MMWR Morb Mortal Wkly Rep. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

[Giuseppe]

Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007 (MMWR Morb Mortal Wkly Rep., edited)


[Source: Centers for Disease Control and Prevention, MMWR Morbidity and Mortality Weekly Report, full text (LINK). Edited.]

Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

Weekly

August 27, 2010 / 59(33);1057-1062

Influenza infections are associated with thousands of deaths every year in the United States, with the majority of deaths from seasonal influenza occurring among adults aged ≥65 years (1--4). For several decades, CDC has made annual estimates of influenza-associated deaths, which have been used in influenza research and to develop influenza control and prevention policy. To update previously published estimates of the numbers and rates of influenza-associated deaths during 1976--2003 by adding four influenza seasons through 2006--07, CDC used statistical models with data from death certificate reports. National mortality data for two categories of underlying cause of death codes, pneumonia and influenza causes and respiratory and circulatory causes, were used in regression models to estimate lower and upper bounds for the number of influenza-associated deaths. Estimates by seasonal influenza virus type and subtype were examined to determine any association between virus type and subtype and the number of deaths in a season. This report summarizes the results of these analyses, which found that, during 1976--2007, estimates of annual influenza-associated deaths from respiratory and circulatory causes (including pneumonia and influenza causes) ranged from 3,349 in 1986--87 to 48,614 in 2003--04. The annual rate of influenza-associated death in the United States overall during this period ranged from 1.4 to 16.7 deaths per 100,000 persons. The findings also indicated the wide variation in the estimated number of deaths from season to season was closely related to the particular influenza virus types and subtypes in circulation.


The current study extends estimates of influenza-associated deaths from two previous CDC studies (2,3) by adding data from four more influenza seasons for a total of 31 influenza seasons (1976--2007). Estimates are provided for three age groups (<19 years, 19--64 years, and ≥65 years) and for two categories of underlying cause of death codes: 1) pneumonia and influenza causes and 2) respiratory and circulatory causes. Deaths from pneumonia and influenza causes are highly correlated with the circulation of influenza (1) and can be considered a lower bound for deaths associated with influenza (2,4). However, a diagnosis of influenza virus infection often is not confirmed with sensitive and specific laboratory diagnostics, particularly among older persons, and even when identified is rarely recorded on death certificates (5). Many deaths associated with influenza infections occur from secondary infections such as bacterial pneumonia or complications of chronic conditions such as congestive heart failure and chronic obstructive pulmonary disease (6). Therefore, estimates using underlying respiratory and circulatory mortality data (which include pneumonia and influenza causes) can provide an upper bound for influenza-associated deaths (2,7).

Using methods published previously (2,3), CDC estimated the numbers and rates of influenza-associated deaths by virus type and subtype by using Poisson regression models that incorporated weekly national respiratory viral surveillance data. Weekly influenza test results by virus type and subtype were provided by approximately 80 World Health Organization (WHO) and 70 National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories in the United States (8). Prominent influenza type and subtype were defined as at least 20% of all isolates that were tested in that season. Mortality data were obtained from the National Vital Statistics System and reflect the underlying cause of death recorded on death certificates (9). Deaths were categorized using the International Classification of Diseases eighth revision (ICD-8), ninth revision (ICD-9), or 10th revision (ICD-10), as appropriate. Weekly estimates of the U.S. population by age group were used as part of the model to correspond to the weekly viral surveillance estimates. All data for deaths with underlying pneumonia and influenza causes and respiratory and circulatory causes were actual counts based on the death certificate ICD codes. To estimate the proportion of deaths that were influenza associated, the average annual number of deaths estimated by the model was divided by the average annual counts of death with underlying pneumonia and influenza causes and respiratory and circulatory causes.

For deaths with underlying pneumonia and influenza causes during 1976--2007 in the United States, the models estimated an annual overall average of 6,309 (range: 961 in 1986--87 to 14,715 in 2003--04) influenza-associated deaths (Table 1). For these underlying causes, the average annual rate of influenza-associated death was 2.4 deaths per 100,000 (range: 0.4--5.1).

Among persons aged <19 years, an estimated annual average of 97 (range: 41 in 1981--82 to 234 in 1977--78) influenza-associated deaths with underlying pneumonia and influenza causes occurred (Table 1). The average annual rate of influenza-associated deaths for this age group was 0.1 deaths per 100,000 persons (range: 0.1--0.3). Among adults aged 19--64 years, an estimated annual average of 666 (range: 173 in 1981--82 to 1,459 in 2004--05) influenza-associated deaths with underlying pneumonia and influenza causes occurred. The average annual rate of influenza-associated deaths for this age group was 0.4 deaths per 100,000 persons (range: 0.1--0.8). Among adults aged ≥65 years, an estimated annual average of 5,546 (range: 673 in 1978--79 to 13,245 in 2003--04) influenza-associated deaths with underlying pneumonia and influenza causes occurred. The average annual rate of influenza-associated deaths for this age group was 17.0 deaths per 100,000 (range: 2.4--36.7). Deaths among persons aged ≥65 years accounted for 87.9% of the overall estimated average annual influenza-associated deaths with underlying pneumonia and influenza causes.

