What Is Swine Flu (Novel H1N1 Influenza A Swine Flu)?
Swine flu (swine influenza) is a respiratory disease caused by viruses
(influenza viruses) that infect the respiratory tract of pigs and result in
nasal secretions, a barking-like cough, decreased appetite, and listless
behavior. Swine flu produces most of the same symptoms in pigs as human flu
produces in people.
Swine flu can last about one to two weeks in pigs that survive. Swine influenza
virus was first isolated from pigs in 1930 in the U.S. and has been recognized
by pork producers and veterinarians to cause infections in pigs worldwide. In a
number of instances, people have developed the swine flu infection when they
are closely associated with pigs (for example, farmers, pork processors), and
likewise, pig populations have occasionally been infected with the human flu
infection. In most instances, the cross-species infections (swine virus to man;
human flu virus to pigs) have remained in local areas and have not caused
national or worldwide infections in either pigs or humans. Unfortunately, this
cross-species situation with influenza viruses has had the potential to change.
Investigators think the 2009 swine flu strain, first seen in Mexico, should be
termed novel H1N1 flu since it is mainly found infecting people and exhibits
two main surface antigens, H1 (hemagglutinin type 1) and N1 (neuraminidase
type1). Recent investigations show the eight RNA strands from novel H1N1 flu
have one strand derived from human flu strains, two from avian (bird) strains,
and five from swine strains.
Why is swine flu (H1N1) now infecting humans?
Many researchers now consider that two main series of events can lead to swine
flu (and also avian or bird flu) becoming a major cause for influenza illness
in humans.
First, the influenza viruses (types A, B, C) are enveloped RNA viruses with a
segmented genome; this means the viral RNA genetic code is not a single strand
of RNA but exists as eight different RNA segments in the influenza viruses. A
human (or bird) influenza virus can infect a pig respiratory cell at the same
time as a swine influenza virus; some of the replicating RNA strands from the
human virus can get mistakenly enclosed inside the enveloped swine influenza
virus. For example, one cell could contain eight swine flu and eight human flu
RNA segments. The total number of RNA types in one cell would be 16; four swine
and four human flu RNA segments could be incorporated into one particle, making
a viable eight RNA segmented flu virus from the 16 available segment types.
Various combinations of RNA segments can result in a new subtype of virus
(known as antigenic shift) that may have the ability to preferentially infect
humans but still show characteristics unique to the swine influenza virus (see
Figure 1). It is even possible to include RNA strands from birds, swine, and
human influenza viruses into one virus if a cell becomes infected with all
three types of influenza (for example, two bird flu, three swine flu, and three
human flu RNA segments to produce a viable eight-segment new type of flu viral
genome). Formation of a new viral type is considered to be antigenic shift;
small changes in an individual RNA segment in flu viruses are termed antigenic
drift and result in minor changes in the virus. However, these can accumulate
over time to produce enough minor changes that cumulatively change the virus'
antigenic makeup over time (usually years).
Second, pigs can play a unique role as an intermediary host to new flu types
because pig respiratory cells can be infected directly with bird, human, and
other mammalian flu viruses. Consequently, pig respiratory cells are able to be
infected with many types of flu and can function as a "mixing pot" for flu RNA
segments (see Figure 1). Bird flu viruses, which usually infect the
gastrointestinal cells of many bird species, are shed in bird feces. Pigs can
pick these viruses up from the environment and seem to be the major way that
bird flu virus RNA segments enter the mammalian flu virus population.
Picture of antigenic shift and antigenic drift in swine flu (H1N1).
What are the symptoms of swine flu (H1N1)?
Symptoms of swine flu are similar to most influenza infections: fever (100F or
greater), cough, nasal secretions, fatigue, and headache, with fatigue being
reported in most infected individuals. Some patients also get nausea, vomiting,
and diarrhea. In Mexico, many of the patients are young adults, which made some
investigators speculate that a strong immune response may cause some collateral
tissue damage.
Some patients develop severe respiratory symptoms and need respiratory support
(such as a ventilator to breathe for the patient). Patients can get pneumonia
(bacterial secondary infection) if the viral infection persists, and some can
develop seizures. Death often occurs from secondary bacterial infection of the
lungs; appropriate antibiotics need to be used in these patients. The usual
mortality (death) rate for typical influenza A is about 0.1%, while the 1918
"Spanish flu" epidemic had an estimated mortality rate ranging from 2%-20%.
Swine flu in Mexico (as of April 2009) has had about 160 deaths and about 2,500
confirmed cases, which would correspond to a mortality rate of about 6%, but
these initial data have been revised and the mortality rate currently in Mexico
is estimated to be much lower. By June 2009, the virus had reached 74 different
countries on every continent except Antarctica, and by September 2009, the
virus had been reported in most countries in the world. Fortunately, the
mortality rate as of October 2009 has been low but higher than for the
conventional flu (average conventional flu mortality rate is about 36,000 per
year; projected novel H1N1 flu mortality rate is 90,000 per year in the U.S. as
determined by the president's advisory committee).
