INTRODUCTION — The common cold is a benign self-limited syndrome representing a group of diseases caused by members of several families of viruses. It is the most frequent acute illness in the United States and throughout the industrialized world . The term "common cold" refers to a mild upper respiratory viral illness. The common cold is a separate and distinctly different entity than influenza, pharyngitis, acute bronchitis, acute bacterial rhinosinusitis, allergic rhinitis, and pertussis.
The common cold is associated with an enormous economic burden as assessed by lost productivity and expenditures for treatment . A United States telephone survey conducted between 2000 and 2001 indicates that about 500 million noninfluenza viral respiratory infections occur yearly, resulting in estimated direct costs of USD $17 billion and indirect costs of $22.5 billion annually .
The average incidence of the common cold is five to seven episodes per year in preschool children, and two to three per year by adulthood . Annual absences from school and work in the United States due to colds caused 26 and 23 million lost days, respectively . Colds account for 40 percent of all time lost from jobs among employed people . It is no surprise then, that tens of millions of research dollars have been spent on ways to prevent and shorten the course of the common cold. (See "The common cold in children: Clinical features and diagnosis" and "The common cold in children: Management and prevention".)
The epidemiology and clinical manifestations of the common cold are discussed here. Treatment and prevention of colds are discussed separately. (See "The common cold in adults: Treatment and prevention".)
VIROLOGY — Over 200 subtypes of viruses have been associated with the common cold. New viruses capable of causing colds, such as the human metapneumovirus and bocaviruses, have been identified using polymerase chain reaction (PCR) and pan-viral DNA microarrays (Virochip) technology. It is anticipated that additional viruses that also cause the common cold will be identified.
Rhinoviruses, which include more than 100 serotypes, are the most common viruses associated with cold symptoms and collectively cause 30 to 50 percent of colds. Coronaviruses cause about 10 to 15 percent of common colds. Viruses with marked seasonal variation, such as influenza and parainfluenza, typically cause more systemic symptoms than other cold viruses; however, they can rarely also cause illnesses similar to the common cold. Influenza virus causes about 5 to 15 percent of colds, and respiratory syncytial virus (RSV) and parainfluenza virus are each responsible for about 5 percent (table 1) [5-7]. (See "Epidemiology, clinical manifestations, and pathogenesis of rhinovirus infections" and "Seasonal influenza in adults: Clinical manifestations and diagnosis" and "Parainfluenza viruses in adults" and "Respiratory syncytial virus infection: Clinical features and diagnosis".)
Adenoviruses and enteroviruses have also been associated with the common cold. Adenovirus more commonly causes pharyngitis and fever than cold symptoms and may also cause epidemics of lower respiratory infections in military quarters as well as severe lower respiratory infections in immunocompromised patients. Infections caused by the enteroviruses (echo and coxsackie) are frequently asymptomatic or produce an undifferentiated febrile illness, and thus there may not be a causal association if isolated from a patient with a cold. Enteroviruses may also be associated with distinctive clinical syndromes such as aseptic meningitis and pleuritis. (See "Pathogenesis, epidemiology, and clinical manifestations of adenovirus infection" and "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention".)
It is not possible to determine the likely viral pathogen on the basis of the observed clinical illness; all of the above viral pathogens may cause similar symptoms. Parainfluenza and RSV are more likely to cause cold symptoms in young children .
Most of the respiratory viruses that cause colds are capable of reinfection after reexposure . However, subsequent infections with the same or similar agents are generally milder and of shorter duration . The molecular and genetic basis for incomplete cross-protection following infection with one strain is not fully understood. However, data from rhinoviruses suggest that this may be due in part to a remarkable degree of structural and molecular variability, both within serotypes and between the divergent field strains that frequently arise from a given reference virus .
Seasonal patterns — Seasonal patterns of infection can be observed for some of the viruses that cause the common cold. Rhinoviruses and the various parainfluenza types typically cause outbreaks of infection in fall and late spring, while respiratory syncytial virus (RSV) and coronaviruses typically produce epidemics in winter and spring [1,5,10]. Enteroviruses most often cause illness in the summer but can be detected throughout the year. Adenoviruses are usually not seasonal, but outbreaks may occur in military facilities, daycare centers, and hospital wards.
