Risk Factors and Diagnosis
Upper respiratory infections (URIs), or colds, can be caused by many families of viruses, such as rhinovirus (which has at least 100 serotypes), coronavirus, and respiratory syncytial virus. URIs are the most common acute illnesses in the industrial world.
Cold symptoms include:
- Rhinitis (sneezing, nasal congestion, and postnasal drip).
- Cough, usually dry.
- Fatigue and myalgias.
- Mild fever.
Direct contact with individuals who have an upper respiratory infection permits viral transfer. In particular, closed settings such as homes and schools have higher attack rates than work settings. Seasonal variations occur for some viral families. However, cold climates are not necessarily a risk factor for disease occurrence or severity.1
Touching 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. Saliva is not an effective mode of transmission.
Common cold symptoms are listed above. Colds and influenza typically have few physical findings and often cannot be distinguished reliably in clinical settings. If a definitive diagnosis of influenza is important, certain tests may be useful (see Influenza chapter). 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.
Prevention and Treatment
Covering the mouth and nose when coughing and sneezing, washing hands appropriately, and avoiding touching one's eyes and nose are the most effective preventive strategies.
Moderation in exercise may help immunity. There is a high incidence of upper respiratory infection in endurance athletes, due to impairments in neutrophil function, reductions in serum and mucosal immunoglobulin production, and, possibly, natural killer cell cytotoxicity. In contrast, moderate physical activity either has a null or a stimulant effect on these parameters.2,3
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 (eg, interleukin-6)4 or a reduction in mucosal production of secretory immunoglobulin A (sIgA).5 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.5,6
When cold symptoms occur, only symptomatic treatment is beneficial. There are no specific treatments for URIs, such as antibiotics. Heated and humidified air may improve symptoms.7 The following agents may also be helpful:
- Decongestants. A brief course of pseudoephedrine may be of benefit, as may topical nasal decongestant sprays. However, topical agents should only be used for 2 to 3 days, as they cause tachyphylaxis, and extended use of pseudoephedrine is unlikely to be helpful. In general, it is best to avoid nasal sprays, except perhaps for sleep. Pseudoephedrine taken with an antihistamine is more effective than when taken alone. Data are lacking on decongestant use in children.8
- Intranasa cromolyn sodium and ipratropium bromide may reduce the severity of cold symptoms. Cromolyn sodium can also be inhaled.
- Antihistamines. Clemastine fumarate improves sneezing and rhinorrhea,9 and diphenhydramine may also be effective. Both drugs 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 symptoms and myalgias. Their use for mild fever is unnecessary. Aspirin should not be used in children with an acute viral illness, due to the risk of Reye's syndrome.
- Evidence supporting mucolytics, such as guaifenesin, and anti-tussives, such as dextromethorphan and codeine, is varied and inconclusive.10 Their use may benefit certain patients, but more research is needed to make global recommendations. Caution: Codeine may be habit-forming.
- Antibiotics should be considered or used only for specific bacterial infections, such as sinusitis, streptococcal pharyngitis, otitis media, and bronchitis. In the case of bronchitis, they should not be used unless the cough is persistent or the patient has underlying lung disease. Not all cases of otitis media and sinusitis require antibiotics. Unnecessary prescribing increases the likelihood of antibiotic resistance.
Antibacterial cleaning products do not affect disease transmission, and may also cause bacterial resistance. Phenol/acetate sprays for household use do have virucidal qualities.
Upper respiratory infections are caused not simply by the presence of an invading microorganism, but also by the failure of the immune system to eliminate the intruder. Diet is a significant modulator of immune function. Notably, high-fat diets are immunosuppressive, while certain micronutrients play important roles in immune function. Unfortunately, many Americans regularly consume too much fat, and up to 50% get less than half the Recommended Dietary Allowance for many micronutrients.11 Deficiencies of these nutrients are known to impair immune function.12
Although diet changes (eg, increasing the intake of carotenoid-containing foods or reducing fat intake) have been found to stimulate immune function,13,14 these improvements have mainly been identified in clinical trials of nutrient supplements, rather than in trials of therapeutic diets. Clinical trials comparing the effects of various diets (eg, high-fat vs. low-fat, omnivore vs. vegetarian) are not yet available, so potential benefits of dietary alterations for the treatment or prevention of colds remain speculative.
The role of certain micronutrients in the prevention or treatment of URIs is discussed below.
