Influenza is comonly referred to as flu is an infectious viral disease caused by RNA Virus of the family Ortho-Myxoviridae (the Influenza Virus), that affect bird and mammals. Common symptoms are Chills, fever, sorethroat, muscle pain, severe headache, coughing, fatigue and general discomfort. Although confused with other influenza like illnesses, especially the common cold, influenza is a more severe disease.

1. SMT. DAKUBEN SAREMALJI SANCHETI NURSING INSTITUTE, SUMERPUR
Community Health
Nursing - I
“Influenza”
Unit – “Communicable Disease”
2020

2. Management of Nursing Services & Education 2020
Kuldeep Vyas M.Sc. CHN
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INFLUENZA
INTRODUCTION
Influenza is comonly referred to as flu is an infectious viral disease caused by RNA
Virus of the family Ortho-Myxoviridae (the Influenza Virus), that affect bird and mammals.
Common symptoms are Chills, fever, sorethroat, muscle pain, severe headache,
coughing, fatigue and general discomfort.
Although confused with other influenza like illnesses, especially the common cold,
influenza is a more severe disease.
DEFINITION
WHO: Influenza is a viral infection that affects mainly the nose, throat, bronchi and,
occasionally, lungs. Infection usually lasts for about a week, and is characterized by sudden
onset of high fever, aching muscles, headache and severe malaise, non-productive cough,
sore throat and rhinitis.
HISTORY
Influenza can be traced as far back as 400 BC
In Hippocrates’ Of the Epidemics, he describes a cough outbreak that occurred in 412 BC in
modern-day Turkey at the turn of the autumn season
17th century:-
1. Between 1781-1782, an influenza epidemic infected 2/3 of Rome’s population
and ¾ of Britain’s population. Later, disease spread to North America, West
Indies, and South America. Spread of pandemic culminated in New England,
New York, and Nova Scotia in 1789.
2. 1781 marked the beginning of the of influenza epidemics and pandemics
EPIDEMILOGICAL DETERMINANTS
AGENT:
 Influenza viruses are classified within the family of Ortho-myxoviridae.
 There are three viral sub–types, namely influenza type A, type B and type C.
 These three viruses are antigenically distinct. There is no cross–immunity between
them.
 Of importance are the influenza A and B viruses which are responsible for epidemics

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of disease throughout the world.
1. Both influenza A & B Viruses have two distinct surface antigens – the Hemoglutinin
(H) and the Neramindase (N) antigens.
2. The H antigen initiates infection following attachment of the virus to susceptible cells.
the N antigen is responsible for the release of the virus from the infected cell.
3. I. The influenza A virus is unique among the viruses because it is frequently subject
virus to antigenic variation, both major and minor.
4. I. When there is a sudden, complete or major change, it is called a shift, and when the
antigenic change is gradual, over a period of time, it is called a drift..
Antigenic shift appears to result from genetic recombination of human with animal or avian
virus, providing a major antigenic change.
This can cause a major epidemic or pandemic involving most or all age groups.
Antigenic drift involves “Point mutation” in the gene owing to selection pressure byimmunity
in the host population.
Antigenic changes occur to a lesser degree in the B group influenza viruses. Influenza C
appears to be antigenically stable.
• Since the isolation of the virus A in 1933, major
antigenic changes have occurred twice
– once in 1957 (H2N2)and then again in
1968 (H3N2).
• Strains occurring between 1946 and 1957 have been called H1N1 strains. The shift in
1968 involved onlythe H antigen.
• In 1977, a new antigenic type appeared in China and the USSR and the virus was
identified as A (H1N1). Within a year, it had been isolated in countries all over the
world.
• Curiously, this was an earlier virus which has appeared after a lapse of over 20
years.
• In the past, the emergence of a new, influenza A sub–type led to the prompt
disappearance of the previously prevalent sub–type. In the 1977 episode, however,
this did not happen.
The prevailing A (H3N2) was not displaced. Dual infection with both viruses was
reported.
As of now, three types of influenza viruses
– A (H1N1), A (H3N2) and B exist.

