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So What?
1) The Centers for Disease Control and Prevention collects, compiles, and analyzes information on influenza activity year round
in the United States. The surveillance system is a collaboration between the CDC and public and private health care providers
and vital statistics offices around the U.S.
2) This graph plots the percent of office visits where an influenza-like illness (ILI) was presented over multiple flu seasons
around the chart. The CDC defines the official flu season starting each year at week 40, in early October. The distance from
the center indicates a higher percent of office visits being for ILI, with the middle being zero.
3) Many ILI cases are not tested for 2009 Influenza A (H1N1) (swine flu), complicating determination of flu type, so we have
plotted all ILI cases without regard to type.
4) One can see a general pattern for the incidence of seasonal flu that peaks around week 7 of the year, in mid- to
late-February each year.
5) There are occasional outbreaks with lower incidence late in the calendar year at week 52, the end of December.
6) During the 2009-2010 flu season, one can see the very early and high prevalence of flu which started near week 33 (late
August 09) and appears to have recently peaked at week 42 (late October 09). This is likely due to 2009 Influenza A (H1N1)
(swine flu).
7) The recent peak of about 8% of office visits is already 50% higher than the seasonal peak around 6% during the 2007-08 flu
season.
8) Note that this chart tells us nothing about the number of flu cases, only the percent of office visits presenting flu-like
symptoms. It does tend to indicate the prevalence and severity of flu relative to other medical conditions requiring office visits.
9) See also Pediatric Influenza Deaths Over Time.
1) The Centers for Disease Control and Prevention collects, compiles, and analyzes information on influenza activity year round
in the United States. The surveillance system is a collaboration between the CDC and public and private health care providers
and vital statistics offices around the U.S.
2) This graph plots the percent of office visits where an influenza-like illness (ILI) was presented over multiple flu seasons
around the chart. The CDC defines the official flu season starting each year at week 40, in early October. The distance from
the center indicates a higher percent of office visits being for ILI, with the middle being zero.
3) Many ILI cases are not tested for 2009 Influenza A (H1N1) (swine flu), complicating determination of flu type, so we have
plotted all ILI cases without regard to type.
4) One can see a general pattern for the incidence of seasonal flu that peaks around week 7 of the year, in mid- to
late-February each year.
5) There are occasional outbreaks with lower incidence late in the calendar year at week 52, the end of December.
6) During the 2009-2010 flu season, one can see the very early and high prevalence of flu which started near week 33 (late
August 09) and appears to have recently peaked at week 42 (late October 09). This is likely due to 2009 Influenza A (H1N1)
(swine flu).
7) The recent peak of about 8% of office visits is already 50% higher than the seasonal peak around 6% during the 2007-08 flu
season.
8) Note that this chart tells us nothing about the number of flu cases, only the percent of office visits presenting flu-like
symptoms. It does tend to indicate the prevalence and severity of flu relative to other medical conditions requiring office visits.
9) See also Pediatric Influenza Deaths Over Time.
Influenza - Doctor Visits Over Time
Supporting Evidence
Source: U.S. Centers for Disease Control and Prevention: Flu Activity & Surveillance
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