Duration of Viral Shedding of 2009 H1N1 Influenza in Critically Ill Ventilated Patients

Duration of Viral Shedding of 2009 H1N1 Influenza in Critically Ill Ventilated Patients

Christy A. Zalewski MPH, Lena M. Napolitano MD, Carol E. Chenoweth MD

University of Michigan Health System, Ann Arbor, MI

Background: Most persons shed influenza virus for 5-7 days from the onset of symptoms; young children and severely immunocompromised persons may shed virus for longer. The duration of viral shedding in the most critically ill 2009 H1N1 influenza patients is not well known. Knowledge of viral shedding is imperative in the hospital setting as it determines the length of isolation precautions and may guide duration of antiviral treatment.

Objective: To determine the duration of viral shedding of 2009 H1N1 Influenza in critically ill patients admitted to our surgical intensive care unit (SICU) to guide both duration of isolation and antiviral treatment.

Methods: Our study population was all patients with confirmed H1N1 infection admitted to a 20 bed SICU from 6/1/09 to 11/12/09. Viral culture and Polymerase Chain Reaction (PCR) testing were performed at regular intervals to assess presence of virus.  Specimen source for testing was bronchoalveolar lavage (BAL) and/or nasopharyngeal (NP) swab. Autopsy specimens were tested for influenza if available. The date of symptom onset was used as the start of viral shedding and the date of the last positive influenza test was used as the end of viral shedding.

 

Results: There were 20 patients with confirmed H1N1 infection admitted to the SICU during the study period; 19 were transferred from an outside hospital for Extracorporeal Membrane Oxygenation (ECMO) evaluation for Acute Respiratory Distress Syndrome.  Of the 20 patients, 7 were placed on ECMO and 5 died. The average duration of viral shedding was 14 days (range 5-24 days). This correlated with 1-15 days from ICU admission.  One patient was found to be positive at time of autopsy; the autopsy was 17 days from onset of symptoms. Of note, 2 patients with both BAL and NP swabs tested concurrently were positive for influenza from BAL and negative from NP swab. Two/20 were positive from BAL, 13/20 were positive from NP swab, and 5/20 were positive from both sites. Five/20 patients were positive from viral culture and 15/20 were positive from PCR. The average duration of antiviral treatment was 15 days (range 7-30). Seven/19 patients were found to be positive for influenza after their antiviral treatment course ended and the average treatment duration for these positive patients was 8 days (range 5-15).

 

Conclusions: The duration of H1N1 shedding as determined by culture or PCR in very critically ill patients is longer than reported for most patients. Serial testing for influenza in these patients may be helpful to guide duration of isolation precautions and antiviral treatment. Shorter courses of treatment were associated with continued viral shedding.