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For those who don't know me after several years here at DK, I am a full-time pediatrician, and author of a regular health column in two newspapers within my region.

With that basic introduction, I offer to you today the following primer on novel influenza A/H1N1 (widely, if somewhat incorrectly, known as "swine flu") that I posted today on our medical clinic website for the benefit of our patients.

I am hopeful that some here will also find this primer informative. Any updates, clarifications, or suggestions would be greatly appreciated within the comments. I am forever amazed and humbled by the number of folks here more knowledgable than I on any given subject.

What is the new influenza A/H1N1?
This is a novel virus of swine origin that has never before circulated among humans. It is thought to have developed within the past 6 years, possibly even in the United States, but was virtually unknown until the outbreak in Mexico that began in March 2009.

How do people become infected with the virus?
The virus spreads person-to-person. It is transmitted as easily as the normal seasonal flu, and can be passed to other people by exposure to infected droplets (expelled by coughing or sneezing) that can
be inhaled, or that can contaminate hands or surfaces. Touching a contaminated surface and then touching your eyes or nose leads to spread of the virus.

The infectious or contagious period for H1N1 is similar to regular seasonal influenza, and is defined as one day before until 7 days after the onset of illness.

There is NO known instance of people getting infected by exposure to pigs or by eating pork products.

How is spread of the virus reduced or prevented?
People who are ill should:
• Cover their mouth and nose when coughing and sneezing (preferably with the sleeve or elbow, or into a tissue, but NOT with a hand). Teach children to "cough in your elbow" and to "sneeze in your sleeve".
• Use tissues to contain respiratory secretions, and dispose of them in the nearest waste receptacle as soon as possible. Hands should be washed, or hand sanitizer used, after each tissue use and disposal.
• Stay home when they are unwell. If someone is known to have H1N1 influenza, they are urged to stay out of public places (including work, stores, and classrooms) for at least 7 days after the onset of your symptoms. Having visitors is best avoided. And if an infected person must go out, a facemask should be worn, and portable hand sanitizer used often.
• Clean their hands regularly. The virus is spread easily when contaminated hands touch faucet handles, door knobs, grocery carts etc.
• Keep some distance, preferably 6 feet, from healthy people as best as possible

Why are we so worried about this flu when hundreds of thousands die worldwide every year from seasonal flu epidemics?
Seasonal influenza occurs every year (peaking in the U.S. between December and March), and the viruses change each year – but many people have at least some immunity to the circulating virus, which helps limit infections. Many are also vaccinated each year against that season’s circulating viruses.

But novel influenza A/H1N1 is a NEW virus, and one to which most people (especially under age 55 years) have little or no immunity, and therefore the virus could cause more infections and more complications than are seen with seasonal flu.

People over the age of 55 do not seem to be getting this new influenza as much as younger people (especially ages 10 to 45 years), possibly because of exposure when very young to flu viruses similar to the new influenza A/H1N1 virus.

This new influenza A virus causes mild illness in the majority of people, and most people recover without anti-viral treatment or medical care. Nonetheless, people should be aware that the virus can cause severe illness, resulting even in death.

What is the difference between new influenza A/H1N1 and regular seasonal flu?
Keep in mind that many people use the word "flu" incorrectly. Influenza is NOT a "twenty-four hour bug", nor is it a "vomiting and diarrhea illness" or the "stomach flu". Influenza seldom causes vomiting, and rarely causes diarrhea.

Instead, influenza is a RESPIRATORY illness, causing sudden onset of cough, sore throat, runny nose, headache, body aches, and fever. Only RARELY in influenza illness does fever NOT occur. Symptoms typically last for 5-7 days, and fever for 3-4 days. Influenza is NOT a "bad cold", but rather a distinct illness by itself.

There are three types of influenza – types A, B, and C. Type A influenza viruses are by far the most common to cause illness in humans. Influenza A viruses are further typed into subtypes according to different kinds of combinations of virus surface proteins. Among the many subtypes of influenza A viruses, currently the influenza A/H1N1 and A/H3N2 subtypes are circulating among humans.

And avian flu (influenza A/H5N1, or "bird flu") is also still out there, causing sporadic illness and high rates of death in countries such as Indonesia, Vietnam, Egypt and others.

Influenza typically causes an average of 25-35,000 deaths in the United States each year, usually in the very young or very old, or in people of any age with certain medical conditions, such as chronic heart, lung, kidney, liver, blood, or metabolic diseases (such as diabetes), or weakened immune systems (such as HIV/AIDS, or due to chemotherapy). The numbers of deaths from the new influenza A/H1N1 is thus far relatively low (see below), but what is concerning is that the deaths are occurring mostly in healthy older children and younger adults.

