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A General Discussion of Human H5N1 Cases in 2009
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H5N1 was widely expected to the first pandemic virus of the 21<sup>st</sup> century. The outbreak of the novel H1N1 in the <st1:place w:st="on">North America</st1:place> in the early months of 2009 caught everyone by surprise. The pandemic spread of novel H1N1 across the globe captured the world?s attention throughout the year, while information and reports on H5N1 were back page news.
<o:p> </o:p>
Number of Human H5N1 Cases in 2009
<o:p> </o:p>
H5N1 avian influenza (?Bird Flu?) is an internationally reportable disease. Since 2003 until December 31, 2009, the World Health Organization (WHO) has reported a total of 467 confirmed human cases of H5N1 (link). The cases associated with the initial human outbreak of H5N1 in <st1:place w:st="on">Hong Kong</st1:place> in 1997 are not included in the official WHO totals (link).
For 2009, the final tabulation for WHO confirmed H5N1 cases is 72 (link). Twenty of these 72 cases occurred throughout the year in <st1:country-region w:st="on">Indonesia</st1:country-region> but were only reported by <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> on December 28<sup>th</sup>, and incorporated into the WHO statistics on December 30, 2009 (link).
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The number of H5N1 cases increased in 2009 relative to 2008. The number of H5N1 cases in 2009 is almost double the number of H5N1 cases reported in 2008 (See graph below). The number of H5N1 cases reached an all time annual high of 115 in 2006, but another doubling of human H5N1 infections in 2010 would exceed this previous annual high.
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In 2009, <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> had the most confirmed cases with 39 reported to WHO. <st1:country-region w:st="on">Indonesia</st1:country-region> is next with 20 reported cases followed by <st1:country-region w:st="on">China</st1:country-region>, <st1:country-region w:st="on">Vietnam</st1:country-region>, and <st1:place w:st="on"><st1:country-region w:st="on">Cambodia</st1:country-region></st1:place> in descending order. All five of these countries had previously reported human H5N1 cases. No other countries reported human H5N1 infections in 2009.
<o:p> </o:p>
Demographics of H5N1 Victims in 2009
<o:p> </o:p>
For about 52 of the WHO confirmed cases demographic information is available in the Disease Outbreak News and translated news posts here at FluTrackers and elsewhere. There is no official information on the 20 reported cases from <st1:country-region w:st="on">Indonesia</st1:country-region>, although internet flu trackers have posted numerous news articles throughout 2009 about human H5N1 infections and deaths in <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region>. Among the 52 cases with reported statistics, 25 males (48%) and 27 (52%) females were infected. This suggests that in 2009 both males and females were about equally susceptible to H5N1 infection. Ages range from 1 to 57 years old for these cases, with a median age of 4. This low median age results from the 39 cases from <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region>. The age statistics from <st1:place w:st="on"><st1:country-region w:st="on">Egypt</st1:country-region></st1:place> for human H5N1 infections in 2009 show an unusual trend. Thirty-one of the 39 human cases were children under 9 years of age. Even more striking is the fact the CFR among the 39 <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> cases in 2009 was only .10.
<o:p> </o:p>
Case Fatality Ratio
<o:p> </o:p>
Based on WHO confirmed human cases, the overall case fatality ratio (CFR) to date is .60. As noted above for 2009 the CFR for <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> was .10. This is lowest annual CFR number of any country since WHO started tracking H5N1 infections. The survival rate for confirmed H5N1 cases in 2009, at least for <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region>, increased compared to preceding years.
<o:p> </o:p>
Seasonality
<o:p> </o:p>
As noted previously human H5N1 cases do not randomly occur throughout the year, but the number of cases fluctuates in a pattern similar to that of seasonal influenza in the northern hemisphere (link). Below is a current graph of the month of onset for almost all of the worldwide confirmed cases (specifically missing is information on the 20 cases from <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> in 2009). It should be apparent that additional H5N1 infections can be expected in the next several months.
<o:p> </o:p>
<o:p> </o:p>
Discussion and Representativeness of the Data
<o:p> </o:p>
Over the past several years here at FluTrackers and elsewhere, there have been debates and discussions about whether or not the WHO data is representative of actual rates of infection and mortality of H5N1 around the world. The current H1N1 pandemic highlights the complexities of case identification, surveillance, and timely reporting of epidemiological data on a novel influenza strain. The statistics of H5N1 infections should be carefully considered in light of the quality of worldwide data on novel H1N1 infections.
<o:p> </o:p>
We do not know the geographic extent or the true morbidity and mortality of circulation H5N1 strains. We can not predict the potential for H5N1 to become another pandemic strain or whether it will reassort with existing influenza strains including novel H1N1. To date at least, transmissibility of H5N1 among humans has been limited suggesting that the circulating strains are not sufficiently viable to cause local epidemics or a world wide pandemic.
I don?t believe there is any scientific data demonstrating that H5N1 can not become a pandemic strain. Nor is there is any compelling data that the current H1N1 pandemic sweeping the world will protect us for another 30 years from the next pandemic whether it is a novel influenza virus, such as H5N1, or some other infectious disease.
