Abstract
Highly pathogenic avian influenza A (HPAI) subtype H5N1 has caused family case clusters, mostly in Southeast Asia, that could be due to human-to-human transmission. Should this virus, or another zoonotic influenza virus, gain the ability of sustained human-to-human transmission, an influenza pandemic could result. We used statistical methods to test whether observed clusters of HPAI (H5N1) illnesses in families in northern Sumatra, Indonesia, and eastern Turkey were due to human-to-human transmission. Given that human-to-human transmission occurs, we estimate the infection secondary attack rates (SARs) and the local basic reproductive number, R0. We find statistical evidence of human-to-human transmission (p = 0.009) in Sumatra but not in Turkey (p = 0.114). For Sumatra, the estimated household SAR was 29% (95% confidence interval [CI] 15%-51%). The estimated lower limit on the local R0 was 1.14 (95% CI 0.61-2.14). Effective HPAI (H5N1) surveillance, containment response, and field evaluation are essential to monitor and contain potential pandemic strains.
Highlights
Should this virus, or another zoonotic influenza virus, gain the ability of sustained human-to-human transmission, an influenza pandemic could result
We determine that human-to-human spread did occur by rejecting the null hypothesis of no human-to-human transmission (p = 0.009)
Because we do not have an estimate of the community secondary attack rates (SARs), we have an estimate of the lower limit of the local R0, i.e., 1.14 with a 95% CI of 0.61–2.14
Summary
Another zoonotic influenza virus, gain the ability of sustained human-to-human transmission, an influenza pandemic could result. Since December 2003, a total of 291 cases of HPAI (H5N1) have been reported in humans, resulting in 172 deaths (i.e., 59% case-fatality ratio) in 12 countries, mostly in Southeast Asia [1] Among these cases, 31 family clusters have been documented, ranging in size from 2 to 8 family members. 31 family clusters have been documented, ranging in size from 2 to 8 family members How many of these clusters are due to a common avian source and how many are due to human-to-human transmission are important facts to determine. Should one of these HPAI (H5N1) strains gain the capacity for sustained human-to-human transmission, the resulting outbreak, if not contained, would spread world-. We analyzed data from 2 of the largest of the familial clusters to ascertain if human-to-human transmission took place, and if so, how transmissible the strain was
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