Impact of Pandemic A/H1N1/2009 Influenza Virus on Patients With CF
The impact of pandemic A/H1N1/2009 influenza on CF patients is also unclear because only a few reports have been published and its role in worsening lung function is poorly understood. In a multicenter survey of ten countries, Viviani et al. found transient but significant morbidity due to pandemic A/H1N1/2009 influenza virus, especially in patients with pre-existing severe lung disease. They documented pandemic A/H1N1/2009 influenza infection in 110 out of 4689 patients (2.3%), only 8.8% of whom had been previously vaccinated. A total of 53% of the respiratory exacerbations required intravenous treatment, 48% of the patients were hospitalized and 31% required oxygen therapy. Six patients were admitted to intensive care units, of whom five required mechanical ventilation and three with severe lung disease died. However, other studies have shown that most CF patients experienced mild disease due to pandemic A/H1N1/2009 influenza virus. One Italian multicenter study found that the disease course was uncomplicated in most cases (85%) with no increased risk of complications in subjects treated with immunosuppressive therapy for organ transplantation. Similarly, no significant decline in lung function was associated with pandemic A/H1N1/2009 infection. Nevertheless, three infected patients with severe pulmonary disease died of respiratory failure, thus confirming that patients in poor clinical condition are exposed to an increased risk of complications and unfavorable outcomes during the course of influenza. Another two studies of adults with CF confirmed the presence of pandemic A/H1N1/2009 infection in a small percentage of cases (2–4%) and the symptoms tended to be mild except in the case of patients with severe lung disease who were found to potentially experience a severe clinical course.
However, once again, some aspects of these studies need to be considered. First, a number of the patients were treated with neuraminidase inhibitors in the presence of pandemic A/H1N1/2009 influenza, although there is no high-level evidence concerning the effectiveness of antiviral treatment in patients with CF; however, this approach may have changed the clinical course of pandemic A/H1N1/2009 influenza in the CF patients. Second, the emergence of oseltamivir-resistant strains related to the administration of the drug has been reported in CF patients, and this has led to the suggestion that patients with CF suffering from pandemic A/H1N1/2009 influenza and receiving oseltamivir should be closely monitored.
Considering the epidemiological data as a whole, it seems clear that more research into the role of influenza viruses in patients with CF and different degrees of pulmonary involvement is needed in order to clarify whether they really worsen respiratory morbidity and mortality. However, bearing in mind that a number of experts support universal influenza vaccination of the healthy population because of its clinical and socioeconomic benefits, annual influenza vaccination of CF patients seems to be a simple and inexpensive means of reducing the potentially negative aspects associated with influenza.