Transmission — Common cold viruses can be spread by three mechanisms :
●Hand contact (via direct contact with an infected person or via indirect contact with a contaminated environmental surface)
●Small particle droplets (droplet nuclei or aerosols) that become airborne from sneezing or coughing
●Large particle droplets (droplet transmission) that typically require close contact with an infected person
The importance of hand-to-hand virus transmission has been repeatedly demonstrated . In one classic study, volunteers were exposed to rhinovirus; 0 of 8 subjects became ill in the group where fingers were treated with 2 percent aqueous iodine, compared with infection in 6 of 10 subjects in the control group .
Cold-inducing viruses may remain viable on human skin for up to two hours. The risk of person-to-person transfer is dependent upon the amount of time people spend together, the proximity of their contact with one another, and the amount of virus shed by the infected patient. (See "Epidemiology, clinical manifestations, and pathogenesis of rhinovirus infections".)
Respiratory viruses including influenza and RSVs can be spread by both large droplet (classic droplet transmission) and small droplet (also called droplet nuclei, or aerosolized particles), although the relative contribution of each particle type to overall spread of a given virus is unproven [5,13]. (See "Respiratory syncytial virus infection: Clinical features and diagnosis", section on 'Transmission and incubation period'.)
Viral spread from contaminated fomites is another mechanism of transmission. Rhinoviruses may survive on environmental surfaces for several hours, thus allowing spread from contact with contaminated surfaces [14,15]. Interestingly, porous materials such as tissues and cotton handkerchiefs do not appear to support virus survival and thus secondary contact with these materials is an inefficient mode of virus transmission . Decontamination of environmental surfaces with virucidal disinfectants such as phenol/alcohol may help decrease the rate of transmission of cold-inducing viruses .
A randomized double-blind study of the effectiveness of various antibacterial home-cleaning products failed to show a difference, compared with standard products, in the incidence of respiratory symptoms among study patients . This finding is not a surprise as antibacterial cleaning products would not be expected to have an effect on viral pathogens. Despite these negative findings, and the unresolved question of whether direct hand-to-hand contact or droplet spread is the more important route of transmission, it is reasonable to assume that proper disposal of nasal secretions and adequate handwashing will help to prevent the spread of colds.
Unproven factors — The possibility that recirculating air in commercial airliners might increase common cold transmission has been proposed. However, a study of 1100 United States air passengers (53 percent aboard airplanes with recirculated cabin air and 47 percent aboard aircraft with exclusively fresh air ventilation) found no difference in the postflight rate of persons reporting a cold, runny nose or a constellation of eight other respiratory symptoms . While this single study does not definitively rule out the possibility that recirculating air in airplanes increases transmission risk, it does indirectly support the contention that hand-to-hand transmission is more important than droplet transmission.
Saliva is not an efficient means of spread of most cold viruses. Over 90 percent of people with colds have no detectable virus in their saliva .
Period of infectivity — Studies that have involved experimental inoculation of subjects with viruses causing the common cold have shown that peak viral shedding with rhinovirus occurs on the second day of illness [19,20]. Viral shedding peaks on the third day of the illness after inoculation, which coincides with a peak in symptoms. However, low levels of viral shedding may persist for up to two weeks. Studies have also shown that nasal washings taken five days after onset of a cold illness can produce symptoms of infection when experimentally inoculated into volunteers .
RISK FACTORS — Risk factors for the common cold include exposure to children in daycare settings; at-home caregivers have greater risk of cold than those who work outside the home . Psychological stress increases the risk of colds , and moderate physical exercise decreases the risk . Individuals who have less sleep and preexisting sleep disturbances may have an increased susceptibility to cold virus infection .
There is no scientific basis for the popular notion that a cold climate increases susceptibility to respiratory illness. As an example, investigators working in a research base in Antarctica noted that the frequency of colds was equivalent in men after six months in the Antarctic and men just arriving from the United States to begin their Antarctica residence .
