Influenza-like illness (ILI) is defined as a temperature of > 100.0?F (> 37.8?C) and either cough or sore throat in the absence of a known cause. Levels of influenza activity are 1) no activity, 2) sporadic-small numbers of laboratory-confirmed influenza cases or a single influenza outbreak reported but no increase in cases of ILI, 3) local-outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in a single region of a state, 4) regional-outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least two but less than half the regions of a state, and 5) widespread-outbreaks of influenza or increases in ILI cases and recent laboratory-confirmed influenza in at least half the regions of a state.
Influenza incidence exhibits strong seasonal fluctuations in temperate regions throughout the world, concentrating the mortality and morbidity burden of the disease into a few months each year. Influenza is more likely to spread in the winter than the summer. This may be caused by an increased infectiousness of the disease, an increased susceptibility of people, or an increased number contacts with others that might result in transmitting the infection during the winter. For example, people may spend more time indoors.
The reason that more people catch the flu in the winter appears to be that small seasonal changes in flu transmission at the individual level are greatly amplified as the disease spreads through communities. The underlying cause of seasonal fluctuations in transmission may be too small to measure. Large fluctuations in the number of flu cases between winter and other seasons may be caused by very small changes in the number of people infected by a single infectious person. These small changes in transmission rate are amplified by interactions between the evolving virus and the changing level of immunity that people have to specific strains.
The cause of influenza's seasonality has remained elusive. Studies have failed to establish whether these transmission changes are due to direct effects of temperature and humidity on transmission, to changes in mixing patterns [e.g., school terms or simply more time spent indoors], or to other factors, such as increased viral production under winter conditions. In fact, it may be impossible to establish the underlying cause of seasonality in influenza epidemics, since the large observed oscillations in incidence can be generated by seasonal changes in the transmission rate that are too small to measure. The large oscillations in incidence may be caused by undetectably small seasonal changes in the influenza transmission rate that are amplified by dynamical resonance.
Data can be evaluated quantitatively, and graphic representation of this information, known as epidemic curves (epi-curves), may prove especially useful in this endeavor. These visual representations depict case frequency over time, and are initially used to obtain tentative answers to questions concerning origin, propagation, incidence, prevalence, and likely modes of transmission. The nature of the epidemic curve varies with the pathogen. The frequency curve for most infectious diseases resembles a logarithmic normal curve. Epidemics such as infuenza have distinctive patterns of initiation and spread.
Showing posts with label flu. Show all posts
Showing posts with label flu. Show all posts
Tuesday, November 6, 2007
FLU FACTS
According to the Centers for Disease Control and Prevention, although October and November are the recommended months for vaccination, a flu vaccine given later in the season -- December through March -- still can help protect from influenza.
This year, flu vaccine manufacturers plan to have more then 130 million doses of influenza vaccine available for distribution in the United States, more than ever before.
The two vaccines available to the public are:
The traditional injectable flu vaccine, which contains inactivated (killed) virus, is for anyone age 6 months and older. Some patients experience soreness at the injection site lasting less than two days, but serious side effects are extremely rare. This vaccine may come in a multiple-dose vial or in single-dose syringes. Syringes for children 3 and younger are thimerosal-free.
A live weakened virus vaccine called LAIV or "FluMist" is sprayed into the nose and is for healthy people ages 2 through 49. A small amount of vaccine is sprayed into each nostril, instead of getting an injection.
Source: CDC, Public Health -- Seattle & King County
This year, flu vaccine manufacturers plan to have more then 130 million doses of influenza vaccine available for distribution in the United States, more than ever before.
The two vaccines available to the public are:
The traditional injectable flu vaccine, which contains inactivated (killed) virus, is for anyone age 6 months and older. Some patients experience soreness at the injection site lasting less than two days, but serious side effects are extremely rare. This vaccine may come in a multiple-dose vial or in single-dose syringes. Syringes for children 3 and younger are thimerosal-free.
A live weakened virus vaccine called LAIV or "FluMist" is sprayed into the nose and is for healthy people ages 2 through 49. A small amount of vaccine is sprayed into each nostril, instead of getting an injection.
Source: CDC, Public Health -- Seattle & King County
Monday, November 5, 2007
Two types of flu vaccine
The single best way to protect against the flu is to get vaccinated each fall.
