So, we can pass this on pretty
easily person to person.
It’s contagious on the first day that
a person with influenza has symptoms,
and it’s spread by coughing and
sneezing, small-particle aerosols,
and these viruses are just
as tiny as they can be
and they remain suspended
in the air for hours.
So you can see why if the
symptoms come on within a day
and they are highly contagious,
then you can see why an
epidemic would occur.
And direct contact with somebody within
three meters of them
is another way.
So if you’re sick with something that
might be influenza or any viral syndrome,
it’s best to alert your
friends and your relatives,
“Look, I’m not going to shake your
hand, I don’t want to give you this.”
So what are the characteristics of
the various types of influenza?
For influenza A, the natural host
range involves humans, swine,
horses, birds, and marine animals,
and you can get both antigenic shifts
and drift, as we talked about,
and the clinical manifestations
can range from mild to death.
Influenza B seems to infect humans only
and you get antigenic
drift, but not shift,
and so therefore, you don’t get
any pandemics of influenza B,
and most of the people who suffer are
older individuals and immunocompromised.
Influenza C can infect
humans and swine,
they only get antigenic drift,
and it’s a mild disease.
So, indirect contact involves fomites,
viral particles that
land on surfaces.
And the virus is shed in an infected
individual from five to ten days.
So even if they have had
their flu for a week
and they’re starting to get better
they still may be contagious.
So let’s discuss the clinical
presentation of the influenza.
The incubation period is short,
as I mentioned, one to two days,
and the illness comes on
generally like gangbusters.
In a typical common cold, you may
start out with a sore throat,
get hoarse, get nasal congestion,
and so forth, but you generally
don’t feel seriously ill.
But in classic influenza, this illness
begins with fever and chills and headache
and actually myalgias are very prominent,
especially extraocular myalgias,
when the patient moves their eyes
side to side it actually hurts.
That’s maybe a clue to influenza.
I mean other viruses can do that but
influenza is notorious for doing that.
And this illness will put you in the
bed, the common cold generally does not,
and you don’t have
much of an appetite.
The respiratory symptoms
start out with a dry cough
and a sore throat and nasal congestion,
and this all gradually gets worse.
The cough becomes productive.
And think about what’s going on.
You’re denuding the respiratory epithelium,
so you’re going to be coughing up a lot of
cellular debris along with polyps.
And so gradually over one to two weeks
you will start getting over this.
But this disease can be complicated.
Probably the worst complication is
primary influenza viral pneumonia
shown in the upper panel here,
and this is where the lung parenchyma
is actually infected by influenza.
We mentioned that it may occur
more commonly in pregnant women,
it also can occur more commonly
in people who have heart failure.
They’re more likely to get that if they
have pulmonary edema for any reason
and also patients who have
and other kinds of pulmonary
problems to start with.
So the primary influenza
typically with influenza, but
rapidly the patient develops cough,
dyspnea, and cyanosis.
So when that develops, that’s
unlike regular influenza.
Regular influenza is pretty
stuck on the bronchial tree,
but influenza pneumonia is going to
start causing problems with hypoxia.
And generally, the patients will have,
on exam, bilateral inspiratory crackles
but no consolidative findings.
It tends to be sort of
an interstitial process
so they won’t have necessarily
dullness to percussion,
bronchial breath sounds.
The other thing is, and I hinted at it,
that when the bronchial tree is denuded,
then you are susceptible to bacterial
pathogens that might get down in there,
and leading the list of course
is the Captain of the Men of
Death, Streptococcus pneumoniae,
and then Staphylococcus aureus.
And that staph aureus has been one of the
more common superinfecting pathogens.
So staph aureus, one of
the settings in which you
frequently see it is
and nowadays that includes
It turns out to be a rather uncommon
cause of community-acquired pneumonia
unless it follows influenza.
And so how do we know
that that’s there?
Well, the patient was
convalescing from their influenza
and then they have recrudescent fever,
then their cough becomes more productive,
and now they do have
as shown in the lower panel on a patient
who got pneumococcal pneumonia.
So we make the diagnosis
because we know that
influenza is going around,
so any kind of influenza-like
illness that’s been in a community
that they already know that it’s around,
and the accuracy there is 80% to 90%.
There are molecular diagnostic tests
that you can do with a nasal swab
and they’ve got a good sensitivity and
specificity, but they cost about $25.
The rapid influenza diagnostic tests
compared to viral culture, their
sensitivity is 40% to 80%.
These are the ones that are done
frequently in the emergency room.
So when would you use one
of these rapid tests?
Only if it’s going to make a difference
in what you do for the patient.
In the normal host,
you’re going to treat them symptomatically,
you may use one of the
but generally it’s supportive
therapy, fluids, rest, and so forth.
Now, in the immunocompromised
patient or a hospitalized patient,
you’re going to use these rapid
tests to confirm the diagnosis
regardless of how long
they’ve had symptoms.