Risk factors for increased severity of upper respiratory infection (URI) include :
●Underlying chronic diseases
●Congenital immunodeficiency disorders
CLINICAL FEATURES — Symptoms of the common cold are largely due to the immune response to infection, rather than to direct viral damage to the respiratory tract. Symptoms may substantially vary from patient to patient; rhinitis and nasal congestion are most common. Other common symptoms include sore throat, cough, and malaise. Fever is uncommon in adults with a cold but may be present in children; conjunctivitis occurs variably in both age groups. The intensity and type of symptoms of the common cold may also be related to host factors including age, underlying illnesses, and prior immunological experience, as well as to the type of infecting virus .
The most common and characteristic initial symptoms are nasal discharge, nasal obstruction, and a dry or "scratchy throat" . Cough is common and tends to appear after the onset of nasal discharge and obstruction. When present, cough often persists past the time that nasal and throat symptoms resolve . Although cough may be prominent and prolonged in some patients, rales and signs of lower respiratory tract involvement typically are not present in adults. Fever, when present, tends to be low grade. Many patients also complain of sneezing, malaise, headache, and pressure or discomfort in their ears and face.
Nasal discharge in patients with the common cold may be clear or purulent. Many patients and clinicians erroneously place diagnostic importance upon the color of nasal discharge when making decisions about antibiotic use . In fact, colored nasal discharge is a normal self-limited phase of the uncomplicated common cold. The presence of purulence alone cannot distinguish between a cold and a sinus infection. (See 'Acute rhinosinusitis' below.)
Incubation period and symptom duration — The incubation period (from the time of contact with infectious material until the onset of symptoms) for most common cold viruses is 24 to 72 hours, although in an experimental setting symptom onset can occur as early as 10 to 12 hours after exposure . Colds usually persist for 3 to 10 days in the normal host [1,5], although clinical illness may last as long as two weeks in up to 25 percent of patients, particularly smokers . Cough can persist for weeks after resolution of other signs and symptoms .
DIAGNOSIS — The diagnosis of the common cold is clinical, based upon reported symptoms and/or observed signs. Physical examination may reveal conjunctival injection, nasal mucosal swelling, nasal congestion, and pharyngeal erythema. Adenopathy is typically absent or minimal; in the absence of secondary bronchospasm, the lung examination is typically clear.
Several clinical scoring systems, such as the Wisconsin Upper Respiratory Symptom Survey (WURSS)  and the Jackson cold scale , have been developed to differentiate viral colds from other causes of respiratory illness and to quantitate illness severity. While commonly used in clinical studies, they have inadequate sensitivity and specificity (85 and 44 percent and 81 and 66 percent, respectively) for use in clinical practice .
Radiologic studies are not routinely indicated. Chest radiograph to evaluate for lower respiratory tract infection is indicated if the physical examination suggests signs of consolidation or other parenchymal disease. Sinus radiographs or computed tomography (CT) scan are not indicated; some form of mucosal abnormality on CT scan may be observed in as many as 42 percent of asymptomatic individuals [31,32]. In one study of 31 patients with self-diagnosed "colds" confirmed by viral culture, mucosal thickening or air-fluid levels of the maxillary sinuses were found on CT scan within two to three days of symptom onset in 87 percent .
Other than influenza-specific assays (when indicated by temporal epidemiology and clinical symptoms), viral polymerase chain reaction (PCR) and bacterial cultures from nasal swabs or washings are not generally indicated.
Although there are novel molecular assays for the detection of many common cold viral pathogens, there are no targeted antiviral therapies approved for use in uncomplicated upper respiratory viral infections in normal hosts.
Furthermore, detection of viral shedding does not necessarily correlate with clinical disease; asymptomatic viral shedding, particularly with rhinovirus, is extremely common. For example, up to 6 percent of asymptomatic adults and up to 35 percent of asymptomatic pediatric patients have a positive viral PCR at any given time [34-36].
