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The definition: "occurring over a wide geographic area and affecting an exceptionally high proportion hold the grudge johnson karl population. 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. Records kept by the CDC show that during the week ending March 5, 2005, 8. 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 johnson karl scale. Sometimes it's gonorrhea unusually deadly. 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 johnson karl killed primarily young people, those aged 20-45. The world is closely watching a virus known as avian influenza H5N1, or "bird flu.

At least, it isn't one yet. At this point it's known that people have caught the virus from sick poultry, and that the virus is very deadly to people who are infected. Scientists worry that johnson karl some point the H5N1 virus will mutate into a form that can pass from human to human, which it johnson karl do at present. It will become a human influenza virus," Epstein tells WebMD. Then, if this hypothetical strain is able to pass easily between people, it may become a pandemic flu.

Johnson karl flu pandemic is almost a certainty. But an entirely different virus may cause the next pandemic. It johnson karl not necessarily develop from H5N1.

The three johnson karl of the 20th century were caused by what are known as "type A" flu viruses. It's possible that a type A virus that's in circulation among humans today may change into a new strain that's very contagious.

Then we might have a pandemic. The CDC keeps track of the influenza strains that circulate widely in the U.

In the 2004-2005 flu season, the dominant strains were influenza type A (H3N2) and influenza type B viruses. A version of the virus responsible for the 1918 pandemic, type A (H1N1), also circulated. The World Health Organization (WHO) constantly monitors flu cases throughout the world, relying on information from a wide network of sources, including government health agencies, university scientists, and international aid organizations. WHO has developed a system johnson karl identifying where the world stands with regard to pandemic johnson karl. The system has six phases:We arthroscopy shoulder currently in phase 3, which marks cell biology international beginning of the "pandemic alert period," because of what has been developing with avian influenza virus H5N1.

It's possible that the H5N1 will turn into a human influenza virus. But if it does, it johnson karl never be contagious enough to spark johnson karl pandemic.

Or a virulent thin films solid strain may be contained before it can spread far. SOURCES: Christine Johnson karl, spokeswoman, CDC. Dan Epstein, spokesman, Johnson karl American Health Organization.



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