How is swine flu (H1N1) diagnosed?
Swine flu is presumptively diagnosed clinically by the patient's history of
association with people known to have the disease and their symptoms listed
above. Usually, a quick test (for example, nasopharyngeal swab sample) is done
to see if the patient is infected with influenza A or B virus. Most of the
tests can distinguish between A and B types. The test can be negative (no flu
infection) or positive for type A and B. If the test is positive for type B,
the flu is not likely to be swine flu (H1N1). If it is positive for type A, the
person could have a conventional flu strain or swine flu (H1N1). However, the
accuracy of these tests has been challenged, and the U.S. Centers for Disease
Control and Prevention (CDC) has not completed their comparative studies of
these tests. However, a new test developed by the CDC and a commercial company
reportedly can detect H1N1 reliably in about one hour; as of October 2009, the
test is only available to the military.
Swine flu (H1N1) is definitively diagnosed by identifying the particular
antigens associated with the virus type. In general, this test is done in a
specialized laboratory and is not done by many doctors' offices or hospital
laboratories. However, doctors' offices are able to send specimens to
specialized laboratories if necessary. Because of the large number of novel
H1N1 swine flu cases (as of October 2009, the vast majority of flu cases [about
99%] are due to novel H1N1 flu viruses), the CDC recommends only hospitalized
patients' flu virus strains be sent to reference labs to be identified.
What treatment is available for swine flu (H1N1)?
The best treatment for influenza infections in humans is prevention by
vaccination. Work by several laboratories has recently produced vaccines. The
first vaccine released in early October 2009 was a nasal spray vaccine. It is
approved for use in healthy individuals ages 2 through 49. This vaccine
consists of a live attenuated H1N1 virus and should not be used in anyone who
is pregnant or immunocompromised.
The injectable vaccine, made from killed H1N1, became available in the second
week of October. This vaccine is approved for use in ages 6 months to the
elderly, including pregnant females. Both of these vaccines have been approved
by the CDC only after they had conducted clinical trials to prove that the
vaccines were safe and effective. However, caregivers should be aware of the
vaccine guidelines that come with the vaccines, as occasionally, the guidelines
change. Please see the sections below titled "Can novel H1N1 swine flu be
prevented with a vaccine?" and the timeline update for the current information
on the vaccines.
Two antiviral agents have been reported to help prevent or reduce the effects
of swine flu. They are zanamivir (Relenza) and oseltamivir (Tamiflu), both of
which are also used to prevent or reduce influenza A and B symptoms. These
drugs should not be used indiscriminately, because viral resistance to them can
and has occurred. Also, they are not recommended if the flu symptoms already
have been present for 48 hours or more, although hospitalized patients may
still be treated past the 48-hour guideline. Severe infections in some patients
may require additional supportive measures such as ventilation support and
treatment of other infections like pneumonia that can occur in patients with a
severe flu infection. The CDC has suggested in their interim guidelines that
pregnant females can be treated with the two antiviral agents.
Picture of oseltamivir (Tamiflu)
Oseltamivir (Tamiflu) is an antiviral agent that may prevent or reduce
influenza A and B symptoms. Photo courtesy of the CDC
Picture of zanamivir (Relenza)
Zanamivir (Relenza) has been reported to help prevent or reduce the effects of
swine flu. Photo courtesy of the CDC
What is the history of swine flu (H1N1) in humans?
In 1976, there was an outbreak of swine flu at Fort Dix. This virus is not the
same as the 2009 outbreak, but it was similar insofar as it was an influenza A
virus that had similarities to the swine flu virus. There was one death at Fort
Dix. The government decided to produce a vaccine against this virus, but the
vaccine was associated with neurological complications (Guillain-Barré
syndrome) and was discontinued. Some individuals speculate that formalin, used
to inactivate the virus, may have played a role in the development of this
complication in 1976. There is no evidence that anyone who obtained this
vaccine would be protected against the 2009 swine flu. One of the reasons it
takes a few months to develop a new vaccine is to test the vaccine for safety
to avoid the complications seen in the 1976 vaccine. New vaccines against any
flu virus type are usually made by growing virus particles in eggs. A serious
side effect (allergic reaction such as swelling of the airway) to vaccines can
occur in people who are allergic to eggs; these people should not get flu
vaccines. Individuals with active infections or diseases of the nervous system
are also not recommended to get flu vaccines.
Can novel H1N1 swine flu be prevented with a vaccine?