<o:p> </o:p>
H5N1 was widely expected to the first pandemic virus of the 21<sup>st</sup> century. The outbreak of the novel H1N1 in the <st1:place w:st="on">North America</st1:place> in the early months of 2009 caught everyone by surprise. The pandemic spread of novel H1N1 across the globe captured the world?s attention throughout the year, while information and reports on H5N1 were back page news.
<o:p> </o:p>
Number of Human H5N1 Cases in 2009
<o:p> </o:p>
H5N1 avian influenza (?Bird Flu?) is an internationally reportable disease. Since 2003 until December 31, 2009, the World Health Organization (WHO) has reported a total of 467 confirmed human cases of H5N1 (link). The cases associated with the initial human outbreak of H5N1 in <st1:place w:st="on">Hong Kong</st1:place> in 1997 are not included in the official WHO totals (link).
For 2009, the final tabulation for WHO confirmed H5N1 cases is 72 (link). Twenty of these 72 cases occurred throughout the year in <st1:country-region w:st="on">Indonesia</st1:country-region> but were only reported by <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> on December 28<sup>th</sup>, and incorporated into the WHO statistics on December 30, 2009 (link).
<o:p> </o:p>
The number of H5N1 cases increased in 2009 relative to 2008. The number of H5N1 cases in 2009 is almost double the number of H5N1 cases reported in 2008 (See graph below). The number of H5N1 cases reached an all time annual high of 115 in 2006, but another doubling of human H5N1 infections in 2010 would exceed this previous annual high.
<o:p> </o:p>
In 2009, <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> had the most confirmed cases with 39 reported to WHO. <st1:country-region w:st="on">Indonesia</st1:country-region> is next with 20 reported cases followed by <st1:country-region w:st="on">China</st1:country-region>, <st1:country-region w:st="on">Vietnam</st1:country-region>, and <st1:place w:st="on"><st1:country-region w:st="on">Cambodia</st1:country-region></st1:place> in descending order. All five of these countries had previously reported human H5N1 cases. No other countries reported human H5N1 infections in 2009.
<o:p> </o:p>
Demographics of H5N1 Victims in 2009
<o:p> </o:p>
For about 52 of the WHO confirmed cases demographic information is available in the Disease Outbreak News and translated news posts here at FluTrackers and elsewhere. There is no official information on the 20 reported cases from <st1:country-region w:st="on">Indonesia</st1:country-region>, although internet flu trackers have posted numerous news articles throughout 2009 about human H5N1 infections and deaths in <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region>. Among the 52 cases with reported statistics, 25 males (48%) and 27 (52%) females were infected. This suggests that in 2009 both males and females were about equally susceptible to H5N1 infection. Ages range from 1 to 57 years old for these cases, with a median age of 4. This low median age results from the 39 cases from <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region>. The age statistics from <st1:place w:st="on"><st1:country-region w:st="on">Egypt</st1:country-region></st1:place> for human H5N1 infections in 2009 show an unusual trend. Thirty-one of the 39 human cases were children under 9 years of age. Even more striking is the fact the CFR among the 39 <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> cases in 2009 was only .10.
<o:p> </o:p>
Case Fatality Ratio
<o:p> </o:p>
Based on WHO confirmed human cases, the overall case fatality ratio (CFR) to date is .60. As noted above for 2009 the CFR for <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region> was .10. This is lowest annual CFR number of any country since WHO started tracking H5N1 infections. The survival rate for confirmed H5N1 cases in 2009, at least for <st1:country-region w:st="on"><st1:place w:st="on">Egypt</st1:place></st1:country-region>, increased compared to preceding years.
<o:p> </o:p>
Seasonality
<o:p> </o:p>
As noted previously human H5N1 cases do not randomly occur throughout the year, but the number of cases fluctuates in a pattern similar to that of seasonal influenza in the northern hemisphere (link). Below is a current graph of the month of onset for almost all of the worldwide confirmed cases (specifically missing is information on the 20 cases from <st1:country-region w:st="on"><st1:place w:st="on">Indonesia</st1:place></st1:country-region> in 2009). It should be apparent that additional H5N1 infections can be expected in the next several months.
<o:p> </o:p>
<o:p> </o:p>
Discussion and Representativeness of the Data
<o:p> </o:p>
Over the past several years here at FluTrackers and elsewhere, there have been debates and discussions about whether or not the WHO data is representative of actual rates of infection and mortality of H5N1 around the world. The current H1N1 pandemic highlights the complexities of case identification, surveillance, and timely reporting of epidemiological data on a novel influenza strain. The statistics of H5N1 infections should be carefully considered in light of the quality of worldwide data on novel H1N1 infections.
<o:p> </o:p>
We do not know the geographic extent or the true morbidity and mortality of circulation H5N1 strains. We can not predict the potential for H5N1 to become another pandemic strain or whether it will reassort with existing influenza strains including novel H1N1. To date at least, transmissibility of H5N1 among humans has been limited suggesting that the circulating strains are not sufficiently viable to cause local epidemics or a world wide pandemic.
I don?t believe there is any scientific data demonstrating that H5N1 can not become a pandemic strain. Nor is there is any compelling data that the current H1N1 pandemic sweeping the world will protect us for another 30 years from the next pandemic whether it is a novel influenza virus, such as H5N1, or some other infectious disease.
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