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IDdx is a Relational Database of 250 Infectious Diseases.

IDdx is a decision-support software tool developed to assist in the diagnosis of infectious diseases. IDdx is like an electronic book that you can query. It is not designed to replace the human mind, but to help the professional with lists and intersections of lists. 

For example, one can make a list of all infections that cause abdominal pain and another list of all infections caused by animal bites. The intersection of these two lists is all infections that fit both criteria. This is what IDdx is designed to do--first to do the research to make the lists and then to design the software that makes the querying of these lists as easy as possible.

IDdx is an offshoot of the Haz-Map project that began in 1991. The diseases in Haz-Map have always included occupational infectious diseases (currently 105). The precursor of IDdx, OutbreakID, was launched in 2001. Both Haz-Map and IDdx were designed to harness the power of medical knowledge with a relational database.

Each finding (signs & symptoms) and epidemiological factor in IDdx requires a lot of research to make these lists as complete and accurate as possible. My method in refining the lists is just plain old iteration, defined by Merriam-Webster as "a procedure in which repetition of a sequence of operations yields results successively closer to a desired result." 

I look for the best and most recent sources of information, and my starting point is the lastest edition of Control of Communicable Diseases Manual (CCDM). The latest edition of Principles and Practice of Infectious Diseases (PPID) edited by Mandell et al. became available in September 2009 with full-text online access, and CCDM became available in 2010. The availability of searchable electronic resources makes the job easier to build and continuously improve lists for differential diagnosis.

IDdx is regularly updated based on the latest editions of PPID, CCDM, CDC Travel, and other peer-reviewed scientific publications. New features added in January 2015 were Ranked Diseases and Weighted FindingsRanked Diseases means that the user can sort the list of diseases returned from a query by cases/year in either the U.S. or worldwide. Weighted Findings means that color coding indicates how frequently a finding is used to describe the disease in the twelve primary references. Findings are color coded to show if they appear in only 1 book, 2 books, or 3 or more booksThe findings of a disease are included only if they are published in the primary references. Weighted Findings enables another new feature: Query Sensitivity. Choose High to get the most diseases that match one or more signs & symptoms. Choose Low to get only those diseases in which the finding was cited in three or more of the 12 references. This screenshot of Microsoft Access shows how the software enables the color coding of symptoms based on the 12 major references.

IDdx is currently free on the App Store (iPhone or iPad). It is no longer available at Google Play (Android).