Pandemic influenza 2009-10: Variation in diagnosis and treatment in an urban center

Background: The 2009-10 influenza pandemic presented challenges to clinicians since national diagnostic and therapeutic guidelines changed over time. Adherence to these guidelines has not been reported.

Objective: To evaluate physician adherence to guidelines for diagnostic testing and appropriateness of oseltamivir use during the H1N1 pandemic.

Methods: We conducted a retrospective cohort study of laboratory-confirmed influenzavirus infection from 5/1-12/31/2009 in a large urban facility. We identified case-patients using rapid and/or PCR tests performed on hospitalized patients and among those seen in the emergency department (ED). We reviewed medical records to identify demographic and clinical information. We used the CDC definition for influenza-like illness (ILI: fever and cough ± sore throat) and defined severe illness as requiring intensive care or documented oxygen saturation of ≤92%.

Results: Preliminary analysis identified ~1600 patients tested for influenzavirus among whom 149 (9.3%) were positive. This included 47 inpatients and 102 outpatients; 118/149 (79%) were <18 yrs of age, and 50 (34%) had an underlying medical condition. There was no difference in the likelihood of a positive test result by age (≤ or >18 years) or by source of test (ED or inpatient). Thirty-six persons (24%) had severe disease; 24 (66%) of whom received oseltamivir. Overall, 65/116 (56%) children and 14/31 (45%) adults received oseltamivir (p>0.05). Adults with ILI were less likely to receive oseltamivir than children with ILI (p<0.04). Overall, we identified an error in drug dose or duration in 8/149 (5%). Among inpatients, 30/47 (64%) patients had ILI at the time of laboratory testing. Oseltamivir was initiated in 33/47 (70%) inpatients and for 21/30 (70%) persons with ILI. Empiric treatment was started in 11/47 (23%) inpatients, prior to laboratory confirmation. Oseltamivir therapy was initiated <48hrs from symptom onset in 29/33 (88%). From the ED, 687 patients were tested of which 378 (55%) were <18 yrs of age. One hundred two of 687 (26%) were positive for influenzavirus and 12/102 (12%) were admitted. Eighty-two of 102 (80%) ED patients had ILI. Oseltamivir therapy was initiated in 46/102 (45%) persons. Thirty-five of 46 (76%) of all ED patients received oseltamivir <48hrs from symptom onset. The most common reasons for not prescribing oseltamivir included ≥48 hrs since symptom onset and lack of an underlying medical condition, consistent with contemporaneous CDC guidelines.

Conclusions: Approximately 25% of persons with influenza did not have ILI. One-third of those hospitalized or with severe disease did not receive oseltamivir. When treated, ~20% of all patients received drug outside the recommended therapeutic window. Adults with ILI were less likely to receive oseltamivir usually due to delayed presentation. We identified potentially important variation in the clinical approach to influenza among practitioners.