Upper respiratory infections (URIs), or colds, can be caused by many families of viruses, including rhinovirus (which has at least 100 serotypes), coronavirus, respiratory syncytial virus (RSV), adenovirus, influenza, parainfluenza, and enterovirus. URIs are the most common acute illnesses in the industrialized world.
Cold symptoms may include:
Stress, sleep deprivation, and exposure to children in daycare or school are all risk factors for development of a cold. Seasonal variations occur for some viral families, and in temperate climates, the "cold" season mirrors that of influenza. Exposure to cold climate is not considered a risk factor for disease occurrence or severity. Smokers and those with chronic diseases are at greater risk of increased severity of illness.
Direct contact with individuals who have an upper respiratory infection permits viral transfer. Touching an infected individual or a contaminated object is the most effective mode of transmission. Typically, a person with a cold rubs his or her eyes or nose and then shakes hands or touches objects that others touch later. Droplet transmission from coughing or sneezing is another effective mode of transmission. Saliva is not an effective mode of transmission.
Most cold viruses have an incubation period of about 24-72 hours, and symptoms typically persist for 3-10 days. Colds are diagnosed based upon the patient’s report of the symptoms listed above, and physical examination may reveal fever, nasal congestion, injected conjunctiva, and pharyngeal erythema. During cold and influenza season, some laboratories also test for viruses such as RSV, adenovirus, and parainfluenza virus when they test a nasopharyngeal swab for influenza. Most colds, however, are diagnosed clinically without confirmatory laboratory testing. Patients with symptoms or signs of lower respiratory infection, such as dyspnea or rales, should be evaluated for pneumonia or exacerbation of chronic lung disease. URIs do not cause signs of systemic inflammatory response; patients who appear seriously ill may require antibiotics or hospital admission. Severe or persistent cough or paroxysms of coughing in adults or adolescents should raise the question of pertussis, a highly infectious but vaccine-preventable URI caused by Bordetella pertussis.
Covering the mouth and nose when coughing and sneezing, washing hands frequently with soap and water or alcohol-based hand rub, and avoiding touching one’s eyes, mouth, and nose are the most effective preventive strategies.
The effect of exercise on upper respiratory infections is debatable. Moderation in exercise may help immunity. There is a high incidence of upper respiratory infection in endurance athletes, which some have attributed to impairments in neutrophil function, reductions in serum and mucosal immunoglobulin production, and, possibly, impaired natural killer cell cytotoxicity. In contrast, some evidence suggests that moderate physical activity has a stimulant effect on these parameters. However, a meta-analysis by the Cochrane Collaboration showed no differences in number, duration, or severity of acute respiratory infections between subjects who exercised and those who did not.
Individuals who have more frequent or long-lasting periods of psychological stress are at greater risk for upper respiratory infection. In this population, studies have shown an increase in certain proinflammatory cytokines (e.g., interleukin-6) or a reduction in mucosal production of secretory immunoglobulin A (sIgA). Although further research is required, some studies have found that stress management techniques (cognitive-behavioral therapy, progressive muscle relaxation, focused breathing, relaxation, guided imagery) increase the production of sIgA and reduce the number of sick days.,
With the exception of influenza, for which specific anti-viral treatment exists, most colds are treated symptomatically. There are no specific treatments for most URIs, such as antibiotics. Heated and humidified air may improve symptoms. The following agents may also be helpful:
Decongestants. A brief course (1-5 days) of pseudoephedrine may be of benefit, as may topical nasal decongestant sprays. However, topical agents should only be used for 2- 3 days, as they result in tachyphylaxis and rebound rhinitis. The combination of a decongestant and an antihistamine is most effective for symptom relief, but the benefit must be weighed against the potential side effects of insomnia, dry mouth, and drowsiness.
Antihistamines. Usefulness of antihistamines such as diphenhydramine in treating cold symptoms is limited to improvement of sneezing and rhinorrhea. Antihistamines can cause sedation and anticholinergic effects and should be used with caution in elderly patients or in individuals taking other anticholinergic agents. Several other antihistamines are also available without a prescription.
