Origin of the H1N1 Virus

Infectious Disease Epidemiology SectionOffice of Public Health

Louisiana Department of Health and Hospitalswww.infectiousdisease.dhh.louisiana.gov

Disclosure

I have no financial interests or other relationship with manufacturers of commercial products, suppliers of

commercial services, or commercial supporters. My

presentation will not include any discussion of the unlabeled use of

a product or a product under investigational use.

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Novel Influenza A Infections

Human infections with influenza A virus subtypes that are different from the currently circulating human subtypes (A/H1 and A/H3)

Human infections with Novel influenza A viruses transmissible from person to person may signal the beginning of an influenza pandemic

Swine influenza virus infection in humans is a novel influenza A virus infection 3

What We Expected…What Happened

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Reporting Requirements

Goal of novel influenza reporting: to facilitate prompt investigation and accelerate the implementation of effective public health responses

June, 2007 - CSTE added novel influenza A infections to the National Notifiable Diseases Surveillance System (NNDSS)

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Increased Diagnostic Capability at Public Health Labs

New Reporting Requirements

Identification of Human Swine Influenza Infections

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Summary of Recent Novel Influenza A Virus Infection Reports

Human Triple Reassortant Swine Influenza Infections N=12

Occurred: 12/2005 – 1/2009Median Age: 12 years, range 1-49

yearsSymptoms: Mild ILI to critically illIncubation Period: 2-4 days, range 1-10

daysExposure: 5 direct exposure to

pigs 6 indirect exposure 1 unknown

Symptomatic Pigs: 8 yes, 1 no, 3 unknownFully Investigated: 8 cases

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A Pig (Virus) of a Different Color

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Summary of Events Between April 15-17, 2009

2 cases of febrile respiratory illness Residents of adjacent counties in southern

California Swine Influenza A (H1N1) virus

Both viruses are genetically closely related to each other Resistant to amantadine and rimantadine Contain a unique combination of gene

segments previously not recognized among swine or human influenza viruses in the United States

Neither child had contact with pigs10

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TimelineApril 15 1st novel H1N1 in the US confirmed by CDC

April 17 2nd case confirmed

April 22 CDC EOC activated

April 26

U.S. government declared a public health emergency

June 3 All 50 states were reporting cases of novel H1N1

June 11 WHO declared a pandemic

July 8WHO reports three H1N1 viruses in Denmark, Japan and China are resistant to Tamiflu

Sept 19 19,161 Hospitalizations, 936 Deaths

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Transmission

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Transmission Person to person Respiratory droplets

5 virions sufficient to cause infection if aerosol reaches lower respiratory tract

Airborne transmission Acheson 1952: factory outbreak in Arkansas – risk

of transmission not related to proximity Moser 1979: airline outbreak in Alaska – 72% of

passengers that sat in plane 4 hours without ventilation became infected

Animal models Large droplets on oropharynx (500) Contact, fomites

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Droplet/Airborne Transmission

A droplet of

Will fall in

100 µm 10 seconds

40 µm 1 minute

20 µm 4 minutes

10 µm 20 minutes

5-10 µm 30-45 minutes

Droplets above 10 µm are trapped in the nose and usually do not make it to the bronchi 16

Influenza Transmission

Cough 1 good cough produces 465

DN After 30 minutes 228 DN

(49%)Speech

Count from 1 to 100 1764 DN After 30 minutes 106 DN

(6%)

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Cough & Artificially Generated Aerosols

Artificial aerosols differ from natural aerosols generated by coughing: Mean artificial aerosols <5-6µ, with

<10% >8µ Natural coughing produces >99.9%

particles >8µTherefore, natural coughing may

produce particles of the correct size to remain suspended in air, but most particles are too large and fall to the ground (Branktson, 2007)

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NOT Another Mode of Transmission

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NOT Another Mode of Transmission

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Transmissibility Period

Incubation

1-5 days

Disease3-8 days

TRANSMISSIBLE Does Shedding =

Infectious???Asymptomatic cases ???

Infectious Period• 1 day before symptom

onset• Peak shedding 1st day of

symptoms• Adults shed 4-6 days• Infants and children may

shed longer• Immunocompromised

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Duration of Viral Shedding

3 days 4 days 5 days > 7 days0

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Leekha S.,2007. Duration of Influenza A Virus Shedding in Hospitalized Patients and Implications for Infection Control 22

Prevention

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Influenza Surveillance – Louisiana Week 0916 (April 19 – April 25)

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Influenza Surveillance – Louisiana Week 0920 (May 17 – May 23)

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Summary of Events

Conference call with CDC on April 23 7 cases : 5 in California, 2 in Texas Human-to-human spread All cases have resolved

Enhanced surveillance: Sentinel Providers Specimens collected on all ILI Daily ILI reports

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Epidemic Curve

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Geographical Distribution

12 Clusters involving 82 casesCluster size ranged from 3 to 23 cases

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Epidemic Curve 2008-2009 2009-2010

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Number of Cases

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Data Summary* 2,396 confirmed cases Real case count near 292,000 Distribution of cases by gender is

similar to the population distribution by gender

68 % of outpatient cases in the 5-24 year age group

62% of inpatient cases between 5-49 years of age

71% of cases had typical influenza-like illness

736 Hospitalizations 53 deaths

*as of April 17, 2010 33

Special Data CollectionPediatric MortalityPregnancyHemorrhagic PneumonitisHospitalization Case SeriesDeath Case SeriesVaccine FailuresRepeat InfectionsTamiflu Resistance

*as of April 17, 2010 34

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