For deaths with underlying respiratory and circulatory causes (including pneumonia and influenza causes) during 1976--2007, the models estimated an annual U.S. average overall of 23,607 (range: 3,349 in 1986--87 to 48,614 in 2003--04) influenza-associated deaths (Table 2). For these underlying causes, the average annual rate of influenza-associated death was 9.0 deaths per 100,000 (range: 1.4--16.7).

Among persons aged <19 years, an estimated annual average of 124 (range: 57 in 1981--82 to 197 in 1977--78) influenza-associated deaths with underlying respiratory and circulatory causes occurred (Table 2). The average annual rate of influenza-associated deaths for this age group was 0.2 deaths per 100,000 persons (range: 0.1--0.3). Among adults aged 19--64 years, an estimated annual average of 2,385 (range: 504 in 1981--82 to 4,752 in 2003--04) influenza-associated deaths with underlying respiratory and circulatory causes occurred. The average annual rate of influenza-associated deaths for this age group was 1.5 deaths per 100,000 persons (range: 0.4--3.1). Among adults aged ≥65 years, an estimated annual average of 21,098 (range: 2,344 in 1986--87 to 43,727 in 2003--04) influenza-associated deaths with underlying respiratory and circulatory causes occurred. The average annual rate of influenza-associated deaths for this age group was 66.1 deaths per 100,000 (range: 8.0--121.1). Deaths among persons aged ≥65 years accounted for 89.4% of the overall estimated average annual influenza-associated deaths with underlying respiratory and circulatory causes.

For both causes, the average mortality rates for the 22 seasons during which influenza A(H3N2) was a prominent strain were 2.7 times higher than for the nine seasons that it was not. The average annual number of influenza-associated deaths during influenza A(H3N2) prominent seasons was 7,722 for pneumonia and influenza causes and 28,909 for respiratory and circulatory causes, compared with 2,856 deaths for pneumonia and influenza causes and 10,648 deaths for respiratory and circulatory causes in seasons in which it was not.

The distribution of mortality across age groups was similar for the two groups of coded deaths. For pneumonia and influenza causes, the proportions of average deaths overall were 1.5%, 10.6%, and 87.9% for persons aged <19 years, 19--64 years, and ≥65 years, respectively. For respiratory and circulatory causes, the proportions were 0.5%, 10.1%, and 89.4%.

Based on an average annual count of 74,363 for all pneumonia and influenza deaths, and an average annual estimate of 6,309 deaths associated with influenza in this category, 8.5% of all pneumonia and influenza deaths were influenza associated. Based on an annual average count of 1,132,319 for all respiratory and circulatory deaths and an average annual estimate of 23,607 deaths associated with influenza in this category, 2.1% of all respiratory and circulatory deaths were influenza associated.


Reported by

MG Thompson, PhD, DK Shay, MD, H Zhou, MSc, MPH, CB Bridges, MD, PY Cheng, PhD, E Burns, MA, JS Bresee, MD, NJ Cox, PhD, Influenza Div, National Center for Immunization and Respiratory Diseases, CDC.


Editorial Note

This report updates estimates of the number of influenza-associated deaths from the 1976--77 through 2006--07 influenza seasons and demonstrates the substantial variability in mortality estimates by year, influenza virus type/subtype, and age group. The estimated rates of influenza-associated hospitalizations and deaths vary substantially from one influenza season to the next, depending, in part, on the characteristics of the circulating influenza virus strains (10). Because of this variability, a single estimate cannot be used to summarize influenza-associated deaths. This report provides estimates for two categories of underlying cause of death codes, pneumonia and influenza causes and respiratory and circulatory causes; if only one category is used to summarize the mortality effects of influenza, the respiratory and circulatory data likely provide the most accurate estimates. During the past three decades, the estimated number of annual influenza- associated deaths from respiratory and circulatory causes ranged from a low of 3,349 to a high of 48,614 deaths.

A previous study (2) presented an average annual estimate of 25,420 influenza-associated respiratory and circulatory deaths during a 23-season period; this study estimated an average of 23,607 annual influenza-associated deaths using the same model but over a 31-year period. The findings in this report are similar to those of previous CDC studies (2,3) and other cross-decade studies that used similar models (4,7).

When describing the severity of seasonal influenza epidemics, examining seasons with the same circulating influenza virus type is useful. For example, during seasons with prominent circulation of influenza A(H3N2) viruses, 2.7 times more deaths occurred than during seasons when A(H3N2) viruses were not prominent. An annual estimate of 36,155 influenza-associated respiratory and circulatory deaths often is quoted from an earlier CDC study (2); however, that average was calculated for the period 1990--1999, when more severe influenza A(H3N2) viruses were prominent for eight of the nine seasons.

