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For the purposes of this discussion the current outbreak of H7N9 began November 1, 2016 and is still continuing. More than 460 human cases have been reported from China. Of these cases, 426 have symptom onset dates reported by the World Health Organization (WHO) for cases with onset before February 10, 2017. Graphing the symptom onset dates for these H7N9 cases provides a count of new daily infections of H7N9. Also included in the graph are the remaining 37 cases based on their reporting date rather than symptom onset date which is not available at this time for cases reported after February 11. The graph, an epidemic curve, shows that the greatest number of H7N9 infections occurred on February 1, 2017, based on a five day moving average. Even if The 37 cases for which symptom onset dates are not available are distributed over the 17 days following February 11, they are an insufficient number of new cases to exceed the five-day moving average which peaked above 10 cases per day on Feb...

As noted in the previous post, there have been at least 460 human cases of H7N9 reported in the current H7N9 outbreak between November 1, 2016 and February 27, 2017. Of great concern is a possibility that many of these cases are a result of human-to-human transmission. There is little publicly available information about the relationships, if any, among these hundreds of cases. To date, only four two-person clusters have been reported by the World Health Organization (WHO, January 17 and February 20) with family members comprising three of the clusters. For all four of these clusters, the WHO notes that human-to-human transmission cannot be ruled out. One important clue to the nature of the outbreak is the geographic distribution of the reported cases. An indirect signal of human-to-human transmission can be multiple cases occurring in a localized geographic area within a short period of time. The recent WHO line listing of H7N9 cases from China ( Influenza at the Human Animal Interfa...

Since November 2016, more than 460 human cases of H7N9 have been reported or imported from China. To put this number in perspective, confirmed cases of H7N9 were first reported in March 2013, four years ago. Of all the cases of human H7N9 infections reported to date, more than one-third (about 36%), have occurred in the last four months. This raises a concern that H7N9 is not only causing outbreaks in China but could lead to epidemics and perhaps even a pandemic. It is difficult to tabulate exactly how many H7N9 cases have occurred since November 1 of 2016, because case reporting and enumeration seem to vary among various public health reporting agencies. Media and blog reports have interpreted variation among these counts of H7N9 cases as a failure of public health officials in China to accurately track H7N9 cases, often leading to exaggerated claims of the rates of infection in China. It is possible to arrive at a close approximation of the actual number of recent cases by using dif...

Based on illness onset dates from January through the end of November 2016, China officially reported about 115 human cases H7N9 infection. Over the course of several days in early January 2017, China notified the World Health Organization of more than 100 additional human cases of H7N9 presumably having been infected in December 2016. It appears that almost as many people were infected in December as all of the preceding months in 2016. The graph below shows the distribution of H7N9 cases by onset date where available and then by reporting date. The graph clearly shows the large increases in the number of infected individual reported recently. Should this increase be a cause for alarm? Increases in human cases of avian influenza always increase the risk for sustained human to human transmission of the disease. Reviewing the minimal data that is available for the 107 recent cases reported by China, some observations can be made. About 36% of these new cases are female and 67% are male...

It is well known that non-pandemic influenza has a seasonal repeating periodicity, especially in temperate climates [1]. The causes of seasonal cycles of influenza infections are not well understood. However, an analysis of seasonality of influenza around the world in a recent PLOS article indicates that cold-dry and humid-rainy conditions are associated with peaks in the frequency of seasonal influenza cases in different regions [2]. The authors in this article suggest that “these two distinct mechanisms account for influenza seasonality in temperate and tropical climates, perhaps due to changes in the dominant mode of transmission.” In the past decade there have been several outbreaks of novel influenza infections, including (A)H5N1, (A)H7N9, and (A)H10N8. Based on limited data, it does appear that novel influenza infections follow the same seasonal pattern as non-pandemic influenza. For example, H7N9 was first reported by the Republic of China to the World Health Organization (WHO) ...