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Πέμπτη, 30 Απριλίου 2009

Pandemic Influenza

History of ...

A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza A virus emerges for which there is little or no immunity in the human population, it begins to cause serious illness, and then spreads easily person-to-person worldwide. Influenza pandemics have occurred at least during the last four centuries. There have been three influenza pandemics in the last 100 years and several ongoing pandemic threats; a very severe pandemic in 1918-1919 (“Spanish Influenza”, “The Great Pandemic”), two milder pandemics in 1957-1958 (“Asian Flu”) and 1968-1969 (“Hong Kong Flu”), two pandemic “threats” in 1976 (“Swine Flu”) and 1977 (“Russian Flu”), and two ongoing pandemic “threats” beginning in 1997 (A/H5N1, “Avian Flu”, “Bird Flu”) and 1999 (A/H9N2).

1918-1919 Influenza Pandemic (“Spanish Influenza”, “The Great Pandemic”)

Nurse

Nurses and doctors attempted, often unsuccessfully, to protect themselves from influenza. [Credit: National Archives and Records Administration]

In 1918 - 1919 the world experienced an influenza pandemic so severe that it infected one fifth of the world’s population. It infected 28% of all Americans (http://virus.stanford.edu/uda). No one knows exactly how many people died during the 1918-1919 influenza pandemic. During the 1920s, researchers estimated that 21.5 million people died as a result of the 1918-1919 pandemic. More recent estimates of global mortality from this pandemic claim between 30 and 100 million people died from influenza during this period. The 1918-1919 influenza pandemic occurred in three waves in the United States killing an estimated 675,000 Americans (Hatchett et al., 2007).

Although commonly referred to as the “Spanish Influenza”, the 1918 influenza pandemic is thought to have originated at Fort Riley, Kansas in March, 1918. American soldiers crowded on troop ships spread the disease to Europe and later back to the United States. Troop movements during World War I (WWI) quickly spread the disease worldwide and killed more soldiers than the fighting did. By fall 1918, the influenza had mutated into a very virulent form. The war brought the virus back into the U.S. for the second wave of the pandemic. The busy port city of Boston was the first in the country to be struck by this wave in late August 1918 and suffered more losses than any other American city. During the week ending October 7 1918, officials reported 1,023 deaths from influenza in Boston alone (now considered to be an underestimate of the actual influenza deaths). Between September 1, 1918 and January 16, 1919, more than 45,000 people died from influenza in Massachusetts (Hatchett et al, 2007). In the month of October 1918, 200,000 Americans died of influenza. The effect of the influenza pandemic was so severe in the U.S., that the average life span was depressed by 10 years (http://virus.stanford.edu/uda/).

The flu was most deadly for people ages 20 to 40. This pattern of morbidity was unusual for influenza which usually kills the very young and the elderly. Of the U.S. soldiers who died in Europe during WWI, half were killed by the flu (43,000) and not by the enemy (http://virus.stanford.edu/uda/.) Many people died very quickly from this flu; some feeling well in the morning were sick by noon and dead by nightfall. Those who survived the first few days of the disease often died later of complications such as bacterial pneumonia.

1918-1919 Influenza Pandemic in Idaho

Pandemic influenza arrived in Idaho sometime before the end of September, 1918. The Public Health Service did not require states to report influenza before September 27, 1918. On September 30th, officials reported several cases of influenza in Canyon County. Less than two weeks later, the number of cases had grown to such an extent that the state was unable to track the disease accurately. By late October, influenza cases were reported from Boise, Coeur d’Alene, Idaho Falls, Lewiston, Moscow, Pocatello, Twin Falls, Wallace, and many other towns.

Boise

Influenza hit Boise, shown here in 1909, in October. [Credit: The Library of Congress]

In 1918-1919 most of the population of Idaho lived in rural areas (1920 census = 431,866 with no cities or towns having a population of more than 70,000). Rural Idaho suffered terribly from the pandemic. Russell Clark, a resident of Paris, Idaho remembered the impact of the pandemic this way: “There was a feeling of depression and sadness because neighbors, you see, were passing away." The mortality rate was nearly 50 percent in Paris, Idaho.