Variations in influenza-associated mortality by age group also should be noted. As reported in this and other studies (2,3), approximately 90% of influenza-associated deaths occur among adults aged ≥65 years. An estimated annual average of 124 persons aged <19 years and 2,385 aged 19--64 years die from influenza-associated respiratory or circulatory causes. Future research that considers years-of-life-lost is needed to better communicate the mortality burden of influenza in these younger populations. Future research also is needed to estimate and communicate the risk for influenza-associated mortality among different demographic and health risk groups.

The findings in this report are subject to at least four limitations. First, the models do not account for cocirculating pathogens such as respiratory syncytial virus (RSV). Future research should replicate and extend models that distinguish between deaths associated with influenza versus RSV (2). Second, estimates over time might not be comparable because the influenza virus surveillance data used to model mortality rely on national influenza testing practices, which have changed over the past decade (8). Future research should consider how trends in testing practices can be included in these models and cross-season estimates of influenza-associated mortality. Third, increases in the U.S. population aged ≥65 years during the study period could have contributed to a general increase in influenza-associated mortality. Age-adjusting future estimates or estimating deaths in smaller age categories among older adults could address this issue. Finally, because the estimates made in this report rely on national death certificate data and these data currently are available only through 2007, preliminary estimates of 2009 influenza A(H1N1)-associated deaths are not directly comparable with these results.(*)

Debate will continue regarding the most appropriate statistical models and cause of death categories to use in estimating the number of influenza-associated deaths (1,7). This study's provision of estimates for more narrow (pneumonia and influenza causes) and more broad (respiratory and circulatory causes) categories continues the strategy of comparing and contrasting results from different models as advocated by CDC (1--3) and others (7).

Influenza infections are associated with substantial medical costs, hospitalizations, lost productivity, and thousands of deaths every year in the United States. Annual influenza vaccination is the best way to reduce the risk for complications from influenza infections and is now recommended for all persons aged ≥6 months in the United States. Prompt treatment with influenza antiviral medications can reduce the risk for severe illness and death among persons at increased risk for influenza or who are hospitalized with suspected or confirmed influenza.


References

1. Thompson WW, Moore MR, Weintraub E, et al. Estimating influenza-associated deaths in the United States. Am J Pub Health 2009;99:S225--30.
2. Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 2003;289:179--86.
3. Thompson WW, Weintraub E, Dhankhar P, et al. Estimates of US influenza-associated deaths made using four different methods. Influenza Other Respi Viruses 2009;3:37--49.
4. Simonsen L, Reichert TA, Viboud C, Blackwelder WC, Taylor RJ, Miller MA. Impact of influenza vaccination on seasonal mortality in the US elderly population. Arch Intern Med 2005;165:265--72.
5. Wiselka M. Influenza: diagnosis, management, and prophylaxis. BMJ 1994;308:1341--5.
6. Schanzer DL, Langley JM, Tam TW. Co-morbidities associated with influenza-attributed mortality, 1994--2000, Canada. Vaccine 2008;26:4697--703.
7. Newall AT, Viboud C, Wood JG. Influenza-attributable mortality in Australians aged more than 50 years: a comparison of different modelling approaches. Epidemiol Infect 2010;138:836--42.
8. Brammer L, Budd A, Cox N. Seasonal and pandemic influenza surveillance considerations for constructing multicomponent systems. Influenza Other Respi Viruses 2009:3,51--8.
9. CDC. Mortality data, multiple cause detail, 1972--2007. Public use data tapes contents and documentation package. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2007.
10. Russell CA, Jones TC, Barr IG, et al. Influenza vaccine strain selection and recent studies on the global migration of seasonal influenza viruses. Vaccine 2008;26(Suppl 4)31--4.

(*) CDC estimates of 2009 H1N1 deaths are available at (LINK).


What is already known on this topic?
Influenza infections result in substantial medical costs, hospitalizations, lost productivity, and thousands of deaths every year in the United States with the majority of deaths from seasonal influenza occurring among adults aged ≥65 years.

What is added by this report?
During 1976--2007, annual estimates of influenza-associated deaths from respiratory and circulatory causes ranged from 3,349 (in 1986--87) to 48,614 (in 2003--04), and the annual rate of influenza-associated death for all ages ranged from 1.4 to 16.7 deaths per 100,000 persons; during seasons when influenza A(H3N2) circulating strains were prominent, 2.7 times more deaths occurred compared with seasons when A(H3N2) was not prominent.

What are the implications for public health practice?
A single estimate should not be used to summarize influenza-associated deaths; a range of estimates should be described in the context of circulating virus strains and underlying causes of death among age groups. Annual influenza vaccination (now recommended for all persons aged ≥6 months) is the best way to avoid influenza complications, and prompt treatment with antiviral medications can reduce the risk for severe illness and death among persons at increased risk for influenza or who are hospitalized with influenza.

