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Influenza pandemic: FluWorkLoss: Software to estimate work days lost
Martin I. Meltzer, Ph.D. Senior Health Economist & Distinguished Consultant Division of Emerging infections and Surveillance Services NCDPCID Centers for Disease Control and Prevention (CDC) Atlanta, GA, USA.
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Influenza epidemiology
Who gets sick? How many get sick? What happens to them (how sick)? When do they get sick?
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Predominant type/subtype
U.S.: Variations by Year in Influenza-Related Respiratory and Circulatory Deaths Estimated annual deaths Predominant type/subtype Year Ave. no. deaths/year H1N1 4,692 40,457 B 16,036 H3N2+ B 24,562 H3N2 52,148 Source: Thompson, et al. JAMA 2003; 289:
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U.S. Influenza-related Respiratory and Circulatory Deaths: By age
Age group (years) Average ‘flu deaths < 1 26 1-4 66 5-49 789 50-64 2,626 65+ 32,651 Average total 36,155 Annual totals vary from 17,056 – 51,296 Source: Thompson, et al. JAMA 2003; 289:
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Source: Meltzer et al. Vaccine 2005;23:1004-1014
Variability: Distribution of risk of hospitalization due to ‘flu: 6-23 mths, (non-high risk) Actual data: Median 194/100,000 Frequency -600 -400 -200 200 600 400 800 1000 1200 1400 Rate of hospitalization/ 100,000 Source: Meltzer et al. Vaccine 2005;23:
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Hospitalizations/ 1,000 for 6–23 months: Non-high and high risk groups
Source: Meltzer et al. Vaccine 2005;23:
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Influenza-related Hospitalizations per 100,000 Persons*
Age Group Non-high Risk High Risk 0 - 4 100 500 5 - 14 20 200 65+ N/A 200 - >1000 *(Barker, Am J Epi, 1980; Glezen, Am Rev Resp Dis, 1987; Can J Infect Dis, 1993)
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Some conclusions: Impact varies
By year, sometimes greatly (range: +/ - 50%) By age (2- 5 times or more) By risk: high risk vs. non-high risk (2 – 10 times) SO: When evaluating potential impact: Must allow for variations – even pandemics
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Pandemic influenza When will the next pandemic occur?
How many deaths, hospitalizations, outpatients, and ill, self care? Economic and other impacts Implications for policy
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When will the next ‘flu pandemic occur?
Time between start of pandemics Years between start of pandemics 52 49 68 10 39 1918 1898 1957 1830 1781 1968 1729 Not a pandemic Source: Adapted from: Potter CW. J Applied Microbiol. 2001;91:
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When will the next ‘flu pandemic occur?
Influenza pandemics occur every 10 – 68 years Last pandemic (’68) was 37 years ago No change in conditions (perhaps “worse”)? Not “if” – but “when” = inevitable When do YOU think the next pandemic will occur? The clock is ticking
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How many might die? (Global estimates of death)
1969 mortality 0.7 million 1968 extrapolated 2 to 7.4 million 1918 mortality 40 – 100 million WHO range 7 to 100 million H5N1 rate extrapolated 1 billion Source: Davis, M. “The monster at our door.” New York, NY: New Press, Table 9.1
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Estimated impact in U.S. of next influenza pandemic: 2 scenarios (30% AR)
Characteristic Moderate 1958/68-like Severe (1918-like) Illness 90 million Outpatient medical care 45 million Hospitalization 865,000 9.9 million ICU care 128,750 1.485 million Mechanical ventilation 64,875 742,500 Deaths 209,000 1.9 million Source: U.S. Dept Health and Human Services Pandemic Influenza Plan: Part 1. Page 18. Available at:
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What is missing from these estimates?
Any precise explanation of how estimates were calculated Probabilities of occurrence
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20th Century Influenza 1918 “Spanish Flu” 1957 “Asian Flu”
Approx. 675,000 deaths (U.S.), young adults affected million worldwide 1957 “Asian Flu” 69,800 deaths (U.S.), mostly elderly & chronically ill 1968 “Hong Kong Flu” 33,800 deaths (U.S.), mostly elderly and chronically ill Interpandemic Flu (U.S.) 36,000 deaths 223,000 hospitalizations
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Source: Meltzer et al. Emerg Infect Dis, 1999, 5:659-671
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Pandemic Planning Tools at CDC
FluAid Estimates total deaths, hospitals and outpatients FluSurge Surge in demand for hospital resources duration of pandemic FluWorkLoss Work days lost due to worker illness or care of ill family members Instructions to calculate 1968 and 1918 scenarios Access:
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FluWorkLoss: Calculate days lost
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FluWorkLoss
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Data Input: Work days lost caring for sick family member
Work days lost are assumptions – little or no data to support Do numerous sensitivity analyses Source: FluWorkloss
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Data Input: Work days lost due to employee illness
Work days lost are assumptions – little or no data to support Do numerous sensitivity analyses Source: FluWorkloss
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Data Input: employment and cohabitation rates
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Data Input: Duration and gross clinical attack rate
Source: FluWorkloss
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Results: 1960/70s scenario: Proportion of lost workdays:
8 week outbreak, 25% attack rate 8% 7% Max 6% Most likely 5% Proportion of lost workdays 4% Min 3% 2% 1% 1 8 15 22 29 36 43 50 Days of outbreak Source: calculated using FluWorkLoss
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What FluWorkLoss does not do
Measure potential impact of other factors (e.g., school closings) Identify exactly who will get ill Smaller the community/ firm, larger the variability Impacts measured from “large communities”
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Calculating 1968 and 1918-type pandemics: Instructions
Basic instructions and template of draft report Document in Word Use FluAid and FluSurge Produce 1968-type and 1918-type estimates Available at:
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Software for estimating impact
Resource:FluAid 2.0 Software for estimating impact (click on FluAid) Goal: State-level estimates of impact suitable for planning Goal: Easy to use - interactive Goal: Can run different scenarios
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FluAid 2.0: Example of data entry: Can use default values or alter
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Examples of FluAid 2.0 output
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Illustrating surge in demand for hospital-based resources
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Locale Y: Results: Hospitalizations by week: two scenarios: 25% AR
10,000 20,000 30,000 1 2 3 4 5 6 7 8 1,000 2,000 3,000 1 2 3 4 5 6 7 8 1918-type scenario 1960s/70s scenario Maximum Most Minimum Weeks of pandemic Weeks of pandemic Source: Generated using FluSurge
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Locale Y: Results: Hospitalizations by week: 1960s/70s scenario
Pandemic Influenza Impact Weeks 1 5 8 Hospital Capacity # patients in hospital 566 1,873 854 % hospital capacity* 7% 24% 11% ICU Capacity # of patients in ICU 98 831 637 % of ICU capacity 35% 300% 230% Ventilator Capacity # patients ventilators 49 416 318 % ventilator use 297% 227% * Percent of all beds: actual beds available will differ
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Conclusions Estimates are illustrative Wide range of potential impacts
Not absolute predictions Value: Aid in planning Wide range of potential impacts Plans must be flexible
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