Severity is classified as “very high” if at least 2 indicators for the overall population peak above the respective systems’ highest ITs.Severity is classified as “high” if at least 2 indicators for the overall population peak between the respective systems’ mid-range and high ITs.Severity is classified as “moderate” if at least 2 indicators for the overall population peak between the respective systems’ lowest and mid-range ITs.Severity is classified as “low” if at least 2 of 3 indicators for the overall population peak below the respective systems’ lowest ITs.

The peak value of an indicator is compared to the respective IT for that indicator to arrive at a severity classification. The Moving Epidemic Method is then used to translate the data into standardized intensity thresholds (ITs) for each indicator. the percentage of deaths resulting from pneumonia or influenza that occurred during each season.the rates of influenza-associated hospitalizations, and.the percentage of visits to outpatient clinics for ILI,.What did researchers do to classify the severity of flu seasons in this study?įlu severity is assessed using the following data : CDC then classifies the severity of individual flu seasons by determining whether the indicator values during the peak of each flu season crossed their respective ITs. CDC first calculates intensity thresholds for three key flu indicators using data from past flu seasons. CDC tracks flu activity through key flu indicators, including the percentage of influenza-like illness (ILI) visits to outpatient clinics, the rates of influenza-associated hospitalizations, and the percentage of deaths resulting from pneumonia or flu.ĬDC began using a new approach published in 2017 to define flu season severity.

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