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[Ronan Kelly]

Re: MMWR Morb Mortal Wkly Rep. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

Press Briefing Transcript
CDC Media Availability, Estimates of Deaths Associated with Seasonal Influenza — United States, 1976–2007
Thursday, August 26, 2010 – 12:00pm ET

•Audio recording (MP3, 4.55MB)http://www.cdc.gov/media/transcripts/2010/audio/0826.mp3
Operator: Welcome and thank you all for standing by. At this time, I will remind parties that your line is in a listen-only mode until the question-and-answer session, at which time you may press star 1 to ask a question. I will now turn the meeting over to Tom Skinner. You may begin.

Tom Skinner: Thank you, Rose, and thank you all for joining us today for this media availability with Dr. David Shay, s-h-a-y, who's a medical officer in CDC's Influenza Division. Dr. Shay is going to open up with a brief statement regarding an article that's published in today's Morbidity and Mortality Weekly Report on estimates of death associated with seasonal influenza. He'll provide an opening statement and then we will open it up for question-and-answer. Dr. Shay.

David Shay: Thank you. And good morning. I'm here today to share some updated information from my team here at CDC about influenza. As you all know, influenza has a significant health burden every year in the United States. It's associated with thousands of deaths, up to 200,000 hospitalizations annually and hundreds of thousands of illnesses that require doctors visits and missed days of school or work. But this report is only going to focus on influenza deaths. As you also know, quantifying the burden of influenza, particularly death, is challenging.

To get at the burden of influenza, we have to rely on statistical models, because many folks who die of influenza aren't ever tested for it or they die of subsequent complications of an initial influenza infection, like worsening heart disease or bacterial pneumonia. So, we look at death certificates here at CDC that go into at least two categories, pneumonia and influenza and respiratory and circulatory causes, and we use, again, a statistical modeling approach to estimate how many of those deaths might be influenza associated. I think it's important to keep in context, which we don't really describe in this article because of space, that there's at least four factors that affect sort of flu mortality in any particular year, and those four would be the specific strain or influenza strains that are in circulation, sort of the length of the season or how long influenza is circulating in the united states, how many people get sick, because of course, the more people get sick, there is more likely to be more serious outcomes, and finally, who gets sick.

The influenza epidemic in a particular year is hitting younger or older people differentially, because as we know, most influenza deaths, a majority, 90% occur in people aged 65 and older. So, what the report being issued in today's MMWR has done is really just update previous estimates last made in 2009 using the same methodology, incorporating an additional four years of data. So, this is an update that confirms really what we have seen previously in terms of flu. The updated estimates encompass data from 31 seasons from 1976, '77 influenza season to the 2006-'07 influenza season, which is the last date we have death certificate data that we can look at. And that range is from about 3,000 deaths in the 1986-'87 season to a maximum, if you will, of about 49,000 deaths that we saw in the 2003-'04 season. So, our major point today really is just to, again, point out the incredible variability of influenza seasons. Influenza's pretty unique in terms of vaccine-preventible diseases and sort of the wide range of outcomes that could happen in a particular season. So, that's the opening statement and we'd be happy to answer questions.

Tom Skinner: Rose, we'll take questions now, please.

Operator: Thank you. At this time, if you would like to ask a question, please press star 1 on your touch-tone phone. Press star 1 if you would like to ask a question. One moment for our first question. Our first question is from Daniel DeNoon from WebMD. Your line is open.

Dan DeNoon: Thanks for taking my question. Dr. Shay, I'm confused by the two different ways of getting numbers. I understand that the lower-bound number – well, can you talk about them, rather than me telling you what I understand, can you explain what the difference is between the lower and upper-bound number is? And I see there is a caution here that we can't use just one number, but of course, just one number is what people want, so can you help me understand what number we should be using when talking about the average flu deaths in a season and when we look at an upcoming flu season and what do we tell people?

David Shay: Thank you. That is an excellent question or excellent set of questions there. We have two categories that we look at, as you said. One is death certificates that have an underlying diagnosis of pneumonia or influenza. 99% of those deaths are actually coded as pneumonia. So, that's to make an estimate of deaths in a particular season from pneumonia that are associated with flu. And typically, that's about 8.5% of deaths over the time period that we looked at. Now, we know that influenza causes more deaths than those just associated with pneumonia. However, that metric or that outcome measure has been used in literature for over four decades. So, that's one thing that we always look at so we have an idea how things are going over time. The broader category of respiratory and circulatory deaths we think encompasses the full picture of influenza-associated deaths, including things such as people who might die because of worsening chronic obstructive pulmonary disease or worsening congestive heart failure that results in death after an infection. And we estimate that about 2% of that broader category in any typical year is associated with influenza. And your second question is what is the one number we want you to use. We understand that that is a difficult communications message. I think, from my perspective is that because we have this very wide range of deaths, from 3,000 to 49,000 in this three-decade time period that we looked at, it's relatively meaningless to say what happens in an average season, because when you look at sort of our data, there are very few of those 31 seasons where you would have an average outcome. So, I think that's one of the reasons that CDC is trying to move towards away from a single number, and rather, give a range over a particular period of time to give a better time text to what flu really means in terms of what it does to the community. And finally, we can't predict what's going to happen in any subsequent influenza season. I mean, that's – you can just look at the numbers and how they vary from season to season to come to that conclusion very rapidly.