The best way to prevent novel H1N1 swine flu would be the same best way to
prevent other influenza infections, and that is vaccination. The CDC has
multiple recommendations for vaccination based on who should obtain the first
doses when the vaccine becomes available (to protect the most susceptible
populations) and according to age groups. The CDC based the recommendations on
data obtained from vaccine trials and infection reports gathered over the last
few months. The current (October 2009) vaccine recommendations from the CDC say
the following groups should get the vaccine as soon as it is available:
* pregnant women,
* people who live with or provide care for children younger than 6 months
of age,
* health-care and emergency medical services personnel,
* people between 6 months and 24 years of age, and
* people from the ages of 25 through 64 who are at higher risk because of
chronic health disorders such as asthma, diabetes, or a weakened immune system.
Currently, the CDC is stating that people ages 10 and above are likely to need
only one vaccine shot to provide protection against novel H1N1 swine flu and
further suggest that these shots will be effective in about 76% of people who
obtain the vaccine. New vaccine trial data showed that healthy adults produce
protective antibodies in about 98% of people in 21 days. Unfortunately, the
vaccine shot in children ages 6 months to 9 years of age is not as effective as
it is in older children and adults. Consequently, the CDC currently recommends
that for ages 6 months up to and including 9 years of age, the children obtain
two shots of the novel H1N1 vaccine, the second shot 21 days after the first
shot.
Pregnant women are strongly suggested to get vaccinated as stated above.
Although some vaccine preparations (multidose vials) contain low levels of
thimerosal preservative (a mercury-containing preservative), the CDC still
considers the vaccine safe for the fetus and mother. However, some vaccine
preparations that are in single-dose vials will not have thimerosal
preservative, so those pregnant individuals who are concerned about thimerosal
can get this vaccine preparation when it is available.
Another type of vaccine (currently named Influenza A [H1N1] 2009 Monovalent
Vaccine Live, Intranasal) has been made available during the first week in
October 2009. It is a live attenuated novel H1N1 flu vaccine that contains no
thimerosal, is produced by MedImmune, LLC, and is sprayed into the nostrils.
This vaccine is only for healthy people 2-49 years of age, and some data
suggest that it is less effective in generating an immune response in adults
than the vaccine injection. The dosing schedule is as follows:
* Children 2-9 years of age should receive two doses (0.1 ml in each
nostril; total equals 0.2 ml per dose) -- the second dose should be given the
same way about one month after the first dose
* Children, adolescents and adults, 10-49 years of age should receive one
dose -- (0.1 ml in each nostril; total equals 0.2 ml per dose)
The CDC occasionally makes changes and updates its information on vaccines and
other recommendations about the current flu pandemic. The CDC states, "for the
most accurate health information, Caregivers should check the vaccine package
inserts for more detailed information on the vaccines when they become
available. This article has an updated timeline for novel H1N1 swine flu
attached (see below) and provides the reader with current details about the
pandemic. The following is a list of the CDC-approved H1N1 vaccines and the
companies that name and manufacture them as of 10/29/09:
* Influenza A (H1N1) 2009 Monovalent Vaccine by Sanofi Pasteur
* Influenza A (H1N1) 2009 Monovalent Vaccine by Novartis
* Influenza A (H1N1) 2009 Monovalent Vaccine Live, Intranasal by MedImmune,
LLC
* Influenza A (H1N1) 2009 Monovalent Vaccine by CSL Limited
The CDC says that a good way to prevent any flu disease is to avoid exposure to
the virus; this is done by frequent hand washing, not touching your hands to
your face (especially the nose and mouth), and avoiding any close proximity to
or touching any person who may have flu symptoms. Since the virus can remain
viable and infectious for about 48 hours on many surfaces, good hygiene and
cleaning with soap and water or alcohol-based hand disinfectants are also
recommended. Some physicians say face masks may help prevent getting airborne
flu viruses (for example, from a cough or sneeze), but others think the better
use for masks would be on those people who have symptoms and sneeze or cough.
The use of Tamiflu or Relenza may help prevent the flu if taken before symptoms
develop or reduce symptoms if taken within about 48 hours after symptoms
develop. Some investigators say that administration of these drugs is still
useful after 48 hours, especially in high-risk patient populations .However,
taking these drugs is not routinely recommended for prevention for the healthy
population because investigators suggest that as occurs with most drugs, flu
strains will develop resistance to these medications. Recently, the CDC made
further suggestions about the use of these antiviral medications. Dr. Schuchat,
a CDC official, indicated that three modifications were being suggested (Sept.
8, 2009) to the interim guidelines for use of Tamiflu and Relenza:
1. Patients with high-risk factors should discuss flu symptoms and when
to use antiviral medications; doctors should provide a prescription for the
antiviral drug for the patient to use if the patient is exposed to flu or
develops flu-like symptoms without having to go in to see the doctor.
2. "Watchful waiting" was added as a response to taking antiviral
medications, with the emphasis on the fact that those people who develop fever
and have a preexisting health condition should then begin the antiviral
medication.
