Earlier this week, we reported on the current rates of influenza-like illness (ILI), based on data from roughly one million patient visits on the athenahealth network. That report showed a steep increase in ILI rates for the week ending Saturday, December 13 (see previous post). It’s not certain that this season will be as severe as that of 2012-2013 (data for pediatrics suggests that is a real possibility); however, providers are testing for flu more consistently than previous years, and prescribing antivirals more often.
Our data shows that the number of flu tests ordered, per patient visit in which ILI is diagnosed, has risen each of the past two years (Figure 1, graph A). This season, providers are ordering flu tests at a rate of 0.53 tests per visit with an ILI diagnosis, compared to 0.37 for last season and 0.34 for 2012-2013. (Note: There can be multiple tests per patient visit, e.g. Type A and B.)
Providers are also more likely to prescribe antivirals for ILI this flu season, compared to the past two seasons (Figure 1, graph B). This is likely a result of the increased number of tests, as well as the CDC issued advisory recommending the prescription of antivirals this season to reduce flu symptoms.
This combination of an increase in flu tests and an increase in prescriptions for antivirals suggests that health care providers have become more proactive about treating the flu. One reason could be a fundamental change in providers’ approach to flu, after the severe season of 2012-2013. An alternative explanation is that providers are aware of, and are responding to, one of this season’s flu strains (H3N2), the same strain that was predominant two seasons ago.
Given the increase in both ILI rates and flu treatment activity, we would not be surprised if this season has yet to peak. With next week’s flu update, we’ll provide state level maps, which we hope will be helpful as people embark on Christmas travel.
Iyue Sung, PhD is the Director of the athenaresearch unit.