Tom Skinner: Okay. Next question, Rose?

Operator: Thank you. The next is from Betsy McKay, Wall Street Journal, your line is open.

Betsy McKay: Hi, Dr. Shay and Tom. Thanks. I didn't hear all of Dan's question, so I hope I'm not asking the same exact question again. But you know, very often, we get this number, this estimate of 36,000 deaths annually from flu. So, I'm wondering if you can just walk us through what that number constitutes, and does this new range replace it? Also, you did give an annual U.S. average overall of deaths from underlying respiratory circulatory causes of 23,607. So, is that an average number we can use and does that compare to the 36,000?

David Shay: Thanks. Excellent question. The 36,000 number that's often used pertains to a very specific time period from 1990 to 1999. And in that decade, where we had prominent circulation of H3N2 viruses, they were prominent in eight of the nine seasons that are contained within the data that were used to make that estimate, and those are, as you know, typically more severe seasons. We had a high mortality for that nine-year period, 36,000. In that paper from which that 36,000 number came from, the overall mortality average for that time period was about 25,000. So, this average that we're coming up with now, 23,600, is consistent with what we've published in the past. And again, our feeling is that it's very difficult to summarize flu with, as we gain more and more data, with a simple average. There are very few average seasons, you know. We have one in the '86 to '87 season there was only about 3,000 deaths, and then we have another one, you know, several years later that's about 50,000, almost 50,000 deaths. So, a simple average, I think, fails to give the impact of flu in an understandable fashion. We could give a standard deviation or some other metric of the variants in our measures, but I don't think that that would be helpful to the public, so that's why we have decided to try to focus more on the range rather than on simple average. Does that answer your question?

Betsy McKay: I mean, your advice would be that instead of saying the flu kills an estimated 36,000 people a year, which is what I and others often do say, that we should say, you know, flu kills between 3,000 and 49,000 – or 3,300 and 49,000 people a year or has over the past, you know, in seasons over the past 30 years?

Tom Skinner: Betsy, this is Tom, and I don't – Dr. Shay will correct me if I'm wrong, but as you report that range, I think it's important to note that there is such a wide range and it depends on the various types of flu that are circulating. So, I think that going a step further and saying that that range is due the fact that the number depends on, you know, the strains that may circulate would help explain it a little bit more.

Tom Skinner: Agreed. Next question, Rose?

Operator: The next is from Julie Steenhuysen from Reuters. Your line is open.

Julie Steenhuysen: Thank you. Yes, I'm just wondering if you can sort of, you know, looking forward, explain the role of better diagnostics, better methods of tracking and what impact that might have? I mean, it looks like, you know, it may be, you know, even this range that you've given us is going to change quite a bit. Is that right? And you know, what are these numbers – how can these numbers be meaningful for us?

David Shay: Well, let me start with your last question first, because I could use some clarification on that. What do you mean by how could the numbers be meaningful to you?

Julie Steenhuysen: Well, it's just in terms of comparing year to year. I mean, we want to be able to give a number that, you know, is a good reflection of what people can expect in a flu season. You know, I'm just wondering if you can sort of – I think we're all sort of struggling with how do we describe flu deaths, because it looks like it's a moving target almost.

David Shay: Absolutely. No, that's absolutely correct. Flu deaths are a moving target. Again, for vaccine-preventible diseases, there isn't another one that sort of has this range of variability, certainly, and mortality each season, so that's one of the important messages we want to get out, if you will. I think another important point to make is that the numbers confirm that influenza has a substantial burden on mortality each year, but that that mortality really can be quite variable. And then, finally, around the question of better diagnostics, that's an excellent one. For an example, since 2004, pediatric influenza-associated deaths have been a nationally notifiable disease in the united states. That's the only category of deaths or the only age group for which flu deaths are nationally notifiable. And as a result of probably better diagnostics and more, better surveillance, we have seen over the first few years of that system an increase in the number of reports that was probably due to a combination of better diagnostics and people looking for flu more actively in younger children who were critically ill.

Tom Skinner: Next question, Rose?

Operator: Thank you. The next is from Lisa Schnirring with CIDRAP News. Your line is open.

