The world now faces a possible pandemic of the H5N1 avian influenza ("bird flu") virus. The world is in preparation for such a pandemic, which could rival the deadly 1918 influenza pandemic.

Definition of terms:

• "Epidemic," also called an "outbreak," is a higher-than-expected number of cases of a disease in a population.
• "Pandemic" is an epidemic that spreads around the world. Pandemics are rare. Only a few known diseases are capable of producing a pandemic, and they include HIV/AIDS and influenza. There have been ten pandemics in the last three centuries.

In the 1918 influena pandemic, there were 500,000 to 750,000 deaths in the United States and 20- to 50-million deaths in the world from influenza.

The influenza virus is capable of infecting a variety of animals, e.g., birds, swine, and humans. Only a few strains of infleunza virus infect humans. Influenza viruses mutate (change their make-up) on an annual basis. Such mutation requires new influenza vaccines to be prepared annually.

In a typical year, there are approximately 36,000 deaths from influenza in the United States, with 95 per cent occurring in persons greater than 65 years of age. In an influenza pandemic, deaths typically occur in younger age groups.

Human influenza spreads by close contact (less than six feet) with an ill person, who is coughing or sneezing, or by touching a surface contaminated by the virus and, then, touching mucous membranes (eye, nose, or mouth).

The present influenza virus of concern is the H5N1 strain, first documented as a cause of human illness in 1997. Hong Kong averted an epidemic, by slaughtering its chickens and ducks. In 2003, the H5N1 strain re-surfaced, and millions of fowl were slaughtered to prevent spread to humans.

Of immediate concern to health officials are these features:

• The H5N1 strain presently infects birds very easily, but infects humans with much difficulty. This strain could mutate to infect humans much more easily. If mutation occurs to make the H5N1 influenza virus readily infectious for humans, the stage is set for a pandemic.
• Migratory birds may bring the H5N1 influenza strain from Asia to Europe, North America, and other parts of the world. There are over-lapping major flyways of migratory birds that connect all continents.

The present status of H5N1 influenza infection is:

• The average age of infected humans is 19 years (range: 4 months to 81 years).
• Most cases have been contracted directly from birds. Previously healthy children and young adults have had direct contact with sick or dead poultry or poultry feces. A few persons have eaten food made with uncooked duck blood. There is no risk of infection from eating properly cooked poultry or eggs (cooking temperatures inactivate the virus).
• Rarely, human-to-human transmission has occurred. If the H5N1 strain makes certain genetic changes, such transmission may be possible.

Health experts divide human infection with a new influenza virus strain into three warning alerts and these are divided into phases:

• Interpandemic (no human infection);
• Pandemic Alert (limited human infection); and
• Pandemic (widespread human infection).

It is unknown whether the present influenza H5N1 threat will become the next pandemic, but these features make it worrisome:

• H5N1 influenza infection (activity) in humans is unprecedented;
• The infection presently is found in humans and other mammals;
• There is persistent outbreaks of infection in poultry; and
• The infection is spreading in migratory birds.

Risk to humans continues, as long as H5N1 influenza virus infects birds, with which humans associate (poultry). If a pandemic does not occur with H5N1 influena virus, the world is always at risk for a pandemic with another strain of influenza virus.

The U.S. Department of Health and Humans Services has issued these objectives:

• Primary Objective: Minimize illness and death; and
• Secondary objective: Minimize societal and economic disruption.

The following assumptions must be made for an influenza pandemic:

• Assumption 1 (disease transmission): No one is immune. Approximately 30 per cent of the population will become ill. Most persons will become ill within one to ten days (average two days) after exposure. People will be contagious, before they feel ill. People are most contagious within the first two days of illness. Ill children are more contagious than ill adults. An infected person infects, on average, two or three other persons (if no precautions are undertaken).
• Assumption 2 (disease transmission): Pandemics cause the number of infections to rise sharply in communities, and occur in "waves" (sudden increase in cases for a period of time, dropping to few or no cases thereafter). Each wave lasts six to eight weeks. Waves are worse in cold months (people live in closer confinement.) There may be two or three waves in a community, separated by weeks or months of no activity. All pandemic waves last for one to two years. Local waves may be separated by wide geographical distances ("popcorn" effect, waves "popping" up in widely separated areas). Sporadic cases or cluster of cases may occur for weeks before the pandemic starts.
• Assumption 3 (social and economic implications): Hospitals will be burdened beyond capacity, with 25-per cent or more patients than usual requiring hospitalization during waves. During a six- to eight-week wave, approximately 40-per cent of employees may be absent because of illness, fear, or need to care for an ill family member. Outbreaks will be unpredictably scattered throughout the country, but volunteers may not be available because they are needed in their own communities. Communities must plan to respond with their own resources. Communities must not plan on receiving outside help from the government or other communities. Communities should not expect a novel treatment to be "found" that would halt the infection any more than present technology provides.
• Assumption 4 (medical burden for Tennessee): In a severe influenza pandemic affecting Tennessee, 1.8-million (30-per cent) of Tennesseans may become ill, requiring outpatient care for 900,000 persons, hospitalization for 198,000 persons, ICU care for 29,700 persons, and mechanical ventilation (respirator) care for 14,850 persons; and, 38,060 persons may die.
• Assumption 5 (national preparedness): Only one company manufactures antiviral medication, and supplies are limited. To be effective, antiviral medication must be started early in the illness, and the benefit is uncertain. Current technology for influenza vaccine is limited. It will take four- to six-months to prepare vaccine, after the pandemic begins. Vaccination is the best solution, and research continues.

The U.S. Department of Health and Human Services has established a priority list of persons who may receive vaccination, if vaccine supplies are inadequate (as they most likely will be).

In a pandemic, medical resources will be tremendously strained. Hospitals will be deluged with patients, but up to 40 per cent of hospital personnel may be ill and absent from work. It will be impossible to provide healthcare as usual, and many procedures (elective surgery, for example) cannot be accommodated. The question of using non-traditional locations (hospitals and schools, for example) will be obviously raised. The challenges will be to provide hospital-quality safety standards, staffing with trained medical personnel, and competing need to support non-traditional sites in conjunction with existing hospitals and clinics.

There is no evidence that a pandemic, once underway, can be stopped, but measures to increase social distance (school closures, cessation of sporting events, ill persons not reporting to work, reduction of mass transit to essential persons only, and cessation of all other non-essential activities) could lower the severity of waves. Strict isolation of ill persons (official quarantine) is of limited use to contain an influenza pandemic.

Personal measures to reduce the risk of infection during an influenza outbreak include:

• Wash hands frequently;
• Respiratory etiquette (no sneezing or coughing in the vicinity of others);
• Avoid ill persons, if possible;
• Stay home (do not go to work), if ill;
• Care for ill household members in a safe manner;
• Use a medical advice hotline for more information; and
• Know about the availability and proper use of antiviral medications, masks, and vaccine.

The Tennessee state government is focused on uniform statewide policies to give guidance for local planning. Local planners must decide how to implement local policies and procedures. The state plan will fit into the existing Tennessee Emergency Management Plan (TEMP). All plans must use current resources and technologies, not plan on something that does not now exist. Plans must be reviewed at least annually, as conditions, resources, and conditions change. Planning resources may be obtained from a federal Website, BirdFlu 411. Additional information can be obtained from the Tennessee Department of Health: 1.615.741.7247.