Swine Flu - Basic Information - A Must Read

[JJackson]

I can see we have a lot of ?lurkers? ? I hate that term as I think it has pejorative overtones when all it means is readers who have not signed up to comment. Many, I suspect, are relatively new to all things Pandemic flu related and will be confused by the ?swine flu? stories appearing in the main stream media (MSM) when up until now ?bird flu? has got all the ink. What follows is some background which I hope will help you in understanding this unfolding story.

All flu?s originally come from birds. There are three Types A, B & C and we are only interested in Type A here. They are simple viruses with eight strands of genetic material (RNA) which include instructions for making eleven proteins. Two of these proteins Hemagglutinin (H) & Neuraminidase (N) are used to classify flu?s. There are 16 Hs & 9 Ns giving 144 possible combinations from H1N1 to H16N9 these are called SeroTypes (also known as SubTypes). Flu mutates very rapidly and each of the RNA strands is constantly varying about a theme and these are called Strains. As mentioned, birds are the natural carriers of flu but occasionally one of these strains drifts to a point where it happens to also be capable of infecting a mammal. Normally when this happens it is due to close contact and the story goes no further and the animal is a ?dead end host? in that it does not spread the infection to others. On extremely rare occasions the animal does spread to other animals of the same type and if this can be sustained the virus may adapt to its new host species and stop being a bird disease and become a swine or horse or human flu. All three of these animals are now the natural hosts for their own flus. In each case the flu would have originated in birds but, now that it is fully adapted to its new host, would have difficulty transferring back to birds.
<o:p> </o:p>
Humans have only two Serotypes of Type A seasonal flu which circulate each winter; H1N1 and H3N2. Occasionally others, like H5N1(avian), cause the odd infection in humans but transmission is not sustained. There are also infections from pigs, but again generally in people who work with pigs, and not sustained. H5N1(avian) has caused a steady trickle of human cases since 2003 and as some of these have managed to infect other people the fear was it might make further changes until it could be self-sustaining in humans starting a new pandemic. While we were aware that any non human flu could start a pandemic this was a particularly lethal strain which had shown some human adaption so got a lot of attention.
<o:p> </o:p>
So much for the background what is happening now?
A new pandemic candidate has emerged this time it is H1N1(swine). H1N1(human) is one of the seasonal flu strains but this is a human adapted flu. There are also H1N1 strains in birds and pigs and they are each adapted to their own host species and normally stay there. Unfortunately a new strain has jumped from pigs into humans and is spreading from human to human. I will use H1N1(2009) as a shorthand for this one as it is now reproducing and spreading in humans but is still genetically very swine like in character. If it gets any better at living in us it may become unstoppable and go pandemic.
<o:p> </o:p>
What about vaccines and antivirals?
Our immune system has many parts but they can be broadly split into two categories Innate & Adaptive. The Innate system needs no prior knowledge of a pathogen, if it does not recognise it as ?self?, it attacks ? however it is generalised and less effective. The Adaptive part of the system is made up of specialised tools for attacking threats it has met before. If an unrecognised virus appears the Innate system will try and deal with it but you may become quite ill while it builds a targeted Adaptive response. If you have had the disease before then both parts come into play and you are said to have immunity ? or partial immunity. In the case of flu it is fighting an evolutionary battle with our immune system and is continuously varying its surface proteins (H & N) to avoid recognition. When we vaccinate someone we are deliberately using something to make the body think it is being attacked by a particular strain so when it meets it again it has a primed Adaptive immunity. After a few years flu can change so much that last years infection, or vaccination, may not be enough to protect you. Any swine or avian H1N1 are likely to be such distant cousins that even if you have just had a shot for seasonal H1N1 it probably will not help much, if at all. Unfortunately it takes several months to make reasonable amounts of flu vaccine and you need a sample of the right strain to start. If the WHO decides this H1N1(2009) is going pandemic it would ask all the seasonal flu manufactures to stop production of seasonal flu vaccine and switch to H1N1(2009) vaccine production.
The CDC, in the US, say that H1N1(2009) is susceptible to both Tamiflu and Relenza, the main antiviral drugs, but not to the older ion blockers. Seasonal human H1N1 is largely resistant to the common Tamiflu (tablet), but still susceptible to the less common Relenza (inhaled powder). A further note is that flu has a habit of swapping genetic material with other flus if you get dual infections and this happens more easily if they are similar strains. While H1N1(seasonal) may be far enough away from H1N1(2009) for the vaccine not to work it is close enough for there to be a real danger of it learning Tamiflu resistance in short order.

