM]. Boston, MA: Fleetwood Multimedia, Inc.; 2004. • Acknowledgments: • This research was supported by grants from the National Science Foundation (IIS-0325581), the Department of Homeland Security (F30602-01-2-0550), and the Pennsylvania Department of Health (ME-01-737). Results The following table shows the results. The derived upper bound on clinician detection time varied from about 9 days for the smallest amount of assumed release to about 3 days for the largest amount.