The coronavirus outbreak in the United States is of a piece with the steady rise in influenza cases over the past 13 years, which is the period for which CDC maintains tallies of flu tests and test results.

Here are some raw statistics, representing weekly results since the 40th week of 1997:

The rate of positive tests has remained steady since 1997, with a slight upward bump coincident with the swine flu epidemic of 2009-2010:

The steadiness of the positive-test percentage suggests that the presence of flu-like symptoms was just as likely to have prompted testing in 1997 as in 2020. Another way to put it is that the first graph accurately represents a steady rise in the occurrence of flu-like symptoms in the population.

This can be seen in the following graph:

Despite the fairly stable incidence of positive tests, the number of positive tests has grown far more rapidly than the population of the U.S.

The bottom line: Americans have become increasingly prone to contract flu-like illnesses. Though the increase can’t be explained by the overall rise in the country’s population, it is probably due in part to greater population density in urban areas. It is probably also due in part to the weakening of immune systems relative to the ability of viruses to mutate.

It is possible that influenza won’t be as prevalent in the future as more Americans take precautions against contagion in the wake of COVID-19. But memories are short, and precautions are easily cast aside when the world seems to have returned to normal. So I expect that in a few years the incidence of flu will resume its long-term rise.