P.S. If you have not signed up for an account then I recommend you do so( Register Link ). It is quick, painless and has a number of advantages. Firstly you can post information and ask questions, your computer will remember which threads you have read and which have new post since your last visit, searching is easier and some sections of the site are only open to members. This Link will take you to the Site Index and you can browse the libraries from there.

[AlaskaDenise]

Re: Swine Flu - Basic Information

Pigs Often Infect Farmers, Meatpackers

Pigs have their own versions of influenza, and studies of farmers and meatpackers suggest that the animals fairly regularly infect people.

Pigs play an important role in the origin of pandemics because they can be infected by both bird and human strains of flu virus. Consequently, they can serve as "mixing vessels" in which different viruses can combine to form new and potentially dangerous strains.

In most cases, the transmission involves common pig flu that does not go beyond the person who had contact with the animal. But in a few, there is evidence of secondary human-to-human transmission -- which appears to be happening in California and Mexico

"I suspect that there has been a lot of transmission of swine influenza, causing mild disease in the United States, for a number of years," said Gregory C. Gray, a physician who heads the Center for Emerging Infectious Diseases at the University of Iowa.

In August 2007, about 25 people and 160 pigs developed flu at a county fair in Ohio. Analysis showed they were infected with the same strain -- an H1N1 type containing genes of human, bird and swine origin.

A 2004 study found that in Iowa, 20 percent of swine veterinarians and 3 percent of meatpackers, but no university workers, had antibodies in their blood indicating they had been infected with swine flu.

Another study, of 804 rural Iowans, found that pig farmers were 50 times more likely, and their spouses about 30 times more likely, than university workers to carry swine flu antibodies. The researchers think that in many cases the spouses were infected by their partners.

http://www.washingtonpost.com/wp-dyn/content/article/2009/04/24/AR2009042403852.html

[AlaskaDenise]

Re: Swine Flu - Basic Information

A little history on the last swine/human mini-epidemic:
-------------------------------------------------------
Influenza Pandemics of the 20th Century

(snipped)

1976: Abortive, Potentially Pandemic, Swine Influenza Virus Epidemic, Fort Dix, New Jersey (H1N1)

In the interest of full disclosure, I predicted the possibility of an imminent pandemic in an op ed piece published in The New York Times on February 13, 1976 (25). On February 13, I was notified that influenza viruses isolated from patients at Fort Dix, New Jersey, a few days earlier and provisionally identified as swine influenza viruses were being mailed to my laboratory in New York City. A high-yield (6:2) genetic reassortant virus (X-53) was produced and later used as a vaccine in a clinical trial in 3,000 people. An even higher yielding HA mutant virus, X-53a, was selected from X-53 and subsequently used in the mass vaccination of 43,000,000 people. (I was a member of a Center for Disease Control advisory committee and an ad hoc advisory committee to President Gerald Ford on actions to be taken to protect the American public against swine influenza.) When no cases were found outside Fort Dix in subsequent months and the neurologic complication of Guillain-Barr? syndrome occurred in association with administration of swine influenza vaccine, the National Immunization Program was abandoned, and the entire effort was assailed as a fiasco and disaster.

I wish only to note here that my unyielding position on the need for vaccine production and immediate vaccination (not stockpiling) had its basis in what science could be brought to bear in an unprecedented situation. This was the cocirculation in crowded recruit barracks of 2 influenza A viruses of different subtypes: H3N2, the major epidemic virus, and H1(swine) N1. The latter virus, which caused a minor (buried) epidemic and was shown to be serially transmissible in humans, was the putative virus of 1918. Would genetic reassortment of the viruses produce a monster, as is now feared with the current avian virus threat, or did interference by the far more prevalent virus H3N2 suppress further transmission of the swine virus?

