Table 1.

Characteristics of etiology and seasonality of viral respiratory infections (VRIs).

Respiratory virus	Family	Structure and genome	Subtypes	Primary routes of transmission	Seasonal patterns
Influenza virus15	Orthomyxoviridae	Enveloped ss − RNA viruses	A, B, C	Droplets and aerosols, contact	Winter peaks in temperate regions
Respiratory syncytial virus (RSV)10	Paramyxoviridae	Enveloped ss − RNA viruses	A, B	Direct and indirect contact, droplets, and aerosols	Winter and early spring peaks in temperate regions
Human Metapneumovirus (HMPV)14	Paramyxoviridae	Enveloped ss − RNA viruses	A, B	Droplets and contact	Late winter and spring peaks in temperate regions
Parainfluenza viruses (PIV)14	Paramyxoviridae	Enveloped ss − RNA viruses	1, 2, 3, 4	Droplets and contact	PIV-1 and PIV-2 peak in the fall and winter in temperate regions, PIV-3 peaks in warm seasons, PIV-4 sporadically all-year
Human coronavirus (HCoV)13,16	Coronaviridae	Enveloped ss + RNA viruses	OC43, 229E, NL63, HKU1a	Droplet spray and/or aerosol, contact	Winter peaks in most temperate regions
Rhinoviruses (RV)17	Picornaviridae	Enveloped ss + RNA viruses	Species A, B, and C, with >100 serotypes	Contact, droplet spray, and/or aerosol	All-year, with peaks in the autumn and spring in temperate regions
Human bocavirus (HBoV)15	Parvoviridae	Non-enveloped ss + DNA viruses	1, 2, 3	Contact, droplet spray, and/or aerosol	All-year, with a possible peak during the summer
Adenoviruses (ADV)13,18	Adenoviridae	Non-enveloped dsDNA viruses	53	Contact, possibly droplet spray and/or aerosol	All-year
Enterovirus (EV)14	Picornaviridae	Non-enveloped ss + RNA viruses	D68	Contact	Summer and autumn

^aOther human coronaviruses include MERS-CoV, SARS-CoV and SARS-CoV-2.