RT Book, Section A1 Crowe, Jr., James E. A2 Jameson, J. Larry A2 Fauci, Anthony S. A2 Kasper, Dennis L. A2 Hauser, Stephen L. A2 Longo, Dan L. A2 Loscalzo, Joseph SR Print(0) ID 1159155004 T1 Common Viral Respiratory Infections T2 Harrison's Principles of Internal Medicine, 20e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259644016 LK accesspharmacy.mhmedical.com/content.aspx?aid=1159155004 RD 2024/03/29 AB The most common and frequent infections in humans are respiratory virus infections. Some classical respiratory viruses (e.g., rhinoviruses) enter the body through the respiratory tract, replicating and causing disease only in cells of the respiratory epithelium. Other, more systemic viruses (e.g., measles virus and severe acute respiratory syndrome [SARS] coronavirus) spread via the bloodstream and cause systemic disease; however, they also may enter through and cause disease in the respiratory tract. Although infections with systemic viruses often induce lifelong immunity against disease, respiratory viruses that do not cause viremia usually can reinfect the same host many times throughout life. Reinfection with the same virus is common because of incomplete or waning immunity after natural infection. Hundreds of different viruses cause infection of the respiratory tract, and within each virus type there can be a nearly unlimited diversity of field strains that vary antigenically, geographically, and over time (e.g., antigenically drifting influenza viruses). Specific antiviral treatment options are limited, and only a few licensed vaccines are available. For further discussion of common respiratory virus infections, see Chap. 31 and syndrome-specific chapters.