This report demonstrates the wide range of respiratory viruses that circulate in LTCFs. Previous reports of viral disease in these populations have focused primarily on outbreaks of specific viruses, most often influenza.7,13–17
There have also been a number of prospective studies that have examined the role of other respiratory viruses such as RSV and parainfluenza in nursing homes, but most have been limited to a single season or institution.2,11,18–20
This study is unique in that 33 nursing homes over a 3-year period were under surveillance, and evaluation of eight different viral infections was undertaken. Although this trial was not designed to examine the specific microbiological etiology of respiratory illnesses, the collection of blood at baseline and 1 year provided an opportunity for serological diagnosis of multiple viral infections over time. In addition to the well-recognized pathogens influenza and RSV, infections due to hMPV, coronaviruses OC43 and 229E, and parainfluenza viruses were identified throughout the study period. Rather than large outbreaks of single pathogens, a veritable cornucopia of viruses circulated in individual nursing homes each year.
A rise in viral-specific antibody according to EIA remains sensitive and specific for detection of infection for most respiratory viruses in elderly people, even when compared with new molecular methods such as reverse transcription polymerase chain reaction (RT-PCR).9,21
Several exceptions are worth noting, one being influenza, in which response to vaccination may complicate the serological diagnosis of infection. In the current study, 24 and 19 residents were diagnosed with influenza A and B, respectively. None of the subjects infected with influenza A showed antibody rises to influenza B, and vice versa, suggesting that antibody rises were not vaccine induced. In addition, vaccine effect was less likely, because serum samples were obtained 7 to 9 months after immunization, when vaccine induced antibody has typically decreased to near baseline.22
Another limitation of serology for viral diagnosis is the inability to identify rhinovirus. Rhinovirus is a ubiquitous pathogen that has been shown to cause outbreaks of respiratory disease in nursing homes, but serological diagnosis is not possible, because multiple serotypes exist.23
Because rhinoviruses are a frequent cause of the common cold, it is not surprising that no association was found between URI and serological viral diagnosis.
Presently, there are limited data in elderly people on the newly described virus hMPV and its role as a cause of illness in LTCFs. Outbreaks of hMPV infection with significant morbidity and mortality in LTCFs have been reported in the United States, Canada, and Japan.16,24
In each report, diagnosis was made using RT-PCR, and the number of documented cases was small. In this study, hMPV was the most common infection diagnosed, accounting for 24% of the documented viral infections. Asymptomatic serological infection has been described in 9.5% of young and 1.5% of elderly adults.9
The clinical syndromes were not assessed in the current study, and therefore the true effect of hMPV could not be assessed. However, the frequency of infection indicates that prospective studies of hMPV in LTCFs are needed.
Similar to hMPV, coronaviruses are difficult to detect using standard viral cultures. Thus, few data are available on the effect of these viruses in long-term care. In a prospective study of 11 nursing homes in the United Kingdom using serology for diagnosis, 11% of acute respiratory infections were due to coronavirus OC43 or 229E.18
Outbreaks of respiratory illness due to coronavirus OC43 mimicking influenza have also been described in nursing homes.25
Coronaviruses OC43 and 229E were common in the current study, accounting for 6% and 11% of infections, respectively. Two new strains of human coronaviruses have recently been identified, NL63 and HKU1, and will require further study to determine whether these viruses are also important pathogens in this population.26,27
The current study demonstrates the complex nature of respiratory tract infections in LTCFs. Influenza infection was identified in 11% of residents, which confirms the need for improved influenza vaccines in this population, yet the broad range of other viruses circulating each year was impressive, underscoring the importance of viral-specific diagnosis during outbreak investigations or clinical trials of vaccines or antivirals. These data should provide useful information for those wishing to pursue clinical trials related to respiratory viral infections in nursing home populations.