Lisa Schnirring: Hi. Thanks so much for your availability today. I was wondering if, when you looked at the numbers and your different modeling with this year's analysis, if you saw anything interesting to you or different that popped out when you looked at the age, demographics and all of those issues?

David Shay: No, not really. The numbers are very consistent. I mean, again, flu was associated in this time period, as in other time periods and in other seasonal studies that have been done in other developed countries with approximately 90% of the deaths being in those 65 years of age and older. One of the things I do think, though, that we're going to do in the future to put these numbers, perhaps, into better context is to also not only report numbers of deaths but report years of life lost. Because, of course, an influenza-associated death in an 80-year-old has less impact on society and less impact on parents than an influenza-associated death in a 2-year-old. So, that's sort of future work that we're going to plan on doing.

Lisa Schnirring: An 80-year-old. You said an 8-year-old.

David Shay: 80-year-old, I'm sorry. It would have less impact on society in the death of an 80-year-old compared to a 2-year-old.

Tom Skinner: All right. Next question, Rose?

Operator: Thank you. The next is from Tom Maugh from Los Angeles Times, your line is open.

Tom Maugh: Two quick questions. First, is this the first time you've really broken down deaths by the strain of the flu virus? And second, how long do you have to go into a flu season before you recognize which is the predominant strain that's circulating?

David Shay: Two great questions. No, this is not the first time that we've done that. Painter that we published in the Journal of the American Medical Association in 2003 was first time we really broke deaths out by strain. And second is, that's a great question, sort of how many weeks into the season will we know which is the predominant or the dominant strain? And again, unfortunately, the answer is that depends. In some seasons, for example, H3N2 will start off big and will be the predominant strain throughout a particular season. In other seasons, we've seen, particularly recent seasons, 2006-'07 where we have some influenza, H1N1, some H3N2, and some b, and most of the b at the end of the season. So, it would have been very difficult to say, except at the end of the season, sort of what proportion of each of the three strains was responsible for illness.

Tom Skinner: Next question, Rose.

Operator: Thank you. The next is from Sabrina Rice from CNN. Your line is open.

Sabrina Rice: Thank you for taking our questions. For what you were just talking about, the differences between the influenza strains, the report says that the, I guess deaths from influenza were 2.7 times higher for the H3N2. I guess, what's the difference between that one and some of the other strains that are out there? And do we know which is out this season that, should people be more concerned or less concerned? And I actually have two questions. And the second part is, with the numbers varying so widely from 3,000 to 49,000, that might freak people out, because you just have no idea. So, what advice would you give to consumers?

David Shay: Well, I think it comes back to one of our messages that we frequently give, that flu really is unpredictable. And it's important to point out, at the beginning of the season, don't know what the impact of flu is going to be in a particular season. In terms of H3N2, what is it about the H3N2 virus, viruses, that causes more severe disease than, for example, H1N1 or b viruses? One of the factors may be that that virus has a tendency to genetically change more quickly than the other two viruses. So, it changes more rapidly, and therefore, even if you've been sick with it in the past, you're more likely, if it changes quicker to get a subsequent influenza infection. So that may be one of the factors that's involved, but we don't understand all of them.

Tom Skinner: Next question, Rose?

Operator: Thank you. The next is from Don Sapatkin from the Philadelphia Inquirer, your line is open.

Don Sapatkin: Hi. Thanks for taking my question. I'm still completely confused. I hope you'll bear with me. My understanding of what you're saying, you're trying to make, I think, essentially two points. One is that the range of numbers is important from year to year, much more important than an average, and you're also changing your estimates based on additional seasons. And so, one question I have is, the old 36,000 number was always based on a range. It wasn't often reported, but I believe the range was 17,000 to 52,000. That what was in the 2003 paper. So, is that essentially equivalent to the new range of 3,300 to 48,000? That's my first question.

David Shay: Let me recap your points. I mean, I think your first point was that because of the variability of flu, we're trying to move away from an average and into giving a range of flu-associated mortality, and that's correct. And your second point is, yes, for that time period of 1990 through 1999, the range of deaths there was what you just said, from approximately 17,000 to 50,000, with an average of 36,000 in that time period. But again, that was a rather of an outlier of a decade, if you will, because of the predominant circulation of H3N2 viruses. So, in that 2003 paper, we actually looked at quite a few seasons of data ended in 1999, which is essentially '76 through '99. That had a broad range of estimates as well, not quite as broad as the range that we're reporting this time, but there was a broad range of flu mortality over the data that were included in that study as well. Does that help?

Don Sapatkin: Sort of. But then where I get lost is when you're talking about 23,000 versus 25,000. In the old study, where did one of those – what was one of those numbers? I'm trying to figure out – I know you don't want us to use a range, but I'm trying –

David Shay: I do want you to use a range –

Don Sapatkin: I mean, average. But what does the 25,000 equate to in the study, even though you don't want us to use it? I'm trying to understand it.

