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1. Influenza
‫رهام‬ ‫مریم‬ ‫دکتر‬
:
‫عفونی‬ ‫گروه‬ ‫استادیار‬
Harrison's Principles of Internal
Medicine2018
1

2. DEFINITION
• The term influenza represents both a clinically
defined respiratory illness accompanied by
systemic symptoms of fever, malaise, and myalgia
and the name of the orthomyxoviruses that cause
this syndrome.
• Although this term is sometimes used more
generally to denote any viral respiratory illness,
many features distinguish influenza from these
other illnesses, most particularly its systemic
symptoms, its propensity to cause sharply peaked
winter epidemics, and its capacity to spread
rapidly among close contacts.
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3. ETIOLOGIC AGENTS
• Three influenza viruses occur in humans: A, B,
and C.
• These viruses are irregularly circular in shape,
measure 80– 120 nm in diameter, and have a lipid
envelope and prominent spikes that are formed
by the two surface glycoproteins, hemagglutinin
(H) and neuraminidase (N).
• The hemagglutinin functions as the viral
attachment protein, binding to sialic acid
receptors on the cells that line the superficial
epithelium of the respiratory tract.
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4. • The neuraminidase cleaves the virus from the cell
membrane to facilitate its release from the cell
and prevents self-aggregation of viruses.
• Influenza A viruses have eight single-strand
negative-sense RNA segments in their genomes
that encode hemagglutinin and neuraminidase as
well as internal genes, including polymerase,
matrix, nucleoprotein, and nonstructural genes.
• The segmented nature of the genome allows
gene reassortment; an analogy for reassortment
is the Reassortment takes place when a single cell
is infected with two different strains.
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5. • The influenza A viruses are further classified
by their surface glycoproteins (H and N), the
geographic location of their isolation, their
sequential number among isolated viruses,
and their year of isolation.
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6. EPIDEMIOLOGY
Influenza virus causes outbreaks during the
cooler months of the year and thus has a
mirror-image season in the antipodes
compared with that in the Northern
Hemisphere.
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7. • A typical outbreak begins in early winter and
lasts 4–5 weeks in a given community,
although its impact on the country as a whole
will be of considerably longer duration.
• When excess mortality occurs, an influenza
outbreak is classified as an epidemic.
• Influenza’s impact is reflected in increased
school and work absenteeism, increased visits
to emergency rooms and primary care
physicians, and increased hospitalizations,
particularly of elderly patients and individuals
with underlying cardiopulmonary disease.
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8. • The impact often is most easily recognized in
the pediatric population, whose school
absenteeism quickly peaks.
• Influenza is largely spread by small- and large-
particle droplets; spread is undoubtedly
facilitated by the coughing and sneezing that
accompany the illness.
• Within families, the illness is often introduced
by a preschool or school-aged child.
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9. • The severity of an epidemic depends on the
transmissibility and virulence of the viral
strain,
the susceptibility of the population,
the adaptation of the virus to its human host,
and the
degree of antigenic match to the
recommended vaccine.
• None of these parameters is totally
predictable for influenza A.
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10. • Influenza A Viruses
• When a major shift in the hemagglutinin
and/or the neuraminidase occurs, with
introduction of a new serotype from an
animal or avian reservoir, an influenza A strain
has the potential to cause a pandemic.
• In modern influenza history, such shifts
occurred in 1918 (H1N1), 1957 (H2N2), 1968
(H3N2), 1977 (H1N1), and 2009 (H1N1pdm).
• Typical Epidemics of influenza have been
documented throughout recorded history.
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11. In some epidemics, a younger age group
proves especially susceptible.
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12. Avian and Swine Influenza Viruses
• The full panoply of influenza viruses is found
in domestic and migratory wild birds.
• It is postulated that epithelial cells in the
swine respiratory tract may play a specific role
as a “mixing vessel,” allowing the
reassortment of genes from avian and human
sources and thereby permitting the transition
of avian viruses to humans.
12

13. Influenza B and C Viruses
• The influenza B viruses are more genetically
stable than the influenza A viruses and have no
animal reservoirs.
• Two lineages of influenza B have circulated for
the past 40 years (B/Yamagata-like and
B/Victoria-like viruses), and it has proven very
difficult to predict which strain will be dominant
in a given year.
• Influenza C viruses cause intermittent mild
disease and have attracted little attention.
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14. Influenza-Associated Morbidity and Mortality
A generalization is that the relative impact of
an epidemic is seen in the youngest age group
with the least prior exposure—and therefore
the least immunity—to influenza.
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15. High-Risk Groups Who Should be Assigned a High
Priority for Influenza Immunization and
Treatment
• Children 6–59 months of age
• Adults ≥50 years of age
• Persons with chronic pulmonary (including
asthma), cardiovascular (except isolated
hypertension), renal, hepatic, neurologic,
hematologic, or metabolic disorders (including
diabetes mellitus)
• Persons who are immunocompromised (any
cause, including medications or HIV infection)
• Women who are or plan to be pregnant during
the influenza season
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16. • Children and adolescents (6 months through
18 years of age) who are receiving aspirin- or
salicylate-containing medications and who
might be at risk for Reye syndrome
• Residents of nursing homes and other long-
term-care facilities
• Native Americans, including Alaska Natives
• Persons who are extremely obese (BMI ≥40)
16

