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Homeland Security

Pandemic Influenza

Homeland Security Planning Scenarios

Scenario 3: Biological Disease Outbreak

The term "influenza" refers to illness caused by influenza virus. This is commonly also called "flu", but many different illnesses cause "flu-like" systemic and respiratory symptoms such as fever, chills, aches and pains, cough, and sore throat. In addition, influenza itself can cause many different illness patterns, ranging from mild common cold symptoms to typical "flu" to life-threatening pneumonia and other complications, including secondary bacterial infections.

In mild cases (in resistant or partially immune hosts), the symptoms are like those of a common cold. In more severe cases, symptoms typically start suddenly with chills and abrupt onset of fever (101F to 102F), prostration and generalized aches and muscular pain or tenderness (most pronounced in the back and legs). Headache may be prominent, often with sensitivity to light and aching behind the eyes. Respiratory tract symptoms may be mild at first, with scratchy sore throat, burning deep to the sternum, non productive cough, and some times runny nasal discharge or stuffy nose. Later, the lower respiratory illness becomes dominant; cough can be persistent and productive. In severe cases, sputum may be bloody. Gastro-intestinal symptoms, such as abdominal pain, nausea and vomiting, may also occur rarely, and are more commonly seen in children than adults. After 2 to 3 days, acute symptoms subside and fever usually resolves, although cough and malaise can persist for over 2 weeks.

Thus, the symptoms of influenza are often non-specific and wide-ranging, making influenza difficult to differentiate from other causes of respiratory illness based on the clinical presentation alone. Complications of influenza include viral and/or bacterial pneumonia, heart failure, muscle aches and inflammation ("myositis"), Reye syndrome, and inflammation of the brain ("encephalopathy"), among others.

The estimated number of influenza-associated hospitalizations among elderly patients has increased substantially over the past two decades. Although national estimates of influenza-associated deaths have been important in understanding the epidemiology of influenza over time and in planning for future epidemics and pandemics, mortality incompletely reflects the severity of influenza infections because many severe illnesses do not result in death.

Researchers at the Centers for Disease Control and Prevention, Atlanta, and colleagues estimated in 2004 that the annual average number of hospitalizations associated with the circulation of the influenza virus over two decades. The researchers found there were 226,054 primary and 294,128 any listed respiratory and circulatory hospitalizations associated with influenza virus infections on average each season (and annual averages of 94,735 primary and 133,900 any listed pneumonia and influenza hospitalizations associated with the influenza virus infections). Highest rates of influenza-associated primary respiratory and circulatory hospitalizations were found in persons 85 years and older.

After adjusting for length of each influenza season, influenza-associated rates of primary pneumonia and influenza hospitalizations increased over time among elderly. There were no significant increases in the rates of influenza-associated primary respiratory and circulatory hospitalizations after adjusting for the length of the influenza season. Children younger than five years had rates similar to those found among the 50 through 64 year-old age group. Persons aged 5 years through 49 years had the lowest rates of hospitalizations associated with influenza. More than 200,000 respiratory and circulatory hospitalizations are associated with influenza each year in the United States, substantially more than estimates of pneumonia and influenza hospitalizations. Significant numbers of influenza-associated hospitalizations in the United States occur among the elderly, and the numbers of these hospitalizations have increased substantially over the last two decades due in part to the aging of the population.

Mission Areas Activated:

Prevention/Deterrence/Protection - Prevention is currently impossible. Protection requires pre-pandemic preparedness, providing more vaccines and conducting more vaccine research and development, antiviral drug stockpiling, and increased surveillance capacity to track illness patterns.

Emergency Assessment/Diagnosis - U.S. influenza surveillance systems will be activated. However, more information is needed regarding attack rate measurements.

Emergency Management/Response - Preparedness plans should contain clear guidelines on setting priorities for the use of scarce resources such as vaccines, drugs, and hospital beds. Federal and state governments have such plans in progress but not all are complete.

Incident/Hazard Mitigation - Success depends on the availability of scarce resources and how well these resources are distributed. Timely, effective public information communication is also important.

Public Protection - Due to late-onset symptoms and the rapid rate at which the disease spreads, evacuation and quarantine are not recommended. Protection will rely on vaccines and antiviral drugs to prevent spread of the disease.

Victim Care - Will rely on the use of antiviral drugs for treatment. Hospitalization and mechanical ventilators will be necessary for many and likely be in short supply. However, at-home care and over-the-counter medications may be helpful for some. A large number of fatalities will likely occur, requiring mortuary and burial services.

Investigation/Apprehension - Investigation is dependent on disease surveillance, although the current system has distinct limitations.

Recovery/Remediation - Not required.

Casualties DHS: 15% attack rate: 87,000 fatalities; 300,000 hospitalizations
DHS: 35% attack rate: 207,000 fatalities; 733,800 hospitalizations
CDC: moderate 89,000 fatalities
CDC: severe: 207,000 fatalities
HHS: Moderate: 209,000 fatalities; 865,000 hospitalizations
HHS: Severe: 1,903,000 fatalities; 9,900,000 hospitalizations
Infrastructure Damage None
Evacuations / Displaced Persons Isolation of exposed persons
Contamination None
Economic Impact DHS: $70 to $200 billion
CDC: $71 to $166 billion
HHS: up to $450 billion
Potential for Multiple Events Yes, would be nearly worldwide, with sucessive waves at intervals of months over several years
Recovery Timeline Several months



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