David Shay: That what from – I may not be understanding your question, so I'm sorry about that. That was from 1990 to 1999. That 2003 paper actually looked at a broader range of seasons, from '76 through 1999. So, from that whole time period, the average was approximately 23,000-25,000 deaths, excuse me. And for this time period, this broader 31-season time period that we're looking at, the average is approximately 23,600. So, they're very similar.

Tom Skinner: Okay, Rose, we've got time for a few more questions.

Operator: Thank you. The next is from Joe Neel from NPR. Your line is open.

Joe Neel: Hi. Well, I also – I'm really scratching my head here wondering what I'm going to use, because we really don't have a lot of time in broadcast to present a lot of numbers, and I think in a sense to say that the range is 3,000 or 3,300 to 49,000 raises a lot of questions, and I think we don't have time to answer those questions in every report. And I also wonder if it's not a bit misleading to use 3,300 as the bottom number since it's been 20 years since it was that low, and even in the last 20 years, the mortality has never been much below 12,000. So, I'm wondering, if you can help me out here, could I possibly just use the average of 23,000, which covers respiratory and circulatory causes? I mean, wouldn't that be a fair number to use in a very condensed broadcast format?

Tom Skinner: Joe, this is Tom Skinner, and I – we certainly appreciate your desire to have one single number for an average, and we fully recognize how difficult it is on you all. I think at the end of the day, if you must use a single number, I would simply say that it's estimated that tens of thousands of people may die each year in an average flu season, and then leave it at that.

David Shay: I would say that – yeah, I would get away from average flu season, because that's one of the points I think we're trying to make, but I agree with Tom, we'd say in many years, influenza is associated with tens of thousands of deaths a year.

Tom Skinner: Yeah.

David Shay: I think that would be a very fair and a very quick way to summarize the data.

Tom Skinner: Yeah. Joe, is that fair?

Joe Neel: Well, I think that – yeah, I mean, I think some people might turn to these data and look at this table and say, kills up to 48,000 a year, which is certainly accurate, but I also think that –

David Shay: True.

Joe Neel: – that can also be misleading, because in 2006 they only had 15,000, so –

Tom Skinner: Correct. You know, again, Joe, I'd go back to what I said to Betsy McKay earlier in this call, is that whatever number you use, if you also include the caveat that the number depends on the strain, strains of influenza that may be predominating, that is a little bit – you know, that's a little bit more information to help put your number into context.

David Shay: And – this is David again. I would also add that when you do cite an average that you – I know time is precious, but give the seasons that that average pertains to. Because again, as you just pointed out, it can vary so dramatically from time period to time period.

Joe Neel: Yeah.

Tom Skinner: Next question, Rose?

Operator: Thank you. The next is from Cathy Clark from Radio Pennsylvania State Network. Your line is open.

Cathy Clark: Thank you very much for taking my question. Is it fair to say, then, that if one of the strains expected to circulate in a certain year is the H3N2, that that given flu season has a potential to be a deadlier flu season?

David Shay: We can't predict. It gets back to – to begin with, we can't predict even, you know, two weeks into the flu season what's the predominant strain is going to be. It is very fair to say that on average, H3N2 seasons are much more severe than h1 and b seasons. And again, 2.7 times more deaths associated with in this 31-year period when there was predominant or prominent—prominent is a better word—prominent circulation of H3N2. And that's another one of our key messages, again, that we're trying to – even though it's a complex message, it really depends quite a bit on the strain of influenza that's in circulation.

Tom Skinner: Last question, Rose?

Operator: The last is from Katherine Hobson from Wall Street Journal, your line is open.

Katherine Hobson: Hi, it's Katie Hobson with the Wall Street Journal health blog. On any one of the seasons, the low death rate in '86-'87 and the high one in '03-'04, was it primarily the strain that caused that? I know you mentioned those four factors, but if you give kind of a snapshot of why the death rates were so low and high respectively?

David Shay: That's an excellent question. And I can't completely answer it because we don't know many of the factors that lead to these dramatic differences. It's certainly true that the specific strain and circulation is very important and that H3N2, again, kills many more people than the other two circulating strains. It's also important, as I mentioned before, the length of the season can vary quite a bit, and a longer flu season, obviously, has potential to result in more people getting sick. And how many people get sick directly influences the number of people who get serious complications who end up in the hospital and who die. And then finally, again, it's really important to think about who's getting sick in a particular year. H3N2 viruses tend to make older people more ill. And if a lot of old people are getting ill in a particular flu season, because 90% of the deaths occur in people 65 and above, the mortality for that season is going to be much higher than a season when few elderly people become ill with flu.

Tom Skinner: Okay. Thank you, Rose. This concludes our call. Thanks to all who joined us. And the report that we're referring to today, you should have received via e-mail. It will be posted on the CDC website as well. So, thank you for joining us.

