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Fatality Rate in Missed Thailand Bird Flu Cases
January 5, 2005
>>The Thai investigators examined all cases in the first 3 months of 2004 in which patients were hospitalized with pneumonia or influenza after exposure to sick poultry. They classified cases with laboratory evidence of H5N1 infection as confirmed. Cases in which patients had been exposed to sick poultry and had either severe pneumonia or laboratory evidence of influenza A, but without confirmation of H5N1, were defined as suspected.
The researchers found 12 confirmed and 21 suspected H5N1 cases among the 610 potential cases reported from 67 of Thailand's 76 provinces. Eight of the 12 confirmed case-patients died. The median age of the confirmed patients was 12 years (range, 2 to 58) and that of the suspected patients was 33 (range, 1-67).<<
The above cases indicates that the number of confirmed bird flu cases was higher than the official WHO count, but the case fatality rate for the confirmed cases was almost identical to rate for the official confirmed cases. The case fatality rate for the suspect cases was 38%, but the true case fatality rate for the suspect cases is not clear because there was not enough clinical sample to determine which of the suspect cases were actually infected with H5N1. However, even a 38% case fatality rate is very high. The large number of the excluded cases suggests that there is not a large number of undetected milder cases. The case fatality rate for the excluded group was 4% and although they had milder cases they did not have evidence of H5N1 infections.
These new data indicate that the number of cases was higher than the official number, consistent with media reports suggesting that there were more infections than were being acknowledged. The new data also supports a very high case fatality rate of about 70% which was found for these missed cases, the early confirmed cases in Thailand and Vietnam and the more recent confirmed cases in both countries.
The condition of the first 3 cases for this season in Vietnam suggests a high case fatality rate will be seen again this season.