In a retrospective analysis of acute influenza visits to primary care clinics, we found that clinicians prescribed antivirals to 58% of patients they diagnosed with influenza. This rate increased significantly over time. In our previous study, the antiviral prescribing rate was 31%.11
This previous study was based on a small set of clinics and fewer visits. More importantly, our prior study was based on data from the 1999–2000 to 2003–2004 influenza seasons. In the present analysis, the antiviral prescribing rate increased from just over 20% in the 2001–2002 and 2002–2003 influenza seasons to over 50% in the 2003–2004 influenza seasons. In multivariate modeling, there was a 20% to 40% increase in antiviral prescribing from season to season. During this time, in accordance with the prescribing recommendations of the CDC, clinicians nearly stopped prescribing adamantanes.20
As before, antiviral prescribing was associated with non-clinical factors such as insurance and race/ethnicity. Antiviral prescribing was positively associated with clinical factors such as age and negatively associated with clinical factors such as cough and otoscopic abnormalities. The strongest independent clinical predictor of antiviral prescribing — in accordance with prescribing guidelines for antivirals — was symptom duration for fewer than 2 days. Seemingly paradoxically, symptom duration was also the factor most strongly related to inappropriate antiviral prescribing: 24% of patients who received antivirals had symptoms for more than 2 days. Overall, 38% of prescriptions were inappropriate, and, as before, we found that about a quarter of patients who were not prescribed antivirals met appropriateness criteria.
Influenza testing was a strong independent predictor of antiviral prescribing. Clinicians prescribed antivirals to 84% of patients who had a positive influenza test and to 75% of patients who had a negative test raising the question of why most testing was performed.
We found good news in regards to antibiotic prescribing. In contrast to patients hospitalized with influenza,9,26
in primary care clinics antibiotic prescribing was infrequent and may have even decreased over time. In addition, the independent predictors of antibiotic prescribing suggest that clinicians tended to restrict antibiotic prescribing to patients who they suspected may have had otitis media or pneumonia. Based on these results, interventions to improve antibiotic prescribing for patients with influenza should not be a high priority.
On the other hand, given the high rate of inappropriate antiviral prescribing, interventions seem warranted. The greatest challenge in the appropriate prescribing of antivirals is that they be prescribed within 2 days. To reduce symptoms and potentially complications, systems should be in place to make it easy for patients to access care when it is likely they have influenza, without overwhelming clinics with patients who have non-specific upper respiratory tract infections.
This analysis has several limitations that should be considered. First, as with our prior analysis, it was difficult to identify influenza visits. A claims diagnosis of influenza had a positive predictive value of only 11% even after excluding emergency department visits from the denominator. Influenza cases included in this study made up few visits to the study clinics, lower than the rate suggested from CDC data,10,25,27
which highlights that we examined a specifically defined group of visits. Second, we used a hybrid method — using both claims diagnoses and electronic antiviral prescribing — of identifying influenza visits. However, there was no substantive difference in results when we limited the analysis to visits identified using only claims data. Third, our review was dependent on clinician documentation. The “gold standard” diagnosis was one in which the treating clinician documented a diagnosis of influenza in the visit note. We used clinicians’ own diagnoses as representative of actual practice, although this almost certainly included visits at which the patient did not actually have influenza and excluded visits in which the patient did have influenza. This allowed us to assess clinician documentation, the internal consistency of clinical decision-making, and appropriateness of antiviral use for visits with a clinical diagnosis of influenza. Finally, our definition of appropriateness allowed for patient-reported fever — as opposed to just measured fever — and did not take into account the actual prevalence of influenza at the time of the visit. As such, it was a forgiving definition.