Influenza

INFLUENZA
Jaime A. Santos

Saturday, May 29, 2010

Influenza

• commonly called “the
flu”
• a contagious respiratory
illness caused by
influenza viruses
• Infection with influenza
viruses can result in
illness ranging from mild
to severe with life-
threatening
complications


1918 Spanish flu pandemic: 20 to 50 million people may have died worldwide


Viral Titers Peak Early


“Flu” symptoms

Fever/ chills
Headache
Nasal congestion
Sore throat
Dry cough
Myalgia/ body aches
GI symptoms
Malaise/ tiredness


Influenza - Clinical Signs and Symptoms

• incubation period for influenza is 1--4 days,
with an average of 2 days
• Adults - infectious from the day before
symptoms begin through approximately 5 days
after onset
• Children - infectious for > 10 days, and young
children can shed virus for < 6 days before
their illness onset
• immunocompromised persons can shed virus
for weeks or months



• resolves after a limited number of days for
the majority of persons, although cough
and malaise can persist for >2 weeks
• young children can have initial symptoms
mimicking bacterial sepsis with high fevers
– < 20% of children hospitalized with
influenza can have febrile seizures



• Influenza infection has also been associated with
encephalopathy
transverse myelitis
Reye syndrome
myositis
myocarditis
pericarditis


Influenza - Hospitalization and Deaths
• Population at risk for complications,
hospitalizations, & deaths:> 65 years old
– young children
– persons of any age with certain
underlying health conditions:
cardiovascular and pulmonary
(including asthma), metabolic e.g. DM,
Hgbpathies, immunosuppression
– receiving long term ASA


“U” Shaped Epidemic Curve of Influenza During the
Interpandemic Period

Visits/100
ARD Hospitalizations/10,000
P&I Mortality/100,000

Rate

Age group


“U” Shaped Epidemic Curve of Influenza During the
Interpandemic Period

120 Visits/100
ARD Hospitalizations/10,000
P&I Mortality/100,000
100

80
Rate 60

40

20

0
<5 5–9 10–14 15-19 20-24 25-34 35-44 45-54 55-64 > 64

Age group


Influenza Responsible for
Substantial Disease
Deaths
36,0001
Hospitalizations
114,0002

Physician visits
25 million3

Infections and illnesses
50–60 million3
Direct medical costs
$1-$3 billion4
1. Thompson WW et al. JAMA. 2003;289:179-186.
2. CDC. MMWR Recomm Rep. 2003;58(RR-8):1-34.
3. Couch RB. Ann Intern Med. 2000;133:992-998.
4. Patriarca PA. JAMA. 1999;282:75-77.


Seasonal

• In colder countries flu
is largely seen during
colder months and
they vaccinate prior
to this season (e.g.
October)
• In tropical countries
flu is seen all year
round


Flu Season in the Philippines
Southern Hemisphere Pattern
Cumulative Data: RITM Influenza Surveillance Data Feb. 1998 – Oct. 2004

B
A


Flu Season in the Philippines
Southern Hemisphere Pattern
Cumulative Data: RITM Influenza Surveillance Data Feb. 1998 – Oct. 2004

80

70

60

50
B
A

40

30

20

10

0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec


Influenza virus types

• Three : Influenza A, B, and C
• Influenza types A or B viruses cause
epidemics; influenza A may cause
pandemics
• Getting a flu shot can prevent illness from
types A and B influenza but not from type C
• Influenza type C causes mild respiratory
illness ; not thought to cause epidemics


Influenza Virus: Segmented genome


Influenza A virus divided into subtypes based on HA and N
proteins on surface

• 15 HA, 9 N
• Nomenclature based
on: site of origin
isolate number
year of isolation
subtype
Example:
influenzaA/
Johannesburg/33/94
(H3N2)


Drift or shift

• “Antigenic drift" - small changes in
the virus that happen continually
(influenza A and B)
• “Antigenic shift” - abrupt, major
change in the influenza A viruses,
resulting in new H &/or new H and
N proteins that infect humans
(influenza A only)


Influenza subtypes in humans

• current subtypes of influenza A viruses
found in people are A(H1N1) and A(H3N2)
• Influenza B virus is not divided into
subtypes
• Influenza A(H1N1), A(H3N2), and influenza
B strains are included in each year's
influenza vaccine
• Protection is serotype specific


Domestic pig:
Domestic poultry
Mixing vessel

Migratory water birds


Avian Influenza
• Caused by 15 subtypes of
influenza A virus subtype
of avian influenza
• Low pathogenicity avian
influenza (LPAI)
• Highly pathogenic avian
influenza (HPAI)
– First recognized in Italy in
1878
– Extremely contagious in
birds
– Rapidly fatal, high
mortality (almost 100%
in a few days)