3. The antiviral medications are the first-line medicines for treatment
of novel H1N1 swine flu, and most current cases of flu are novel H1N1 and are,
to date, susceptible to Tamiflu and Relenza.
Your doctor should be consulted before these drugs are prescribed.
In general, preventive measures to prevent the spread of flu are often
undertaken by those people who have symptoms. Symptomatic people should stay at
home, avoid crowds, and take off from work or school until the disease is no
longer transmittable (about two to three weeks) or until medical help and
advice is sought. Sneezing, coughing, and nasal secretions need to be kept away
from other people; simply using tissues and disposing of them will help others.
Quarantining patients is usually not warranted, but such measures depend on the
severity of the disease. The CDC recommends that people who appear to have an
influenza-like illness upon arrival at work or school or become ill during the
day be promptly separated from other people and be advised to go home until at
least 24 hours after they are free of fever (100 F [37.8 C] or greater), or
signs of a fever, without the use of fever-reducing medications. The novel H1N1
swine flu disease takes about seven to 10 days before fevers stop, but new
research data (Sept. 14, 2009) suggests waiting until the cough is gone since
many people are still infectious about one week after fever is gone. The CDC
has not yet extended their recommendations to stay home for that extra week
Can H1N1 be prevented if the H1N1 flu vaccine is not readily available?
Although vaccination is the best way to "prevent" H1N1, currently (November
2009), there is not enough available for everyone who wants or needs H1N1
vaccination. Until H1N1 vaccine supplies meet demand, there are some things
people can do to try and prevent infection. Without vaccination, the best
strategy is to not allow H1N1 virus to contact a person's mucus membranes
because if the virus does not reach cells in which it can grow, it cannot cause
infection. Quarantining H1N1-infected people is an extreme measure that may
work in some instances (for example, China uses this method), but even with
quarantining, the virus may still spread by people who have minimal or no
symptoms.
The next step that is easier to be implemented by individuals is for people
with the disease to self-quarantine until they become noninfectious (about
seven to 10 days after flu symptoms abate). Infected people can wear surgical
masks to reduce the amount of droplet spray from coughs and sneezes and throw
away contaminated tissues. Unfortunately, these approaches depend on the
compliance of many other people, and the likelihood that such methods will be
highly successful in preventing H1N1 infections, at best, is only fair. Such
methods have not stopped the current pandemic. Yet there are still some other
methods available to individuals. Perhaps the best way for individuals to try
to prevent H1N1 infection is a combination of methods that are aimed at
fulfilling the very basic principle that if H1N1 doesn't reach an individual's
mucus membrane cells, infection will be prevented. The methods are as follows:
1. Kill or inactivate the virus before it reaches a human cell by using
soap and water to clean your hands; washing clothing and taking a shower will
do the same for the rest of your body.
2. Use an alcohol-based hand sanitizer if soap and water are not readily
available.
3. Use sanitizers on objects that many people may touch (for example,
doorknobs, computer keyboards, handrails, phones).
4. Do not touch your mouth, eyes, nose, unless you first do items 1 or 2
above.
5. Avoid crowds, parties, and especially people who are coughing and
sneezing (most virus-containing droplets do not travel more than 4 feet, so
experts suggest 6 feet away is a good distance to stay). If you cannot avoid
crowds (or parties), try to remain aware of people around you and use the
6-foot rule with anyone coughing or sneezing. Do not reach for or eat snacks
out of canisters or other containers at parties.
6. Avoid touching anything within about 6 feet of an uncovered
cough/sneeze, because the droplets that contain virus fall and land on anything
usually within that range.
7. Studies show that individuals who wear surgical or N95 particle masks
may prevent inhalation of some H1N1 virus, but the masks may prevent only about
50% of airborne exposures and offer no protection against surface droplets.
However, masks on H1N1 infected people can markedly reduce the spread of
infected droplets.
These seven steps can help prevent individuals from getting H1N1 infection, but
for many people, adherence to them may be difficult at best. However, there are
some additional strategies that may also help prevent H1N1 infections in
unvaccinated people according to some investigators. Saline nasal washes and
gargling with saline (or a commercial product) as a way to reduce or eliminate
H1N1 virus from mucus membranes has been suggested. Proponents of these methods
base their rationale on the fact that flu viruses usually take about two to
three days to proliferate in nasal/throat cells. While nasal washes and
gargling may be soothing to some people, there are no studies that indicate
H1N1 is killed, inactivated, or completely removed by these methods;
conversely, there are no data suggesting these methods cannot have any effect
on H1N1. However, with long-term nasal washes using Neti pots, sinus infection
with other pathogens may be encouraged.
Other investigators and physicians have offered additional methods that may
help reduce exposure to H1N1 virus. For example, Dr. Gerberding, a former CDC
director, had several suggestions about how to avoid H1N1 infection on an
airplane. She suggested the following:
1. If a person is next to you or near (within 6 feet) and is
coughing/sneezing, ask the flight attendant to offer the person a mask.
