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Disease outbreaks are a common public health problem but can be challenging to investigate because of the many different pathogens that can cause them. Control measures depend on finding a cause (etiology), but often diagnostic test results are missing or difficult to interpret or an appropriate diagnostic test may not be available locally. This website is designed to help health professionals and public health partners investigate unexplained respiratory disease outbreaks (URDO) and identify an etiology. The following webpages provide information and resources to assist in URDO investigations.

Investigate an Outbreak

Investigate an Outbreak
Initial steps, line lists, epidemiology curve template, case questionnaire, sample data collection forms…

Types of Radiation Emergencies

Generate a Differential Diagnosis
Tools to create a list of the most likely infectious causes or etiologies of an outbreak…

Specimen Collection & Handling

Specimen Collection and Handling
Guidelines and forms for specimen collection, handling, storage, and shipping…

Diagnostic Testing

Detect and Characterize the Pathogen
Summary of diagnostic methods to identify pathogens…


Prevent Disease Transmission
Guidelines on infection control measures, respiratory hygiene…

Request Assistance

Request CDC Assistance
Instructions, description of how CDC can help in URDO investigations, directory of tests that can be ordered, specimen submission requirements…

Additional Resources

Publications and Resources
Publications, information on select respiratory diseases, national, state, and local resources…

URDO fact sheet

Unexplained Respiratory Disease Outbreaks Work Group Factsheet
Did you know CDC can provide support if you have a respiratory disease outbreak of unknown etiology? Learn more about how you can get CDC's help to investigate your outbreak.