Tuesday, June 26, 2012

Lancet: Estimating Global 2009 Pandemic Mortality

 

 

# 6505

 

 

Sounding a bit like a broken record, during the first 12 months of the 2009 pandemic I wrote repeatedly on our inability to accurate count – or even estimate – the number of H1N1 flu deaths in the United States and around the globe.

 

Just a few of those posts include:

 

Dead Reckoning
The Tip Of The Iceberg
When No Number Is Right
Apples, Oranges, And Influenza Death Tolls

 

The CFR, or case fatality ratio is generally seen as the most important statistic in any pandemic, and yet it is often the hardest to quantify. This number is the percentage of people who, once infected, die (either directly or indirectly) as a result of that infection.

 

While that may seem a simple enough task , the truth is that even during a `normal’ flu season the CDC can only estimate the number of deaths in the United States related to influenza.

 

The problem is, influenza can provoke or exacerbate many other medical problems. Influenza can obviously lead to pneumonia and death, but it has also been linked to heart attacks, strokes (CVAs), and other potentially fatal health crises.

   

Most of the time, the attending doctor signs the death certificate and puts down the most immediate or obvious cause of death.  If influenza was a factor, it rarely is noticed or noted.

 

The official numbers we get from the CDC, the World Health Organization, and from individual countries are almost always referred to as `the tip of the iceberg’, or as in the graphic below, the tip of the pyramid.

 

surveillance

 

And this is the best we can do in developed countries, where the majority of people have at least some access to medical care and where governments make an attempt to maintain public health records and death registries.

 

For much of the rest of the world, these are luxuries that are too often unavailable.

 

As an example, in November of 2009, in Zhong Nanshan On China’s Death Toll, one of the real heroes of the 2003 SARS epidemic, openly questioned the low number of deaths being reported out of China.

 

The truth is, in many countries, no one was counting the dead. 

 

In South Africa, where nearly 1,000 AIDS/HIV deaths occur each day, no one was looking to see if flu was a factor.  No one had the time, and it simply wasn’t in the budget.  

 

The `official’ death toll, as reported by the World Health Organization was roughly 18,000 deaths globally,  but the WHO offered this disclaimer:

 

The reported number of fatal cases is an under representation of the actual numbers as many deaths are never tested or recognized as influenza related.World Health Organization.

 

Unfortunately, the mainstream media often reported the low official number of deaths without adequately explaining the acknowledged gaps in the data, leading many to believe that the 2009 pandemic was a damp squib.

 

The CDC stopped counting H1N1 influenza deaths in the summer of 2009, realizing that their official tally was more misleading that helpful.

 

In November of that year, they released their first estimate of the number of U.S. pandemic flu infections, hospitalizations, and deaths (see  CDC Releases Revised Hospitalization & Death Estimates), where they estimated that between about 2,500 and 6,000 2009 H1N1-related deaths occurred between April and October 17, 2009.

 

Two months later (see CDC Updates Estimates Of Infections, Hospitalizations, and Deaths From H1N1) the the CDC updated their estimates to carry through to the 12th of December. Their mid-range estimates were of 55 million infections and 11,160 deaths in the US from H1N1 since April of 2009.

 

Today, a study appears in The Lancet that attempts to estimate the number of global H1N1 deaths during the first year of the pandemic, and it comes up with a number than runs between 15 and 30 times higher than reported to the WHO.

Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study

Dr Fatimah S Dawood MD , A Danielle Iuliano PhD, Carrie Reed DSc , Martin I Meltzer PhD , David K Shay MD, Po-Yung Cheng PhD, Don Bandaranayake MBBS , Robert F Breiman MD , W Abdullah Brooks MD , Philippe Buchy MD , Daniel R Feikin MD, Karen B Fowler DrPH , Aubree Gordon PhD , Nguyen Tran Hien MD , Peter Horby MBBSl, Q Sue Huang PhD , Mark A Katz MD , Anand Krishnan MBBS , Renu Lal PhD , Joel M Montgomery PhD , Kåre Mølbak MDo, Richard Pebody MBBS, Anne M Presanis PhD , Hugo Razuri MD , Anneke Steens MSc , Yeny O Tinoco DVM , Jacco Wallinga PhD , Hongjie Yu MDr, Sirenda Vong MD , Joseph Bresee MD , Dr Marc-Alain Widdowson VetMB

Findings

We estimate that globally there were 201 200 respiratory deaths (range 105 700—395 600) with an additional 83 300 cardiovascular deaths (46 000—179 900) associated with 2009 pandemic influenza A H1N1. 80% of the respiratory and cardiovascular deaths were in people younger than 65 years and 59% occurred in southeast Asia and Africa.

 

While most of this report is behind a pay wall, the CDC - which co-authored the study -  has posted a summary on their website.

 

CDC Releases First Global Estimates of 2009 H1N1 Pandemic Mortality

Photo: transparent globe representing the scope of the global estimates used in the CDC study of 2009 H1N1 pandemic mortality.

June 25, 2012 -- A study published today in The Lancet Infectious Diseases Online FirstExternal Web Site Icon provides the first global estimates of how many people died as a result of the 2009 H1N1 influenza pandemic. The study, co-authored by 9 members of the CDC Influenza Division, used an improved modeling approach which resulted in an estimated range of deaths from between 151,700 and 575,400 people who perished worldwide from 2009 H1N1 virus infection during the first year the virus circulated. A disproportionate number of deaths occurred in Southeast Asia and Africa, where access to prevention and treatment resources are more likely to be limited. Study authors hope that this work can be used not only to improve how influenza deaths are estimated, but also to improve the public health response during future pandemics in parts of the world that suffer more influenza-related deaths.

 

These global estimates are more than 15 times higher than the number of laboratory-confirmed deaths reported to the World Health Organization (WHO). WHO has acknowledged for some time that official, lab-confirmed reports are an underestimate of actual number of influenza deaths. Diagnostic specimens are not always collected from people who die with influenza; for others, influenza virus may not be detectable by the time of death. Because of these challenges, modeling is used to estimate the actual burden of disease.

<SNIP>

2009 H1N1 Pandemic Hits the Young Especially Hard

This study estimated that 80% of 2009 H1N1 deaths were in people younger than 65 years of age which differs from typical seasonal influenza epidemics during which 80-90% of deaths are estimated to occur in people 65 years of age and older. To illustrate the impact of the shift in the age distribution of influenza deaths to younger age groups during the pandemic, researchers calculated the number of years of life lost due to 2009 H1N1-associated deaths. They estimated that 3 times as many years of life were lost during the first year of 2009 H1N1 virus circulation than would have occurred for the same number of deaths during a typical influenza season.

(Continue . . . )

 

 

This age shift to younger victims was frequently noted during the pandemic, and in the spring of 2010 a study appeared that found that the mean age of death from the novel H1N1 virus has been calculated to be half that of seasonal flu, or 37.4 years.

 

In terms of years of life lost (YLL), the average pandemic flu death had a many fold greater impact than the average seasonal flu fatality – often robbing decades of potential life from its victims.

 

Preliminary Estimates of Mortality and Years of Life Lost Associated with the 2009 A/H1N1 Pandemic in the US and Comparison with Past Influenza Seasons

By Cecile Viboud, Mark Miller, Don Olson, Michael Osterholm et al (5 authors)

 

 

All of which makes the impact of the 2009 pandemic – in real terms – greater than most people realize.


Today’s new estimate is unlikely to be the last word on this subject. As more data is analyzed and new mathematical models are developed, better estimates will be generated.

 

We’ll never know the true number, of course.  Some things are not directly measureable. But having more accurate estimates can go a long ways towards helping us plan for the next pandemic.

 

And as most researchers acknowledge: that isn’t a matter of `if’, it’s just a matter of `when’.

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