The common cold (viral upper respiratory tract infection (VURI), acute viral rhinopharyngitis, acute coryza, or cold) is a contagious, viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a sore throat, runny nose, and fever. There is no cure, however symptoms usually resolve spontaneously in 7 to 10 days, with some symptoms possibly lasting for up to three weeks.^[1]The common cold is the most frequent infectious disease in humans^[2] with on average two to four infections a year in adults and up to 6 - 12 in children. Collectively, colds, influenza, and other infections with similar symptoms are included in the diagnosis of influenza-like illness. They may also be termed upper respiratory tract infections (URTI). Influenza involves the lungs while the common cold does not.

Signs and symptoms

Symptoms are cough, sore throat, runny nose, and nasal congestion; sometimes this may be accompanied by conjunctivitis ( pink eye ), muscle aches, fatigue, headaches, shivering, and loss of appetite. Fever is often present thus creating a symptom picture which overlaps with influenza.^[3] The symptoms of influenza howerver are usually more severe.^[4] The common cold usually resolves spontaneously in 7 to 10 days, but some symptoms can last for up to three weeks.^[1] In children the cough lasts for more than 10 days in 35-40% and continue for more than 25 days in 10%.^[5]Those suffering from colds often report a sensation of chilliness even though the cold is not generally accompanied by fever, and although chills are generally associated with fever, the sensation may not always be caused by actual fever.^[3] In one study, 60% of those suffering from a sore throat and upper respiratory tract infection reported headaches^[3], often due to nasal congestion.

Progression

The viral replication begins 8 to 12 hours after initial contact.^[6] Symptoms usually begin 2 to 5 days after initial infection but occasionally occur in as little as 10 hours.^[7] Symptoms peak 2–3 days after symptom onset, whereas influenza symptom onset is constant and immediate.^[3] The symptoms usually resolve spontaneously in 7 to 10 days but some can last for up to three weeks.^[1]The first indication of an upper respiratory virus is often a sore or scratchy throat. Other common symptoms are runny nose, congestion, and sneezing.^[8] These are sometimes accompanied by muscle aches, fatigue, malaise, headache, weakness, or loss of appetite.^[9] Cough and fever generally indicate influenza rather than an upper respiratory virus with a positive predictive value of around 80%.^[3] Symptoms may be more severe in infants and young children, and in these cases it may include fever and hives.^[10] Upper respiratory viruses may also be more severe in smokers.^[11]

Complications

The common cold can lead to symptoms of acute bronchitis, bronchiolitis, croup, pneumonia, sinusitis, otitis media, or strep throat. People with chronic lung diseases such as asthma and COPD are especially vulnerable. Colds may cause acute exacerbations of asthma, emphysema or chronic bronchitis.^[6]

Cause

Viruses

The common cold is due to a viral infection of the upper respiratory tract. The most common implicated is rhinovirus (30-50%), a type of picornavirus with 99 known serotypes.^[12][13][3] Others include: coronavirus (10-15%), influenza (5-15%)^[3], human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, and metapneumovirus.^[8]In total over 200 serologically different viral types cause colds.^[3] Coronaviruses are particularly implicated in adult colds. Of over 30 coronaviruses, 3 or 4 cause infections in humans, but they are difficult to grow in the laboratory and their significance is thus less well-understood.^[8] Due to the many different types of viruses and their tendency for continuous mutation, it is impossible to gain complete immunity to the common cold.