2. If there are available seats 6 feet or more away from the
coughing/sneezing person, ask to change your seat (planes are good means of
travel because the air is recirculated through HEPA filters that can capture
viruses, but even the filters will not help if people touch areas where
droplets have landed; HEPA filters are usually not available in buses, cars,
ships, or trains).
3. Turn away from the coughing/sneezing person and turn the air vent
toward the person to blow the droplets away from yourself.
Variations of her suggestions may be applicable in many different social, work,
or travel situations, but there are no data to prove these methods are
effective. In addition, common-sense precautions such as not drinking or eating
things touched by others, avoiding casual physical contacts (for example,
handshakes, social hugs or kisses, public water fountains [these are OK if you
touch nothing and lips only touch flowing water], banisters on stairways, and
restroom door handles) will limit exposure to H1N1. Again, these common sense
suggestions lack data substantiation.
Many investigators suggest that people stay well hydrated, take vitamins, and
get plenty of rest, but these precautions will not prevent H1N1 infections
although they may help reduce the effects of infection by strengthening the
person's immune system to fight infection. Similarly, current antiviral
medications (described in the preceding section) act on H1N1 viruses that have
already infected cells; they work by preventing or reducing viral particles
from aggregating and being released from infected cells. Timing is important;
if only a few cells are infected and the antiviral medications are administered
quickly (usually before flu symptoms develop or within 48 hours), the viruses
are reduced in number (they cannot easily bud out from the cell surface), so
few, if any, other respiratory or mucus membrane cells become infected. This
can result in either no flu symptoms or, if a larger number of cells were
initially infected, less severe symptoms. The overall effect for the person is
that the H1N1 infection was prevented (it was not; the symptoms were prevented
from developing) or that symptoms were reduced.
In the strictest sense of the word prevention, even effective vaccines do not
"prevent" infections. What they do accomplish is to alert the immune system to
be on guard for certain antigens that are associated with a pathogen (for
example, H1N1 virus, pneumococcal bacteria). When the pathogen first infects
the host, its antigens are recognized, and these cause a rapid immunoprotective
response to occur that prevents the pathogen from proliferating and developing
symptoms in the host. People, including physicians and researchers, often term
this complex response to vaccination as "prevention of infection" but what
actually occurs is the prevention of further infection so well that symptoms do
not develop or are minimal in the host.
In summary, if H1N1 viruses fail to contact cells they can infect, the disease
will be prevented. As stated above, this is difficult, but not impossible, to
do in almost all societies. Prevention of H1N1 symptoms of infection is
possible with antiviral medications if these are given very early in the
infection. There are many other methods that may reduce the chance of getting
the virus on a person's mucosal surface, but most methods have not been backed
up with objective data. Most doctors and investigators suggest that items that
help boost or allow the immune response to function well will help people
resist H1N1 infections and reduce symptoms, but these also do not prevent
infections. Consequently, while waiting for H1N1 vaccine, these are some ways
individuals can improve their chances of preventing or reducing the symptoms of
H1N1 infections.
Is swine flu (H1N1) a cause of an epidemic or pandemic in 2009?
An epidemic is defined as an outbreak of a contagious disease that is rapid and
widespread, affecting many individuals at the same time. The swine flu outbreak
in Mexico fit this definition. A pandemic is an epidemic that becomes so
widespread that it affects a region, continent, or the world. As of April 2009,
the H1N1 swine flu outbreak did not meet this definition. However, as of June
11, 2009, WHO officials determined that H1N1 2009 influenza A swine flu reached
WHO level 6 criteria (person-to-person transmission in two separate
WHO-determined world regions) and declared the first flu pandemic in 41 years.
To date, the flu has reached over 74 different countries on every continent
except Antarctica in about three month's time; fortunately, the severity of the
disease has not increased.
What is the prognosis (outlook) for patients who get swine flu (H1N1)?
The following is speculation on the prognosis for swine flu (H1N1) because this
disease has only been recently diagnosed and the data is changing daily. This
section is based on currently available information.
In general, the majority (about 90%-95%) of people who get the disease feel
terrible (see symptoms) but recover with no problems, as seen in patients in
both Mexico and the U.S. Caution must be taken as the swine flu (H1N1) is still
spreading and has become a pandemic. So far, young adults have not done well,
and in Mexico, this group currently has the highest mortality rate, but this
data could quickly change.