State officials and newspapers urged calm. In Rexburg, the local paper insisted that there was “no occasion for panic” but then went on to discuss the need to enforce the town’s quarantine. The Northern Idaho News of Sandpoint also urged calm, but then noted that, as a precautionary measure, schools would be closed indefinitely, and churches, picture shows and all public gatherings of every kind would be prohibited. The newspaper also issued a warning to parents to keep their children away from the railway depots as a precaution against infection. To their dismay, many officials found that quarantines had no real impact on the spread of the disease.

Postal Carrier

1918, Because service workers, who frequently came into contact with the public, were at a greater risk of contracting influenza, they often wore masks in attempt to ward off the disease. The masks, however, were ineffective in preventing the spread of influenza. [Credit: National Archives and Records Administration]

Watkin L. Roe from The Franklin County Citizen Newspaper wrote to Surgeon General Rupert Blue on the behalf of “many prominent citizens” in January 1919. He wrote “this county has been closed tight, that is so far as schools, academy, theaters, and picture shows are concerned.” But, he noted, “In looking up similar conditions in other towns, we find that the said towns have been opened in spite of the prevalence of the epidemic. And reviewing these cases, we find that the conditions in those places have been much worse that what we have had in this section.” Roe wrote that 1,300 of the county’s 7,500-8,000 residents had been sickened by the flu and 31 had died. Mr. Roe asked the Surgeon General if there was “any virtue in the vaccines and serums which the doctors are using.” What was a community to do? How could officials know when the disease had truly run its course? The Surgeon General did not send an answer.

Though social distancing measures likely helped, many Idahoans were still afflicted. In Idaho, as elsewhere, the disease simply ran its course, unchecked by actions taken by state, local or federal officials. While influenza rates lessened during the late fall, it was not until the summer of 1919 that the disease began to disappear from the state.

At the Idaho State Pandemic Influenza Summit held in Boise on March 27, 2006 the Secretary of Health and Human Services, Mike Leavitt warned Idahoans:

The final toll that the pandemic took in Idaho will never be known. But the echoes of suffering and loss remain. When it comes to pandemics, there is no rational basis to believe that the early years of the 21st century will be different than the past. If a pandemic strikes, it will come to Idaho.

Influenza among the American Indians 1918-1919

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The Bureau of Indian Affairs found themselves overwhelmed as influenza swept through the state’s reservations. Influenza swept through rural reservations, killing thousands in its wake. [Credit: The Library of Congress]

Native Americans suffered disproportionately from the 1918 influenza pandemic. The Bureau of Indian Affairs was overwhelmed as influenza swept through rural reservations, killing thousands. During the period from October 1st 1918 to March 31st 1919, there were 73,651 reported cases of influenza and 6,270 deaths out of a total Indian population of 304,854. This case mortality rate of 8.5% was substantially higher than that of the general population (2.5%). The reporting of the attacks is probably incomplete, suggesting even higher mortality in the American Indian population. The mortality varied in different localities especially being high among the Indians of the Mountain States (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah and Wyoming). Out of a total Indian population in these Mountain States of 91,475, the attacks numbered 32,285 and of these 3,553 or 11 per cent, died. The highest mortality occurred among the Indians in Utah, Colorado, Idaho, Arizona, and New Mexico. Out of a reported population of 4,208 Indians in Idaho, there were 650 influenza cases and 75 deaths (case mortality of 11.5%). These figures are taken from a statement furnished to the U.S. Public Health Service by the Office of Indian Affairs, Department of the Interior.* (* U.S. Public Health Reports, 9th May 1919, http://ykalaska.wordpress.com/2006/12/20/.)

Deaths among Indians 1918-1919

A second wave of influenza developed among the Indian population in April 1919.

