"..Most cases described during the three pandemics of the 20th century and during seasonal influenza involve transient illness not requiring hospitalisation. Most deaths are described in the very young or the elderly or those with underlying disease. The 1918-1919 pandemic, however, was characterised by a high mortality rate in healthy young adults and an estimated CFR of 2-3% . Even with a low CFR, seasonal influenza epidemics cause significant morbidity and mortality with an estimated three to five million cases of severe illness and about 250,000 to 500,000 deaths worldwide .
To date, the CFR attributable to the current H1N1 pandemic has been estimated at around 0.4%, based on surveillance data from Mexico and mathematical modelling . This CFR is higher than that of average seasonal influenza but remains of the same order of magnitude. Whether this will change before the expected epidemic peak in the northern hemisphere in the autumn is unknown.
Evaluating CFR during a pandemic is a hazardous exercise. Aside from the issue of whether or not a death has been caused by the influenza infection, cases tend to be detected initially among severely ill patients with a higher probability of dying. This leads to an overestimation of the computed CFR at the beginning of an outbreak. The computed CFR subsequently evolves as the case reporting strategy is adapted to the situation. When the situation no longer requires exhaustive reporting of cases, the computed CFR will inevitably increase and grossly overestimate the true CFR..."
I searched the WHO and CDC websites, but couldn't find A(H1N1) statistics by country. Wikipedia has compiled the figures below, from the European Centre for Disease Prevention and Control website (daily updates, as of Aug 19, 2009) and Pan American Health Organization website, and in some cases from national websites:
1) these figures cannot be used to asess the virulence of the virus circulating in the reporting country (case fatality rate, A(H1N1) deaths divided by laboratory-confirmed cases), since the pandemic has reached the stage where lab confimration of cases would overwhelm testing capacity, and most countries are now reporting only lab confirmed fatalities, i.e. the CFR is inflated to varying degrees in different countries).
2) among Malaysia's 68 reported fatalities (lab confirmed), up to 11 cases remain ambiguous as to A(H1N1) causality, although they were virus positive. perhaps our legislators (and the media) could request clarification from the relevant authorities
3) were there unregistered migrant workers among the Malaysian fatalities? if so, was treatment delayed because they were hesitant to identify themselves to health agencies or healthcare providers?
4) since the case fatality rate is not useful at this point for tracking virulence, surveillance has now shifted to unusual clustering, changes in transmission patterns, in patient profile, in natural history of the disease, etc which might suggest an evolutionary shift. Prof Adeeba's observations of rapid decline in cases with pneumonia complications deserve close attention.
‡Qualitative indicators as defined by WHO. Parameter values:
Impact on health care services
*** (very high)
* (low - moderate)
‡‡Many countries are not recommending laboratory tests for all suspect cases. As far as known, the affected numbers have been put in brackets. Comparisons in time or between these countries should not be made. The number of confirmed cases is lower than the total number of cases, and may grossly underestimate the true infection rate.
********************* CHAN Chee Khoon, ScD Professor & Convenor Health & Social Policy Research Cluster Women's Development Research Centre (KANITA) Universiti Sains Malaysia 11800 Penang, Malaysia tel : + 60 4 6533437 fax : + 60 4 6566379 mobile: + 60 (0)17 4808317 email : email@example.com