Experience had shown a decrease or even disappearance of epidemic viruses in the summer. However, they return in winter to produce disease in conditions favoring transmission: indoor crowding and decreased relative humidity. None of these facts was noted by critics of the program.

http://www.cdc.gov/ncidod/EID/vol12no01/05-1254.htm

[AlaskaDenise]

Re: Swine Flu - Basic Information

More history...
---------------
Swine Influenza A Outbreak, Fort Dix, New Jersey, 1976

(snipped)

Summary and Speculation

A/New Jersey/76 (Hsw1N1) was likely introduced into Fort Dix early in 1976, after the holidays (15). The virus caused disease with radiologic evidence of pneumonia in at least 4 soldiers and 1 death; all of these patients had previously been healthy (7,15). The virus was transmitted to close contacts in the unique basic training environment, with limited transmission outside the basic training group. A/New Jersey probably circulated for a month and disappeared. The source of the virus, the exact time of its introduction into Fort Dix, and factors limiting its spread and duration are unknown (15).

The Fort Dix outbreak may have been a zoonotic anomaly caused by introduction of an animal virus into a stressed population in close contact in crowded facilities during a cold winter. However, the impact of A/New Jersey virus on this healthy young population was severe in terms of estimated infections, hospitalizations, and duration of the outbreak.

If the outbreak was more than an anomaly, why did it not extend beyond basic trainees? Several factors merit consideration. Contact between basic trainees and others was limited. Moreover, a swine influenza antigen was included in annual military influenza vaccine formulations from 1955 through 1969 (10). The high antibody titers to A/Mayo Clinic antigen observed with increasing age in the Phlebotomy Clinic population may reflect earlier influenza A (H1N1) infections or vaccine exposure and some protection (11). Also, competition between A/New Jersey and A/Victoria viruses must be considered. The A/Victoria virus spread widely and may have limited the impact of A/New Jersey virus with its lesser ability for human transmission.

Could the Fort Dix outbreak have resulted from interaction between swine influenza A and A/Victoria viruses? A/Victoria transmission occurred in New Jersey before A/New Jersey was identified at Fort Dix. Is it possible that A/Victoria virus and an early A/New Jersey virus coinfected a soldier with genetic exchange, resulting in a recombinant virus with enhanced human transmission capability? The rapid disappearance of A/New Jersey prohibited studies of virus interactions. Genetic analyses of A/New Jersey, A/Victoria and contemporary A/swine viruses might elucidate a relationship.

Communication and collaboration existed at the onset of the outbreak and continued throughout the investigation. The points of contact at the NJ Department of Health, Fort Dix, CDC, and WRAIR had been established before the outbreak, so time was not lost identifying organizations and persons who needed to be contacted. Organizational roles were defined early and respected. The development of outbreak investigation plans, collaboration in field and laboratory work, and exchange of information occurred smoothly. An important part of the Army investigation was establishment of points of contact at WRAIR who communicated with military leaders, the NJ Department of Health, CDC, and the press. Military epidemiology and laboratory teams reported to WRAIR points of contact. This system protected these teams from disruptive inquiries.

The burden on the laboratories supporting this investigation was intense, lasting for weeks. In 1976, WRAIR was a research and field epidemiology laboratory that also operated as a public health reference laboratory. The WRAIR commander had the authority to reallocate and mobilize scientists and laboratory resources. Today, WRAIR no longer functions as a public health laboratory. The depth of resources and flexibility that existed at WRAIR in 1976 cannot be found in other military laboratories (16). Duplicating the 1976 laboratory effort today, in timely fashion, would be difficult.

http://www.cdc.gov/ncidod/EID/vol12no01/05-0965.htm

[JJackson]

Re: Swine Flu - Basic Information


If you read my opening post in this thread please note that this post is much more speculative in nature and that all opinions are mine alone and not those of FluTrackers.

Things are very confused at the moment and listening to the CDC news casts with journalists it is obviously frustrating for all concerned that there are many more questions than answers.
What is clear is that a new H1N1 flu strain with a predominantly swine background has emerged as a novel virus in humans. It has been confirmed in 6 states so far 3 each for Mexico & the US with additional presumptive positives.

