2009 H1N1: Overview of a Pandemic

Impact of 2009 H1N1

Global Impact

• More than 214 countries and overseas territories or communities had reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 18,449 deaths (World Health Organization, August 6, 2010)
• Reported cases and deaths are likely a substantial under-estimate of true impact of 2009 H1N1
• Estimating the true number of individual flu cases and deaths is very challenging
  • Many people with flu don’t seek medical care
  • Only a small number of those that do seek care are tested
  • More people who are hospitalized or die of flu-related causes are tested and reported, but under-reporting of hospitalizations and deaths occurs as well

Impact of 2009 H1N1 Flu

Domestic Impact

 
http://www.cdc.gov/h1n1flu/estimates_2009_h1n1.htm

Characteristics of 2009 H1N1 Influenza
April 15, 2009 to April 10, 2010

Groups at Increased Risk of Severe Influenza (2009 H1N1)

• Most impacted populations
  • Children, young adults
  • Persons with underlying chronic medical conditions (e.g. chronic lung disease, heart disease, immunosuppression, neurological and neurodevelopment diseases)
  • Pregnant women
  • Indigenous populations
• Possible risk groups
  • Obesity (Body Mass Index ≥35), Extreme/Morbid obesity (Body Mass Index ≥40)

2009 H1N1 Hospitalizations Frequency of Underlying Conditions in Adults EIP April 15, 2009 – February 16, 2010 (n=4,987)

Underlying conditions among hospitalized patients and those who died from H1N1 compared to the general population

*Excludes hypertension

** Morbid obesity is defined as BMI of 40 or higher. For Hospitalized H1N1 patients, BMI calculation was performed on non-pregnant adults ≥ 20 years (n=119). 45% of 119 non-pregnant hospitalized adults ≥ 20 years were missing height and weight information. For Novel H1N1 Deaths, morbid obesity % was calculated for adults only. Prevalence for US non-pregnant adults is based on NHANES (JAMA. 2006;295(13):1577)

Source O Morgan, et al.

Obesity: a New Risk Factor for Severe Illness due to 2009 H1N1

• Disproportionate number of obese, particularly morbidly obese, among severely ill during 2009 H1N1 pandemic
• Morbid obesity (BMI≥40) was associated with hospitalization, and possibly death, due to 2009 H1N1 infection among adults without chronic medical conditions
• Additional studies with larger sample of patients and appropriate comparison groups are needed

Morgan OW, Bramley A, et al. (2010)

PLoS ONE 5(3): e9694. doi:10.1371/journal.pone.0009694

Age-adjusted and Season-specific 2009 H1N1 Influenza-related Hospitalization Rates (per 100,000) by race & ethnicity – Emerging Infections Program, 2009-10

2009 H1N1 Cumulative Lab-Confirmed Death Rate, by Age Group – April 2009 through March 27, 2010