This table gives the incidence of influenza and the mortality from it among the Indian population of the various States, from October 1918 to June 1919.

1957-1958 Influenza Pandemic (“Asian Flu”)

The 1957-1958 Pandemic was first detected in Asia in February 1957. Because of improved surveillance and technology, the novel virus was identified quickly and vaccine production began in May 1957. Limited supplies of vaccine were available by August. The pandemic arrived in the United States during the summer of 1957. Infection rates were highest in school-age children, young adults, and pregnant women while death rates were highest in the elderly. A second wave hit the U.S. in January and February of 1958, this time infecting mostly elderly people. The Asian Flu pandemic caused at least 70,000 deaths in the United States and an estimated 1-2 million deaths worldwide. In Idaho, 49 deaths were attributed to the pandemic (Idaho Department of Health and Welfare Bureau of Health Policy and Vital Statistics).

1968-1969 Influenza Pandemic (“Hong Kong Flu”)

Boise

Policemen in Seattle wore masks in the belief that these would protect them from influenza. The masks provided no real protection. c. 1918.

The mildest pandemic of the 20th century was first detected in Hong Kong in early 1968. The first cases in the United States began in September, but the pandemic didn’t become widespread there until December. Deaths peaked in December 1968 and January 1969, mostly in those over 65 years old. A combination of factors are credited with the relatively mild nature of this pandemic. First, the Hong Kong Flu was similar to the Asian Flu of 1958-1959, affording some immunity to those living during those years. Second, infection rates did not become high until near the school holidays in December so school children were not infecting each other or their families. Lastly, improved medical care and medications reduced the number of complications from flu and probably reduced mortality attributed to the pandemic. The Hong Kong flu caused nearly 34,000 deaths in the United States. In Idaho, 61 people died from pandemic influenza in 1968-1969 (Idaho Department of Health and Welfare Bureau of Health Policy and Vital Statistics).

Pandemic “Threats” in the 20th and 21st Centuries

The “Swine Flu” of 1976 was identified in Fort Dix, New Jersey and at first was thought to be related to the 1918 virus. A mass vaccination of US citizens contained the threat to the Fort Dix area and later research determined that the virus would probably not have been as serious at the 1918 pandemic if it had spread.

In May 1977 the “Russian Flu” emerged in north China and spread rapidly in children and young adults worldwide. Because of similarities to other A/H1N1 viruses that had circulated before 1957, most people over 23 years of age had some immunity to the disease and therefore the epidemic was not considered a true pandemic. Vaccine for this virus was not available during the 1977-1978 flu season, but the virus was included in the seasonal vaccine for the 1978-1979 flu season.

In 1997 (A/H5N1, “Avian Flu”, “Bird Flu”) and 1999 (A/H9N2) two new influenza pandemic threats emerged in Hong Kong. Both of these avian viruses have infected humans directly without having been altered first by infecting pigs as an intermediate host. These viruses are currently found in birds. In 1999, two children were infected and became ill with A/H9N1. After initially killing 18 people in Hong Kong in 1997 (www.PandemicFlu.gov), the A/H5N1 virus has gone on to infect at least 387 people (confirmed by WHO) in 15 countries killing 245 (confirmed by WHO) as of September 10, 2008. The highest number of deaths has occurred in Indonesia where 82% of those who are infected have died. Much of the current pandemic preparedness efforts in Idaho, the United States, and elsewhere in the world have been predicated on the potential of A/H5N1 becoming the next pandemic influenza. Human-to-human transmission of the virus has occurred, but only in a few instances on a very limited basis between family members and close contacts.

Unless the virus becomes easily transmissible between humans through mutations or genetic drift, A/H5N1 will not become a pandemic. To learn more about A/H5N1, see an updated map of the countries with cases of H5N1 in humans confirmed by the World Health Organization (WHO), and see the H5N1 timeline visit PandemicFlu.gov. For additional information about H5N1 and other viruses in animals please visit the OIE (Organisation for Animal Health) Website.