Summary of human infection with highly pathogenic avian influenza A (H5N1) virus reported to WHO, January 2003?March 2009: cluster-associated cases
Weekly epidemiological record 15 JANUARY 2010, 85th YEAR
No. 3, 2010, 85, 13?20 http://www.who.int/wer
Full pdf at: http://www.who.int/wer/2010/wer8503.pdf
excerpt
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During 2003?2009, 480 confirmed (n=443) or probable (n=37) human cases of H5N1 virus infection were identified and reported to WHO. Of these, 54 clusters were identified involving 138 cases (29% of cases; 104 cases confirmed and 34 probable); the remaining 342 cases (71% of cases) were sporadic (339 confirmed cases and 3 probable).
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Case investigation
For 44 clusters, information was available on whether the primary case (that is, the case with the earliest onset) triggered an investigation that led to the identification of additional cases. During 2003?2004, an investigation was triggered for 1/4 clusters (25%), compared with 6/12 (50%) during 2005, 7/18 (39%) during 2006, 3/5 (67%) during 2007, and 3/5 (67%) during 2008?2009.
Discussion
This analysis demonstrates the importance of clusters in the overall epidemiology of human H5N1 virus infection; almost one third of cases occurred in a cluster. Detection of the primary case often triggered an investigation that led to identification of other cases.
Clustering suggests that there is the potential for wide-spread transmission of the virus. In this context, it is reassuring that the absolute number of clusters and the proportion of all cases associated with clusters have both decreased; only 2 countries (Indonesia and Viet Nam) have reported the clustering of cases for an extended time. It also is reassuring that only 3 clusters had cases occurring beyond 2 weeks; none lasted beyond 23 days.
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Weekly epidemiological record 15 JANUARY 2010, 85th YEAR
No. 3, 2010, 85, 13?20 http://www.who.int/wer
Full pdf at: http://www.who.int/wer/2010/wer8503.pdf
excerpt
. . .
During 2003?2009, 480 confirmed (n=443) or probable (n=37) human cases of H5N1 virus infection were identified and reported to WHO. Of these, 54 clusters were identified involving 138 cases (29% of cases; 104 cases confirmed and 34 probable); the remaining 342 cases (71% of cases) were sporadic (339 confirmed cases and 3 probable).
. . .
Case investigation
For 44 clusters, information was available on whether the primary case (that is, the case with the earliest onset) triggered an investigation that led to the identification of additional cases. During 2003?2004, an investigation was triggered for 1/4 clusters (25%), compared with 6/12 (50%) during 2005, 7/18 (39%) during 2006, 3/5 (67%) during 2007, and 3/5 (67%) during 2008?2009.
Discussion
This analysis demonstrates the importance of clusters in the overall epidemiology of human H5N1 virus infection; almost one third of cases occurred in a cluster. Detection of the primary case often triggered an investigation that led to identification of other cases.
Clustering suggests that there is the potential for wide-spread transmission of the virus. In this context, it is reassuring that the absolute number of clusters and the proportion of all cases associated with clusters have both decreased; only 2 countries (Indonesia and Viet Nam) have reported the clustering of cases for an extended time. It also is reassuring that only 3 clusters had cases occurring beyond 2 weeks; none lasted beyond 23 days.
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Comment