The common cold is an acute respiratory tract infection characterized by mild coryzal symptoms, rhinorrhea, nasal obstruction, and sneezing. Although the incidence of the cold cannot be clearly defined because of seasonal and locational variability, it is estimated to vary from 3-6 cases per person per year. Children younger than 1 year have experienced an average of 6-8 episodes per year. This figure decreases to 3-4 episodes per year by adulthood. Although the list of agents that cause the common cold is large, 66-75% of cases are due to 200 antigenically distinct viruses from 8 different genera. The most common of these are the rhinoviruses (25-80% of cases), followed by coronaviruses (10-20%), influenza viruses (10-15%), and adenoviruses (5%).
Rhinoviral infections are chiefly limited to the upper respiratory tract but may cause otitis media and sinusitis. Rhinoviral infections may exacerbate asthma, cystic fibrosis, chronic bronchitis, and serious lower respiratory tract illness in infants, elderly persons, and immunocompromised persons. Although infections occur year-round, the greatest incidence occurs in the fall and spring. Of persons exposed to the virus, 70-80% have symptomatic disease.
Rhinoviruses are transmitted to susceptible individuals by direct contact or by aerosol particles infecting both ciliated areas of the nose and nonciliated areas of the nasopharynx. Few cells are actually infected by the virus, and the infection involves only a small portion of the epithelium. Symptoms develop 1-2 days after viral infection, peaking 2-4 days after inoculation, although reports have described symptoms as early as 2 hours after inoculation with primary symptoms 8-16 hours later.
The virus grows in a limited temperature range (33-35°C) and cannot tolerate an acidic environment. Thus, finding the virus outside of the nasopharynx is unlikely because of the acidic environment of the stomach and the increased temperature in both the lower respiratory and gastrointestinal tracts.
Individual patients exhibit a wide variety of signs and symptoms:
- The incubation period is 12-72 hours, averaging 8-16 hours after viral inoculation of the nose. Symptomatic complaints 2 hours after viral inoculation have been described.
- Illness initially begins with a sore throat, which is frequently the most bothersome of the early symptoms. This is followed by nasal discharge, nasal congestion, and sneezing, which intensify over the next 2-3 days.
- Other associated complaints include headache, facial and ear pressure, and loss of smell and taste.
- Thirty percent of infected individuals develop a cough, and 20% develop hoarseness, both of which may persist up to a week, although they seldom become bothersome until nasal symptoms improve.
- Systemic signs and symptoms, such as fever and malaise, are unusual. If they are present, consider an alternative diagnosis.
- Symptoms generally last 7-11 days, although they persist up to 2 weeks in a quarter of patients. Rarely, patients complain of lingering symptoms that last more than 30 days.
- Infants and toddlers may display only nasal discharge. However, Calvo et al recently reported that, among infants younger than 2 years with viral respiratory tract infection requiring hospitalization in Spain, rhinoviral infections are second only to respiratory syncytial virus infections in terms of frequency.
- School-aged children usually complain of nasal congestion, cough, and runny nose. These symptoms persist for an average of at least 10 days.
- Most patients have obstruction and mucosal abnormalities of sinuses, eustachian tubes, and middle ear, which causes a predisposition to secondary bacterial infection in up to 2% of patients.
- Infection may exacerbate underlying asthma and chronic pulmonary disease.
- People who smoke do not appear to have more frequent rhinoviral infections; however, their infections are more severe and their symptoms of longer duration.
The physical examination findings are typically less severe than those reported by the patient.
- Red nose with dripping nasal discharge may be present.
- Nasal mucous membranes have a glistening glassy appearance without obvious erythema or edema. Yellow or green nasal discharge does not indicate bacterial infection because a large number of white blood cells migrate to the site of viral infection.
- If marked erythema, edema, exudates, or small vesicles are observed in the oropharynx or if conjunctivitis or polyps in the nasal mucosa occur, consider other etiologies, including infection with adenovirus, herpes simplex virus, mononucleosis, diphtheria, coxsackievirus A, or group A streptococci.
- Auscultation of the chest may reveal rhonchi, but the chest is usually clear.
Transmission
- Rhinoviral transmission occurs with close exposure to infected respiratory secretions, including hand-to-hand, self-inoculation of eyes or nose, and, possibly, large- and small-particle aerosolization. The virus has been cultured from the skin after up to 2 hours and after up to 4 days on inanimate objects in ideal conditions. Donors are typically symptomatic with a cold at the time of transmission, and virus is detected on their hands and nasal mucosa.
- One recent study assessed the transfer of virus to surfaces in 15 adults with rhinoviral infection. Each stayed overnight in a hotel room. Afterward, 10 commonly-touched sites in each room were tested for viral contaminants. They found that virus could be recovered from 35% of these sites. Furthermore, they found that virus could be transferred back from inanimate objects to fingertips in many cases.
- Higher rates occur in humid, crowded conditions, as found in nurseries, daycare centers, and schools, especially during cooler months in temperate regions and the rainy season in tropical regions.
- The likelihood of transmission does not appear to be related to exposure to cold temperatures, fatigue, or sleep deprivation.
Treatment
Rhinoviral infections are predominately mild and self-limited; thus, treatment is generally focused on symptomatic relief and prevention of person-to-person spread and complications. The mainstays of therapy include rest, hydration, antihistamines, and nasal decongestants.
Antibacterial agents are not effective unless bacterial superinfection occurs. Development of effective antiviral medications has been hampered by the short course of these infections. Because peak symptom severity occurs at 24-36 hours after inoculation, antivirals have only a narrow window to positively affect a rhinoviral infection. In addition, the cause of the common cold is not always rhinoviral infection. Therefore, rapid and accurate diagnostic tests would be needed if a specific antiviral therapy were developed.
- Because of the large number of rhinovirus immunotypes and the inaccessibility of the conserved region of the viral capsid (the most likely effective site for targeting a vaccine), no rhinovirus vaccine is on the horizon.
- Because infection is spread by hand-to-hand contact, autoinoculation, and, possibly, aerosol particles, emphasize appropriate hand washing, avoidance of finger-to-eyes or finger-to-nose contact, and use of nasal tissue.
- Heated humidified air has been used for decades for the alleviation of symptoms due to rhinoviral infections but has never been shown to improve objective outcome measures.
Dietary supplements have been touted as possible therapeutic or preventive measures.
- Although large doses of vitamin C have been used for prevention and treatment of colds, controlled trials reveal minimal therapeutic benefit and no preventive qualities.
- Zinc has been found to inhibit rhinovirus replication in vitro, but no proven benefit has been shown in vivo on virus activity or immune modulation.
Drugs used in the symptomatic treatment include nonsteroidal anti-inflammatory drugs (NSAIDs), antihistamines, and anticholinergic nasal solutions. These agents have no preventive activity and appear to have no impact on complications. The combined effect of NSAIDs and antihistamines often relieves nasal obstruction; therefore, decongestion therapy is rarely needed. Oral (pseudoephedrine) and topical (oxymetazoline and phenylephrine) decongestants are commonly used for symptomatic relief.
First-generation antihistamines reduce rhinorrhea by 25-35%, as do topical anticholinergics and ipratropium bromide. Second-generation or nonsedating antihistamines appear to have no effect on common cold symptoms. Corticosteroids may actually increase viral replication and have no impact on cold symptoms.