People with depressed immune systems historically have worse outcomes than
uncompromised individuals; investigators suspect that as swine flu (H1N1)
spreads, the mortality rates may rise and be high in this population. Current
data suggest that pregnant individuals, children under 2 years of age, young
adults, and individuals with any immune compromise or debilitation are likely
to have a worse prognosis. Unfortunately, the problem with the prognosis is
still unclear. If the mortality is like the conventional flu that causes
mortality rates of about 0.1%, the result would be about 36,000 deaths per year
because of the huge number of people who get infected. If the Mexico swine flu
(H1N1) ends up with a mortality rate of about 6% and infects the same number of
millions of people as conventional flu viruses, the projected numbers could be
as high as 2 million deaths in the U.S. alone. This is a bad prognosis for
about 2 million people and their families; these potential deaths are major
reasons that health officials are so concerned about the spread of this new
virus. As of September 2009, the current estimates are that about 90,000 deaths
will occur in the U.S. from novel H1N1 swine flu (estimated by the president's
advisory committee). As of October, these estimates have not been revised by
the advisory committee or the CDC.
Another confounding problem with the prognosis of swine flu (H1N1) is that the
disease is occurring and spreading in high numbers at the usual end of the flu
season. Most flu outbreaks happen between November to the following April, with
peak activity between late December to March. This outbreak is not following
the usual flu pattern since novel H1N1 began its outbreak in April and had
spread throughout the world by September. Some scientists think that swine flu
(H1N1) will die down but return with many more cases in the fall, and still
others speculate the current pandemic will eventually resemble the outcomes
similar to the 1918 influenza pandemic. Some suggest it may resemble the SARS
(severe acute respiratory syndrome caused by a coronavirus strain) outbreak in
2002-2003 in which the disease spread to about 10 countries with over 7,000
cases, over 700 deaths, and had a 10% mortality rate. Effective isolation of
patients was done in this case, and many investigators think the outbreak was
stopped due to this measure. Because swine flu (H1N1) is a new virus and does
not seem to be following the usual flu disease pattern, any prognosis is
speculative, although as of October 2009, the numbers of people with flu-like
illness are higher than usual and the illness is affecting a much younger
population than the conventional flu. As the pandemic progresses, this article
will be updated. The best news about this novel H1N1 swine flu is that the
majority of people, as of October 2009, who have caught the flu recover without
medical treatment and have an excellent prognosis.
CDC on Swine Flu (H1N1) - What is the swine flu?
The swine influenza A (H1N1) virus that has infected humans in the U.S. and
Mexico is a novel influenza A virus that has not previously been identified in
North America. This virus is resistant to the antiviral medications amantadine
(Symmetrel) and rimantadine (Flumadine), but is sensitive to oseltamivir
(Tamiflu) and zanamivir (Relenza). Investigations of these cases suggest that
on-going human-to-human swine influenza A (H1N1) virus is occurring.
CDC - What are the symptoms of swine flu (H1N1)?
Although uncomplicated influenza-like illness (fever, cough or sore throat) has
been reported in many cases, mild respiratory illness (nasal congestion,
rhinorrhea) without fever and occasional severe disease also has been reported.
Other symptoms reported with swine influenza A virus infection include
vomiting, diarrhea, myalgia, headache, chills, fatigue, and dyspnea.
Conjunctivitis is rare, but has been reported. Severe disease (pneumonia,
respiratory failure) and fatal outcomes have been reported with swine influenza
A virus infection. The potential for exacerbation of underlying chronic medical
conditions or invasive bacterial infection with swine influenza A virus
infection should be considered.
CDC - Interim Recommendations
For clinical care or collection of respiratory specimens from a symptomatic
individual (acute respiratory symptoms with or without fever) who is a
confirmed case, or a suspected case (ill close contact of a confirmed case) of
swine influenza A (H1N1) virus infection:
Infectious Period
Persons with swine influenza A (H1N1) virus infection should be considered
potentially contagious for up to 7 days following illness onset. Persons who
continue to be ill longer than 7 days after illness onset should be considered
potentially contagious until symptoms have resolved. Children, especially
younger children, might potentially be contagious for longer periods. The
duration of infectiousness might vary by swine influenza A (H1N1) virus strain.
Non-hospitalized ill persons who are a confirmed or suspected case of swine
influenza A (H1N1) virus infection are recommended to stay at home (voluntary
isolation) for at least the first 7 days after illness onset except to seek
medical care.
Case definitions
A confirmed case of swine influenza A (H1N1) virus infection is defined as a
person with an acute respiratory illness with laboratory confirmed swine
influenza A (H1N1) virus infection at CDC by one or more of the following tests:
* real-time RT-PCR
* viral culture
* four-fold rise in swine influenza A (H1N1) virus-specific neutralizing
antibodies
A suspected case of swine influenza A (H1N1) virus infection is defined as a
person with acute febrile respiratory illness with onset within 7 days of close
contact with a person who is a confirmed case of swine influenza A (H1N1) virus
infection.
Close contact is defined as: within about 6 feet of an ill person who is a
confirmed or suspected case of swine influenza A (H1N1) virus infection.
