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Update on H1N1 Activity: Insights from Montgomery County Epidemiology (March 2009)

In March 2009, Montgomery County reported two cases of febrile respiratory illness in children, with no common exposures or swine contact. Enhanced influenza surveillance led to the identification of a novel swine influenza A (H1N1) virus, detected at the CDC. This new virus exhibits unique genetic characteristics and has shown efficient person-to-person transmission. The epidemiological data reveal higher disease severity in younger age groups and emphasize the importance of monitoring high-risk populations. Understanding these trends can aid in effective public health responses to influenza outbreaks.

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Update on H1N1 Activity: Insights from Montgomery County Epidemiology (March 2009)

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  1. An update on H1N1 activity Jamaal A. Russell, MPH, MT Senior Epidemiologist Montgomery County DHHS

  2. March 2009 • 2 cases of febrile respiratory illness in children in late March • No common exposures, no pig contact • Uneventful recovery • Residents of adjacent counties in southern California • Tested because part of enhanced influenza surveillance • Reported to CDC as possible Novel influenza A virus infections • Swine influenza A (H1N1) virus detected on April 15th,17th at CDC • Both viruses genetically identical • Contain a unique combination of gene segments previously not recognized among swine or human influenza viruses in the US

  3. Epidemiology • Earliest reports • – North America • – Travelers, contacts, schools, cities with community • spread •  Efficient person-to-person transmission from start •  Some aspects very different from seasonal influenza • – High levels of summer disease activity in northern • hemisphere • – Severe and fatal disease focused in younger age • groups • – Deaths primarily associated with rapid respiratory • failure

  4. Montgomery County ESSENCE & Flu Flu Season 9/2006-4/2007 Flu Season 9/2007-4/2008 Flu Season 9/2008-4/2009 Pandemic H1N1 April 1, 2009- July 30, 2009

  5. Epidemiology/SurveillancePercentage of Visits for Influenza-like Illness (ILI) Reported by the US Outpatient Influenza-like Illness Surveillance Network (ILINet),National Summary 2008-09 and Previous Two Seasons novel 2009-H1N1 – 11 SEPT 2009

  6. Epidemiology/SurveillanceWeekly Influenza Activity Reported by SLTT’s novel 2009-H1N1 – 5 SEPT 2009

  7. Risk Factors for Severe Illness Children younger than 5 years old, and especially children younger than 2 years old Persons aged 65 years or older Pregnant women Persons with certain chronic medical or immunosuppressive conditions Persons younger than 19 years of age who are receiving long-term aspirin therapy

  8. Rate per 100,000 Population by Age Group novel 2009-H1N1 – 24 JUL 2009 (n=37,030*) n=4816 n=7434 n=2187 n=513 *Excludes 6,741 cases with missing ages. Rate / 100,000 by Single Year Age Groups: Denominator source: 2008 Census Estimates, U.S. Census Bureau at: http://www.census.gov/popest/national/asrh/files/NC-EST2007-ALLDATA-R-File24.csv

  9. Hospitalization Rate per 100,000 Population by Age Group (n=4,738*) novel 2009-H1N1 – 24 JUL 2009 *Hospitalizations with unknown ages are not included (n=273) *Rate / 100,000 by Single Year Age Groups: Denominator source: 2008 Census Estimates, U.S. Census Bureau at: http://www.census.gov/popest/national/asrh/files/NC-EST2007-ALLDATA-R-File24.csv

  10. *April 12 – June 30 Distribution by Age Group of Influenza Hospitalized Cases Emerging Infections Program - Pandemic H1N1 -14 JUL 2009

  11. Approximately 70% of persons hospitalized from 2009 H1N1 influenza have had a recognized high risk condition (~60% of children and ~ 80% adults) • Influenza-Related Pediatric Deaths MMWR – Sept. 3, 2009: • 67% percent of children who died with 2009 H1N1 influenza had a high-risk medical condition • 4 of 7 children <5 years old who died with 2009 H1N1 influenza did not have a high-risk medical condition • Among children with high-risk medical conditions, >90% had neurodevelopmental conditions • 59% had > 1 neurodevelopmental diagnoses • 41% had a pulmonary problem

  12. Montgomery County ILI activity 3/1/09-9/25/09

  13. What have we learned? • It’s here! • Younger age groups are more susceptible • Case Fatality Rate (CFR) is the same as seasonal flu • H1N1 is the predominate flu strain in the US • 67% of H1N1-related pediatric deaths had a high risk medical condition

  14. Acknowledgments • CDC- Dr. Joseph Bresee • DHMH- EDCP • Montgomery County DHHS • Disease Control • Emergency Preparedness • Immunization

  15. ?Questions?

  16. Thank you

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