Avian Influenza Infections in Humans
Confirmed instances of avian influenza viruses infecting humans since 1997

• 1997: Hong Kong, avian influenza A (H5N1)
• 1999: Hong Kong, avian influenza A(H9N2)
• 2003: 2 cases of avian influenza A (H5N1)
• 2003:H9N2 infection was confirmed in a child
in Hong Kong
• 2003: Avian influenza A (H7N7) infections
among poultry workers / families in the
Netherlands (> 80 cases )


Characteristics of Avian Influenza Infections in
Humans
• reported symptoms of avian influenza :
typical influenza-like symptoms (e.g.,
fever, cough, sore throat and muscle aches)
to eye infections, pneumonia, acute
respiratory distress, viral pneumonia, and
other severe and life-threatening
complications
• It is believed that most cases of H5N1
infection in humans have resulted from
contact with infected poultry or
contaminated surfaces
CDC


Current Avian Flu (H5N1) Strain

– genetically sequenced: all bird origin
– antiviral resistance to amantadine and
rimantadine
– oseltamavir and zanamivir should still be
effective


Avian Influenza (Bird Flu) Outbreak
Why H5N1 is of particular concern

• H5N1 mutates and acquires genes rapidly from
other species
• Documented to cause severe disease in humans
• avian influenza virus could change so that it could
infect humans and could spread easily from
person to person
• no immune protection against them in the human
population
• If an avian virus were able to infect people and
gain the ability to spread easily from person to
person, an “influenza pandemic” could begin


FLU PANDEMICS: THEN AND NOW

1918 Year 2005
WHAT HAPPENED WHAT COULD HAPPEN

1.8 billion World Population 7 billion

Troop ships, Primary mode of
transportation Jets
railroad

Time for virus to circle
4 months the globe 4 days

Gauze masks, Preventive measures Vaccines
disinfectants

Bed rest, Treatments Some antiviral drugs
aspirin

20+ million Estimated dead 60 million?
Janet Englund, MD
PIDSP Feb. 2005


Treatment of Influenza
• Antiviral Medications:
– antiviral drugs:
adamantanes: amantadine,
rimantadine
neuraminidase inhibitors: zanamivir,
oseltamivir

– Antiviral treatment lasts for 3-5
days and must be started within the
first 2 days of illness.


Antiviral treatment and prophylaxis

• amantadine [4.4-8.8 mg/kg/day, not to
exceed 150 mg/day] can be given for 3-5
days; for treatment of influenza A
• oseltamivir [2 mg/kg/dose BID] can be
given for 5 days for treatment of influenza
A and B.
Its use for treatment and prophylaxis of
household contacts has been effective for
children > 12 years old


Do I Need A
Flu Shot?


Target Groups For Vaccination

1. Those with increased risk of complications:
• Persons age 50 yrs old and above
• Children from 6 to 23 months old
• Adults and children with the following risk
factors:
– Chronic cardiovascular disease (e.g. congestive
heart failure, Hypertensive cardiovascular
disease, valvular heart disease, rheumatic
heart disease, stroke)
– Chronic lung disease (e.g COPD, asthma,
bronchiectasis, malignancies, chronic PTB)


• Chronic metabolic disease (diabetes mellitus)
• Chronic renal dysfunction
• Hemoglobinopathies
• Immunosuppressed (e.g.HIV, malignancies,
immunosuppressive drugs, radiation therapy,
transplant patients)
• Children and adolescents who are receiving long-
term aspirin therapy
• Residents of nursing homes and other chronic
care facilities
• Pregnant women on their 2nd or 3rd trimester
who have not received their flu vaccine within the
last 12 months.


Target Groups For Vaccination

2. Those who can transmit the disease to others

• Health care workers and other personnel
of out patient care settings, hospitals, nursing
homes, and chronic care facilities.
• Household contacts (including children) and
caregivers of person at high risk.


When Should You Give the Flu Shot?
Highlights Influenza Consensus – Flu TWG Oct. 2004

• Data from the five-year epidemiologic data
(February 1998 – September 2003) shows
increased influenza activity June to November.
• Vaccination should be given once a year
preferrably from February to June
• The Southern Hemisphere vaccine which is made
available starting February of each year is
recommended to cover the expected increase in
influenza activity from June to November.


Vaccine dosage by age group
Age Dose No. doses Route

6 – 35 mos 0.25 ml 1 or 2* IM

3 – 8 yrs 0.5 ml 1 or 2* IM

= or > 9 0.5 ml 1 IM
yrs

* 2 if receiving vaccine for 1st time, 1 month apart


Thank You!

38


Influenza

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