A Summary of Human H5N1 Cases in 2010
In 2010, while the pH1N1 virus continued to infect people and be the focus of influenza news stories, human H5N1 infections continued to be identified in several countries. As discussed below, the virulence based on confirmed case has not declined and the potential for an H5N1 pandemic has not diminished.
H5N1 avian influenza (“Bird Flu”) is an internationally reportable disease. Since 2003 until December 29, 2010, the World Health Organization (WHO) has reported a total of 512 confirmed human cases of H5N1 (link)
. The 18 cases associated with the initial human outbreak of H5N1 in Hong Kong in 1997 are not included in the official WHO totals (link
). WHO provides a current time line of significant events associated with the H5N1 virus (link
Number of Human H5N1 Cases in 2010
The tabulation for WHO confirmed H5N1 cases in 2010 is 44 (link
), but will mostly likely include the two most recently reported cases in Egypt (link
) bringing the total to at least 46 in 2010. The number of worldwide H5N1 cases has decreased in 2010 relative to 2009. The number of H5N1 cases in 2010 is a little more than 60% of the number of cases in 2009, although the 2010 confirmed count will exceed the 2008 total reported by WHO.
Worldwide, 15 countries have reported human H5N1 cases. In 2010, only 5 countries reported human cases of H5N1, Cambodia, China, Egypt, Indonesia, and Viet Nam. All five of these countries have previously reported human H5N1 cases. In 2009, Egypt had the most confirmed cases reported to WHO. In 2010, Egypt again led the world’s countries with 25 confirmed cases. Indonesia is next with 9 cases, followed by Viet Nam (7 cases), China (2 cases), and Cambodia with one confirmed case. No other countries reported human H5N1 infections in 2009. The last of the 15 countries to report its first case of H5N1 was Bangladesh in 2008.
Currently, Indonesia with 171 confirmed H5N1 cases leads the world countries, followed by Viet Nam with 119. Egypt will have 117 cases when the above two reported cases are confirmed by WHO. Given the rate at which Egypt is experiencing human infections, it will most likely surpass Viet Nam in the next 30-60 days.
Recent H5N1 Cases
Since September, 2010 there was 1 confirmed case from Hong Kong, 2 from Indonesia, and 5 from Egypt, including the two reported today (link
). The latest reported H5N1 case from Indonesia was a 21-year-old woman from Bandung who was reported ill in November. She was treated with Tamiflu, improved, and was released (link
Although there have been several media reports over the past several weeks of infected poultry in Indonesia (link
) there have been no other media reports of suspected human bird flu cases. Because of reporting delays by the Ministry of Health in Indonesia it is possible that there will be some late reports of human cases during the next week or two with onset in December of 2010. Indonesia has shown some improvement in timely reporting of H5N1 cases. In 2010, Indonesia has been more regularly reporting human cases usually on a monthly basis unlike the report in December of 2009 where Indonesia reported a cumulative total of 20 cases spread throughout the year without any kind of public detail about the sex, age, or location of the cases (link
Demographics of H5N1 Cases in 2010
For the 46 H5N1 cases from 2010 some demographic information is available in the Disease Outbreak News and translated news posts here at FluTrackers and elsewhere. Among the 46 cases with reported statistics, 15 males (33%) and 31 (67%) females were infected. In the past males and females were about equally infected. In 2010 there was a significant departure with females being twice as likely to be infected as males. This differential attack rate by sex deserved further scrutiny.
Ages range from 1 to 53 years old for these cases, with a median age of 25. The median age of infection in 2010 is much higher than in 2009 when numerous infections of children in Egypt lowered the median age to 4 years. However, about 1/3 (34%) of all confirmed cases in 2010 were children under 18 years old, 10 of which were from Egypt.
Case Fatality Rate (CFR)
The CFR for H5N1 victims in 2010 was .50. Based on WHO confirmed human cases, the overall case fatality rate (CFR) to date is .59, an insignificant drop of .01 since December 31, 2009. In 2010, Indonesia again suffered the highest mortality rate with 7 of 9 confirmed cases dying and continues to lead the world in deaths from H5N1 with a staggering cumulative CFR of .82. In contrast the CFR for Egypt was .44 for 2010.
Human H5N1 cases seem to fluctuate in a pattern similar to that of seasonal influenza in the northern hemisphere. Below is a current graph of the month of onset for almost all of the worldwide confirmed cases including 36 cases from 2010 for which information is available. Additional H5N1 infections can be expected in the next several months.
Sequences have been publicly released for 14 individuals infected with H5N1 in 2010, one from Hong Kong and 13 from Egypt. None seems to have been released for any other cases in 2010.
Once again at the close of 2010, the debate and discussions continue about rates of H5N1 infection and mortality around the world and how representative the WHO H5N1 data is. In 2010, the CFR varied greatly among countries. Indonesia had a poor recovery rate, while in Egypt the recovery rate was much higher. These differences most likely are a result of the surveillance and testing capacities of public health officials in these countries. Antiviral treatment is most efficacious with 48 hours of onset and, in Egypt at least, antivirals appear to be given upon suspicion of H5N1 infection, whereas in Indonesia treatment is not always immediate.
There seems to be some disturbing trends in Egypt over the past several months regarding identification of H5N1 cases. H5N1 and pH1N1 infections seem to exhibit the same initial symptoms in Egypt. In the past, such symptoms in association with sick or died poultry were the basis of a preliminary diagnosis of “bird flu” (H5N1). But several recent H5N1 cases had no known poultry associations. So far, in Egypt and elsewhere, there is no evidence of sustained H2H2H of transmission of the virus. But there is no reason why that could not change very quickly. A cluster outbreak of H5N1 cases could be mistaken for pH1N1.
Farther East, China at least seems to be taking the threat of an H5N1 pandemic seriously. In 2010 China instituted a series of bird flu exercises (both human and poultry) in at least six provinces, Anhui, Gansu, Guangdong, Hunan, Shangdong, and Zhejiang (links
). And in the western hemisphere, HPAI has not yet been officially reported from any species. But the emergence and spread of pH1N1 in 2009 and recent announcement of possible limited human to human spread of trH3N2 (link
) reminds us that novel influenza viruses could emerge as a new pandemic threats at any time. These potential threats, including H5N1, require that the world embark on a systematic effort to create a universal vaccine and develop an early warning system for monitoring “wild influenza viruses”.