17. Contacts and Caregivers
• Caregivers and contacts of those at risk:
health care personnel in inpatient and outpatient
care settings, medical emergency-response
workers, employees of nursing home and long-
term-care facilities who have contact with
patients or residents, and students in these
professions who have contact with patients
Household contacts and caregivers of children
≤59 months (i.e., <5 years) of age (particularly
contacts of infants <6 months old) and adults ≥50
years of age
Household contacts and caregivers of persons
who are in a high-risk group
17

18. CLINICAL MANIFESTATIONS
• Influenza is primarily a respiratory illness causing
rhinorrhea, sore throat, conjunctivitis, and cough.
The illness has a sudden onset and is
epidemiologically linked to close contact with
persons who have similar symptoms and often to
community-wide respiratory illness.
• What distinguishes influenza from other
respiratory illnesses is the degree of
accompanying fever, fatigue, myalgia, and
malaise.
• The symptoms typically begin within 48–72 h
of exposure.
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19. • Respiratory symptoms, particularly recurrent
cough, persist well beyond the 2–5 days of
systemic symptoms.
• There is a postinfectious delay in return to
normal levels of activity.
• Pulmonary function is persistently decreased
after acute influenza.
• Persons with a regular exercise routine (e.g.,
runners) note a decrease from their prior level
of performance that typically lasts for a month
or more.
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20. • In the elderly, the respiratory presentation
may be less prominent, but there is often a
decline in baseline activity and a loss of
appetite.
• On physical examination, the patient with
influenza appears ill and rheumy, with
sweating, coughing, diffuse pharyngeal
erythema, nonpurulent conjunctivitis.
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21. • Pulmonary examination typically reveals
nonlocalizing scattered rales, rhonchi, and
wheezes.
• When present, localized pulmonary findings
suggest relatively complicated pneumonia
with a bacterial component.
• Muscle pain may be elicited by pressure,
particularly in the calves and thighs.
• There are rare gastrointestinal findings.
• No rash is associated with influenza.
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22. COMPLICATIONS
• Complications of influenza occur most
commonly in persons >65 years of age, those
with underlying cardiopulmonary disease,
those with immunosuppression, and women
who are in the second or third trimester of
pregnancy.
• In recent years, there has been mortality
attributable to influenza among often
previously healthy children <5 years of age in
the United States, with ~100 deaths per year.
22

23. Respiratory Complications
• Pneumonia characterized by progressive air
hunger, localized pulmonary findings on physical
examination, and radiographic findings of
infiltrates and consolidation is the most common
complication of influenza.
• Pneumonia in influenza can be primary influenza
viral pneumonia, secondary bacterial pneumonia,
or mixed viral and bacterial pneumonia.
• Primary viral pneumonia is characterized by
increasing dyspnea, persistent fever, and—in
more severe cases—cyanosis.
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24. • In secondary bacterial pneumonia or mixed
viral and bacterial pneumonia, illness may be
biphasic, with evidence of recovery from the
primary influenza illness followed by
recrudescence of fever and pulmonary
symptoms.
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25. • Localizing findings may be detected on
pulmonary examination and/or x-ray.
• The development of secondary bacterial
infection is not surprising, as influenza de-
epithelializes the airways and destroys ciliary
function, allowing bacterial contamination.
• The risk of secondary bacterial disease is
greatest in elderly patients and those with
chronic obstructive pulmonary disease.
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26. • Some influenza strains cause
laryngotracheobronchitis or croup in children.
• Otitis media —a common accompaniment to
influenza in children—may also be due to a
combination of influenza virus and bacteria.
26