Operator: This concludes today's conference call. Thank you for joining. You may disconnect at this time.

###
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
http://www.cdc.gov/media/transcripts/2010/t100826.htm

 

[sharon sanders]

Re: MMWR Morb Mortal Wkly Rep. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

hat tip Maryn McKenna -


26 August 2010

New CDC flu numbers: This may not go well


(Constant readers: Apologies for the slow blogging. Casa Superbug's little medical crisis from a week ago has recurred, and things are a bit distracting. Back to normal soon, I hope.)

In public health, one of the numbers you hear most often — and especially so the past few years — is 36,000. That's the number of deaths that the CDC estimates occur in an average year from influenza.

Or rather, estimated. Because today, in its weekly bulletin MMWR and also in a teleconference for the press, the CDC announced that it is discarding that widely used number, in favor of newer numbers from newer studies that take into account the wide variation in illness and death from one flu season to the next.

The new estimate is: 23,607. Or, a range that goes from 3,349 to 48,614. Or, in the language recommended by a CDC scientist and a communications specialist in the press call, "tens of thousands of people [who] may die each year in an average flu season."


more....

http://www.superbugtheblog.com/2010/08/new-cdc-flu-numbers-this-may-not-go.html

 

[gsgs]

Re: MMWR Morb Mortal Wkly Rep. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5933a1.htm?s_cid=mm5933a1_w

that figure of 36000 flu-deaths was recently updated to 40000, AFAIK.
This was the estimated number of total excess deaths attributed to respiratory or circulatory diseases
that happened in a yearly period and would not have happened in that period if there had been no flu.

Average total yearly US flu-induced deaths 1990/1-1998/9 = 51203
Average yearly US flu-induced deaths in people having respiratory or circulatory cause on
their death-certificate in 1990-1999 = 36155

Now reduced by 35% for the period 1976-2007
So, ~33000 US flu-deaths per year and ~11000 RSV-deaths , standard deviation : +-10000(!) and +-700

--------------------------------------------------------------------------------------------

http://jama.ama-assn.org/cgi/content/full/289/2/179

1990/1-1998/9
Influenza was associated with annual means of 8097 underlying pneumonia and influenza deaths
36155 underlying respiratory and circulatory deaths
51203 all-cause deaths


Annual influenza-associated deaths in USA
1990/1 - 1998/9
flu,P+I: 8097
RSV,P+I:2707
flu,r+c:36155
RSV,r+c:11321
flu,total:51203
RSV,total:17358


> David Shay: Thanks. Excellent question. The 36,000 number that's often used pertains
> to a very specific time period from 1990 to 1999
> In that paper from which that 36,000 number came from, the overall mortality average
> for that time period was about 25,000.

Why did they only take 1990-1999 in the 2003 paper ? 1976-1990 was available at that time.
And why do they move away from an average to a less-informative range now ?
And why did they only take respiratory and circulatory causes and not all causes ?



there are ~120000 more yearly total deaths in winter than in summer in USA.
~2.4M total yearly deaths in USA


summary: I think 33000(+-10000) is the appropriate number here

----edit------
well, not quite. US-population did change 1976-2007 from 215M-->301M
average for the period:258M, so multiply with 1.17 to get 38500
estimated yearly flu-deaths in USA for the next years

discarding the situation with ****** and H5N1 and possible advances in
antivirals (laninamivir) and vaccines(cell-based,univeral)

there should be a betting market to predict this !
e.g. :
Total winter excess deaths reported by MMWR for the 225 cities
for weeks 44-17 minus deaths for the previous weeks 18-43
and/or
Total winter excess P+I deaths reported by MMWR for the 225 cities
for weeks 44-17 minus deaths for the previous weeks 18-43


why can't they just give that one number (38000) of estimated
predicted flu-deaths for next season instead of talking around it and
complicating and declarifying and sidetracking it

 

[gsgs]

Re: MMWR Morb Mortal Wkly Rep. Estimates of Deaths Associated with Seasonal Influenza --- United States, 1976--2007

season (April=change)
number of winter-deaths in the 225 US-cities
number of summer-deaths in the 225 US-cities
proportion of excess winter deaths
flu-deaths as calculated from Thompson/Shay (their number *51203/36155 for total deaths)
------------------------------------

 1997  330642  302147  4.50% 47235
 1998  339207  304769  5.34% 45660
 1999  335215  298850  5.73% 45217
 2000  339016  307259  4.91% 51720
 2001  334463  310661  3.68% 17061
 2002  341026  301440  6.16% 63687
 2003  326871  294012  5.29% 26830
 2004  334881  291408  6.94% 68848
 2005  326537  289361  6.03% 66724
 2006  317404  291615  4.23% 56791
 2007  304529  290026  2.43% 22055
 2008  317842  288733  4.79% ?
 2009  315064  288457  4.40% ?
----------------------------------
USA   1187304 1311599  4.96% 46530