Evaluation of diagnostic and therapeutic approaches for suspected influenza A(H1N1)pdm09 infection, 2009-2010.

In April 2009, the novel influenza A(H1N1) pandemic influenza virus (influenza A[H1N1]pdm09) was identified as the cause of influenza outbreaks. Influenza disease caused by this strain rapidly spread, and in June 2009, the World Health Organization (WHO) declared a global pandemic. Disease activity peaked during May–June 2009, again in October 2009, and essentially disappeared by May 2010 (1–3). As with previous pandemics, the strain reemerged in the United States during the subsequent 2010–2011 influenza season and accounted for ≈25% of characterized strains (4). During the pandemic, the Centers for Disease Control and Prevention (CDC) issued several guidances for healthcare providers for the identification and treatment of patients with suspected influenza A(H1N1)pdm09 disease (Figure 1). Several rapid influenza diagnostic tests for identification of the 2009 H1N1 strain were available, but their poor sensitivity soon became clear (5–7). CDC recommended that the neuraminidase inhibitor oseltamivir be used as a first-line treatment during the pandemic (8). Available data suggested that the drug was clinically effective, but only when given within <48 hours of symptom onset (9–11). These guidelines changed during the course of the pandemic as real-time epidemiologic, virologic, and clinical data emerged (8,12–15). Figure 1 Centers for Disease Control and Prevention (CDC) guidance during the 2009 pandemic of influenza A(H1N1)pdm09 disease. LRTI, lower respiratory tract infection. CDC initially recommended priority use of antiviral drugs for only hospitalized patients and those at increased risk for influenza-related complications. This recommendation reflected the knowledge that most persons infected with A(H1N1)pdm09 virus had self-limited, mild-to-moderate disease; that commercial and stockpiled supplies of oseltamivir were limited; and that the development of resistance was a concern, particularly since no other effective and easily administered antiviral drugs were available (15–18). Questions remained, however, with regard to the overall risks and benefits and appropriate dosage of the drug for very young and obese patients. In September 2009, CDC advised that rapid influenza diagnostic tests be prioritized for patients who were hospitalized or for whom a diagnosis of influenza could inform clinical decision making. Furthermore, CDC reinforced the idea that presumptive treatment should be administered to this group of patients and expanded the target group for treatment to include outpatients with risk factors for severe disease, even when test results were unknown (5). Clinical judgment was clearly a key factor in the clinical management of patients with possible A(H1N1)pdm09 disease. Much has been published with regard to the epidemiology, virology, and clinical spectrum of A(H1N1)pdm09 illness (19,20), but no information is available with regard to diagnostic and therapeutic decision making of physicians or their adherence to national guidelines for ill patients. We conducted this study to evaluate the adherence of physicians to contemporaneous national guidelines for diagnosis and use of oseltamivir among patients with suspected or confirmed A(H1N1)pdm09 virus infection in the inpatient and outpatient settings.