27. Extrapulmonary Complications
• The most common extrapulmonary
manifestation of influenza is myositis, which is
seen more often in influenza B and is
characterized by severe muscle pain, elevated
creatinine phosphokinase levels, and
myoglobinuria that can lead to renal failure.
• The muscles are extremely tender to touch.
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28. • Myo/pericarditis is seen less frequently and
has been reported only in selected epidemics,
notably the pandemic of 1918.
• However, a consistent epidemiologic link
exists between influenza epidemics and excess
cardiovascular hospitalizations.
• Postinfectious acute demyelinating
encephalomyelitis can follow influenza as well
as other viral infections.
• Encephalitis and transverse myelitis may
accompany influenza infection.
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29. • Guillain-Barré syndrome can develop after influenza
and was reported after a widespread influenza
vaccination effort in the fall of 1976 that was
undertaken in anticipation of a swine influenza
epidemic (which never materialized).
• Until aspirin was recognized as a cofactor in it
precipitation, Reye syndrome, an acute hepatic
decompensation, was seen commonly in children and
adolescents with influenza, particularly those infected
with influenza B virus.
• Subsequently, the use of aspirin for fever control and
symptom relief in children with viral infections was
strongly discouraged, and Reye syndrome has virtually
disappeared from clinical practice.
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30. LABORATORY FINDINGS AND DIAGNOSIS
• There is a strong argument for establishing a
microbiologic diagnosis from both an
individual-patient and a public-health
perspective.
• This information is particularly valuable early
in the season, when the extent of influenza
and the precise circulating strain(s) are
uncertain; in the management of complicated
cases in hospitalized patients; and in settings
such as long-term-care facilities and hospitals,
where the institution of specific infection-
control measures is appropriate.
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31. • Influenza virus is most easily recovered from
nasopharygeal specimens.
• These samples are most effectively collected
with a flocked swab that is inserted 1–2 inches
into the nose (following the course of the inferior
meatus), twirled, placed in viral transport
medium that supports viral viability, and
transported on ice to the laboratory as promptly
as possible.
• The available rapid tests based on antigen
detection vary in complexity and cost.
• These tests are highly specific but have a
sensitivity of only 50–70%.
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32. • Their sensitivity is strongly dependent on sample
collection early in the course of illness—ideally
within 48 h of the onset of symptoms.
• Traditionally, viruses have been isolated in tissue
culture or with the use of embryonated eggs, and
infection has been confirmed with
hemadsorption or hemagglutination.
• The most useful clinical approach today is to use
a PCR-based molecular probe that amplifies
specific segments of the influenza genome.
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33. • Not only is this the most sensitive and specific
method; it also provides opportunities to
identify the strain with some specificity.
• Testing by multiplex PCR can simultaneously
identify multiple respiratory pathogens—an
advantage in the ill hospitalized patient.
• Serologic confirmation of infection is also
possible but requires paired serum samples,
with the convalescent-phase sample obtained
2 weeks after infection.
33

34. • Mucosal antibody assays that are now being
developed can detect strain-specific
antibodies in paired mucosal specimens and
yield insights into the importance of mucosal
immunity in protection against influenza.
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35. • Other laboratory tests are of limited value.
• Mild leukopenia is seen in influenza, and a
white blood cell count above 15,000/μL
suggests a secondary bacterial component in
influenzal pneumonia.
35

36. DIFFERENTIAL DIAGNOSIS
• The distinctive nature of influenza is such that
clinical diagnoses by experienced pediatric
physicians are 85% concordant with microbiologic
etiologic confirmation.
• Respiratory syncytial virus often co-circulates
with influenza virus; it particularly affects the
youngest children, causing bronchiolitis, but it
can also infect the elderly, leading to an
influenza-like nonspecific respiratory illness and a
decline in mobility, nutrition, and pulmonary
function, with resultant hospitalization.
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37. PROPHYLAXIS
• The major intervention to limit influenza illness is
vaccination, which is conducted on a yearly basis
because of variation in the predicted circulating
strains for the coming year and which enhances
existing immunity in advance of the influenza
season.
• The decision about vaccine composition must be
made ~10 months before the seasonal peak in
influenza virus circulation; this decision is made
by committees at the WHO and the CDC.
• This timing can result in a mismatch of vaccine
composition with the viral strains that are
actually prevalent in the upcoming season.
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38. • The overall accuracy of the prediction is at
least 70% for all strains in the recommended
vaccine.
• The currently available vaccines are all based
on purified subunit inactivated virus produced
in eggs, in tissue culture, or through a
baculovirus-expressed hemagglutinin protein.
Depending on the vaccine, they are
administered intramuscularly or intradermally.
38

39. • Some influenza vaccines include MF-59 as an adjuvant
or have elevated hemagglutinin content for enhanced
immunogenicity in the elderly.
• The protection (and licensure) of all influenza vaccines
depend on their stimulation of antibodies to the
hemagglutinin; all are 50–75% effective at preventing
clinical influenza.
• No effort is made to standardize the neuraminidase
content.
• The contraindications to inactivated influenza vaccine
administration are limited to individuals who have
experienced a Guillain-Barré reaction within 6 weeks of
a prior influenza vaccination.
• Egg allergy is not considered a contraindication to
vaccination.
39

