Pandemic influenza preparedness

Physician Executive, Sept-Oct, 2004 by Georges C. Benjamin

Influenza kills an average of 36,000 Americans and is responsible for 142,000 hospitalizations every year.

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While these are tragic events, they do not compare to the morbidity and mortality that occurs with a pandemic. There have been three influenza pandemics this century.

* The first in 1918 (Spanish flu) was responsible for the worse infectious epidemic in modern history. During this period, influenza circled the globe and killed over 20 million people worldwide. In the United States 500,000 died.

* The second epidemic in 1957 (Asian flu) left 70,000 dead in the U.S.

* And the third in 1968 (Hong Kong flu) resulted in 34,000 deaths in the country.

Public health officials are preparing for the next pandemic of influenza. The recent outbreak of Severe Acute Respiratory Syndrome (SARS) brought some urgency to pandemic planning.

Influenza

The three major types of influenza viruses A, B and C all cause human disease. Types A and B are responsible for the majority of significant disease in humans. Type A viruses are divided into subtypes based on two surface antigens nuraminidase (N) and hemagglutinin (H); the B virus is not categorized by subtypes.

The influenza viruses currently circulating in the community undergo mutations or genetic reassortment in their surface antigens frequently enough that an annual reformulation of the influenza vaccine is required to achieve adequate protection.

On occasion, there is a mutation in key major antigenic components such that the population-based background immunity provides no protection from the virus. Should the prepared immunization also not contain protection from the new viral strain and the virus is transmissible from person to person, a global pandemic can occur.

Influenza viruses also infect animals other than humans. In fact pigs, horses and birds are also commonly infected. The reservoir for influenza A is believed to be wild birds. In general these animal viruses can occasionally jump species or reformulate in a third species to create a novel virus that is highly pathogenic. These novel viruses are a potential cause of pandemic disease.

Vaccine decisions

The World Health Organization (WHO) works through a network of collaborating national influenza centers to track the types of influenza strains infecting humans and measure the effectiveness of current vaccines. Twice a year an international consultation is held to evaluate the various virus strains and make decisions concerning future vaccine composition.

In the spring and fall of each year a recommendation is made to the vaccine manufactures concerning the makeup of the vaccine to be used.

Pandemic influenza planning

An influenza pandemic is defined by six functional stages:

1. Novel Virus Alert -- During this stage a novel virus is detected in one or more humans where there is little or no immunity in the general population. There is no clearly documented person-to-person spread. The WHO has subdivided this phase into several levels that are useful to define the stage of investigation of a novel virus found in humans prior to the recognition of disease spread.

2. Pandemic Alert -- The virus shows person-to-person transmission and demonstrates geographic spread.

3. Pandemic Imminent -- Novel virus is causing increased rates of death and morbidity in multiple, widespread areas.

4. Pandemic Phase -- Virus continues to spread over several continents.

5. Second Wave -- Recrudescence of disease activity within several months following the initial wave of infection.

6. Pandemic Ends -- Successive pandemic waves cease and the traditional seasonal epidemic pattern returns.

Major components of a traditional plan include: command and control, surveillance, disease control (vaccine delivery, antiviral medication delivery, isolation and quarantine), prehospital care, hospital care, communications and logistics. Health system administrators should build these components into their disaster response plans.

Hospital planning

The annual influenza season results in significant strain on the overburdened hospital. The chief management problem is anticipating and managing surge.

Two tools available to hospital administrators and disaster planners to manage the surge capacity in a large influenza outbreak are available from the U.S. Centers for Disease Control and Prevention (CDC). The programs called FluAid 2.0 and FluSurge 1.0 are available to help plan for the epidemic.

FluAid 2.0 is used to estimate the number of visits (inpatient and outpatient) and deaths from an outbreak. FluSurge 1.0 is a planning tool used to estimate the demand for regular and intensive care hospital beds as well as ventilators. These tools are available free of charge at www.dhhs.gov/nvpo/pandemics.> Hospital laboratory plans should also ensure appropriate protocols are in place to handle highly infectious specimens. Highly pathogenic strains should not be cultured routinely and require Biosafety Level 3 (BSL) or higher facilities for culture. They should not be routinely cultured in most hospital laboratories and plans should provide proper guidance to prevent inadvertent culture.