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Influenza viruses of the H1N1 sub–type have caused epidemics of the disease in two
periods of this century – from about 1946 up until 1957, and from 1977 until the present.
RESERVOIR OF INFECTION
It has become increasinglyevident that a major reservoir of influenza virus exists in animals
and birds.
Many influenza viruses have been isolated from a wide variety of animals and birds (e.g.
swine, horses, dogs, cats, domestic poultry, wild birds, etc.)
Some of these include the major H and N antigens related to human strains.
There is increasing evidence that the animal reservoir provides new strains of the Influenza
virus by recombination between the influenza viruses of man, animals and birds.
SOURCE OF INFECTION
The source of infection usuallyis a case or sub–clinical case.
During epidemics, a large number of mild and asymptomatic infections occur, which play an
important role in the spread of infection.
The secretions of the respiratorytract are infective.
PERIOD OF INFECTIVITY
The Virus is present in the naso-pharynx a couple of days before and a couple of day after
the onset of symptoms.
HOST FACTORS
AGE AND SEX:
o Influenza affects all ages and people of both sexes. In general, the attack rate is
lower among adults. Children constitute an important link in the transmission chain.
o The highest mortality rate during an epidemic occurs among certain high–risk
groups in the population such as old people (generally over 65 years of age), infants
under 18 months, and persons with diabetes or chronic heart disease, kidney and
respiratoryailments.
HUMAN MOBILITY:
o This is an important factor in the spread of the infection.
IMMUNITY
Antibodies appear in about seven days after an attack and reach a maximum level in about

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two weeks. After about 8 to 12 months, antibody levels drop to pre–infection levels.
The antibodyto H neutralizes the virus while the antibodyto N modifies the infection.
Secondaryantibodies develop in the respiratory and consist predominantly of lgG.
Antibodies must be present in sufficient concentrations at the superficial cells (the site of
virus invasion) of the respiratorytract.
ENVIRONMENTAL FACTORS OF INFLUENZA
Season
The seasonal incidence is striking, epidemics usually occur in the winter months in the
northern hemisphere. In India, however, epidemics have often occurred in summer
Overcrowding
Overcrowding enhances transmission of the infection. The attack rates are high in closed
population groups e.g. schools, institutions, ships, etc.
INCUBATION PERIOD FOR INFLUENZA
The incubation period is about 18 to 72 hours.
PATHOGENESIS
 The virus enters the respiratory tract and causes inflammation and necrosis of the
superficial epithelium of the tracheal and bronchial mucosa, followed by secondary
bacterial invasion.
 There is no viraemia.
SIGNS AND SYMPTOMS
Symptoms begin 1-4 days after infection.
The following symptoms of the flu can vary depending on the type of virus, a person’s age
and overall health:
• Sudden onset of chills and fever (101 – 103 F)
• Sore throat, drycough
• Fatigue, malaise
• Terrible muscle aches, headaches
• Diarrhea
• Dizziness

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Both viruses cause the same symptoms. Fever lasts from one to five days, averaging about
three days in adults.
The most dreaded complication is pneumonia, which should be suspected if fever persists
beyond four or five days, or recurs abruptly after convalescence.
COMPLICATIONS IN CHILDREN
Studies show a link between the development of Reye’s syndrome and the use of aspirin for
relieving fevers caused bythe influenza virus.
The disease involves the CNS and the liver and children exhibit symptoms of drowsiness,
persistent vomiting and change in personality.
DIAGNOSIS OF INFLUENZA
1. VIRUS ISOLATION :
a) Nasopharyngeal secretions are the best specimens for obtaining large quantities
of virus–infected cells.
b) Thevirus can be detected by the indirect fluorescent
antibodytechnique.
c) However, egg inoculation is required for virus isolation and antigenic analysis.
2. PAIRED SERA :
A sero diagnosis of influenza A or B can be made by the examination of two serum
specimens from a patient. One taken as early as possible in the acute phase of the
disease (not later than the fifth day), and another taken about 10 to 14 days after the
onset, i.e. the convalescent stage of illness.
The titer of influenza antibodies in the human sera is so variable that only by detecting a
rise in Complement Fixing (CF) antibodies during the course of illness, can a diagnosis be
established. Hence, the need for two specimens. Fourfold or greater rise in titer are
considered diagnostic of infection.
RAPID INFLUENZA TESTS
These tests are 70% accurate for determining if the patient has been infected with the
influenza virus and 90% accurate for determining the type of influenza pathogen.
Examples of rapid influenza tests: Directigen Flu A, Directigen Flu A + B, Flu OIA, Quick Vue,
and Zstat flu.