It may be helpful to give a little more back ground on the testing to explain the presumptive positives, and some of the other numbers and what they mean. A temperature with some combination of cough, sore throat, runny nose are all likely to be given a preliminary diagnosis of ILI (Influenza like illness) as a catchall. Most of these patients will be told ?you probably have a virus, go home drink plenty of fluids, rest and come back if you do not start feeling better in a few days?. A few clinics will be part of a national surveillance program and will take swabs so a picture can be built up of how much of the ILI is actually influenza and which strains are dominant. In addition to this random sampling those of the ILI patients who did not get better on their own and returned may also be swabbed. There are 2 Type A flu serotypes H1N1 & H3N2 and Type B in seasonal flu (N.B. this seasonal H1N1 is genetically distinct from the new swine H1N1). All the collected swabs go to a regional lab where they are tested against reagents which can distinguish the A from B and split the two seasonal Type As. They have two other categories ?not flu? and ?untyped?, the new H1N1 is coming up as an ?untyped? Type A flu. The untyped are usually just errors but get sent on to large central labs for more detailed analysis. It is at this stage that the novel swine H1N1 was found.

Obviously all this takes time and until anyone was aware there was a new strain circulating not much could be done. Now tests will be developed that can identify the new H1N1 strain and then these can be distributed to the regional labs. In the meantime there are lots of swabs already in the pipeline many of which are likely to come back positive and many more suspicious cases will be swabbed - although there is a limit to how many more can be processed until the regional labs are able to separate H1N1(seasonal) from H1N1(new). Back to the presumptive positives, like the New York school children, they have been confirmed as Type A but did not score a match against H3N2 or H1N1(seasonal) hence the presumptive positives.

The other number which is a problem is the estimated 1000 Mexican cases. As most of these will never have got past the ILI diagnosis, which is a statement of symptoms and does not define the causative agent, we have no way of telling how accurate this is and it could be off by a long way. This is important because it was released along side an estimate of the number of deaths caused by the H1N1(new) and the number of cases divided by the number of deaths gives an important variable called the Case Fatality Rate (CFR). Normally expressed as a %; this is the proportion of those who get clinically ill who then go on to die. For seasonal flu this is about 2 in 1000 or 0.2%. In 1918 this was about 2%. The Mexican data is just a wild guess, in my opinion, at the moment and will probably settle some where between the two. This is based on the general symptoms described not on the data in the media, which would give a CFR of 6% which is highly improbable given that clinicians are having difficulty distinguishing it from seasonal flu. I regret that given the number and distribution of clusters it seems unlikely this virus will just die out so it does look as if we are in a new pandemic (this is my opinion only and not FluTrackers? or anyone of any authority).

This is not necessarily as bad as it sounds. While pandemic forms of flu will tend to infect a higher percentage of the population than seasonal flu, due to there being no adaptive immunity, it is not this but the virulence that is the main problem. The US confirmed cases have not been radically different to seasonal flu and while there have been some confirmed deaths in Mexico it is likely these have been against a much higher number of cases than the 1000 or so estimated. This is good and bad. It is good because the CFR is lower, implying it is not too virulent, but it is bad in that means the virus has infected many more people and is, therefore, at a latter stage in its pandemic development.

As this is a new virus to humans it will be rapidly evolving to adjust itself to our metabolism and as such a number of its characteristics may change. It would be reasonable to expect it to improve its ability to spread and it may also change its clinical effects. If the surface proteins undergo rapid change this may be a problem for any vaccines that are based on the first samples isolated.

I hope these posts have been of some help and if you have questions please use the link in the first post and I, or someone more knowledgeable, will try and address them.

Update as of 28th of April 2009
Things have moved on somewhat. The WHO has raised the pandemic threat level to 4.
Countries with confirmed cases now include Mexico, USA, Canada, Spain, UK, Israel & NZ and many more have suspect cases.
At present while more countries have been added to the list the individuals concerned are largely those who have been infected in Mexico prior to traveling. The key point to watch for over the next few days are cases seeded by these travelers among nationals who have not been abroad. If this occurs then the WHO will raise the level again and a pandemic becomes very likely. One other item you may see in the news are stories about it being the end of flu season and that the pandemic may die out along with the seasonal flu ? or at least do so in the northern hemisphere. I do not know how to advise you on this as we have so little previous experience to go on. In 1918 there was a milder ?wave? in the spring followed by a more severe one in the following autumn but that was a different strain in a different time. Factors to consider are that as a novel virus it is easier for this flu to find new host as none of its potential targets has any adaptive immunity. Another consideration is that the level of international travel between the Northern and Southern hemisphere means each can be continuously re-seeding the other. Added to which although the marked seasonality of flu is well documented the cause of this seasonality is not understood.

