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Origin of the H1N1 Virus

Infectious Disease Epidemiology Section Office of Public Health Louisiana Department of Health and Hospitals www.infectiousdisease.dhh.louisiana.gov. Origin of the H1N1 Virus. Disclosure .

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Origin of the H1N1 Virus

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  1. Infectious Disease Epidemiology Section Office of Public Health Louisiana Department of Health and Hospitals www.infectiousdisease.dhh.louisiana.gov Origin of the H1N1 Virus

  2. 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.

  3. 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

  4. What We Expected…What Happened

  5. 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)

  6. Increased Diagnostic Capability at Public Health Labs New Reporting Requirements Identification of Human Swine Influenza Infections

  7. Summary of Recent Novel Influenza A Virus Infection Reports Human Triple Reassortant Swine Influenza Infections N=12 Occurred: 12/2005 – 1/2009 Median Age: 12 years, range 1-49 years Symptoms: Mild ILI to critically ill Incubation Period: 2-4 days, range 1-10 days Exposure: 5 direct exposure to pigs 6 indirect exposure 1 unknown Symptomatic Pigs: 8 yes, 1 no, 3 unknown Fully Investigated: 8 cases

  8. A Pig (Virus) of a Different Color

  9. 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 pigs

  10. Timeline

  11. Transmission Respiratory Droplets Contact, fomites ??? Airborne Transmission ???

  12. 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

  13. Droplet/Airborne Transmission Droplets above 10 µm are trapped in the nose and usually do not make it to the bronchi

  14. 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%)

  15. 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 >8µ • Therefore, 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)

  16. NOT Another Mode of Transmission

  17. NOT Another Mode of Transmission

  18. Transmissibility Period Incubation 1-5 days Disease 3-8 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

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

  20. Prevention

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

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

  23. 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

  24. Epidemic Curve

  25. Geographical Distribution 12 Clusters involving 82 cases Cluster size ranged from 3 to 23 cases

  26. 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

  27. Special Data Collection • Pediatric Mortality • Pregnancy • Hemorrhagic Pneumonitis • Hospitalization Case Series • Death Case Series • Vaccine Failures • Repeat Infections • Tamiflu Resistance *as of April 17, 2010

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