Influenza World Scenario and Epidemiology

Dr. Dharmendra Gahwai(MD-Community Medicine, DAE, DHA)

D.D. & State Epidemiologist (IDSP)Directorate of Health Services

Chhattisgarh

Seasonal Influenza

• Seasonal influenza is a major public health problem worldwide.

• Annually, it is estimated that it attacks 5-10% of adults and 20-

30% of children globally.

• Worldwide, these annual epidemics are estimated to result in

about 3 to 5 million cases of severe illness, and about 250000 to

500000 deaths.

Definition

• Influenza is a acute respiratory infection caused by virus. Three Types- A, B and C.

• characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough, sore throat and rhinitis.

Influenza Virus: 3 Types

Influenza Type A Type B Type CDisease ++ ++ -

Epidemics/Pandemics Epidemics & Pandemics

Milder epidemics No

Host Humans & other species !

Humans only Humans only

Antigenic variation Frequent Infrequent Stable

RNA virusAntigenically distinctNo cross-immunity

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Influenza: A Viral infection

• Currently viruses circulating in human population –

Influenza A (H3N2), A (H1N1) and B Strains

• All known pandemics were caused by Influenza A.

(Pandemic Influenza- H1N1)

• Avian Influenza- Bird Flu: A (H5N1).

• Influenza is truly an International Disease.

• Pandemic - 10-40 years

• Epidemic – every 2-3 years

• Sporadic outbreaks- every year

Pandemics of Influenza in 20th Century

• 1918-19 “Spanish flu” H1N1

• 1957 “Asian flu” H2N2

• 1968 “Hong Kong flu” H3N2

• 1976 “Swine flu” episode H1N1

• 1977 “Russian flu” H1N1

• 1997 “Bird flu” in HK H5N1

• 1999 “Bird flu” in HK H9N2

• 2003 “Bird flu” in Netherlands H7N7

• 2004 “Bird flu” in SE Asia H5N1

• 2009 “Swine Flu” (worldwide) H1N1

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Pandemic influenza in the 20th Century

1920 1940 1960 1980 2000

H1N1 H2N2 H3N2

1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu”

20-40 million deaths 1 million deaths 1 million deaths

World Scenario

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Influenza Antigenic Changes• Antigenic Shift

– major change, new subtype– caused by exchange of gene segments– may result in pandemic

• Example-– H2N2 virus circulated in 1957-1967– H3N2 virus appeared in 1968 and completely replaced

H2N2 virus

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• Antigenic Drift– minor change, same subtype– caused by point mutations in gene– may result in epidemic

• Example- – in 2002-2003, A/Panama/2007/99 (H3N2) virus was

dominant– A/Fujian/411/2002 (H3N2) appeared in late 2003 and

caused widespread illness in 2003-2004

Influenza Antigenic Changes

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Priority Groups/CDC Recommendations

• People 65 years of age and older

• Children 6-23 months

• Pregnant women

• Healthcare personnel who provide direct patient care

• Household contact and out-of-home caregivers of children

less than 6 months of age.

• People 2-64 years with chronic health conditions. (DM,HIV)

Seasonality Incubation period• Time from exposure to onset of symptoms• 1 to 4 days.• Peak shedding first 3 days of illness

Seasonality• In temperate zones, increases in winter months

– Driven by mutations and viral preference for cold, dry weather conditions

• In tropical zones, circulates year-round – Fall-winter and rainy season increase has been observed– More international data is needed

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Northern hemisphere

Southern hemisphere

Tropics

Influenza activity peak: November-March2,3

.

Influenza activity peak: April-September4,5

Year-round activity3,4

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1 3 5 7 9 11 13 15 40 42 44 46 48 50 52Week

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1 5 9 13 17 21 25 29 33 37 41 49Week

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Seasonal Patterns

E.g. India

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Karnataka

Andhra Pradesh

Maharashtra

Orissa

Gujarat

Rajasthan

Madhya Pradesh

Uttar Pradesh

Jharkhand

Jammu Kashmir

Punjab

Chattisgarh

Uttaranchal

Himachal Pradesh

Haryana

Bihar

New Delhi

Tamil NaduKerala

West Bengal

Sikkim

Arunachal Pradesh

Assam Nagaland

Manipur

Tripura

Mizoram

Meghalaya

• Location: Chennai (22nd Feb-22nd March 2008) Total Sample Collected : 55 Samples Total No. of Sample +ve : 23 Samples % + ve : 41.82 % +ve Influenza A :13 Samples (56.5%) Influenza B : 10 Samples (43.3%)

MONTHLY INFLUENZA ACTIVITY REPORTED BY-INDIAN SENTINEL DOCTOR’S NETWORK FEB-MAR 2008

No Report

• Location: Delhi ( Jan- Mar 2008 ) Total Sample Collected :86 samples Total No. of Sample +ve :12 Samples % +ve :14%+ve Influenza A/H1N1 : 6 Samples Influenza B : 4 Samples Not determined but +ve : 2 Samples

Source: Sentinel Doctor’s Network,March 2008

> 10 % positvity

> 40% positivity

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March- April August - October

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Influenza: Transmission

• Incubation period: 1-4 days, average 2 days.

