2017–2018 United States flu season

The 2017-2018 flu season was a flu season of high severity in the United States. Influenza-like illness (ILI) has a high rate of outpatient and emergency clinic visits, and a high rate of influenza-related hospitalizations, and influenza activities have been on the rise for a long period of time and are widely distributed geographically. In 2017, the Centers for Disease Control and Prevention began using a new method to classify seasonal severity and applied the method to the seasons from 2003-2004 to 2016-2017. The 2017-18 season was the first season to be classified as highly serious among all age groups. 
Origin.
In the 2017-2018 season, influenza-like illness (ILI) activities began to increase in November, and reached a long period of high activity nationwide in January and February, and continued until the end of March. The peak of ILI was 7.5%, the highest percentage since the 2009 influenza pandemic (7.7%). Influenza-like illness (ILI) reached or exceeded the national benchmark for 19 weeks, making 2017-2018 one of the longest seasons in recent years.
Infections and Deaths.
According to the US Centers for Disease Control and Prevention (CDC), there are no reports of childhood flu deaths nationwide. To monitor influenza-related deaths of all ages, the CDC tracks deaths caused by pneumonia and influenza (P&amp;I) through the National Center for Health Statistics (NCHS) mortality reporting system. The system tracks the proportion of death certificates that list pneumonia or influenza as a potential cause of death. The system provides an overall indication of whether influenza-related mortality has increased, but does not provide an exact number to indicate the number of deaths from influenza. During the 2017-2018 season, the percentage of deaths due to pneumonia and influenza (P&amp;I) reached or exceeded the epidemic threshold for 16 consecutive weeks.