Red wine has been touted for its health benefits but these don’t seem to extend to warding off swine flu. The virology laboratory in Bordeaux in the southwest of France tested via RT-PCR over 1200 nasopharyngeal swabs between May 1 and the first week in October and found 186 positive for the new pandemic strain. They looked at five of these cases more closely, monitoring them for duration of viral shedding. Two of the five kept shedding for 2 to 4 weeks (paper in Eurosurveillance by Fleury et al., v. 14, #49, December 10, 2009).
The first case was a non-obese previously healthy male in his mid fifties. Shortly after returning to France from California in the beginning of July he developed fever and had difficulty catching his breath. Within a day he was in the intensive care unit. A swab was positive for the presence of the swine flu virus. He was started on the recommended dose of oseltamivir (Tamiflu, 150 mg daily) and improved rapidly. He was soon transferred out of the ICU, but repeat swabs showed he was continuing to shed virus. Oseltamivir was continued and then changed to zanamivir (Relenza). He continued to shed virus for another 7 days, until day 15, when he was discharged. He was evaluated for immunosuppressive illness and found not to have any signs of one.
The second case was a morbidly obese (BMI over 50) woman in her late twenties, just returned from Spain in late July. She had flu-like symptoms for 5 days while at home but began to deteriorate and wound up in an intensive care unit on 31 July. A nasopharyngeal swab revealed the presence of the virus and she, too, was started on oseltamivir at the recommended dose. Her conditioned worsened and she developed acute respiratory distress syndrome (ARDS) and was put on a ventilator and then extracorporeal membrane oxygenation (ECMO), essentially a heart lung machine that allows the blood to get oxygen without requiring the lungs to work. Oseltamivir was increased to a double dose (300 mg per day) on 2 August. Her condition allowed deep respiratory secretions to be obtained and they remained positive for the virus for 13 samples (19 days). Of interest was that nasopharyngeal swabs were negative when deep lung secretions were positive in this patient. Virus continued to be detected until day 31 after symptom onset. Miraculously, this critically ill woman with a major risk factor made a full recovery and left the hospital at the beginning of September. She, too, was evaluated for immunosuppressive conditions but no sign of one was found.
What about the virus? These patients were treated intensively with the antiviral neuriminidase inhibitors but had prolonged viral shedding, although both did well clinically. The viral isolates were checked for the main mutation that confers resistance (H274Y) and neither had it. The virus was apparently sensitive to the drugs. So there was no apparent explanation for why these patients continued to shed virus for much longer than the usually claimed period of 5 to 7 days from onset. This was despite the use of antivirals which in experimental challenge studies with human volunteers have cut the length of viral shedding in half (a median of 107 hours to 58 hours). Prolonged viral shedding can occur in children and the immunocompromised, but that describes neither of these patients.
There is data on viral shedding in influenza but not a great deal of it. Our guess is that the previous estimates, based on rather small samples, do not adequately account for a substantial number of prolonged shedders there might be when millions of people are infected. Even if prolonged shedding occurs infrequently, say in one in a thousand cases, this could still produce thousands of people who continue to shed influenza virus for weeks after they are apparently recovered.
It may be that people can continue to harbor infection and even shed virus to some extent, but not enough to infect others. It’s another of the many things we don’t know about flu. But now we know that prolonged shedding of virus can and does occur. We just don’t know what it means.