As health experts, governments and journalists investigate and report on the current outbreak of swine flu, statistics compiled by various government agencies show that past flu outbreaks -- both seasonal and pandemic -- have been more deadly and widespread.

The swine flu outbreak appears to have started in Mexico. By Wednesday, Mexican authorities said that swine flu was suspected of causing the death of more than 150 people.

In the United States, there were 91 confirmed cases so far, and one infant from Mexico died in Texas.

Compare that to an average of 36,000 Americans who die every year from common, seasonal flu despite the generally wide availability of vaccines, according to statistics provided by the U.S. Centers for Disease Control and Prevention in Atlanta.

Unlike the predictable and treatable annual outbreaks of seasonal flu, the CDC defines a pandemic as a disease outbreak that occurs rarely, spreads quickly and with little resistance, overwhelms health systems, cripples public services, impacts the economy severely and causes high rates of death.

Using that set of guidelines, the 1918-1919 global influenza outbreak was pandemic in scale, resulting in the deaths of anywhere between 30 million and 50 million people, including about 675,000 Americans, CDC said.

Another pandemic from 1957-1958 in the United States killed at least 70,000. A third, from 1968-1967, killed an estimated 33,000 Americans.

Avian flu, or bird flu, which began making headlines in 2003 after an outbreak in Southeast Asia, resulted in the deaths of 257 people, the majority of whom lived in Thailand, Vietnam and Indonesia. The CDC found no U.S. deaths attributed to avian flu.

What about other headline-grabbing disease outbreaks?

Severe Acute Respiratory Syndrome, or SARS, spread around the world in 2002-2003, infecting about 8,000 people, of which 774 died, according to the World Health Organization. Of those deaths, 648 were in China and Hong Kong. A few dozen people in the United States were infected, but no one died.

Measles, another disease that can be deadly, has been on the decline, from 763,094 cases in 1958 to fewer than 150 cases since 1997, according to WHO. In the spring of 2008, 64 preliminary confirmed measles cases were reported. Fourteen patients were hospitalized and no deaths were reported.