Nosocomial Transmission of the novel H1N1 virus: An outbreak investigation

Background: Preventing nosocomial transmission of the novel H1N1 influenza A virus is essential. However, the type and optimal duration of isolation precautions is unknown.

Objective: To investigate nosocomial viral transmission in a cluster of healthcare workers and patients with the novel influenza A(H1N1) virus infection.

Methods: Descriptive outbreak investigation of 4 healthcare workers and 2 immunocompromised patients, one of whom had two episodes, with the novel H1N1 influenza virus infection on the hematology-oncology ward of a children's hospital.

Results: In October 2009, the index patient, who was a 6 year old boy with sickle cell anemia and the novel H1N1 influenza A infection, was hospitalized on the hematology inpatient unit. There was delay in instituting isolation precautions for H1N1 and 2 days later the nurse taking care of the patient contracted novel H1N1 infection. This nurse had been involved in the care of a 2 year old immunocompromised child with hepatoblastoma who subsequently developed H1N1 infection. Two other staff members exposed to the hepatoblastoma patient also developed influenza-like illness proven to be H1N1 infection. Immunocompromised patients exposed to these nursing staff members were given chemoprophylaxis. The epidemic curve is shown in the figure. Emphasis was placed on strict droplet, N-95 respirator and standard precautions; nursing staff were cohorted and vaccinated. No further transmission occurred until the patient with hepatoblastoma developed fever and respiratory symptoms following chemotherapy and a second nasopharyngeal swab was positive for Influenza A (novel H1N1) by PCR  fifteen days after the first one. Isolation precautions had been discontinued after the first episode had resolved; the patient remained hospitalized the entire time. While it is possible that the second episode represented new nosocomial acquisition, given lack of evidence of ongoing transmission, we believe that reactivation is a more likely explanation of the patient's recurrent infection. A healthcare worker caring for this patient when he was not in isolation subsequently developed H1N1 infection.

Conclusions: We found that our immunocompromised patient had reactivation of H1N1 infection which has implications for recommendations regarding duration of isolation for this vulnerable group of patients. Our results suggest that immunocompromised patients remain in isolation precautions for the duration of hospitalization. Our cluster of nosocomial transmission by the novel H1N1 virus demonstrates the ease of spread of the novel H1N1 virus in an institution. It is imperative that isolation precautions be immediately implemented upon suspicion of illness.  Nurse cohorting, and judicious use of chemoproprophylaxis proved useful adjunctive measures for containing our outbreak.