Surveillance of respiratory virus infections in adult hospital admissions using rapid methods.

Both influenza and respiratory syncytial virus (RSV) cause epidemics of respiratory illness of variable severity during the winter season. Influenza in particular has been blamed for hospital winter bed pressures, although it is thought that RSV may also play a role. Human metapneumovirus (hMPV) is a new respiratory virus reported to be important in children; only a limited number of studies are available for adult populations. We aimed to determine initially the burden of virologically confirmed infections, i.e. influenza, RSV and hMPV using polymerase chain reaction (PCR) technology and, in addition, to assess the feasibility of this approach as a surveillance tool for these respiratory viruses. Adult patients admitted to hospital in the previous 24 hours with onset of acute respiratory symptoms in the last 14 days were asked to participate. Informed written consent was obtained and nose and throat swabs taken. Multiplex PCR for influenza A (H1N1 and H3N2), influenza B and RSV A and B were carried out together with a separate PCR for hMPV. A total of 219 patients in 2001-2002 and 216 in 2002-2003 were tested and the combined results for both seasons were: 8 positive for influenza A/H1N1, 14 for influenza A/H3N2, 2 for influenza B, 14 for RSV A and 6 for RSV B. Most patients (261/435) were >65 years and most positives (30/44) were found within this age group. A number of patients aged >65 years who were positive for influenza (12/15) reported having had vaccine. In total, 373 samples were tested for hMPV and 20 were found positive across all age groups except the 45-54 years age group. As influenza activity was low during the study period the impact of infection on admissions could not be assessed. Nevertheless the viruses studied accounted for 15% of hospital admissions for respiratory infection. Most patients were aged >65 years, as expected. In the two years studied RSV and hMPV were each responsible for as many hospitalized cases of respiratory infection as influenza. Influenza infection must be considered even in those who give a history of vaccination. The molecular methods used in this study showed that surveillance of these respiratory viruses can be conducted and may help in the management of patients.