Abstract
Dozens of human cases infected with H7N9 subtype avian influenza virus (AIV) have been confirmed in China since March, 2013. Distribution data of sexes, ages, professions and regions of the cases were analyzed in this report. The results showed that the elderly cases, especially the male elderly, were significantly more than expected, which is different from human cases of H5N1 avian influenza and human cases of the pandemic H1N1 influenza. The outbreak was rated as a Grade III (severe) outbreak, and it would evolve into a Grade IV (very severe) outbreak soon, using a method reported previously. The H7N9 AIV will probably circulate in humans, birds and pigs for years. Moreover, with the driving force of natural selection, the virus will probably evolve into highly pathogenic AIV in birds, and into a deadly pandemic influenza virus in humans. Therefore, the H7N9 outbreak has been assumed severe, and it is likely to become very or extremely severe in the future, highlighting the emergent need of forceful scientific measures to eliminate any infected animal flocks. We also described two possible mild scenarios of the future evolution of the outbreak.
Highlights
Dozens of human cases infected with H7N9 subtype avian influenza virus (AIV) have been confirmed in China since March, 2013
Human cases infected with H7N9 subtype avian influenza virus (AIV) emerged in China in recent months [1 3]
As of April 18, 2013, the scores of the severity of clinical signs, transmission of the infectious disease, case number and the infection source were 5, 1, 3 and 3, respectively. The product of these scores was 45, which indicates that the severity of the current H7N9 influenza outbreak was at the severe level (Grade III)
Summary
Of the first 91 cases, 86 were of known clinical signs. Among them, 88.37% (76/86) developed severe and acute respiratory symptoms including pneumonia, and 17 had died. Compared with the age distribution of the total population in China [5], the cases were significantly fewer for the groups of 0 19-year-old and 20 39-year-old, and significantly more for the group of ≥60-year-old (Figure 1). The sex and age distribution of the H7N9 cases was quite different from that of the human cases of H5N1 avian influenza occurring in 2003 2006, and that of human cases of the pandemic H1N1 influenza in 2009 (Figure 1). Among the total of 1108 close contacts of the first cases reported online, only two (namely the two in the two pairs from the same families) were identified as H7N9 cases All these data suggest that the virus could not transmit among humans. This further suggests that most of the first 91 cases were infected with the virus from infected animals
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