"Pandemic flu" has been one of the buzzwords of late 2005. But how
does the phrase that's on everyone's lips differ from "epidemic," that
other well-worn disease term?
Apparently, a lot of people aren't sure. Merriam-Webster reports that
"pandemic" is the seventh most frequently looked-up word in its online
dictionary this year. The definition: "occurring over a wide geographic
area and affecting an exceptionally high proportion of the population."
Person to Person
The main way that influenza viruses are thought to spread is from person to
person in respiratory droplets of coughs and sneezes. (This is called "droplet
spread.") This can happen when droplets from a cough or sneeze of an infected
person are propelled through the air and deposited on the mouth or nose of
people nearby. Influenza viruses may also be spread when a person touches
respiratory droplets on another person or an object and then touches their own
mouth or nose (or...
This is almost the same as the dictionary definition for "epidemic,"
and it doesn't explain much when it comes to influenza -- a.k.a. the flu.
An epidemic of influenza is different from the dreaded pandemic that
scientists and world health officials fear is nigh. We might see an epidemic of
seasonal influenza during any given year. In fact, we just had one.
Flu reached epidemic levels in the U.S. for 10 weeks in a row during the
2004-2005 season. Records kept by the CDC show that during the week ending
March 5, 2005, 8.9% of all deaths reported in 122 U.S. cities were due to
influenza and pneumonia (a common complication of the flu).
The CDC's definition of a flu epidemic relates to the percentage of deaths
in a given week caused by influenza and pneumonia. The "epidemic
threshold" is a certain percentage above what is considered normal for that
period. The normal level, or baseline, is statistically determined based on
data from past flu seasons.
Christine Pearson, a spokeswoman for the CDC, cautions that the definition
of an influenza epidemic doesn't apply to other diseases.
Seasonal flu epidemics may sicken millions, but those who die are typically
a small number of the elderly, very young children, and people with weak immune
systems. That's not the case during the worst influenza pandemics.
There are two main features of an influenza pandemic. First, the virus is a
new strain that has never infected people before. Second, it's on a global
scale. Sometimes it's also unusually deadly.
"A pandemic is basically a global epidemic -- an epidemic that spreads
to more than one continent," says Dan Epstein, a spokesman for the Pan
American Health Organization, a regional office of the World Health
Influenza pandemics have struck about three times every century since the
1500s, or roughly every 10-50 years. There was one in 1957-1958 and one in
1968-1969. The most infamous pandemic flu of the 20th century, however, was
that of 1918-1919. An estimated 40 million people died in less than a year, and
what made it so different from seasonal flu epidemics is that it killed
primarily young people, those aged 20-45.
The Next Pandemic
The world is closely watching a virus known as avian influenza H5N1, or
"bird flu." Don't confuse it with pandemic flu. It isn't one. At least,
it isn't one yet.