40. • In recent years, a live, attenuated, intranasally
administered vaccine (LAIV) has been used in
children and has exhibited an efficacy exceeding
that of injected inactivated vaccines.
• However, beginning in 2014–2015 and continuing
in the following season, LAIV had no
demonstrable efficacy assignable to the vaccine’s
H1N1 component.
• This change led advisory committees in the
United States not to recommend the use of LAIV
despite its prior effectiveness, ease of
administration, and theoretical advantage of
stimulating mucosal immunity by the topical
route.
40

41. • In the United States, the recommendation is
that all individuals >6 months of age receive
inactivated influenza
• vaccine yearly and that two doses of vaccine
be given to children <9 years of age who are
getting their first or second yearly vaccination.
• Groups at special risk of experiencing or
transmitting influenza for whom influenza
immunization is a particularly high priority .
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42. • Especially in hospital settings, considerable
attention is paid to hand washing and the use
of masks by persons with respiratory
symptoms and those who are at particular risk
of acquisition (typically, immunocompromised
patients).
• Studies have demonstrated the benefit of face
masks and hand hygiene in the hospital
setting.
42

43. TREATMENT
• Antiviral therapy for influenza has been limited by the
paucity of available drugs, the short duration of
symptoms in uncomplicated influenza, and the
changing patterns of drug resistance in influenza viral
strains.
• In the past, influenza A infection could be treated with
the M-2 channel blockers amantadine and
rimantadine.
• Widespread resistance has currently relegated these
compounds to historical interest only.
• The currently available class of drugs for treatment of
influenza A and B viruses consists of neuraminidase
inhibitors.
43

44. • As their name implies, these drugs act by inhibiting the
influenza neuraminidase and thus limiting the egress of
influenza virus from an infected cell.
• They are most effective in patients whose influenza
illness is recognized early and confirmed by rapid
antigen detection or on the basis of clinical and
epidemiologic evidence.
• In experimental trials, these drugs hasten the
resolution of symptoms if given within 48 h of
infection.
• There are indications for their use both
prophylactically—either throughout the season or,
when a case is recognized in a close contact, in the
short term—and therapeutically.
44

45. • The anticipated effect of early administration is
the resolution of symptoms 1–2 days sooner than
without treatment.
• The use of neuraminidase inhibitors is
recommended for complicated influenza
infections in hospitalized patients in the absence
of formal proof of efficacy and when diagnosis
may have been delayed.
• All the available neuraminidase inhibitors carry a
risk of development of resistance, particularly
with prolonged administration (e.g., to an
immunodeficient individual with persistent
recovery of influenza virus).
45

46. • Resistance to neuraminidase inhibitors is not widespread
among currently circulating influenza A or B strains, but its
development has been demonstrated in the laboratory, and
clinical resistance could influence the utility of these drugs.
• The defined risk groups who can benefit from
neuraminidase inhibitors include
 children <2 years of age,
 adults >65 years of age,
 patients with chronic conditions,
 immunosuppressed individuals,
 pregnant women,
 women who have delivered infants ≤2 weeks previously,
 patients <19 years old who are receiving long-term aspirin
treatment,
 Native Americans (including Alaska Natives),
 morbidly obese individuals, and
 residents of nursing homes or chronic-care facilities.
46

47. • Use of neuraminidase inhibitors should be
considered in selected high-risk cases despite a
history of vaccination.
• The available neuraminidase inhibitors are oral
oseltamivir, nasal-spray zanamivir, and
intravenous peramivir and zanamivir.
• Oseltamivir, which is most widely used, is an
orally absorbed drug that is converted to its activ
component, oseltamivir carboxylate, in the liver.
Gastrointestinal symptoms, especially nausea,
may accompany the administration of oseltamivir.
• Because zanamivir is not orally bioavailable, it is
given as an inhaled dry powder dispersed
through a Diskhaler device.
47

48. • The usual duration of therapy with either oral
oseltamivir or intranasal zanamivir is 5 days, with
twice-a-day dosing.
• Oseltamivir is preferred for treatment of pregnant
women and is approved for children ≥1 year of age.
• Poor oral intake or absorption is a contraindication to
the use of oseltamivir, although this drug can also be
given by oro/nasal tube.
• Asthma and chronic obstructive pulmonary disease are
relative contraindications to the use of intranasal
zanamivir; this agent is approved for children ≥5 years
of age.
48

49. 1
• The use of the intravenous preparations of peramivir
and zanamivir is indicated in severely ill patients.
• Peramivir is licensed for individuals >18 years of age,
and intravenous zanamivir may be available through
the manufacturer via an individual Emergency
Investigational New Drug request.
• Other critical aspects of treatment include
maintenance of fluid and electrolyte balance, oxygen
supplementation, fever control with nonsteroidal anti-
inflammatory drugs, and treatment of suspected
secondary bacterial complications with antibiotics.
• Appropriate respiratory isolation of patients should be
practiced in accordance with local hospital guidelines.
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50. ‫باشید‬ ‫شادکام‬ ‫و‬ ‫موفق‬
50