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Background: Estimation of incidence of the state of undiagnosed chronic disease provides a crucial missing link for the monitoring of chronic disease epidemics and determining the degree to which changes in prevalence are affected or biased by detection.Methods: We developed a four-part compartment model for undiagnosed cases of irreversible chronic diseases with a preclinical state that precedes the diagnosis. Applicability of the model is tested in a simulation study of a hypothetical chronic disease and using diabetes data from the Health and Retirement Study (HRS).Results: A two dimensional system of partial differential equations forms the basis for estimating incidence of the undiagnosed and diagnosed disease states from the prevalence of the associated states. In the simulation study we reach very good agreement between the estimates and the true values. Application to the HRS data demonstrates practical relevance of the methods.Discussion: We have demonstrated the applicability of the modeling framework in a simulation study and in the analysis of the Health and Retirement Study. The model provides insight into the epidemiology of undiagnosed chronic diseases. [ABSTRACT FROM AUTHOR]

Background: Although total influenza vaccine doses available in the 2005/2006 influenza season were over 80 million, CDC received many reports of delayed and diminished vaccine shipments in October to November of 2005. To better understand the supply problems, CDC and partners surveyed several health care professional groups. Methods: Surveys were sent to representative samples of influenza vaccine providers including pediatricians, internists, federally qualified health centers, visiting nurse organizations, and all 64 state and other health departments receiving federal immunization funds directly. In November and December, 2005, providers were asked questions about their experience in ordering influenza vaccine, sources where orders were placed, proportion of orders received, and referral of patients to other vaccination sites. Results: The number of providers surveyed (median: 154; range: 64 - 308) and response rates (median: 62%; range: 51% - 77%) varied among groups. Less than half of the providers in most groups placed a single order that was accepted (median: 31%; range: 8% - 53%), and most placed multiple orders. Only 57% of federally qualified health centers and 60% of internists reported they received at least 40% of their orders by the middle of December; the other provider groups received a greater proportion of their orders. Most internists (80%) and federally qualified health centers (54%) reported that they had referred priority group patients to other locations to receive the influenza vaccine due to inadequate supplies. Vaccine providers who ordered only from Chiron received a lower proportion of their orders than providers that ordered from another source or ordered from multiple sources. Conclusion: Most of the providers surveyed received only part of their orders by the middle of December. Disruptions in receipt of influenza vaccine during the fall of 2005 were due primarily to shortfalls in vaccine from Chiron and also due to delays and partial shipments from other distributors. [ABSTRACT FROM AUTHOR]