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 Interface: Summary and Assessment, February 14, 2017), only provides the province or region for each of the reported cases. Line lists of cases provided by the Centre for Health Protection (CHP) Weekly Influenza Report provide additional geographic locational information to the prefecture level (administrative level 2) for individual cases. The Food and Agricultural Organization of the United Nations (FAO) line list of H7N9 cases occasionally provides the geographic locale of the county or administrative level 3 for some individual cases.
The most accurate locational information for individual cases is reported in local public health reports on Chinese websites. This information has been translated to English by members at FluTrackers. Sharon Sanders at FluTrackers has linked to these translated reports in the FluTrackers running list of H7N9 cases. Unfortunately, local publication of data of confirmed H7N9 cases in China are infrequent, so geographic details about individual cases beyond administrative level 2, the prefecture level, are limited to only a handful of the reported cases in this outbreak.
However, even with limited geo-locational information for individual H7N9 cases, the geographic distribution of cases can be plotted and is very informative. The map below provides a heat map of the distribution of cases in eastern China computed from the prefecture level data. Overlaid on this map are plotted locations of individual cases. The map shows the concentrations of cases in the 2016-2017 H7N9 outbreak in the provinces of Jiangsu, Zhejiang, Anhui, and Guangdong. In southern Jiangsu, hot spots include Suzhou, Wuxi, Taizhou, and Changzhou. In northern and eastern Zhejiang, the hot spots are Hangzhou, Ningbo, and Wenzhou. Hefei is the hot spot in central Anhui province and in central Guangdong, Guangzhou is the location with the most reported infections.
This map also shows that cases are widely scattered throughout many provinces during the current outbreak. The widely dispersed nature of these cases provides indirect support that human-to-human transmission is not occurring in these areas and the infections are resulting primarily from animal-to-human transmission. Even the increased number of cases in the hot spot locations does not mean that human-to-human transmission is occurring. The prefecture level cities mentioned above have very large populations most exceeding several million people. Were human-to-human transmission occurring in these areas we would expect many more reported cases.