Background: Seasonal influenza vaccination is recommended for patients with end-stage renal disease, although the efficacy of the vaccination among these patients is unknown. We characterize a recent outbreak of pandemic influenza A(H1N1pdm) among patients early after kidney transplantation in a kidney transplant unit.

Methods: Annually 180-200 kidney transplantations are performed in our institution. Baseline immunosuppression is cyclosporine or tacrolimus, mycophenolate and steroids. Induction with basiliximab is used only in patients with higher immunological risk. Due to renovations the kidney transplant unit was relocated in a ward not designed for the treatment of immunosuppressed patients.

Results: Altogether 23 patients were treated on the ward for postoperative care after kidney transplantion during the outbreak. After the first positive case, all patients were tested with nasopharyngeal swab tests, and 7 patients were diagnosed with an influenza A(H1N1pdm) with qualitative PCR. Altogether 14/23 patients had received a seasonal influenza vaccination the autumn before, of whom 2/14 were tested positive for influenza (one asymptomatic, one only with mild cough). All 5 unvaccinated patients were diagnosed with influenza A(H1N1pdm); 3/5 suffered from severe respiratory failure, and were treated with ventilator support in the ICU, but all died due to acute respiratory distress syndrome despite maximal treatment efforts, whereas 2/5 suffered from mild viral pneumonitis and recovered fully. Vaccination history of 4 patients was unknown; none of these patients were diagnosed with influenza. The risk of influenza infection and mortality were significantly increased in unvaccinated patients (P=0.01 and 0.002, respectively). Reasons for the outbreak were suboptimal conditions at the ward, unlikely season for influenza, and failure to test samples from the upper respiratory tract in a timely manner.

Conclusions: Influenza A(H1N1pdm) has a high mortality (60%) in nonvaccinated immunosuppressed patients early after kidney transplantation. None of the previously vaccinated patients suffered from serious disease, suggesting that seasonal influenza vaccine is very effective also among end-stage renal disease patients.

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