6 July 2006

 

WHO review epidemiology of human cases of avian influenza

The World Health Organization (WHO) has reviewed the epidemiology of human cases of avian influenza (H5N1) that have occurred since the current outbreak in birds began in south-east Asia in mid 2003 [1]. An improved understanding of the epidemiology will help to develop studies on exposure risks and target prevention strategies.

Highlights of the report are:

Between 1 December 2003 and 30 April 2006, there were 205 laboratory-confirmed cases of human avian influenza.

Cases occurred in nine countries (Viet Nam, Thailand, Cambodia, Indonesia, China, Turkey, Iraq, Azerbaijan and Egypt) and followed the introduction of wild bird and poultry cases of avian influenza into these countries.

The peak incidence for human cases roughly corresponded to the winter and spring months of the northern hemisphere.

The median age of cases was 20 years (range 3 months to 75 years); 90% of cases occurred in persons < 40 years of age.

For cases in which the date of onset of symptoms and the date of hospitalisation was known, the median interval between symptom onset and hospitalisation was 4 days (range 0 to 18 days).

The overall case fatality rate was 56%. However, rates varied by age group with the highest rates in persons aged 10 to 39 years (range of 61% for persons 30 to 39 years to 73% for persons aged 10 to 19 years), and the lowest in those ≥ 50 years (18%).

In fatal cases the median duration between onset of symptoms and death was 9 days (range 2 to 31 days). Assessment of mortality rates, and time intervals between symptoms, hospitalisation and death suggest that the illness pattern has not substantially changed over the period reported.

Reference

1. World Health Organization. Epidemiology of WHO-confirmed human cases of avian influenza A(H5N1) infection. Wkly Epidemiol Rec. 2006;81:249-57. Available at: http://www.who.int/wer/wer8126.pdf

Links

NaTHNaC clinical updates on avian influenza: www.NaTHNaC.org/pro/clinical_updates/avian_influenza_index.ht

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World Health Organization advice on avian influenza: www.who.int/csr/disease/avian_influenza/en/

Health Protection Agency Algorithm for the management of returning travellers from countries affected by avian influenza presenting with febrile respiratory illness: recognition, investigation and initial management.

World Organisation for Animal Health (information on the status of animal outbreaks of avian influenza) at www.oie.int/eng/en_index.htm