The Common Cold

Definition

The common cold is a clinical syndrome characterized by upper respiratory signs and symptoms (e.g., rhinorrhea, sneezing, nasal obstruction), which are frequently accompanied by sore throat, cough, and general malaise. The common cold is among the most prevalent of illness syndromes and is very costly in aggregate, especially considering the resulting absenteeism from school and work. Common cold is both a clinical and a cultural construction, and it results from a variety of etiologic agents.

Epidemiology

The incidence of common cold decreases with age, from an average of about six symptomatic episodes per year in young children to approximately two episodes per year in adults. Asymptomatic infections are also common. The incidence of illness is higher in adults who have occupational or household exposure to children and in young children who are cared for in child care centers. Common cold illnesses occur year-round in temperate climates but have a substantially increased incidence between the early autumn and late spring. Reasons for the seasonality of respiratory viruses are poorly understood. In tropical climates, colds can occur year-round without defined seasonality.

Pathobiology

Respiratory pathogens are spread from person to person by direct contact with either infected individuals or contaminated objects in the environment, by large-particle aerosols, or by small-particle aerosols. Modes of transmission vary by agent and are influenced by a variety of factors, including distancing, mask-wearing, and handwashing. For example, respiratory syncytial virus ( Chapter 330 ) may be spread by either direct contact or large-particle aerosols, and influenza ( Chapter 332 ) may be spread more by small-particle aerosols. The SARS-CoV-2 virus appears to be spread more by respiratory droplets and aerosols than by direct contact.

The common cold syndrome is initiated by viral infection of the epithelial cells in the nasal passageways or upper pharynx. Influenza and adenovirus produce obvious damage to the respiratory epithelium. Rhinovirus and respiratory syncytial virus, in contrast, have little or no detectable impact on the epithelium. Pathologic consequences of infection by SARS-CoV-2 are highly variable, from asymptomatic infection with minimal inflammation to highly invasive disease with a variety of pathologic manifestations and sequelae. Regardless of the histopathology, all of these viruses stimulate a nonspecific host inflammatory response that appears to be responsible for many of the symptoms associated with the common cold.

Nasal obstruction results from increased nasal blood flow and pooling of blood in the capacitance vessels of the nasal passageway. Sympathetic and parasympathetic pathways are involved. The increase in nasal secretion associated with the common cold may also contribute to nasal obstruction. Rhinorrhea is primarily a result of increased vascular permeability, with leakage of serum into the nasal secretions, which are composed of both transudates and exudates. Increased mucus production tends to contribute more to the secretions during the later stages of the illness.

Cough ( Chapter 71 ) occurs in the majority of colds and tends to last longer than other symptoms. Cough during colds is produced by several different mechanisms, including infection-induced airway inflammation and irritation from mucus secretion or postnasal drip. Patients who smoke or who have asthma, reactive airway disease, or chronic obstructive pulmonary disease are at higher risk for cough.

The risk of infection after exposure to the respiratory viruses is primarily dependent on adaptive immune mechanisms, as indicated by the presence of specific neutralizing antibodies. Antibody responses to the rhinoviruses, adenoviruses, coronaviruses, and influenza viruses tend to be protective against subsequent infection. The frequency of infection with these viruses is a result of the large number of distinct serotypes of rhinovirus and adenovirus and the ability of the influenza viruses to behave as though there are multiple virus serotypes by virtue of the rapid mutation of surface antigens. The parainfluenza viruses, respiratory syncytial viruses, and metapneumoviruses produce very little protective immunity, so reinfection is common. As seen with SARS-CoV-2, relatively small genetic changes may result in variants that have different virulence, infectivity, and resistance to immune mechanisms.

Susceptibility to and pathogenesis of the common cold are multifactorial processes, with innate and adaptive immune mechanisms influenced by genetic predisposition, by previous antigen exposure, and by general health. Polymorphisms of mannose-binding lectin and various toll-like receptors may confer susceptibility or partial protection. Inflammatory cytokines associated with the severity of disease include various interferons, interleukins, and other factors, which rise markedly in nasal secretions but usually do not change much in the serum. Recent research suggests that the respiratory microbiome may be involved. Specific genes and epigenetic influences on the expression of those genes may predispose toward higher levels of inflammatory cytokines, and more severe respiratory illness.

Although specific mechanisms are not well understood, several decades of research have shown that susceptibility to common cold is influenced by mental health. Risk factors include perceived stress, social isolation, negative emotional style, and a history of stressful life events.

Clinical Manifestations

The incubation of common cold illness is generally short, ranging from 2 to 8 days, although some adenoviruses may have an incubation of as long as 13 days. The common cold illness syndrome generally persists for 5 to 10 days, but a substantial proportion of individuals have colds that persist for longer or shorter periods of time. A sore or scratchy throat is frequently reported as the first symptom. Sneezing is also a common early symptom. Nasal obstruction and rhinorrhea develop rapidly and are often the most bothersome symptoms. Cough generally develops later in the illness, frequently is the most bothersome symptom during the latter phases of the common cold, and may persist for several weeks after all other symptoms have resolved. When asked to rate what bothers them most about their colds, people tend to identify general malaise or interference with daily activities as more important than the presence or severity of specific symptoms.

Physical findings are generally restricted to the upper respiratory tract. Swelling of the nasal epithelia and increased nasal secretion may be obvious to the examiner. A change in the color or consistency of nasal secretions is common during the course of the illness and is not indicative of sinusitis or bacterial superinfection. The posterior pharynx may show signs of inflammation similar to streptococcal pharyngitis. Paroxysmal cough or wheezing may occur.