[JJackson]

Re: Swine Flu - Basic Information

Over the last couple of days I, and many of the other moderators, have been trying to answer new member?s questions and help them with links to relevant threads. As we have 30,000+ threads and 150,000+ posts even using the search engine it is not always easy to find what you need.

One thing that has come up, and I think it might help new visitors to understand, relates to flu?s very variable virulence. Virulence is a measure of the severity of illness caused and can, very crudely, be approximated by Case Fatality Rate (CFR), which I introduced in an earlier post. While there have always been some historians and virologists warning of our failure to take zoonotic (diseases newly jumped from animals) pandemics seriously a lot of the posts here have been written by Johnny-come-latelies, like my self, who were alarmed by HPAI H5N1 (AKA ?bird flu?) which started looking like a pandemic candidate from about 2003. H5N1 has killed over half those it infected and many of the post written up until last week will have been written with a flu pandemic based on that virus ? rather than H1N1(2009) (AKA ?swine flu?) in mind. You should bear this in mind particularly if some of the discussion on wide spread infrastructure failure and economic collapse seem alarmist. Just bear in mind they were probably written based on a flu that kills most people and has few mild cases rather than one that has mainly mild cases but can also kill.
Keep asking the questions (link in first post) and if I see a common theme I will try and add another post in this thread. Oh and welcome.

[JJackson]

Re: Swine Flu - Basic Information

Having been immersed in what is going on it is sometimes difficult to believe that this time last week almost no one knew there was a new form of flu in humans. Since then the pandemic phase has been raised first to 4 and then to 5 with 6 ? a declaration of Pandemic ? probably not far off. If you measure time in terms of infection cycles this is probably only enough time for one or two generations so it is not surprising we have yet to see large patient numbers outside Mexico.

I said I would post if I saw a theme that I felt needed an explanation. I have and it relates to the Pandemic levels and 'what is a pandemic?'. A pandemic is an epidemic with global reach; it does not say anything about the virulence or the speed at which it spreads. Some pandemics, like, HIV spread very slowly others like flu tend to be fast. The virulence is quite independent. This seems to be causing some confusion in the media and in the public?s expectations. It is too early to say how virulent this strain is now and, even if we could, it is quite likely to change. Just be aware as you watch things unfold and as you make your own personal preparations to remember to factor this in.
You may find this helpful it is a graph from the UK pandemic plan and shows an average pandemic wave based on the three 20th Century pandemics. Note when the first case appears in your area and read along in weeks to see what you might expect - again allow for surprises. I have added a black vertical line to show approximately where residents of Mexico city would be, almost everyone else will be at zero, or somewhere between the two. All this assumes this is about to be a pandemic.

[sharon sanders]

Re: Swine Flu - Basic Information

via email -


Understanding Swine Flu?s World Spread: Questions and Answers
2009-04-30 18:42:01.153 GMT


(For related stories, see {EXT3 <GO>}.)

By John Lauerman

April 30 (Bloomberg) -- Swine flu has sickened at least 257
people in 11 countries, including Mexico, the U.S., New Zealand,
Canada and the U.K., according to the World Health Organization.
The organization raised its six-tier pandemic alert to 5
and said the world?s first influenza pandemic since 1968 may
soon be declared. Hundreds of more cases are suspected, as
health officials around the world check to see whether
infections have occurred in their countries and ready measures
to prevent its spread.
Here are answers to some frequently asked questions about
swine flu. The information is drawn from the data released by
the World Health Organization in Geneva and the U.S. Centers for
Disease Control and Prevention in Atlanta.

Q: What is swine flu?
A: Influenza is a virus that infects people, birds, pigs
and other animals such as ferrets. Swine flu, or swine
influenza, is a form of the virus that normally infects pigs.
There are many forms of flu, and the different varieties have
the ability to exchange genes with one another. The form of flu
that originated in Mexico is a genetic mixture of viruses that
have been seen in pigs, birds and people. It?s being called a
swine flu because the overall structure of the virus is of the
type that affects pigs, said Keiji Fukuda, a WHO official.

Q: How do people catch swine flu?
A: Studies are ongoing about how this particular swine flu
is transmitted. Flu is generally transmitted through the
respiratory tract. Droplets of infected body fluids may carry
flu when people cough or sneeze. Studies indicate that masks
called N95 respirators, when properly used, filter germs from
the breath and hamper the spread of flu. Neither contact with
pigs nor eating pork has been linked to the spread of the flu,
Fukuda said.