* Close contact is defined as: within about 6 feet of an ill person who is
a confirmed case of swine influenza A virus infection
Acute respiratory illness is defined as recent onset of at least two of the
following: rhinorrhea or nasal congestion, sore throat, cough (with or without
fever or feverishness)
Recommendations for public health personnel
For interviews of healthy individuals (i.e. without a current respiratory
illness), including close contacts of cases of confirmed swine influenza virus
infection, no personal protective equipment or antiviral chemoprophylaxis is
needed. See section on antiviral chemoprophylaxis for further guidance.
For interviews of an ill, suspected or confirmed swine influenza A virus case,
the following is recommended:
* Keep a distance of at least 6 feet from the ill person; or
* Personal protective equipment: fit-tested N95 respirator [if unavailable,
wear a medical (surgical mask)].
For collecting respiratory specimens from an ill confirmed or suspected swine
influenza A virus case, the following is recommended:
* Personal protective equipment: fit-tested disposable N95 respirator [if
unavailable, wear a medical (surgical mask)], disposable gloves, gown, and
goggles.
* When completed, place all PPE in a biohazard bag for appropriate disposal.
* Wash hands thoroughly with soap and water or alcohol-based hand ge
CDC - Infection Control
Recommended Infection Control for a non-hospitalized patient (ER, clinic or
home visit):
1. Separation from others in single room if available until asymptomatic. If
the ill person needs to move to another part of the house, they should wear a
mask. The ill person should be encouraged to wash hand frequently and follow
respiratory hygiene practices. Cups and other utensils used by the ill person
should be thoroughly washed with soap and water before use by other persons.
CDC - Antiviral Treatment
Suspected Cases
Empiric antiviral treatment is recommended for any ill person suspected to have
swine influenza A (H1N1) virus infection. Antiviral treatment with either
zanamivir alone or with a combination of oseltamivir and either amantadine or
rimantadine should be initiated as soon as possible after the onset of
symptoms. Recommended duration of treatment is five days. Recommendations for
use of antivirals may change as data on antiviral susceptibilities become
available. Antiviral doses and schedules (http://www.cdc.gov/flu/professionals
/antivirals/dosagetable.htm#table) recommended for treatment of swine influenza
A (H1N1) virus infection are the same as those recommended for seasonal
influenza:
Confirmed Cases
For antiviral treatment of a confirmed case of swine influenza A (H1N1) virus
infection, either oseltamivir or zanamivir may be administered. Recommended
duration of treatment is five days. These same antivirals should be considered
for treatment of cases that test positive for influenza A but test negative for
seasonal influenza viruses H3 and H1 by PCR.
Pregnant Women
Oseltamivir, zanamivir, amantadine, and rimantadine are all "Pregnancy Category
C" medications, indicating that no clinical studies have been conducted to
assess the safety of these medications for pregnant women. Only two cases of
amantadine use for severe influenza illness during the third trimester have
been reported. However, both amantadine and rimantadine have been demonstrated
in animal studies to be teratogenic and embryotoxic when administered at
substantially high doses. Because of the unknown effects of influenza antiviral
drugs on pregnant women and their fetuses, these four drugs should be used
during pregnancy only if the potential benefit justifies the potential risk to
the embryo or fetus; the manufacturers' package inserts should be consulted.
However, no adverse effects have been reported among women who received
oseltamivir or zanamivir during pregnancy or among infants born to such women.
Antiviral Chemoprophylaxis
For antiviral chemoprophylaxis of swine influenza A (H1N1) virus infection,
either oseltamivir or zanamivir are recommended. Duration of antiviral
chemoprophylaxis is 7 days after the last known exposure to an ill confirmed
case of swine influenza A (H1N1) virus infection. Antiviral dosing and
schedules recommended for chemoprophylaxis of swine influenza A (H1N1) virus
infection are the same as those recommended for seasonal influenza:
Antiviral chemoprophylaxis (pre-exposure or post-exposure) with either
oseltamivir or zanamivir is recommended for the following individuals:
1. Household close contacts who are at high-risk for complications of
influenza (persons with certain chronic medical conditions, elderly) of a
confirmed or suspected case.
2. School children who are at high-risk for complications of influenza
(persons with certain chronic medical conditions) who had close contact
(face-to-face) with a confirmed or suspected case.
3. Travelers to Mexico who are at high-risk for complications of influenza
(persons with certain chronic medical conditions, elderly).
4. Border workers (Mexico) who are at high-risk for complications of
influenza (persons with certain chronic medical conditions, elderly).
5. Health care workers or public health workers who had unprotected close
contact with an ill confirmed case of swine influenza A (H1N1) virus infection
during the case's infectious period.
Antiviral chemoprophylaxis (pre-exposure or post-exposure) with either
oseltamivir or zanamivir can be considered for the following:
* Any health care worker who is at high-risk for complications of influenza
(persons with certain chronic medical conditions, elderly) who is working in an
area with confirmed swine influenza A (H1N1) cases, and who is caring for
patients with any acute febrile respiratory illness.
