Outbreak of influenza virus A/H1N1 in a hospital ward for immunocompromised patients

In February 2008, five patients were infected with the H1N1 subtype of influenza A virus in one hospital ward for immunocompromised patients at a hospital in North Rhine-Westphalia, Germany. All of these patients had an established haematologic disease and tested positive either for viral RNA or antigen shortly after the beginning of respiratory illness. In three of the patients, influenza virus was repeatedly detected, and four of the patients died in coincidence with the virus infection. Sequencing of the amplified (HA1) haemagglutinin yielded identical nucleotide sequences in isolates from three of the patients, whereas one nucleotide difference was found in the isolate of the fourth patient, resulting in an amino acid substitution (G153R). To investigate the source of infection, the medical staff (n = 104) of the hospital unit was tested and found negative for influenza virus RNA and antigen in pharyngeal lavages. Testing for influenza virus antibodies by immunofluorescence assay revealed that 12 staff members were positive for influenza virus A IgA antibodies. These findings suggest that wild-type influenza virus infections occurred within the medical staff at the same time the patients were infected and that the staff might have contributed to the circulation of virus in the hospital ward.