Stats to Watch: Flu Affects 1 to 4 Percent of Americans on Any Given Day
The Gallup-Healthways Well-Being Index (WBI), the largest and most comprehensive daily tracking survey of American health and well-being, showed no significant increase in the percentage of Americans reporting flu-related illness in April 2009. On any given day, between 1 to 4 percent of the adult population reports being sick with the flu. The April average was 2.1 percent, slightly less than the average during the same period a year ago.
The Gallup-Healthways Well-Being Index surveys a random sample of 1,000 adults each day, or roughly 30,000 interviews each month on a variety of topics related to health and well-being, making it one of the most accurate barometers of population health trends in existence. One of the questions asked daily is, “Were you sick with any of the following yesterday?” The question specifies four illnesses: the flu, a cold, a headache and allergies. The WBI does not specifically differentiate between flu strains. Given the current swine flu situation, these data provide a baseline for monitoring increases or decreases in the incidence of flu at both the population and community levels.
It is unlikely that the spread of swine flu in the United States will be so massive that it would move the percentages in these reports in and of itself. Each percentage of the adult population represents about 2.2 million people, so even tens of thousands of cases of swine flu would not by themselves have a major impact on national samples.
Still, widespread publicity about a disease such as swine flu no doubt will increase Americans’ focus on their health and symptoms. Thus, it is possible that those who in the past may have ignored symptoms will find themselves rushing to the doctor to have their symptoms diagnosed, and this could cause the self-reported incidence of flu to increase as a secondary byproduct of the swine flu situation. There has, however, been no increase in self-reports of flu in the last several days by WBI respondents.
Many people confuse flu symptoms with common-cold symptoms. Colds, at least as reported by average Americans, are significantly more prevalent than flu. The percentage of the adult population that reports having been “sick with a cold” on any given day throughout the year ranges from a little more than 2% to nearly 11%. As with flu, there is apparently predictable cyclicality. Colds are most commonly reported in the late fall and winter, and drop off significantly in the summer months.
There is a significant inverse correlation between age and reports of having been “sick with the flu yesterday” in the Gallup-Healthways data. These data are an aggregate of more than 110,000 interviews conducted so far in 2009, from Jan. 2 through April 27. Younger adults are most likely to report being sick with the flu, and the percentage drops fairly steadily with age. Incidence of flu among children and among teenagers aged 13 to 17 is not reflected in the data.
It is important to remember that these data reflect being “sick with the flu” and do not indicate mortality as a result of flu. It’s likely that the consequences of having the flu are much more significant among older people, even if the prevalence of the disease itself is lower. Additionally, older Americans who are so sick with flu that they are hospitalized would not be available for interviewing.