It
is spread by sneezing, coughing or direct contact with the
infected person.
Children
and adults with long-term illness like asthmas and diabetes
are more prone to serious flu complications such as pneumonia,
dehydration, meningitis, and even death.
Influenza
infection is a major cause of death in the elderly.
The virus has 3 subtypes A, B, and C.
Type
A causes moderate to severe disease, affects only humans and
affects all age groups.
Type
B causes mild disease affects only humans, mostly children.
Type
C affects animals and rarely humans and is not associated
with epidemics.
The
influenza virus also mutate frequently.
Antigenic
shifts and drifts are major and minor changes in the antigens,
or parts of the virus recognized by the body's immune system.
These changes allow the virus to persist in the population
and give rise to epidemics of the flu.
Epidemics
and Pandemics
Epidemics
occur when incidence of influenza cases increase and mortality
rises.
Pandemics
occur with high incidence in all age groups and increased
mortality.
Influenza
pandemic could affect up to 200 million people with an estimated
400,000 deaths.
Sporadic
outbreaks occur when clusters of cases occur in families,
schools or small communities.
Influenza
infections
The
virus is acquired from respiratory droplets.
It
replicated in the trachea and bronchi causing local destruction
and is shed for 5-10 days.
Maximal
communicatability occurs 1-2 days before onset and 4-5 days
after.
Symptoms
appear after an incubation of 1-2 days.
Abrupt
onset of fever, muscle aches, non-productive coughs, and headaches
occur.
Severity
is less if the person has encountered a similar antigened
virus before.
Only
50% of people have the above classical symptoms of influenza.
Symptoms
last 2-3 days and rarely more than 5.
Aspirin should not be taken because of its association with
Reye's syndrome, an often-fatal affliction
Complications
of Influenza
Complications
of the flu include pneumonia (either a bacterial superinfection
on top of the influenza or an influenza pneumonia which is
rarer). Reye's syndrome is a rare complication in children
with the development of coma and brain swelling. Other complications
include myocarditis (heart inflammation), and worsening of
chronic bronchitis. Death occurs in 0.5-1 cases per 1000 cases,
usually in ages >65 years.
Diagnosing influenza can be difficult and is largely on the
clinical appearance along with its prevalence in the community.
Influenza peaks between December and March in temperate climates
but can vary. It is year long in the tropics and outbreaks
are common aboard cruise ships.
Vaccination
Vaccination is done with an inactivated virus of circulating
strains of type A and B influenza.
Egg
protein is present.
The
vaccine is effective in protecting 90% of healthy adults but
only 30-40% of the elderly.
It
is not highly effective in preventing illness but is effective
in preventing complications and death particularly in the
elderly.
The
vaccine is most effective if given 2-4 months prior to flu
exposure and is usually available in September. The vaccine
may be given annually for people older than 9 years.
Children
from 6 months to 8 years receiving it for the first time should
receive 2 doses 1 month apart.
Flu shots are recommended for all people over 50 (over 65
are covered by Manitoba Health), children >6 months with chronic
disease, long term care residents, health care workers, students,
travelers, pregnant women, and persons 6 months to 18 years
taking chronic aspirin therapy (so that they do not develop
Reye's Syndrome).
Any
person who wishes to decrease the likelihood of becoming ill
from influenza should receive the flu shot although Manitoba
Health does not cover all the above groups.
Adverse effects of the Flu Vaccine
Local reactions occur at the site if vaccination with soreness
and redness lasting 1-2 days in 15-20% of people.
Non-specific
fever and aches last 1-2 days in <1% of people.
Hives
and allergic reactions occur rarely particularly in people
allergic to eggs.
People
with egg allergies should not receive the vaccine.
At
present the flu vaccine is injected but a nasal preparation
is being developed.
For people with flu like symptoms antiviral therapy is available
with new drugs that can block viral replication and prevent
illness if started as early as possible (within 48 hrs).
Vaccination
still remains the best way of controlling the flu.
Influenza links
CDC http://www.cdc.gov/flu/
Who http://www.who.int/health_topics/influenza/en/
American Lung Association http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=22542
Vaccine Information Statements http://www.immunize.org/vis/
influenza.com http://www.influenza.com/
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