Influenza viruses circulate in every part of the world, though at different times. The new influenza A/H1N1 is currently spreading rapidly in the Southern Hemisphere, where the season is winter. However, what is very different about novel influenza A/H1N1 is that, rather than die down in the summer in the northern hemisphere, as influenza viruses typically do, H1N1 is continuing to flourish and spread across the U.S. and Europe (especially the United Kingdom).

What do we know so far about influenza A/H1N1?
The WHO declared on June 11 that H1N1 was now a global pandemic, a decision based on the spread of the new virus, not the severity of illness caused by the virus. The 2009 influenza pandemic has spread internationally with unprecedented speed. In past pandemics, influenza viruses have needed more than 6 months to spread as widely as the new H1N1 virus spread in the first six weeks.  

The overall severity of the H1N1 pandemic appears to be moderate. Cases have been reported in over 70 countries. The overwhelming majority of people are recovering without the need for hospitalization or medical care.

Rates of disease complication appear to be similar to those seen during the regular seasonal influenza outbreaks. Thus far within the U.S., there have been just over 40,000 reported cases (there have likely been as many as one million unreported, and therefore mild, cases) in all fifty states, and 263 deaths since April; about 3/4ths of the deaths have occurred in individuals with underlying chronic medical conditions.

Rates of illness from H1N1 are currently decreasing somewhat in most, though not all, states. However, 99% of cases of influenza currently in the U.S. are the new influenza A/H1N1; regular seasonal influenza is rarely seen during the summer months.

Different than regular seasonal influenza, the highest rates of illness from influenza A/H1N1 are among people under age 50, and especially under age 25. Eighty percent of those hospitalized as a result of H1N1 thus far in the US have been under age 50, with 19 years the median age at hospitalization. The median age for those who have died is 37 years, much younger than with regular seasonal influenza.

As this is a new virus, we do not yet know whether it will mutate and strengthen. So far, it has done neither. However, the World Health Organization and the U.S. Centers for Disease Control & Prevention are continuing to monitor H1N1 cases and complications extremely closely.

At this time the WHO is NOT recommending any travel restrictions.

What can we expect this fall?
We anticipate that there will be more cases, more hospitalizations, and more deaths associated with this pandemic in the United States over the summer and into the fall and winter. Best-case scenarios put the number of influenza A/H1N1 deaths in the U.S. over the next 6-12 months in the thousands; the worst case scenarios in the hundreds of thousands.

The new influenza A/H1N1 virus will circulate in conjunction with regular seasonal influenza viruses. It is because of this that there exists a significant potential over the fall and winter of 2009-2010 for a higher (possibly much higher) than average yearly number of flu-related illness, complications, and death. Staying informed is crucial, as is following the advice of medical and public health experts who will be working hard to reduce the spread of the new virus.

When should medical care be sought?
Any adult or child should seek medical care if they experience shortness of breath or difficulty breathing, purple or blue discoloration of the lips, seizures, or if a fever continues for more than 72 hours. All babies younger than two months of age should be seen by a doctor in the event of a fever above 100.4F (38.0C).

If a close contact (friend, co-worker, or relative) is diagnosed with influenza A/H1N1, consider seeking medical care if you develop a cough with sore throat, stuffy nose AND fever greater than 100.4F. If started within the first 24-48 hours, anti-viral treatment may be effective at reducing the duration and severity of your illness.

What is the best prevention of influenza?
The most effective way to prevent the disease or severe illness due to influenza is vaccination. Safe and effective vaccines have been available and used for more than 60 years. Among healthy adults, influenza vaccine can prevent 70-90% of cases of influenza. Among the elderly, the vaccine reduces severe illness and complications by 60%, and deaths by 80%.

Annual vaccination of regular seasonal influenza typically begins in late September, and continues through January. This year, however, supplies are expected to begin being made available in August, and physicians and pharmacies are being urged to begin vaccinating patients as soon as possible, before the expected H1N1 vaccination program begins.

This fall, nothing will change as to the need for vaccinating those at highest risk of death or severe illness against regular seasonal influenza. People over the age of 65 (especially nursing-home residents), and people with the chronic medical conditions mentioned above should absolutely be vaccinated against regular seasonal influenza. Also, young children ages 6 months to 2 years should be vaccinated, as should pregnant women, and health care workers.

