19 November 2005

Epidemic? Pandemic? Why Should I Care?

Should You Be Scared About "Bird Flu"?

Photo of mergency hospital during 1918 influenza epidemic, Camp Funston, Kansas (from National Museum of Health and Medicine) from http://www.public-health.uiowa.edu/ceid/Pathogens.htmWe read a lot in the news recently about the threat of a bird-flu pandemic. Is this just media scare, or is it something we should really be worried about? A severe pandemic of a novel, virulent avian influenza would kill millions, stunt economic growth, and maybe even topple governments. However, some of the current scare is overblown. Here are some facts:

A "pandemic" is an epidemic that covers a large geographical area. A "global epidemic".

An "epidemic" is a significant outbreak of an infectious disease, more cases than expected. So malaria in most tropical poor countries is not "epidemic", even though it kills millions of people every year, because this is the "expected" rate. If malaria broke out in Washington, D.C., and killed even ten people, it might be considered a malaria "epidemic". Similarly, about 36,000 people die every year from influenza in the U.S. So an "epidemic" would have to infect a much larger number.


The "flu" is caused by a virus. It affects the upper respiratory tract (nose, throat and lungs), and is spread by transfer of virus particles in saliva or mucus droplets, usually expelled in coughs or sneezes. The infection causes fever, body aches, headache, sore throat, fatigue, and coughing and sneezing. Most people will recover in one to two weeks. The disease is life-threatening particularly for the elderly and the young, and for people with underlying medical conditions such as heart or lung disease.

Bird Flu

"Bird flu" or "avian influenza" is a disease of aquatic birds. Sometimes people catch it (if they have been in very close contact with infected birds, usually involved in raising domestic fowl) and if they catch a virulent strain like H5N1 it is very serious. More than half the infected individuals die. Around 100 people have died of bird flu world wide in recent months.

The reason for global concern about bird flu is that influenza viruses can mutate to become more infectious (more easily transmitted). If one of the dangerous (pathogenic = disease-causing) strains of the virus were to mutate to become "human-adapted", so that it could be easily transmitted from one person to another, the stage would be set for a very serious epidemic, or even a pandemic.

The Great Influenza Pandemic of 1918-1919

This global disaster was caused by a novel and deadly strain of avian influenza virus. More than 25 million people died, most of them in poorer countries. In the United States about 28% of the population became ill and more than half a million people died. For comparison, HIV/AIDS has killed about 25 million people over 25 years, while the 1918 pandemic killed the same number in a few months. This is why public health officials are so concerned.

Samples of the 1918 pathogen have been recovered and analyzed. Recently its complete genetic makeup has been published.

What would a flu pandemic be like today?

In contrast to 1918, today we know what causes influenza (a virus) and how it is transmitted. We have some anti-viral drugs (but not many, and they would not be widely available, especially to the poor). We know how to produce flu vaccines, though it takes time to manufacture and administer them. Would these advances enable us to prevent or control a flu pandemic?

Current models of the possible impact of a flu epidemic in the U.S. suggest that between 15% and 35% of the population would be affected, and 100,000 to 200,000 would die ("medium-level" case). Rates of infection and mortality would probably be similar in other developed economies. In poorer countries the impact would be greater. The World Health Organization base case predicts 2 million to 7.5 million deaths world wide.

Political and economic effects could be severe. Restrictions on travel and trade, and reduced business activity due to closed businesses and reduced productivity, would be like a recession. Political instability could develop in places where governments do not appear to be responding effectively or fairly to the crisis. Reduced agricultural productivity and restrictions on food trade could create localized food crises.

Recent disasters have hurt the government in power if their responses are perceived as ineffective (Hurricane Katrina). On the other hand, crises can be used to consolidate political power (September 11th).

Managing A Pandemic Today

Flu epidemics in 1957-1958 and in 1968 killed about 70,000 and 34,000 Americans, respectively. The primary public health tools used to minimize the impact of these outbreaks were vaccination, information, regulation, and more effective treatment.
  • Vaccination -- After a new strain of influenza virus emerges and is determined to present a threat of widespread human disease, it takes several months for vaccine targeted at that strain to be developed and manufactured. As the vaccine first becomes available it will be used to protect health care workers and others who are both at high risk of being exposed to the disease and in a position to spread it to others. As larger quantities of vaccine are available they will be allocated by public health services to stop the spread of the disease in particular areas, such as specific cities, military bases, or the like. The standard "flu vaccine" available now is not designed to prevent avian influenza, but is targeted at the normal influenza strains identified earlier this year as most likely to be dominant during the current "flu season".

  • Information -- Public health agencies will try to teach people behaviors that will protect them from catching and spreading the disease.

    • "Hygiene" and "sneeze etiquette" will be strongly recommended. Covering your nose and mouth when you sneeze can reduce the dispersal of airborne droplets of mucus which can potentially carry the virus to others.

    • Washing your hands frequently can prevent infecting yourself with virus you have picked up, and can help prevent you from spreading the virus to others. Regular soap and water or alcohol hand cleaning solutions work fine. Antibacterial soaps provide zero additional effect.

    • Poster urging SARS prevention methods from http://www.cuhk.edu.hk/sars_and_flu/oldsars/mask.htmMasks may be suggested, or even required in some places. One key benefit of a mask is to remind you not to touch your face, thus reducing transmission of virus on the hands. Masks will not filter out viruses, but may prevent dispersal of mucus droplets when you sneeze. Proper disposal of contaminated masks is important. Wearing of masks by the non-infected public may not actually do much to slow the spread of the disease, but it may make people feel more secure.

    • People with flu symptoms will be encouraged, or indeed in some cases required, to stay at home.
  • Regulation -- To reduce the rate of spread of any new, contagious, virulent flu virus several public health measures are likely to be put in place:

    • Travel from regions where the new strain has broken out will be discouraged or forbidden.

    • More aggressive monitoring of flu cases will be required, and cases or clusters of cases may have to be isolated (quarantined).

    • Schools will be closed when the disease breaks out, and some other activities where people gather may be curtailed (e.g. entertainment and sporting events). Some businesses will close or be required to close.
  • Treatment -- There are some antiviral drugs which may be used to reduce the severity of the disease, and even some which appear to prevent getting it. Unfortunately, existing flu strains are already evolving resistance to some of these drugs. The drugs would effectively be rationed to be used to protect health-care workers and other essential workers, and to treat the elderly, the young, and others at high risk of complications or death.

    Antibiotics do not affect viruses, but many flu deaths are due to secondary bacterial infections such as pneumonia. Antibiotics would be used to treat these cases.


Flu epidemics will happen in the future, but nobody knows when. Preparations are under way to minimize the social, economic, and public-health impact of the next big one. The best protections against any influenza virus are washing your hands and avoiding getting sneezed on by an infected person. Those most at risk of death in a flu epidemic are those without access to an effective health care system, which includes people in poor countries, people in regions of conflict, and elderly people living alone in developed countries.

Additional Information

CDC site

WHO bird flu site

U.S. Government site

WHO "10 Things You Need To Know" site

WHO Influenza site

WHO January 2005 threat assessment report

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

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