What is the DiseaseCast definition of a forecast?

Our simple definition of a forecast is this:

To provide you with information you may not have known about a disease’s activity levels before it happens.

We do not believe it is possible to forecast “black swans“, or extremely rare or unusual disease activity.  When we observe this happening, we highlight that information for our clients as an alert.

 

What is an advisory?

We issue two basic types of alerts: forecast and live event alerts.  Forecast alerts are intended to provide our clients with pre-event information regarding an imminent change in the activity level of a disease.  Live event alerts reflect an unexpected change from normal disease activity.  It is a an indication of unusual disease activity.

For both forecast and live event alerts, we use a simple three-tier system of Warning, Watch, and Advisory, in order of decreasing severity.

 

What is the Infectious Disease Impact Scale (IDIS)?

The IDIS is similar to the Fujita (F) or Saffir-Simpson Scales used to describe the severity of tornadoes or hurricanes.

The IDIS Categories are as follows:

Category 0.  Routine disease activity.

Category 1 / 2.  Non-crisis disease activity that has become noticeable to the public.

Category 3.  Crisis conditions.  The disease event requires non-routine public health intervention.

Category 4.  A disease event (or perceived disease threat) that triggers socio-economically disruptive countermeasures.

Category 5.  A disease event that results in so many incapacitated patients that the socio-economic well being of a community has been acutely compromised.

Category 6.  Disaster conditions.  The disease in question is responsible for significant disease causing significant socio-economic disruption, regardless of any countermeasures.  This is a situation where response efforts have failed to contain the event.

Category 7.  Apocalyptic conditions.  This is usually an extremely rare situation involving undeveloped nations at the individual village level, where a disease has killed enough of a village it ceases to continue functioning as a social unit.

Like the Fujita and Saffir-Simpson Scales, the highest categories of IDIS are relatively rare compared to lower categories.  In the United States, for example, we only occasionally observe IDIS Category 3 conditions.  However, in Africa we routinely see IDIS Category 6 (and sometimes 7) conditions in the context of Ebola outbreaks.

 

What is a disruptor?

In developed nations, there is a different dynamic used to describe the acute impact of highly transmissible infectious disease.  Here we use the term disruptor to describe a disease capable of acutely compromising a medical infrastructure.  Here is the classification system we use:

Class 0 Disruptor. Infectious agent typically does not cause acute medical infrastructure strain. This classification represents the majority of infectious disease we see in the United States.

Class 1 Disruptor. Infectious agent associated with potential to cause acute, medical infrastructure strain at the single facility or outpatient network level. Because emergency departments often play a role in outpatient level care, strain may be observed in this setting as well. This is what is typically observed during a routine influenza season.

Class 2 Disruptor. Infectious agent associated with potential to cause acute grid-level medical infrastructure strain. This situation typically describes the hospital reporting inundation of the inpatient ward with some cases seen in the intensive care unit. This is typically what is observed during a “severe” season of influenza.

Class 3 Disruptor. Infectious agent associated with potential to acutely collapse routine functioning of a medical facility. This refers to an acute care facility forced to go on ambulance diversion status because the emergency department-intensive care unit axis of care has been compromised. In other words, the intensive care unit is unable to manage additional patients. This was seen during the 2009 influenza pandemic.

Class 4 Disruptor. Infectious agent associated with potential to acutely collapse a medical infrastructure grid. This refers to multiple acute care facilities in the same metropolitan area on ambulance diversion status. This is occasionally seen during combined severe seasons of influenza, RSV, and other non-infectious disease acute events such as a mass casualty event. A single infectious agent causing this kind of disruption would be highly unusual and rare, however it was observed during the emergence of SARS in 2003.

The disruption classification is used only for developed countries and is an approximation representation that helps us explain why we are paying attention to one particular infectious disease versus another.