Any child older than age 2 years can receive the vaccination, and should if they have asthma or another chronic medical condition, or have a new younger sibling under the age of 6 months.

However, the routine influenza vaccine will NOT protect against the new influenza A/H1N1, but only against the other strains of influenza A expected to circulate.

A vaccine against H1N1 has been rapidly developed, and is just this week going into the testing phase. At the same time, it is also going into mass production (though early reports are that the vaccine is proving difficult to manufacture) in hopes of making stockpiles available by this fall, when the virus is likely to reappear in greater numbers in the northern hemisphere, especially when children return to school. The earliest the new vaccine is expected to be available is in early- to mid-October.

A final decision has not yet been reached as to who will receive the vaccine, other than health care workers. The vaccination campaign will likely be massive. Children 6 months to 4 years of age will be among the first to be vaccinated, and there is serious and warranted talk of vaccinating all children (who are the greatest spreaders of influenza), possibly in the school setting. Pregnant women (who seem to be getting hit especially hard by this new virus) will also be advised to receive the new vaccine, as will people with chronic lung, heart, liver, kidney, or metabolic disease.

There remains much to be worked out, and public health authorities at the federal, state, and local level are meeting frequently to determine the best approach to reducing the anticipated spread of H1N1. We will provide updates as more information becomes available.

What is the best treatment for the new influenza A/H1N1 virus?
Most people will experience only mild symptoms if infected with the new virus, and therefore will not need treated.

Additionally, by the time most people would seek medical care, for instance after running a fever for more than 72 hours, the time has passed for anti-viral medications to help.

But for those with a known close exposure (having cared for or lived with a person who is a confirmed, probable, or suspected case of H1N1), quick testing for influenza (preferably within the first 24-36 hours of developing symptoms of cough, sore throat, runny nose, AND fever) may then lead to anti-viral treatment, especially if you are pregnant, a resident of a chronic-care facility, older than 65 years, or have one of the chronic medical conditions mentioned earlier.

Children under the age of 5 years confirmed as having influenza A will also be candidates for receiving anti-viral treatment. Older children and otherwise healthy adults under the age of 65 years not a risk for influenza complications generally do not require treatment.

The only medications effective for treatment of H1N1 are oseltamivir (Tamiflu™) and zanamivir (Relenza™). Tamiflu is the drug of choice for pregnant women, and for children, who often cannot tolerate Relenza™, which is administered by inhalation.

To be effective, medication must be started within 48 hours of the onset of symptoms. The recommended duration of treatment is 5 days. Side effects are few, and may include nausea and vomiting (in about 10% of individuals).

Individuals at high risk for developing complications of influenza, or health-care workers who have had a recognized unprotected contact exposure to a person with H1N1, may be treated with anti-viral medications for 10 days post-exposure to H1N1.

What can we do NOW to prepare?
• Educate children as to cough and sneeze etiquette
• Educate children as to the importance of not sharing cups, glasses, or utensils
• Educate all adults in your immediate life as to the signs of influenza
• Stockpile facial tissues, hand soap, and alcohol-based hand sanitizer (minimum alcohol content 60%)
• Stockpile disinfectant spray, such as Lysol™
• Purchase small vials of hand sanitizer to keep in pockets or purses for use this fall and winter when in public places, such as after opening doors or pushing grocery carts
• Be in the habit of carrying your own pen to use to sign receipts in the check-out aisle
• Make certain each person in your household has his or her own hand towel, and that everyone understands the need to use only their own.
• Purchase a small supply of respiratory masks (facemasks) for use during coughing illnesses this fall and winter. Facemasks should not be re-used once taken off, but should be immediately disposed of.
• Have acetaminophen and ibuprofen on-hand for fevers and body aches. Remember that children should NEVER be given aspirin, and if your child becomes ill with influenza they should not receive aspirin-containing products such as PeptoBismol™

Where can we get more information?
http://www.pandemicflu.gov/
http://www.cdc.gov/...
http://www.cdc.gov/...
http://www.getpandemicready.org/
http://www.medpagetoday.com/...
http://www.newsweek.com/...

Also consider reading pandemic expert John Barry’s recent White Paper on Novel H1N1: http://esd.mit.edu/... (warning, highly technical)

And for yet another good source of information, one that is regularly updated, click here: http://www.webmd.com/...

I hope this helps. We all need to be getting prepared.

Originally posted to StrangeAnimals on Tue Jul 21, 2009 at 12:02 PM PDT.

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