Influenza

V.Biaukula

Influenza Virus Subtypes

• Influenza A• Influenza B• Influenza C

Annual Epidemics

Pandemic

Structure of influenza virus

Two surface antigens

HA (hemagglutinin)

NA (neuraminidase)

Why influenza epidemics every year?

• ‘Antigenic drift’ - Minor changes in

surface antigen

- No protection from previous immunity

Subtypes of Influenza A

Virus

(Karl G Nicholson, et al Lancet 2003; 362: 1733-45)

• Many subtypes (H and N)• 3 subtypes have caused

human epidemics• H1N1• H2N2• H3N2

H1

H2

H3

H4

H5

H6H7

H8

H9H10

H12

H13H14

H15

H11

N1

N2N3

N4

N5

N6

N7N8

N9

Avian Influenza (H5N1)• 1st seen in 1997• History of contact to dead/sick poultry• Highly pathogenic (Case Fatality Rate 60%)• Most cases seen in children and adults

<40yrs, most deaths in 10-19 yr old.

Avian Influenza (Bird flu)Year Cases Deaths

2003 4 42004 46 322005 98 432006 115 792007 88 592008 44 332009 73 322010 31 13Total 500 295

Influenza Pandemics

Influenza Pandemics cause high morbidity & mortality

A(H1N1) A(H2N2) A(H3N2)

1918 1957“Hong Kong Flu”

20 - 40 m deaths 1 - 4 m deaths 1 - 4 m deaths

Credit: US National Museum of Health and Medicine

“Spanish Flu” “Asian Flu”1968

INFLUENZA PANDEMIC in the PACIFIC ISLAND HISTORY - 1918

Some Pacific Islands amongst the worst affected:1/3 to ½ of the pop. affected & ¼ died in some PICTs Samoa (22% pop. Killed -7542 deaths),

Fiji (5% ~9000), Tonga (6%), Nauru (6%) French Polynesia: Tahiti (25%) Guam (5%)Others were totally spared: American Samoa (strict maritime quarantine) Kiribati, Tuvalu, Solomon Islands & Vanuatu (Australian

quarantine policy for outgoing steamships exclusively servicing these islands)

• 1st wave generally mild• Historically 2nd wave associated with

greater morbidity and mortality.• Pandemics occur when a novel virus

infects a community

Pandemic H1N1

• As of 12 July lab confirmed cases in 214 WHO member states; 18337 deaths

• World wide pandemic activity is low.

Nasophaeyngeal swab to confirm influenza

• Must be collected within 3 days of onset of symptoms

• Must have fever with cough or sore throat.

Critical issues for Infection control

• Avoid crowding patients together, promote distance between patients

• Protect mucosa of mouth and nose

• Perform hand hygiene

Standard precautions

• Hand hygiene• Respiratory hygiene/cough etiquette• Avoid touching your face

Environmental cleaning

• Environmental surfaces to be kept clean; wipe with Sodium hypochlorite 1% (Janola). Also hydrogen peroxide, chlorine, detergents, iodine based antiseptics and alcohols.

• Influenza can survive on environmental surfaces:2-8hours

Pandemic (H1N1) 2009

Clinical management

Influenza Like Illness (ILI)

•Sudden onset of fever (38ºC or higher, if no thermometer available, reported chills or high temperature)

•At leas one of the following symptoms: cough, sore throat, runny nose, nasal congestion; in the absence of alternative diagnosis.

Severe Acute Respiratory Illness (SARI)

• Meets ILI case definition AND• Shortness of breath or difficulty breathing AND• Requiring hospital admission.

High risk group for severe disease

• 3rd trimester pregnancy, under 2yrs, 65+ yrs, diabetics, long term steroid therapy, chronic lung and heart disease, hematological disorder.

• Neurological disorders can increase risk of severe disease in children.

• Large proportion of severe & fatal cases: obese & morbidly obese, ye obesity hasn’t been recognized as a risk factor.

• Majority have uncomplicated ILI, recovery within a week, even with no medical Rx.

• Severe cases deteriorate about day 3 to 5• Rapid deterioration, many progress to

respiratory failure within 24 hours – require IMMEDIATE ICU admission.

Treatment

• Oseltamivir (Tamiflu): used in cases with high risk of severe disease

• Rx must be started early to reduce disease severity & improve survival chances, even without confirmatory test.

• Paracetamol, Vit. C, Increase fluid intake

Vaccination

• Most effective preventive tool• May prove less effective if virus evolves

rapidly, and virus may get around growing immunity in the population.

Must remain alert

• Second wave may or may not occur• Pandemic continues, virus may evolve

without it being possible to predict when.

References

• http://www.cdc.gov/flu/avian/outbreaks/current.htm

• http://www.who.int/csr/don/2010_07_16/en/index.html