This course introduces learners to a variety of infectious diseases using a patient-centered, story-based approach. Through illustrated, short videos, learners will follow the course of each patient’s illness, from initial presentation to resolution. Integrating the relevant microbiology, pathophysiology and immunology, this course aims to engage and entice the learner towards future studies in microbiology, immunology and infectious diseases. The patient-centered videos included in this course were created as part of the Re-imagining Medical Education initiative, led by Charles Prober MD, Senior Associate Dean of Medical Education at the Stanford School of Medicine. This initiative was the first of its kind to explore the collaborative creation of foundational medical education online content by inter-institutional teams of faculty. The content presented in this course was created by faculty from Stanford University School of Medicine, in collaboration with The University of Washington School of Medicine, Duke University School of Medicine, UCSF School of Medicine, and The University of Michigan Medical School. Support for this initiative was provided by the Robert Wood Johnson Foundation and the Burke Family Foundation. PLEASE NOTE: Information provided in this course is for educational purposes only and is not intended to be used for diagnostic and/or treatment purposes.
Influenza
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Из курса от партнера Stanford University
Stories of Infection
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Viral Infections Part 1
In Module Four, we will explore five cases of infectious disease involving viruses. We will see how factors like social stigma, prior infections, access to medications, and family history can play a role in infectious disease. We will also examine the link between viruses and some cancers. By the end of this module, learners will be able to interpret the clinical presentation of these five infectious diseases and describe the relevant microbiology, pathophysiology, and immunology.
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Maya Adam, MDLecturer
Stanford School of Medicine
Today we'll be talking about influenza, a viral infection that causes yearly
epidemics, typically affecting up to 15 to 20% of the world's population.
These annual epidemics lead to approximately half a million deaths
around the world each year.
And pregnant women, like this 28-year-old freelance photographer,
are at especially high risk of developing severe complications.
Mel was 32 weeks pregnant when she was brought to the One night by her worried
husband.
She had been suffering from what she thought was a minor cold,
that began with a cough, headache and sore throat two days ago.
She later also developed a runny nose and itchy, watery eyes.
Her husband thought she may have been slightly febrile over the past two days.
But tonight she became noticeably warm and started to look very pale.
She was lying in bed breathing rapidly when her husband came home from work.
Mel told her husband that she felt short of breath, but she wasn't sure if that was
a normal pregnancy symptom for someone in the third trimester.
This was her first pregnancy, so neither Mel nor
her husband knew exactly what to expect.
But the pregnancy had gone smoothly and
Mel had received regular prenatal care from an obstetrician and a doula.
She had also established a birth plan, which had her giving birth naturally
at home, with minimal medical intervention, including pain medication.
Throughout the pregnancy,
she had been meticulous about trying to minimize potentially harmful exposures.
And had even refused the flu shot, which her obstetrician had recommended,
since Mel would be pregnant during the peak flu season.
At the The physician on duty noted that Mel looked fatigued and unwell.
With a fever of 102 degrees Fahrenheit, an elevated heart rate and breathing rate,
and an O2 saturation that was decrease to 90% on room air.
She was pale and sweating and appeared anxious.
On examination of her lungs, the Physician noted coarse rhonchi and
decreased breath sounds over the bases of her lungs.
Her mucous membranes also appear dry,
suggesting that she was dehydrated from poor fluid intake during her illness.
Because of these concerning findings, the Physician suspected influenza infection.
He decided to admit Mel and started her on IV fluids and supplemental oxygen.
He then performed a nasal swab and sent it for viral PCR to test for influenza virus,
as well as obtaining a sputum sample which he sent for gram stain and culture.
After some consideration, he also ordered a chest X-ray.
Despite the fact that radiation exposure from X-rays is avoided,
if possible, during pregnancy.
He knew that the risk from this small dose of radiation
was outweighed by the need to determine if Mel had developed pneumonia.
A complication for which she was at high risk because of her pregnancy.
The influence virus, which enters the host via respiratory droplets from
infected individuals, owes its virulence to two major glycoproteins
on the virion surface, hemagglutinin and neuraminidase.
Hemagglutinin is the protein responsible for viral binding to
respiratory epithelial cells via sialic acid on the cell surface.
Neuraminidase cleaves the sialic acid,
which releases newly formed virions from the host cell surface.
Neuraminidase also decreases the viscosity of the mucous film coating
the respiratory tract, exposing the cell surface and
facilitating the spread of virus-containing fluid.
Within a short time, many cells in the respiratory tract become infected and
eventually killed directly by the virus.
This damaged respiratory epithelium
is then susceptible to secondary bacterial invaders or superinfection.
In addition to being important virulent factors, hemagglutinin and neuraminidase
are also the primary targets of the host immune response against influenza.
So they're constantly evolving to avoid immune recognition.
When these proteins evolve by gradually accumulating point mutations
during viral replication, the process is called antigenic drift.
Antigenic drift is responsible for
the new influenza strains that cause yearly global epidemics.
And explains why a new flu vaccine has to be developed for each new flu season.
The new strains are different enough from previous years
to evade host memory responses from previous infection or vaccination.
But influenza is also unique in its propensity to
evolve through a different process called antigenic shift.
In which an entirely new hemagglutinin subtype
is introduced into the human population.
This can occur either when a non-human strain of influenza
gains the ability to infect a human host.
Or when both human and non-human strains of influenza co-infect
a single animal and undergo genetic reassortment.
Influenza virus readily undergoes this kind of reassortment
due to its segmented genome.
And the resulting novel strains are especially dangerous
because the entire population lacks protective immunity against them.
Antigenic shift has resulted in deadly worldwide pandemics,
striking once every generation since the beginning of the 20th century.
Pregnant women like Mel are at especially high risk of developing serious
complications from influenza.
In response to the hormonal milieu of pregnancy,
the immune system under goes important adaptations to
tolerate the presence of the paternally-derived antigens of the fetus.
But because these adaptations induce a shift away from cell mediated immunity,
they put the woman at risk for inadequate response to infections.
Mel's doctors knew that prompt antiviral treatment for
influenza in pregnancy is associated with significantly better outcomes.
So shortly after arrival in the hospital, Mel was empirically started on
oseltamivir, which targets the influenza glycoprotein neuraminidase.
Mel was also given acetaminophen to control her fever,
since elevated body temperature can be harmful to the fetus.
Mel's chest x-ray results showed bilateral hazy opacities
consistent with a viral pneumonia.
But there was no evidence of a focal consolidation that would
suggest a bacterial pneumonia.
Her sputum gram stain was also negative.
So although her cultures wouldn't be finalized for a few days,
it appeared most likely that she did not have a bacterial superinfection.
Mel's PCR result came back eight hours later and
confirm the diagnosis of influenza.
Her condition improved over the next few days and she was discharged home and
continued to be closely followed by her obstetrician.
Once she had recovered,
Mel agreed to receive the flu vaccine to protect herself and
her fetus from infection with different circulating strings of influenza.
The doctor explained that even after delivery, her newborn would be protected
by Mel's vaccination due to passive immunity acquired across the placenta.
After the influenza scare,
Mel decided to give birth at the hospital instead of at home.
But otherwise, she was able to follow her birth plan and
she delivered a healthy baby girl at 39 weeks.
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