Just about every state, if not all, has now been hit by the flu, said the Centers for Disease Control and Prevention. The type of strain circulating this year is particularly ?robust.? Called type A, strain H3N2, it tends to be associated with higher death rates than type B.

Nineteen states reported widespread or regional flu activity during the week of Dec. 12-18, according to the most recent CDC data. Roughly 3 percent of doctor visits in the states were related to flu-like symptoms. The rate was 6 percent in the Southwest and Pacific states. An average of 20,000 deaths are expected in the average year, according to the CDC, but the CDC expects more this season.

A history of worldwide Influenza

The origins of influenza are unknown, but the malady is never absent for more than a few decades. The worst pandemic occurred in the late 19th century, when more than 20 million people were killed.

400 B.C.: Hippocrates records an outbreak of a cough, followed by pneumonia and other symptoms, at Perinthus in northern Greece (now part of Turkey). Several possible identifications have been suggested, including influenza, whooping cough and diphtheria.

212 B.C.: The historian Livy describes an infectious disease, perhaps influenza, which strikes the Roman army.

1781-'82: Considered among the greatest manifestations of disease in history, this pandemic afflicts two-thirds of the people of Rome and three-quarters of the population of Britain. Influenza also spreads widely in North America, the West Indies and Spanish America.

1789: A widespread epidemic hits New England, New York and Nova Scotia in the fall. Most deaths appear to come from secondary pneumonia.

1829-'32, 1836-'37: An epidemic begins in Asia, probably China, late in 1829. From there it spreads to the Philippines in September 1830, to Indonesia in January 1831, through the Malay Peninsula and into Asia in 1832. The disease also breaks out in Russia (in Moscow and St. Petersburg) in the winter of 1830-'31 and spreads westward overland through the summer of 1831. By November it reaches the United States, and continues to spread in 1832. Another outbreak of influenza spreads through Asia and Europe in 1836-'37 but except for a single outbreak in Canada, does not reach North America.

1889-'90: Named the Russian flu, this worldwide influenza epidemic, the most devastating to that time, begins in Central Asia in the summer of 1889, spreads north into Russia, east to China and west to Europe. It eventually strikes North America, parts of Africa and major Pacific Rim countries. By conservative estimates, 250,000 die in Europe, and the world death total is two to three times that.

1917-'19: The Spanish flu, the most lethal influenza pandemic ever, kills half a million people. More people die as a result of this flu than die during World War I. Troop movements in the closing months of the war facilitate its spread. Mortality rates are unusually high for flu, especially among young, otherwise healthy adults.

1957-'58: The Asian flu starts in southwest China in February 1957, possibly having originated in 1956 in Vladivostok, Russia, then spreads throughout the Pacific. Globally it affects 10 percent to 35 percent of the population, but overall mortality is much lower than in the 1918 epidemic, about 0.25 percent.

1968-'69: Hong Kong flu claims 700,000 lives worldwide, 34,000 in the United States. 1976: The Swine flu, isolated in New Jersey in a young army recruit, instills fear of a new pandemic and leads to a massive influenza-immunization program. The vaccinations lead to Guillain-Barre syndrome, an ascending paralysis, in 100,000 people and kills 5 percent of those afflicted.

1986: Avain variation of the swine flue in the Netherlands results in one severe case of pneumonia.

1988: The Swine flu kills a pregnant woman exposed to a sick pig in Wisconsin.

1993: Strain of the swine flu in the Netherlands sickens two children. The fathers are believed to have come in contact with infected pigs.

1995: One adult contracts conjunctivitis in the United Kingdom after infection with the duck virus.

1997: The Hong Kong Poultry virus infects at least 18 people, killing 6 of them.