Severe Respiratory Illness Associated with Delayed Virus Clearance in H1N1 Patients

The first influenza pandemic of the 21th century was ignited by a new strain of influenza A virus (A/H1N1pdm). Specific patient groups, including those with comorbidities, pregnant women, young children, older and immunocompromised patients, are at increased risk for serious influenza-related disease. Silvia Meschi, of the Laboratory of Virology at the National Institute for Infectious Diseases in Rome, and colleagues, sought to study the influence of clinical presentation, antiviral treatment and possible drug resistance-associated mutations on the extent and duration of viral shedding in patients infected with A/H1N1.

An observational study was performed, based on retrospective review of clinical and laboratory records of patients who were hospitalized for A/H1N1pdm infection at the National Institute for Infectious Diseases between April 24 and Dec. 31, 2009. Among 119 hospitalized patients, 39 were selected for a post hoc analysis, based on the availability of serial nasopharyngeal swabs samples and related information.

Eleven out of the 39 study patients (28.2 percent) presented with pneumonia; 29 (74.4 percent) received antiviral treatment. Patients with pneumonia were significantly older than patients without pneumonia. The mean values of viral RNA concentration were not significantly increased in patients with pneumonia, but a significant increase in the duration of viral shedding was observed as compared to patients without pneumonia. In patients receiving antivirals, the viral RNA concentration was significantly reduced in comparison to untreated patients at days four to five after symptom onset, while the overall duration of viral shedding was only marginally affected. A significant correlation between duration of viral shedding and time elapsed between symptom onset and therapy start was observed, with a significant reduction of days of viral shedding when therapy was initiated within two days of symptoms appearance. No known drug resistance mutations were detected in patients with prolonged viral shedding.

The researchers say their results show that severe respiratory illness is associated with delayed virus clearance in patients with A/H1N1pdm infection. Antivirals caused an early reduction of viral load, but only marginally affected the overall duration of shedding. Prolonged shedding was not associated with the emergence of strains carrying known drug-resistance mutations. Their work was published in BMC Infectious Diseases.

Reference: Meschi S, Selleri M, Lalle E, Bordi L, Valli MB, Ferraro F, Ippolito G, Petrosillo N, Lauria FN and Capobianchi MR. Duration of viral shedding in hospitalized patients infected with pandemic H1N1. BMC Infectious Diseases 2011, 11:140doi:10.1186/1471-2334-11-140