Virus	Estimated annual proportion of cases	References
Rhinoviruses	30% to 50%; during autumn 80%. Once considered to be limited to the upper airway, now recognised as an important cause of lower respiratory infections	Arruda 1997; Gwaltney 1985; Heikkinen 2003; Lemanske 2005; Monto 1993; Mäkelä 1998; Regamey 2008
Coronaviruses	7% to 18% in adults with upper respiratory infections. Responsible for 2.1% of hospital admissions for acute respiratory tract infections in all age groups	Larson 1980; Lau 2006; Mäkelä 1998; Nicholson 1997
Influenza viruses	5% to 15%	Heikkinen 2003
Respiratory syncytial virus (RSV)	In low‐income countries, 15% to 20% In hospital the proportion of children aged between birth and 5 months with RSV acute lower respiratory tract infections ranged between 9% and 87%. Among children up to at least 5 years of age reported with RSV, on average 39% (range 20% to 62%) were < 6 months old; on average 24% of cases (range 14% to 38%) were children aged 6 to 11 months. An average of 63% of children were thus under 1 year of age. On average 20% (range 13% to 29%) of the children were between 1 and 2 years of age. Respiratory syncytial virus accounts for approximately 10,000 deaths annually in people over the age of 65 years in the USA. Respiratory syncytial virus in adults, 5% infection annually	Berman 1991; Falsey 2005; Thompson 2003
Parainfluenza viruses	Acute respiratory infections cause 3% to 18% of all admissions to paediatric hospitals; 9% to 30% of these patients depending on the time of year. Parainfluenza viruses account for 17% of hospitalised illness‐associated virus isolation. In low‐income countries 7% to 10% This virus causes 50% to 74.2% of croup cases.	Berman 1991; Denny 1983; Henrickson 2003
Adenoviruses	In low‐income countries can be summarised as 2% to 4%	Berman 1991
Metapneumovirus	10% short epidemic	Esper 2003; Kahn 2003; Nissen 2002; Risnes 2005
Unknown	20% to 30%	Monto 1993; Mäkelä 1998