CMAJ. 2014 Feb 18; 186(3): 190–199. doi: 10.1503/cmaj.121442
G. Michael Allan, MD and Bruce Arroll, MB ChB PhD
The common cold is an acute, self-limiting viral infection of the upper respiratory tract involving the nose, sinuses, pharynx and larynx. The virus is spread by hand contact with secretions from an infected person (direct or indirect) or aerosol of the secretions and virus.1 The incubation period varies but is just under two days for rhinovirus.2 Symptoms, which generally relate to the infected mucosa, typically peak at 1–3 days and last 7–10 days, although they occasionally persist for three weeks.1,3–5 They include sore throat, rhinitis, rhinorrhea, cough and malaise.1,4 The severity and type of symptoms will vary among individuals and with different infective agents. For example, fever is common in children but rare and mild in adults.1 The incidence of the common cold declines with age.5–7 Children under two years have about six infections a year, adults two to three and older people about one per year.5–9 Stress10 and poor sleep11 may increase the risk of the common cold among adults, whereas attendance at a daycare centre12 increases the risk among preschool children.
Rhinovirus accounts for 24%–52% of clinical cases or 52%–76% of infections with an identified pathogen.6–8,13 No pathogen is identified in 31%–57% of upper respiratory tract infections,8,13 likely because of a host of reasons, including poor collection technique, low pathogen count due to sampling late in the illness, or previously unidentified agents.1 Only about 5% of clinically diagnosed cases were found to have bacterial infection (with or without viral co-infection).13
Although self-limiting, the common cold is highly prevalent and may be debilitating. It causes declines in function and productivity at work14,15 and may affect other activities such as driving.16 Its impact on society and health care is large. Of individuals with an upper respiratory tract infection, 7%–17% of adults17,18 and 33% of children17 visit a physician. Upper respiratory tract infections result in an estimated increase of 12.5% in patient visits per month during cold and flu season.19
In the United States, direct medical costs related to the common cold (physician visits, secondary infections and medications)
were an estimated $17 billion a year in 1997.17
Indirect costs owing to missed work because of illness or caring for an ill child were an estimated $25 billion a year.17
We review the evidence underpinning preventive and treatment interventions for the common cold. We do not explore the proposed biologic mechanisms for the different products, because most are not substantiated and generally represent more supposition than science. The quality of the evidence was frequently poor, with a moderate to high risk of bias. Although preventive interventions have somewhat discrete outcomes (presence of an upper respiratory tract infection), interpretation of the evidence for treatment of the common cold is challenged by the complexity of outcome reporting. The evidence used in this review is described in Box 1.