• Transmission may start 1 or 2 days before onset of symptoms

and last for a week.

• Virus particles spread through coughing and sneezing .

• One infectious particle can generate up to 1,000 virus particles.

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Influenza transmission is by 3 ways :

1. Direct transmission into the mucous membrane of a person .2. Airborne route – that is via droplets .(0.5-5 µm diameter)3. Contaminated surfaces, handles etc…

Influenza: Transmission

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What is Pandemic Influenza?

• Pandemic influenza is a respiratory (or breathing) illness that is new to humans and can make them very sick.

• It happens about 3 times per century and spreads around the world, killing many people and making many people sick.

• Pandemic influenza also causes many serious problems in municipalities, such as problems with food, water, and electricity.

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The new virus must be efficiently transmitted from one human to another

Prerequisites for pandemic influenza

A new influenza virus emerges to which the general population has little/no immunity

The new virus must be able to replicate in humans and cause disease

Human Influenza

A public health problem each year

– Usually some immunity built up from previous exposures to the same subtype

– Infants and elderly most at risk

– Result of Antigenic Drift

Influenza Pandemics– Appear in the human

population rarely and unpredictably

– Human population lacks immunity to a new influenza A virus subtype

– All age groups, including healthy young adults, may be at increased risk for serious complications

– Result of Antigenic Shift28

Seasonal Epidemics vs. Pandemics

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What is H1N1?• A new virus that emerged in 2009 in Mexico City

and quickly spread across the globe.

• H1N1 declared a pandemic in June 2009.Initially referred to as “swine” influenza because the virus was found to contain genetic material from swine influenza A strains, as well as avian and human strains.

-A human virus, and people get it from people – not from pigs. During 2011 India reported 603 cases,275 deaths, case fatality rate=12.44%.

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Case definitions for pandemic Influenza

• Suspected case: with onset in 7 days of close contact OR within 7 days of travel to community OR residing in community with a confirm case of pandemic influenza A.

• Probable case: suspected case + positive for influenza A by immunofluorescence assay.

• Confirmed case: laboratory confirmed pandemic influenza A case by: RT-PCR,VIRUS CULTURE and FOUR FOLD RISE IN ANTIBODY TITRE.

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STARTMarch 2009

April 2009

May 2009

Pandemic H1N1 rapidly spread worldwide: May 2009

29 May *, 15,510 cases including 99 deaths reported by 53 countries

1-1011-5051–500

500-5,000

Cumulative cases

>5,000

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Pandemic influenza in the 20th Century

1920 1940 1960 1980 2000

H1N1 H2N2 H3N2

1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu”

20-40 million deaths 1 million deaths 1 million deaths

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Pandemic Phases

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WHO Pandemic Phases and Currently Circulating Novel Viruses

• H1N1– April 25, 2009: Declaration of a Public Health Emergency of International

Concern– April 28, 2009: WHO declares Phase 4– April 29, 2009: WHO declares Phase 5– June 11, 2009: WHO declares Phase 6

• H5N1– First human cases reported 1997– Increase in reports of human cases began in 2003– WHO Phase 3

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Pandemic Precautions

• If a pandemic occurs:– Avoid crowded conditions and close contact with

other people – Consider wearing respirators or other protective

equipment– Follow good hygiene measures– Practice social distancing– Quarantine ill individuals– Vaccination

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What is Avian Influenza (Bird Flu)?• It is a disease that spreads from bird to bird, causing

some birds to become very sick or die.

• It can spread from birds to humans, but not easily.

• It is not yet capable of spreading from human to human except in very rare cases.

• There is a risk that it could become pandemic influenza, but this has not happened yet with the type of bird flu that has recently killed so many chickens.

– Direct and close contact with sick or dead poultry.• Visiting a live poultry market.

– No evidence of sustained person-to-person spread.

– Limited probable person-to-person spread.37

Human H5N1 Epidemiology

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Pathogenicity • High pathogenicity avian influenza (HPAI)

– Causes severe disease in poultry– Contains subtypes H5 or H7

• Low pathogenicity avian influenza (LPAI)– Causes mild disease in poultry– Contains other H subtypes

• Includes non-HPAI H5 and H7.

• LPAI H5 or H7 subtypes can mutate into HPAI.

Worldwide H5N1 Outbreak in Humans: 2003 - 2007

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Avian Influenza (outbreaks)

• In 2003, the avian influenza virus strain H7N7 occurred in poultry farms in the Netherlands, spreading to Germany and Belgium. Infection, mainly conjunctivitis occurred in 83 humans with 1 death. The outbreak was controlled by destroying over 30 million domestic poultry.In 2003, the avian influenza virus, H9N2 was identified in a child in Hong Kong with influenza who recovered.

• 2011- 62 cases in cambodia,indonesia,china,bangladesh.

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