Vitamin mineral supplements. Older individuals are often deficient in a number of vitamins and minerals, predisposing them to a blunting of the innate and the adaptive immune responses.15,16 Some studies suggest that multiple vitamin-mineral supplements may reduce sick days and antibiotic use. The trace elements zinc and selenium, known to be important in immune function, may be responsible for this effect.15
Zinc. Zinc ions inhibit rhinoviruses through several mechanisms: prevention of viral replication;17 potentiation of the antiviral action of native human interferon; and stimulation of T-cells18. Consequently, zinc lozenges can significantly reduce the duration of colds.19 The formulation of zinc lozenges seems to influence their effectiveness. Many (zinc aspartate, zinc glycinate, zinc orotate) bind zinc tightly and do not release the positively charged zinc ions that are the active principle, or they release negatively charged zinc ions that may actually increase the duration of colds. In comparison, studies using other forms of zinc (eg, zinc gluconate, zinc acetate) have found them to be an effective treatment.17,19,20 Several studies have also confirmed that intranasal zinc gel was effective for reducing the duration of colds.17
Patients should be cautioned that irritation of the oral mucosa and mild gastrointestinal complaints are common with zinc lozenges, while nasal irritation occurs more frequently with gel and spray forms. In addition, zinc lozenges are maximally effective only when used every 2 hours. Nasal gel/spray formulations are most effective when used every 4 hours.
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.21,22 In these persons, the relative risk for developing colds was reduced by 50% when they took vitamin C supplements, compared with individuals not using the supplements.21 Among the same groups, those taking vitamin C had 80% to 100% reductions in pneumonia incidence, compared with persons given placebo treatment.22
Vitamin E. In pharmacologic amounts, vitamin E reduces the production by cyclo-oxygenase of prostaglandin E2, a suppressor of T-cell function, and enhances lymphocyte proliferation and interleukin-2 production.23 In elderly nursing home residents, 200 IU of vitamin E per day significantly reduced the incidence of common colds and the number of persons who got colds.24 Further research is required to determine whether vitamin E can reduce the incidence of infections.
Vitamin E supplementation may have the opposite effect in persons with established respiratory infections. Supplements of 200 mg/day caused longer illness duration, more symptoms, and higher fever frequency.23
Echinacea. Anecdotal reports support the effectiveness of the common botanical echinacea, but clinical trials to date have been negative or inconclusive. A lack of standardization of purportedly active ingredients is another stumbling block that must be overcome before echinacea can be recommended for URI.25
Excessive alcohol intake can increase susceptibility to infection. Although small amounts (1-2 drinks per day) do not appear to adversely affect immunity,26,27 alcohol abuse increases the incidence of infectious diseases through depleting circulating lymphocyte populations and suppressing production of cytokines important in antimicrobial immunity.26
What to Tell the Family
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. 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.
1. Warshauer DM, Dick EC, Mandel AD, Flynn TC, Jerde RS. Rhinovirus infections in an isolated Antarctic station. Transmission of the viruses and susceptibility of the population. Am J Epidemiol. 1989;129:319-340.
2. Nieman DC. Exercise immunology: nutritional countermeasures. Can J Appl Physiol. 2001;26(suppl):S45-S55.
3. Mackinnon LT. Chronic exercise training effects on immune function. Med Sci Sports Exerc. 2000;32(suppl 7):S369-S376.
4. Cohen S. Keynote Presentation at the Eight International Congress of Behavioral Medicine: the Pittsburgh common cold studies: psychosocial predictors of susceptibility to respiratory infectious illness. Int J Behav Med. 2005;12:123-131.
5. Reid MR, Mackinnon LT, Drummond PD. The effects of stress management on symptoms of upper respiratory tract infection, secretory immunoglobulin A, and mood in young adults. J Psychosom Res. 2001;51:721-728.
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16. El-Kadiki A, Sutton AJ. Role of multivitamins and mineral supplements in preventing infections in elderly people: systematic review and meta-analysis of randomised controlled trials. BMJ. 2005;330:871-874.
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18. Mossad SB. Effect of zincum gluconicum nasal gel on the duration and symptom severity of the common cold in otherwise healthy adults. QJM. 2003;96:35-43.
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23. Graat JM, Schouten EG, Kok FJ. Effect of daily vitamin E and multivitamin-mineral supplementation on acute respiratory tract infections in elderly persons: a randomized controlled trial. JAMA. 2002;288:715-721.