The potential benefit of nasal bacterial cultures was examined in a double-blind, placebo-controlled trial involving 314 patients who presented with symptoms typical of the common cold. Subjects were randomly assigned to receive five days of treatment with amoxicillin-clavulanate (375 mg three times daily) or placebo . Seventy-two of 300 patients who had nasal aspirates performed had negative bacterial cultures, 167 had cultures that were positive only for bacteria not responsible for respiratory infections, and 61 had cultures positive for Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae. Antibiotic therapy benefited only those in the latter group; 27 percent of those in the latter group versus 4 percent of placebo-treated patients had better symptom scores on antibiotics. Because the majority of bacterial cultures of nasal discharge taken from patients with colds are negative or reveal nonpathogenic bacteria, and because results of cultures are not immediately available to guide treatment, we consider bacterial cultures of nasal secretions in patients with the common cold cost-ineffective, impractical, and unnecessary.
The vast majority of patients who present with typical signs and symptoms of the common cold do not require any laboratory testing. However, in rare situations where corroboration of a presumed viral etiology of symptoms would be useful (eg, for patient education or management of a particularly severe presentation), procalcitonin testing may provide supporting evidence that a patient has a viral infection, thus avoiding unnecessary antibiotics [38-40].
DIFFERENTIAL DIAGNOSIS — Although the common cold is usually diagnosed clinically and readily identified by symptoms, several other conditions may mimic the common cold:
●Allergic or seasonal rhinitis
●Coronavirus disease 2019 (COVID-19) due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
●Bacterial pharyngitis or tonsillitis
●Acute bacterial rhinosinusitis
The common cold can be differentiated from simple rhinitis, by the presence of sore throat and cough, and from bacterial tonsillitis, by the presence of prominent rhinorrhea and nasal stuffiness. Patients with acute rhinosinusitis typically experience facial pain in conjunction with purulent nasal discharge, while patients with influenza typically have a high fever, headache, and myalgias. Pertussis in particular has experienced a marked resurgence  and may begin with symptoms similar to the common cold. However, pertussis is also associated with prolonged coughing, typically paroxysmal, and with vomiting and sometimes apnea. Pertussis may present atypically, particularly in previously immunized adults, and the persistence of severe coughing for more than two weeks is suggestive of pertussis. (See "Allergic rhinitis: Clinical manifestations, epidemiology, and diagnosis" and "Evaluation of acute pharyngitis in adults" and "Acute sinusitis and rhinosinusitis in adults: Clinical manifestations and diagnosis" and "Seasonal influenza in adults: Clinical manifestations and diagnosis" and "Pertussis infection in adolescents and adults: Clinical manifestations and diagnosis".)
Clinically differentiating common cold symptoms from SARS-CoV-2-19 infection is challenging, as there is a high degree of variability in the presentation of COVID-19 and many symptoms overlap with those of the common cold. Findings that may make COVID-19 more likely include a history of exposure to someone with known SARS-CoV-2 infection, presence of anosmia or ageusia, and progressive moderate to severe shortness of breath (see "COVID-19: Clinical features"). However, given the clinical overlap between the two syndromes, testing for SARS-CoV-2 in the setting of symptoms of the common cold is reasonable as long as SARS-CoV-2 transmission continues at moderate to high rates in local communities. (See "COVID-19: Diagnosis", section on 'Whom to test'.)
Acute rhinosinusitis — Patients with the common cold may also develop acute rhinosinusitis. Viral sinusitis occurs far more frequently than secondary bacterial sinusitis. Patients with acute rhinosinusitis have purulent nasal discharge and nasal obstruction or facial pain/pressure/fullness or both. However, these symptoms may also occur to a variable degree in patients with a simple common cold. The diagnosis of viral and bacterial acute rhinosinusitis is discussed separately. (See "Acute sinusitis and rhinosinusitis in adults: Clinical manifestations and diagnosis".)