There are two types of vaccines:
The "flu shot"— an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions. For more, please read the Flu Vaccine article.
The nasal-spray flu vaccine — a vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). LAIV is approved for use in healthy people 5 years to 49 years of age who are not pregnant. Each vaccine contains three influenza viruses—one A (H3N2) virus, one A (H1N1) virus, and one B virus. The viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year. For more, please read the Influenza Nasal Vaccine (FluMist) article.
About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.
When should you get vaccinated?
October or November is the best time to get vaccinated, but you can still get vaccinated in December and later. Flu season can begin as early as October and last as late as May.
Who should get vaccinated this season?
In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. However, certain people should get vaccinated each year. They are either people who are at high risk of having serious flu complications or people who live with or care for those at high risk for serious complications.
There are two types of vaccines:
The "flu shot"— an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. The flu shot is approved for use in people older than 6 months, including healthy people and people with chronic medical conditions. For more, please read the Flu Vaccine article.
The nasal-spray flu vaccine — a vaccine made with live, weakened flu viruses that do not cause the flu (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). LAIV is approved for use in healthy people 5 years to 49 years of age who are not pregnant. Each vaccine contains three influenza viruses—one A (H3N2) virus, one A (H1N1) virus, and one B virus. The viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year. For more, please read the Influenza Nasal Vaccine (FluMist) article.
About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.
When should you get vaccinated?
October or November is the best time to get vaccinated, but you can still get vaccinated in December and later. Flu season can begin as early as October and last as late as May.
Who should get vaccinated this season?
In general, anyone who wants to reduce their chances of getting the flu can get vaccinated. However, certain people should get vaccinated each year. They are either people who are at high risk of having serious flu complications or people who live with or care for those at high risk for serious complications.
Widespread vitamin D deficiency may be cause of post-Winter flu outbreaks, scientists suggest
A team of researchers is gathering data in an attempt to determine why flu outbreaks hit the Northern Hemisphere during winter months and tend to peak between December and March, and a new theory suggests it may be a lack of sunshine-produced vitamin D.
In the past, many theories have been put forward to explain the seasonal flu flux, but explanations such as cold air and the tendency of people to group together "remain astonishingly superficial and full of inconsistencies," said Dr. Scott Dowell, director of the Global Disease Protection Program at the Centers for Disease Control and Prevention in Atlanta.
Theories about a chill causing the disease's prevalence is upended by evidence from tropical locations, where flu remains common and follows a similar seasonal pattern to its cold-climate counterpart. The grouping theory is debunked by the fact that certain groups of people are stuck in small spaces together year round, with no greater likelihood of contracting flu than anyone else.
Now, the Harvard-University-led team is investigating whether inadequate sun exposure during the winter may open people up to infection, since exposure to ultraviolet B radiation (UVB) radiation from the sun causes vitamin D production in the skin. If the lack of vitamin D and increased flu cases in the winter are connected, it could have a significant impact on public health, as an average of 36,000 people die from flu in the United States every winter, primarily the elderly or the very young.
R. Edgar Hope-Simpson published the first paper that identified a link between flu epidemics and the winter solstice -- usually indentified as the start of winter and the shortest day of the year -- in 1981, despite having no formal training in the field of epidemiology. Simpson noted that flu infections spiked just before and after the winter solstice, and theorized that solar radiation might cause a sort of "seasonal stimulus" in the virus, the host or both, although he could not identify the stimulus.
Simpson's work was largely ignored, according to Dr. John Cannell, a psychiatrist at the Atascadero State Hospital in California. However, Cannel and his Harvard colleagues suggest the stimulus to which Simpson referred may be vitamin D. Cannell began investigating the possibility when a flu outbreak hit Atascadero in April of 2005 and all the wards surrounding his were infected, Cannell's patients were not. All of his patients, he said, were taking high daily doses of vitamin D.
During the winter, people are outdoors less often and the skin has less opportunity to produce vitamin D, and the atmosphere during that season is adept at blocking UVB radiation. This is why some health experts warn that Americans may not be getting sufficient vitamin D, especially with the resurgence of the vitamin-deficiency-related bone disorder known as rickets.
