Abstract
A fifth or more of hospital-acquired pneumonias may be attributable to respiratory
viruses. The SARS-CoV-2 pandemic has clearly demonstrated the potential morbidity
and mortality of respiratory viruses and the constant threat of nosocomial transmission
and hospital-based clusters. Data from before the pandemic suggest the same can be
true of influenza, respiratory syncytial virus, and other respiratory viruses. The
pandemic has also helped clarify the primary mechanisms and risk factors for viral
transmission. Respiratory viruses are primarily transmitted by respiratory aerosols
that are routinely emitted when people exhale, talk, and cough. Labored breathing
and coughing increase aerosol generation to a much greater extent than intubation,
extubation, positive pressure ventilation, and other so-called aerosol-generating
procedures. Transmission risk is proportional to the amount of viral exposure. Most
transmissions take place over short distances because respiratory emissions are densest
immediately adjacent to the source but then rapidly dilute and diffuse with distance
leading to less viral exposure. The primary risk factors for transmission then are
high viral loads, proximity, sustained exposure, and poor ventilation as these all
increase net viral exposure. Poor ventilation increases the risk of long-distance
transmission by allowing aerosol-borne viruses to accumulate over time leading to
higher levels of exposure throughout an enclosed space. Surgical and procedural masks
reduce viral exposure but do not eradicate it and thus lower but do not eliminate
transmission risk. Most hospital-based clusters have been attributed to delayed diagnoses,
transmission between roommates, and staff-to-patient infections. Strategies to prevent
nosocomial respiratory viral infections include testing all patients upon admission,
preventing healthcare providers from working while sick, assuring adequate ventilation,
universal masking, and vaccinating both patients and healthcare workers.
Keywords
hospital-acquired pneumonia - respiratory viruses - nosocomial infection - infection
control - masking - ventilation