Q: What are the symptoms of swine flu?
A: About one to four days usually elapse between the time a
person is infected and the onset of symptoms. Influenza normally
causes symptoms such as coughing, sneezing, headaches and body
aches, fever, chills, and sometimes vomiting and diarrhea. Swine
flu causes the same symptoms, and may be difficult to
distinguish from other strains of flu and respiratory illnesses.
Severe cases of flu that lead to death are normally seen in very
young and very old people whose immune systems are too weak to
fight off the virus. Adults with severe illness may also have
difficulty breathing, dizziness, confusion, or severe vomiting
and diarrhea.

Q: Is there a vaccine against the swine flu that?s now
spreading?
A: Flu vaccines generally contain a dead or weakened form
of a circulating virus. The vaccine prepares the body?s immune
system to fend off a true infection. For the vaccine to work, it
must match the circulating, ?wild-type? virus relatively
closely. There is no vaccine currently that exactly matches the
swine flu. The seasonal flu vaccine isn?t effective against
swine flu, said Richard Besser, acting head of the CDC.
Vaccine makers have contacted the World Health Organization
about obtaining samples of the virus needed to make a vaccine.
Making flu vaccine can take three to six months. No decision has
been made to order a vaccine against swine flu, Besser said.

Q: How can I tell if my child is sick?
A: Children who are breathing abnormally fast or slowly may
have respiratory illness. Bluish skin indicates a need for quick
attention. Children who are abnormally sluggish and sleepy,
irritable, or have fever or rash may also need attention.

Q: Have there been outbreaks of swine flu before?
A: Yes. Health officials said in 1976 that an outbreak of
swine flu in people might lead to a pandemic. Widespread
vaccination was carried out in the U.S. before experts
determined that the virus was not dangerous enough to cause a
pandemic. Swine flu occasionally infects people in the U.S.
without causing large outbreaks. From 2005 through January 2009,
there were 12 reported swine flu cases in the U.S. None of them
caused deaths.

Q: Why are health officials concerned about the outbreak
of swine flu?
A: When flu viruses mix genes with one another, they can
take on new forms. New flu viruses are harder for the human
immune system to defend against. With little or no opposition
from the immune resistance, the virus can grow quickly and
invade many tissues and organs. They may also set off a harmful
immune overreaction in the body, called a ?cytokine storm,?
that may be lethal in itself. The swine flu virus from Mexico
may have the ability to spread quickly and kill people, possibly
causing a worldwide pandemic, according to the WHO. Researchers
are conducting studies to determine how easily the virus spreads
in people and how dangerous it is.

Q: What?s a flu pandemic?
A: A flu pandemic occurs when a new influenza virus spreads
quickly and few people have immunity. While influenza viruses
were only discovered about a century ago, researchers believe
flu pandemics hit about two or three times each century. Some
pandemics kill a few million people globally. The most severe
flu pandemic on record was the 1918 Spanish Flu. Researchers
estimate it killed about 50 million people around the world.

Q: Are there any similarities between the swine flu and
earlier pandemic viruses?
A: Flu viruses are classified by two proteins on their
surface, called H for hemagglutinin and N for neuraminidase. The
swine flu found in Mexico and the 1918 Spanish Flu viruses are
of the H1N1 subtype. Both viruses appear to have originated in
animals. Researchers believe the Spanish Flu spread to people
from birds. The two viruses are not identical, and there are
still many genetic differences between them that researchers are
studying.

Q: Do all H1N1 viruses cause pandemics?
A: No. H1N1 descendants of the Spanish Flu virus continue
to circulate in people and sometimes cause outbreaks of seasonal
flu.

Q: Are there drugs that treat swine flu?
A: Yes. Roche Holding AG?s Tamiflu and GlaxoSmithKline
Plc?s Relenza both react against swine flu. The U.S. Department
of Homeland Security has released 25 percent of its stockpile of
Tamiflu and Relenza, according to Secretary Janet Napolitano.
Flu viruses sometimes develop resistance to antiviral drugs. The
human form of H1N1 seasonal flu that?s currently circulating is
resistant to Roche?s Tamiflu (not Relenza). If the two viruses
were to exchange genes, the swine flu might become resistant,
too. The drugs should be administered within the first 48 hours
of the onset of symptoms, according to the CDC.
Tamiflu and Relenza may also help prevent swine flu in
people who have been exposed to someone who was sick.

