The Current Status of the 2016 – 2017 H7N9 Outbreak in China as of March 1, 2017 (Geographic Distribution)

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.

Details of an A(H7N9) Family Cluster in February from Dongyang, Jinhua, Zhejiang Province

Although more than 400 people have been infected with A(H7N9), reports of clusters of cases are rare. Based on publicly available information, only 14 H7N9 human cluster have been reported. Most of these clusters are family or neighborhood clusters of 2-3 individuals. These clusters are almost never officially reported by the Chinese public health authorities.

The most recent reported cluster is family cluster of two sisters from Dongyang in Zhejiang Province. An extended media report details the identifications and treatment of 3 children infected with H7N9 from Dongyang.[1] Computer translation of the article reports that three infected children with ages ranging from 2-8 were identified over the course of four days in February, 2014.[2]  Two of the children were sisters from one family with different onset dates. The two children apparently observed, but did not participate, in the slaughter of several chickens by one of the parents. The report is not clear whether the third child from the same city, surname Ren, is related to or had contact with the two sisters.

The three children hospitalized in Dongyang are reported to have recovered and been released from the hospital between 4 and 12 days after admission. The article mentions that one health care worker treating the patient also had a fever, but apparently was not infected with H7N9. Although the two girls are a family cluster, the infections may have resulted from exposure to a common source rather than human to human transmission. This small family cluster is at least the 14^th H7N9 cluster reported since March of 2013.

[1] Original Chinese media link

[2] FluTrackers translation

Hat tip to Pathfinder at FluTrackers.com

Is Taihu Lake, Zhejiang Province the Geographic Source of the H7N9 Virus? (Map)

An important ahead-of-print article on the possible origins of the H7N9 virus has been published by researchers from the Zhejiang Provincial Center for Disease Control and Prevention in Hangzhou, China in the journal Zoonoses and Public Health. The researchers conducted genetic analyses of environment samples, human samples, and domestic and wild avian samples of the H7N9 virus from several provinces in the eastern portion of the People‘s Republic of China (PRC).

The article, entitled Hypothesis On The Source, Transmission and Characteristics of Infection of Avian Influenza A (H7N9) Virus – Based On Analysis of Field Epidemiological Investigation and Gene Sequence Analysis is behind a John Wiley & Sons paywall. However, within the freely available abstract, these Chinese researchers propose that the H7N9 virus now infecting people and domestic poultry originated with migratory bird populations in the Taihu Lake area of Zhejiang Province.

Their analysis suggests that . . . avian viruses carried by waterfowl combined with the virus carried by migratory birds, giving rise to avian influenza virus H7N9, which is highly pathogenic to humans. It is possible that the virus was transmitted by local wildfowl to domestic poultry and then to humans, or spread further by means of trading in wholesale poultry markets.

The authors speculate that . . . the infection source in the triangular area around Taihu Lake still remains. They also forecast that . . . The H7N9 epidemic will probably hit the area later in the year and next spring when the migratory birds return and may even spread to other areas.

This is a sobering forecast of future outbreaks of H7N9. Researchers from Zhejiang Province ought to know. More than 1/3 of all human H7N9 cases have been reported from Zhejiang Province.

Map

 

Map: H7N9 cases concentrated in northern Zhejiang Province, PRC

Since novel A(H7N9) human infections were first discovered last year in the People's Republic of China, Zhejiang Province has reported the most cases. The map below depicts in aggregate, the general locations of 80 confirmed and unconfirmed cases through January 21, 2014. The cases are concentrated in the northern portion of the country in the Hangzhou and Huzhou. About 70% of all H7N9 cases reported from Zhejiang are from these two prefectures.