* Non-high risk persons who are travelers to Mexico, first responders, or
border workers who are working in areas with confirmed cases of swine influenza
A (H1N1) virus infection.
CDC - Will a face mask protect me from getting the swine flu (H1N1), and are
there differences in face masks?
Information on the effectiveness of facemasks and respirators for the control
of influenza in community settings is extremely limited. Thus, it is difficult
to assess their potential effectiveness in controlling swine influenza A (H1N1)
virus transmission in these settings. In the absence of clear scientific data,
the interim recommendations below have been developed on the basis of public
health judgment and the historical use of facemasks and respirators in other
settings.
Picture of a facemask
When used properly, facemasks may help reduce one's influenza risk. Photo
courtesy of the CDC
In areas with confirmed human cases of swine influenza A (H1N1) virus
infection, the risk for infection can be reduced through a combination of
actions. No single action will provide complete protection, but an approach
combining the following steps can help decrease the likelihood of transmission.
These actions include frequent handwashing, covering coughs, and having ill
persons stay home, except to seek medical care, and minimize contact with
others in the household. Additional measures that can limit transmission of a
new influenza strain include voluntary home quarantine of members of households
with confirmed or probable swine influenza cases, reduction of unnecessary
social contacts, and avoidance whenever possible of crowded settings.
When it is absolutely necessary to enter a crowded setting or to have close
contact with persons who might be ill, the time spent in that setting should be
as short as possible. If used correctly, facemasks and respirators may help
reduce the risk of getting influenza, but they should be used along with other
preventive measures, such as avoiding close contact and maintaining good hand
hygiene. A respirator that fits snugly on your face can filter out small
particles that can be inhaled around the edges of a facemask, but compared with
a facemask it is harder to breathe through a respirator for long periods of
time.
When crowded settings or close contact with others cannot be avoided, the use
of facemasks or respirators in areas where transmission of swine influenza A
(H1N1) virus has been confirmed should be considered as follows:
1. Whenever possible, rather than relying on the use of facemasks or
respirators, close contact with people who might be ill and being in crowded
settings should be avoided.
2. Facemasks should be considered for use by individuals who enter crowded
settings, both to protect their nose and mouth from other people's coughs and
to reduce the wearers' likelihood of coughing on others; the time spent in
crowded settings should be as short as possible.
3. Respirators should be considered for use by individuals for whom close
contact with an infectious person is unavoidable. This can include selected
individuals who must care for a sick person (e.g., family member with a
respiratory infection) at home.
These interim recommendations will be revised as new information about the use
of facemasks and respirators in the current setting becomes available.
What are the types of face masks and respirators?
*
Unless otherwise specified, the term "facemasks" refers to disposable
masks cleared by the U.S. Food and Drug Administration (FDA) for use as medical
devices. This includes facemasks labeled as surgical, dental, medical
procedure, isolation, or laser masks. Such facemasks have several designs. One
type is affixed to the head with two ties, conforms to the face with the aid of
a flexible adjustment for the nose bridge, and may be flat/pleated or
duck-billed in shape. Another type of facemask is pre-molded, adheres to the
head with a single elastic band, and has a flexible adjustment for the nose
bridge. A third type is flat/pleated and affixes to the head with ear loops.
Facemasks cleared by the FDA for use as medical devices have been determined to
have specific levels of protection from penetration of blood and body fluids.
* Unless otherwise specified, "respirator" refers to an N95 or higher
filtering facepiece respirator certified by the U.S. National Institute for
Occupational Safety and Health (NIOSH).
*
Three feet has often been used by infection control professionals to
define close contact and is based on studies of respiratory infections;
however, for practical purposes, this distance may range up to 6 feet. The
World Health Organization uses "approximately 1 meter"; the U.S. Occupational
Safety and Health Administration uses "within 6 feet." For consistency with
these estimates, this document defines close contact as a distance of up to 6
feet.
Swine Flu (H1N1 Influenza Virus) At A Glance
* Swine flu (swine influenza) is a respiratory disease caused by viruses
(influenza viruses) that infect the respiratory tract of pigs and result in
nasal secretions, a barking-like cough, decreased appetite, and listless
behavior.
* Swine flu viruses may mutate (change) so that they are easily
transmissible among humans.
* The 2009 swine flu outbreak is due to infection with the so-called H1N1
virus and was first observed in Mexico.
* Symptoms of swine flu in humans are similar to most influenza infections:
fever (100 F or greater), cough, nasal secretions, fatigue, and headache.
* Two antiviral agents, zanamivir (Relenza) and oseltamivir (Tamiflu), have
been reported to help prevent or reduce the effects of swine flu if taken
within 48 hours of the onset of symptoms.
<http://www.heartcare-info.com/swineflu.html>
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