Q: How else can I protect myself from swine flu?
A: Personal hygiene measures, such as avoiding people who
are coughing or sneezing and frequent hand-washing, may prevent
flu infection. Those who aren?t health professionals should
avoid contact with sick people. People who get sick with flu
symptoms should stay home. Studies have suggested that closing
schools, theaters, and canceling gatherings in the early stages
of a pandemic can limit its spread. Such measures would likely
take place if health officials determine that the virus is
spreading quickly enough and is deadly enough to cause a
pandemic.


For Related News and Information:
Today?s most popular health-care stories: MNI HEA <GO>
Top health stories: HTOP <GO>
Stories about pandemic: NI BIRDFLU BN <GO>
Stories about drugs: NI DRG BN <GO>

--With assistance from Michelle Fay Cortez in Cannes, France,
Tom Randall in New York and Jason Gale in Singapore. Editors:
Robin D. Schatz, Kurt Heine

[JJackson]

Re: Swine Flu - Basic Information

In anticipation of the confusion that case numbers were going to cause I devoted most of post #5 in this thread (written one week ago) to explaining how they are collected and how to interpret them. The problem is now very evident and the gap between confirmed cases, probable cases, suspected cases and estimated cases is enormous and widening.
If we take each in turn.
A confirmed case is one in which a sample has been grown, or RT PCR tested, in a lab. Until a day or two ago in reality that meant at the CDC in Atlanta because there were no primers for the new strain at regional testing centres. The CDC has a budget many times bigger than the WHO and I noted in a recent release that they said they could ?test about 100 samples over night?. It is also reported that there are 35,000 swabs from Mexico alone awaiting testing. Taking these two bits of information along with the graph in post #7 you should see that looking at confirmed cases is unlikely to give an accurate picture. It is more likely to reflect how good a country?s lab facilities are than the realities of disease spread.
Probable cases are those that have been tested ? where no specific H1N1(2009) primer was available ? and have been positive for Type A but negative for either of the seasonal flus. While this can be done at regional level there is still nothing like the capacity needed given the number of potential cases. As more labs get the new primer more will be able to make their own ?positive? diagnosis and ?probables? will cease to be an issue.
Suspected cases are those that clinically look like H1N1(2009) and the patient has had contact with a know positive ? or been in an infected area - in the last week. This is going to become less useful as more areas meet the infected area criteria.
Estimated cases are the rest and very difficult to calculate. As most people with seasonal flu self medicate and don?t even bother to contact a doctor those that do and end up in a hospital are the tip of the iceberg. Media coverage of severe/fatal cases will change this pattern and people with a cold ? who would normally tough it out ? will now seek medical attention early just in case it is H1N1(2009). The only widely available treatment is Tamiflu and this needs to be taken as soon as possible after symptom onset and ?within 48hrs? by the packet which will also, rightly, lead people to get an early diagnosis. Taken together all these things, plus the worried well, are going to make it very difficult to get an accurate picture.

As the first two categories are the only reasonably reliable ones they tend to be used by official bodies in there pronouncements. However, as should be obvious from the above, they give an indication more of the confirmed geographical spread rather than a realistic picture of total numbers of cases, particularly if most are mild.

[JJackson]

Re: Swine Flu - Basic Information

This post is again trying to provide a little background information to assist in understanding what is happening and what may happen. I aim to address a pandemic more from the virus? point of view and introduce a few more numbers to help understand the epidemiology.

