Significantly Elevated Number of Human Infections with H7N9 Virus in Jiangsu in Eastern China October 2016 to January 2017

The authors conducted statistical analysis of human and environmental surveillance data, meteorological factors, and phylogenetic analysis on human cases of H7N9 virus infection between October 2016 and January 2017 in Jiangsu, China. Jiangsu is one of the most affected of the seven Chinese provinces that have seen human cases, and the number of human cases in Jiangsu during the ongoing fifth wave of the outbreak exceeds the combined total cases from the first four seasons. Despite greater treatment experience and a shorter interval between illness onset and use of antivirals, the authors observed an acceleration in disease progression with median time interval from onset of disease to intensive care unit admission dropping from 10 days in the first wave and 9 days in the second wave to 7 days in the last three waves and a median time interval from onset of disease to death in the fifth wave dropping to 13.5 days in comparison to a range of 15 to 28 days in previous waves. The number of human cases increased in December. The authors noted that the number of days in December with high risk ambient temperatures was also elevated, suggesting the need for further research. The environmental H7N9 detection rate was also elevated in December and the authors suggested that closures of live poultry markets may have contributed to a drop in cases in January. Other patient characteristics, exposure history to poultry or live poultry markets, and proportion of severe infections and deaths were similar in the fifth wave to previous waves.