Analgesics. Acetaminophen, aspirin, and ibuprofen may improve sore throat, headache, and myalgia. Their use for mild fever is unnecessary, and in the case of aspirin, caution should be exercised around its use in children with cold or flu symptoms due to the increased risk of Reye's syndrome.
Evidence supporting mucolytics, such as guaifenesin, and anti-tussives, such as dextromethorphan and codeine, is varied and inconclusive. A Cochrane Review of studies of over-the-counter cough medication concluded there was insufficient evidence for or against their effectiveness. The American College of Chest Physicians recommends against the use of cough suppressants for URI-associated coughs. Their use may benefit certain patients, but more research is needed to make global recommendations. Caution: Codeine may be habit-forming.
Antibiotics should not be prescribed for the common cold, and should be considered only for specific secondary bacterial infections, such as sinusitis, streptococcal pharyngitis, otitis media, and bronchitis. Unnecessary prescribing increases the likelihood of antibiotic resistance and associated adverse events such as C. difficile colitis.
Antibacterial cleaning products do not affect disease transmission, and they may cause bacterial resistance. Phenol/acetate sprays for household use do have virucidal properties.
Probiotic supplements. Several meta-analyses have supported the ability of probiotic supplements to reduce the incidence and duration of URI in both children and adults. A Cochrane review found that probiotics reduced the number of participants experiencing episodes of acute URI by nearly 50% and decreased the duration of infection by nearly 2 days. In healthy adults challenged with rhinovirus, those treated with probiotics had demonstrable reductions of viral shedding in the nasal mucosa.
Echinacea. A systematic review and meta-analysis of various formulations of Echinacea published by the Cochrane collaboration demonstrated a pooled relative risk reduction of cold symptoms of 10%-20% when Echinacea was used as a prophylactic agent during cold and flu season. However, for 6 of 7 treatment trials included in the analysis, no benefit was observed with Echinacea over placebo.
Complications of upper respiratory illness include sinusitis, asthma exacerbation, otitis media, and other respiratory illnesses. See the chapters on these conditions for more information.
Diet is a significant modulator of immunity. Certain macro- and micronutrients play especially important roles in immune function and have been demonstrated to alter both the risk for URI and its duration. Unfortunately, up to 50% of Americans get less than half the Recommended Dietary Allowance for many micronutrients, and deficiencies are known to impair immune function.
The role of certain dietary supplements in the prevention or treatment of URIs is discussed below.
Zinc lozenges. Zinc ions inhibit rhinoviruses (which constitute roughly 80% of cold viruses) through several mechanisms: prevention of viral replication; potentiation of the antiviral action of native human interferon; and stimulation of T-cells. One meta-analysis found that zinc lozenges reduce the duration of colds by nearly three days, while a systematic review found zinc lozenges reduced the duration of colds by 42%. Patients should be cautioned that irritation of the oral mucosa and mild gastrointestinal complaints are common with zinc lozenges. Zinc in intranasal gel or spray forms have not been found effective.
Fatty acids. Several studies have found that supplementation with long chain omega-3 fatty acids (EPA and DHA) reduces the incidence of URI in infants and children.
Vitamin C. The utility of vitamin C for preventing or treating colds is widely accepted in the general population. However, most evidence supports the efficacy of megadoses for upper respiratory infections only for individuals who are under significant physical or environmental stress, such as marathon runners, skiers, soldiers, and people exposed to severe cold. In these persons, the relative risk for developing colds was reduced by 50% when they took vitamin C supplements, compared with the risk in individuals not using supplements.
The common cold is easily transmitted within the household. Family members should be encouraged to cover their mouths and noses while coughing and sneezing and to promptly wash their hands, taking care not to contaminate handles and light switches. Refraining from touching the eyes and nose may also help prevent respiratory infections. Vitamins and other supplements may be beneficial in some, but not all, individuals.