Of the many strains circulating in non humans, at some point, one manages to infect a human, replicate and spread. Influenza viruses are notoriously sloppy at copying their genetic information from generation to generation and, while all subsequent human infections will be descendants from this one zoonotic emergence, changes in the genetics can already be seen in the sequences. Most variations are duds; of those that do work they compete with their siblings and, in the best Darwinian tradition, the fittest survive with the dominant strain becoming the ?wild type?. While living in its natural pig host the ancestral strain was fairly well ?swine optimised? but now it is adapted to pigs but living in humans which leads to severe selection pressure. While the genetic changes may be random the promotion of those that improve human adaption is not; it is strongly selected for. As a consequence pathogens in a new host undergo rapid change until they become optimised to the new host species. H1N1(2009) is currently in this transference stage and as it adapts it should improve its ability to infect and reproduce in humans. From the viruses point of view it is not preying on humans but on cells - each infection, reproduction, release and re-infection cycle is per cell not per person. As the virus gets better at infecting human cells it is likely to spread faster. By getting into more cells more quickly it should cause more rapid and severe symptoms. This general ?improvement? by optimisation would not cause a sudden jump in virulence it is just a gradual honing of skills. There are also some critical changes, like the acquisition of antiviral resistance, which could occur with a lucky ? or unlucky depending on your perspective ? hit which would have more dramatic consequences.
I have covered this because it is important to an understanding of the next section as comparisons to past pandemics are based, in their cases, on historical data collected after the event on the pandemic virus i.e. on the fully optimised human wild type form. The data being generated now is from a transitional pre-pandemic form. The WHO are holding the pandemic level at 5 due to a strict interpretation of ?community spread? on two continents. For seasonal flu it is often not obvious where you got it, it was generally ?about? and you could easily have been infected by a complete stranger. At present, outside of North America, it is generally possible to trace infection to close contacts. This an indication that it is still in a pre-pandemic but it should adapt past this point soon, and the more infections the more opportunities to adapt the quicker the change ? up until the point it is close to human optimisation, at which time the reduced selection pressure slows the rate of change.

We are now just beginning to reach a point where it is possible to draw some initial conclusion about the course the epidemic is following to date ? again to be read with all the provisos in the previous section. Clinically this is not following the seasonal flu pattern. Most cases are mild but severe cases have been found in those with other medical conditions ? as with seasonal flu ? plus the immunocompromised. More worryingly ? because of its similarities to 1918 and H5N1 ? it is also causing severe illness/death in pregnant women and a few cases in otherwise fit healthy young adults (who have the most robust immune systems). When looking at communicable diseases there are some common terms
The Reproductive Number (Ro) is the number of new cases each infected person seeds, for Ro < 1 the disease dies out if Ro > 1 it spreads the higher the number the faster the spread. While diseases have typical Ro?s medical intervention, social distancing, population density etc. can all moderate the value.
The Clinical Attack Rate (CAR) is the portion of those who when exposed become clinically ill. From past flu pandemics it would be reasonable to expect this to be about a third, the other two thirds having some natural immunity. Typically everyone will at some stage come in contact with the virus so we should expect about 2 billion people to catch flu in the next year or so.
The Case Fatality Rate (CFR) is the proportion of those that did become clinically ill that died rather than recovered - this is very variable for flu. For seasonal flu it is about 0.2%, for H1N1(1918) it was about 3% & for H5N1 it is over 50%. The first figures for H1N1(2009) give it 1.4% but this is higher than it should be, as it is based on confirmed cases only, and due to limited lab capacity samples from severe cases have been prioritised, which has skewed the data.
Total deaths in a community are calculated by CARxCFRxpopulation=fatalities. However this is not the pandemic form of the virus, the CAR can only really be calculated after the event by sampling the community to ask how many in each household got ill. It is not calculated from lab tested confirmed cases which only include those sick enough to go to a doctor and have a swab taken. As the CFR is calculated from the CAR the only numbers that are valid are the population and the fatalities.

Beware the numbers: you are going to see them used in the media but they will not be comparing like with like.

[JJackson]

Re: Swine Flu - Basic Information

As I have locked this thread to keep it manageable I have started a 'Swine flu - Basic Information (Discussion)' thread for comments, questions etc.

Please post anything relating to this thread there.

Thanks JJ

[JJackson]

Re: Swine Flu - Basic Information

WHO have now raised the Pandemic level to 6 but what does this mean to the public in general? The short answer is not much.

That H1N1(2009) met the generally accepted definition of a pandemic has been evident for a while the WHO has just been reluctant to call it by its true name lest the public misinterpreted this as a message of doom. As I hope you will have gathered this relates to the degree of spread and is not a measure of severity, nothing has changed. This virus is capable of significant change in a fairly short period of time and there are several known mutations which could significantly affect the ease of transmission, virulence and antiviral resistance. Any one of these could occur with a single mutation so it is important to maintain vigilance and make preparations with this in mind, but for now the announcement means little.