Lower respiratory tract disease — Most patients with common colds do not have lower respiratory tract signs or symptoms. However, certain pathogens that cause the common cold, particularly respiratory syncytial virus (RSV) and parainfluenza virus, can also produce lower respiratory tract findings. These findings can range from bronchitis, to bronchiolitis, to pneumonia. For example, RSV is an important cause of lower respiratory tract disease among children, older adults, and immunocompromised patients in addition to its ability to trigger symptoms of the common cold [42-44]. (See "Respiratory syncytial virus infection: Clinical features and diagnosis" and "Acute bronchitis in adults".)
Asthma exacerbation — Viral upper respiratory infections (URIs) have also been linked to up to 40 percent of acute asthma attacks in adults [45,46]. It is uncertain whether increased airway hyperreactivity is the result of local inflammation caused by viral infection of lower airway epithelial cells , or if infection is limited to the upper airway with inflammatory mediators acting distantly in the lower airways. (See "Risk factors for asthma".)
Rhinovirus has emerged as the most frequent common cold virus associated with asthma exacerbations. It is thought that the epithelial airway antiviral response to rhinovirus may be defective in patients with asthma . However, in a study that compared experimental inoculation of rhinovirus in 20 subjects with mild persistent allergic asthma and 18 healthy adults, there was no difference in peak cold symptom score, peak nasal viral titers, peak airway flow, or measures of cellular and cytokine responses .
Rhinovirus-induced changes in airway reactivity may persist for up to four weeks following infection . These changes in airway reactivity may explain why some individuals develop a persistent cough following upper respiratory tract infections. However, other causes of cough, such as pertussis, should be considered when individuals develop persistent cough following a presumed viral respiratory tract infection. (See "Pertussis infection in adolescents and adults: Clinical manifestations and diagnosis".)
Acute otitis media — Viral URI often causes eustachian tube dysfunction; impaired clearance and pressure regulation of the middle ear may then lead to acute otitis media . Although otitis media following URI is more common in children than adults, 50 to 80 percent of normal adults developed eustachian tube dysfunction after they were experimentally exposed to rhinovirus or influenza A virus . In addition to inducing eustachian tube disturbance, respiratory viruses can be isolated directly from middle-ear fluid, suggesting that viruses may also actively invade the middle ear and cause acute otitis media . (See "Acute otitis media in children: Epidemiology, microbiology, and complications", section on 'Viral pathogens'.)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Sinusitis in adults (The Basics)")
●Beyond the Basics topics (see "Patient education: Acute sinusitis (sinus infection) (Beyond the Basics)" and "Patient education: The common cold in adults (Beyond the Basics)")
●The common cold is the most frequent acute illness in the industrialized world, with two to three episodes of illness per year in adults. (See 'Introduction' above.)
●Over 200 subtypes of viruses have been associated with the common cold. Rhinoviruses cause 30 to 50 percent of colds but are also commonly found in asymptomatic subjects. It is not possible to identify the likely viral pathogen on the basis of clinical symptoms. (See 'Virology' above.)
●The majority of upper respiratory infections (URIs) are transmitted by hand contact; cold-inducing viruses may remain viable on human skin for up to two hours. Recirculated air on commercial airplanes and cold temperature exposure do not seem to increase risk. (See 'Transmission' above and 'Risk factors' above.)
●Symptoms of the common cold are largely due to the immune response to infection. Colds usually persist for 3 to 10 days in the normal host, although clinical illness may last as long as two weeks in up to 25 percent of patients. (See 'Clinical features' above.)
●With the exception of mild or early COVID-19 due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the diagnosis of the common cold is clinical, based upon reported symptoms and/or observed signs. Sinus radiographs or computed tomography (CT) scan are not indicated; some form of mucosal abnormality on CT scan may be observed in as many as 42 percent of asymptomatic individuals. Molecular tests for viral etiologies other than SARS-CoV-2 are not generally helpful or indicated for uncomplicated disease. Cultures of nasal secretions are not practical or cost-effective to identify patients with bacterial infection. Colored nasal secretions should not be considered as evidence of secondary bacterial infection. (See 'Diagnosis' above.)
●Complications of the common cold may include acute rhinosinusitis, lower respiratory tract disease, asthma exacerbation, or acute otitis media. (See 'Complications' above.)
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