Chapter 371 The Common Cold
Etiology
The most common pathogens associated with the common cold are the rhinoviruses (Chapter 255), but the syndrome can be caused by many different viruses (Table 371-1). The role of bocavirus as a cause of colds is uncertain because the virus is often isolated from patients who are co-infected with other recognized pathogens.
ASSOCIATION | PATHOGEN | RELATIVE FREQUENCY* |
---|---|---|
Agents primarily associated with colds | Rhinoviruses | Frequent |
Coronaviruses | Occasional | |
Agents primarily associated with other clinical syndromes that also cause common cold symptoms | Respiratory syncytial viruses | Occasional |
Human metapneumovirus | Occasional | |
Influenza viruses | Uncommon | |
Parainfluenza viruses | Uncommon | |
Adenoviruses | Uncommon | |
Enteroviruses | Uncommon | |
Bocavirus | Uncommon |
Epidemiology
Colds occur year-round, but the incidence is greatest from the early fall until the late spring, reflecting the seasonal prevalence of the viral pathogens associated with cold symptoms. The highest incidence of rhinovirus infection occurs in the early fall (August-October) and in the late spring (April-May). The seasonal incidence for parainfluenza viruses (Chapter 251) usually peaks in the late fall and late spring and is highest between December and April for respiratory syncytial virus (RSV; Chapter 252) and influenza viruses (Chapter 250).
Pathogenesis
The respiratory viruses have evolved different mechanisms to avoid host defenses. Infections with rhinoviruses and adenoviruses result in the development of serotype-specific protective immunity. Repeated infections with these pathogens occur because there are a large number of distinct serotypes of each virus. Influenza viruses have the ability to change the antigens presented on the surface of the virus and thus behave as though there were multiple viral serotypes. The interaction of coronaviruses (Chapter 256) with host immunity is not well defined, but it appears that multiple distinct strains of coronaviruses are capable of inducing at least short-term protective immunity. The parainfluenza viruses and RSV each have a small number of distinct serotypes. Reinfection with these viruses occurs because protective immunity to these pathogens does not develop after an infection. Although reinfection is not prevented by the adaptive host response to these viruses, the severity of subsequent illness is moderated by pre-existing immunity.
Diagnosis
The most important task of the physician caring for a patient with a cold is to exclude other conditions that are potentially more serious or treatable. The differential diagnosis of the common cold includes noninfectious disorders as well as other upper respiratory tract infections (Table 371-2).
CONDITION | DIFFERENTIATING FEATURES |
---|---|
Allergic rhinitis | Prominent itching and sneezing Nasal eosinophils |
Foreign body | Unilateral, foul-smelling secretions Bloody nasal secretions |
Sinusitis | Presence of fever, headache or facial pain, or periorbital edema or persistence of rhinorrhea or cough for >14 days |
Streptococcosis | Mucopurulent nasal discharge that excoriates the nares |
Pertussis |