In the report -- published in the December issue of Epidemiology and Infection -- the researchers posit that the vitamin D stimulated by sunlight may, in turn, cause the body to produce the infection-fighting peptide cathelcidin. No studies been conducted that to show whether cathelcidin effects influenza, but previous studies in the March issue of Science have shown it attacks a range of fungi, viruses and bacteria, including the bacteria that causes tuberculosis.
The tropical evidence that upsets the chill theory does not preclude the vitamin D theory, as Cannell and colleagues point out, as studies show that vitamin D deficiencies have even been recorded in equatorial locations. Additionally, a 2003 analysis of flu cases found they were greatest during the rainy season, when there is a significant cloud cover and reduced sun exposure.
Despite the evidence offered by Cannell and colleagues, some members of the scientific community remain skeptical about the theory.
"They have manipulated the literature -- some of it very bad literature -- to prove their points," said Dr. James Cherry, a pediatric infectious disease specialist at UCLA's David Geffen School of Medicine. However, he added, "The hypothesis should be easy to prove or disprove with a controlled, blinded study."
Cannell, for his part, said he takes more than twice the recommended daily dose of vitamin D during winter months and reports he rarely gets sick.
In the past, many theories have been put forward to explain the seasonal flu flux, but explanations such as cold air and the tendency of people to group together "remain astonishingly superficial and full of inconsistencies," said Dr. Scott Dowell, director of the Global Disease Protection Program at the Centers for Disease Control and Prevention in Atlanta.
Theories about a chill causing the disease's prevalence is upended by evidence from tropical locations, where flu remains common and follows a similar seasonal pattern to its cold-climate counterpart. The grouping theory is debunked by the fact that certain groups of people are stuck in small spaces together year round, with no greater likelihood of contracting flu than anyone else.
Now, the Harvard-University-led team is investigating whether inadequate sun exposure during the winter may open people up to infection, since exposure to ultraviolet B radiation (UVB) radiation from the sun causes vitamin D production in the skin. If the lack of vitamin D and increased flu cases in the winter are connected, it could have a significant impact on public health, as an average of 36,000 people die from flu in the United States every winter, primarily the elderly or the very young.
R. Edgar Hope-Simpson published the first paper that identified a link between flu epidemics and the winter solstice -- usually indentified as the start of winter and the shortest day of the year -- in 1981, despite having no formal training in the field of epidemiology. Simpson noted that flu infections spiked just before and after the winter solstice, and theorized that solar radiation might cause a sort of "seasonal stimulus" in the virus, the host or both, although he could not identify the stimulus.
Simpson's work was largely ignored, according to Dr. John Cannell, a psychiatrist at the Atascadero State Hospital in California. However, Cannel and his Harvard colleagues suggest the stimulus to which Simpson referred may be vitamin D. Cannell began investigating the possibility when a flu outbreak hit Atascadero in April of 2005 and all the wards surrounding his were infected, Cannell's patients were not. All of his patients, he said, were taking high daily doses of vitamin D.
During the winter, people are outdoors less often and the skin has less opportunity to produce vitamin D, and the atmosphere during that season is adept at blocking UVB radiation. This is why some health experts warn that Americans may not be getting sufficient vitamin D, especially with the resurgence of the vitamin-deficiency-related bone disorder known as rickets.
In the report -- published in the December issue of Epidemiology and Infection -- the researchers posit that the vitamin D stimulated by sunlight may, in turn, cause the body to produce the infection-fighting peptide cathelcidin. No studies been conducted that to show whether cathelcidin effects influenza, but previous studies in the March issue of Science have shown it attacks a range of fungi, viruses and bacteria, including the bacteria that causes tuberculosis.
The tropical evidence that upsets the chill theory does not preclude the vitamin D theory, as Cannell and colleagues point out, as studies show that vitamin D deficiencies have even been recorded in equatorial locations. Additionally, a 2003 analysis of flu cases found they were greatest during the rainy season, when there is a significant cloud cover and reduced sun exposure.
Despite the evidence offered by Cannell and colleagues, some members of the scientific community remain skeptical about the theory.
"They have manipulated the literature -- some of it very bad literature -- to prove their points," said Dr. James Cherry, a pediatric infectious disease specialist at UCLA's David Geffen School of Medicine. However, he added, "The hypothesis should be easy to prove or disprove with a controlled, blinded study."
Cannell, for his part, said he takes more than twice the recommended daily dose of vitamin D during winter months and reports he rarely gets sick.
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