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Rapid influenza tests provide results in 24 hours and can be performed in the physician’s
office.
ANTI-VIRAL DRUGS
All anti-viral drugs inhibit viral replication but they act in different ways to achieve this.
Drugs that are effective against influenza A viruses: amantadine and rimantadine.Drugs that
are effective against influenza A viruses and influenza B viruses: zanamivir and oseltamivir.
Amantadine Rimantadine Zanamivir Oseltamivir
Type of Influenza virus infection
indicated for use
Influenza A Influenza A Influenza A
Influenza B
Influenza A
Influenza B
Administration oral oral oral inhalation oral
Ages approved for treatmentof flu 1 year 14 year 7 years 18 years
Ages approved for prevention
of flu
1 year 1 year not approved not approved
PREVENTION OF INFLUENZA
The only proven method for preventing influenza is a yearly vaccination approximately 2
weeks before the “flu season” begins.
Since the influenza virus is subject to genetic mutations with the HA and NA proteins, new
vaccines that consist of different influenza strains need to be developed each year.
Vaccine is trivalent, meaning that it provides resistance to three strains of influenza viruses.
The vaccine consists of2 influenza A virus pathogens and 1 influenza B pathogen.
• Since influenza vaccines will not control epidemics, they are recommended only in
certain select population groups – e.g. in industry, to reduce absenteeism and in
public services, to prevent disruption of critical public services such as the police,
fire protection, transport and medical care.
• Moreover, certain groups e.g. the elderly and individuals in any age group who have a

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known underlying chronic or debilitating disease are selectively immunized because
of the high risk of severe complications including death.
INFLUENZA VACCINES
KILLED VACCINES
Most influenza vaccination programs make use of inactivated vaccines.
Subcutaneous route. A single inoculation (0.5ml) is usually given. However, in persons with
no previous immunological experience two doses of the vaccine, separated by an interval of
three to four weeks are considered necessary to induce satisfactory antibody levels
• The protective value of the vaccine varies between 70 to 90 per cent and immunity
lasts for only three to six months. Re–vaccination on an annual basis is
recommended.
• The killed vaccine can produce fever, local inflammation at the site of injection, and
very rarely Guillain–Barre syndrome (an ascending paralysis).
• Since the vaccine strains are grown in eggs, persons allergic to eggs may develop
the symptoms and signs of hypersensitivity.
LIVE ATTENUATED VACCINES
Live attenuated vaccines based on temperature–sensitive (ts) mutants have been
extensively used in the USSR. They may be administered as “Nose drops” into the
respiratory tract.
They stimulate local as well as systemic immunity. The frequent antigenic mutations of the
influenza virus present difficulties in the production of effective vaccines particularly live
vaccines.
NEWER VACCINES
“Split–virus Vaccine”
It is also known as the sub–virion vaccine. It is a highly purified vaccine, producing fewer
side effects than the “Whole virus” vaccine. Due to its lower antigenicity, it requires several
injections instead of a single one. It is recommended for children.
NEURAMINIDASE–SPECIFIC VACCINE
It is a sub–unit vaccine containing only the N antigen, which induces antibodies only to the
neuraminidase antigen of the prevailing influenza virus.
The antibody to neuraminidase reduces both the amount of virus replicating in the
respiratorytract and the ability to transmit virus to contacts.