How to Investigate Unexplained Respiratory Disease Outbreaks (URDO)

Generate a Differential Diagnosis

Differential Diagnosis

One of the most important initial “exercises” when investigating an outbreak of unknown respiratory illness is generation of the “differential diagnosis”, a list of the most likely infectious causes or etiologies of the outbreak. Differential diagnosis also refers to the process of weighing the probability that the disease observed is caused by one pathogen versus another.

Generating a differential diagnosis enables the investigators to use time and resources most efficiently and effectively. The process helps focus questionnaire development, appropriate specimen collection, laboratory testing, empiric treatment regimens, and targeted urgent public health interventions. Also, a thoughtful differential diagnosis ensures that all likely etiologies are considered early in the outbreak investigation, making it less likely that an etiology is missed or overlooked.

Differential Diagnosis Spreadsheets

Below are three spreadsheets that summarize information on the principle pathogens or groups of infectious agents that are known to cause respiratory illness. For each etiology, the spreadsheets summarize the following:

1. Host demographics and epidemiologic features of infection,
2. Clinical features of infection and disease control
3. Known risk factors for disease

Investigators should use all information or “clues” available throughout the outbreak to determine the most likely etiology of the unexplained respiratory outbreak.

Demographic and Epidemiologic Data (22K, 1 page)
Spreadsheet includes incubation period, means of disease transmission, the age groups most often affected and case fatality categories.  For each of the pathogens, the spreadsheet may also be used to include or exclude an infectious etiology based on the geographic distribution of the pathogen, both in the US and worldwide.

Clinical Information (31K, 1 page)
Spreadsheet lists the predominant respiratory syndrome for each pathogen, in addition to other clinical manifestations that may enable the investigator to identify the most likely etiology for the outbreak. It also includes the most common findings on chest x-ray and unique laboratory or pathology findings. To aid disease control efforts, available vaccine and general infection control precautions for each pathogen are listed.

Risk Factors for Disease (24K, 1 page)
Spreadsheet lists the most common risk groups affected by various infectious agents. It also includes specific occupations, animal and environmental exposures or other activities that place a person at increased risk for certain respiratory illnesses. Each year respiratory pathogens circulate in communities and these pathogens may demonstrate a specific seasonal pattern.  However, respiratory outbreaks have been frequently described among specific risk groups such as school children, residents of long-term care facilities or nursing homes, and military recruits. Because some infectious agents have the potential to be used for bioterrorism, we have identified these agents in the spreadsheet.

Persons with disabilities having problems accessing the above file may call 1-800-CDC-INFO (1-800-232-4636) for assistance.