Types of Colds

Colds are mild upper respiratory tract infections caused by different viruses. Unless a more serious illness develops, there is seldom any reason to perform tests to identify the specific type of virus causing the symptoms. Although more serious illness can develop in any person, at any age, infants, young children, the elderly and those with other chronic illnesses (i.e. lung disease, heart disease or immunosuppressed) are the most vulnerable.

Symptoms caused by different cold viruses are similar, with subtle differences sometimes seen in how quickly they develop, the severity, the time of year they tend to occur, how long they last and the likelihood of complications developing. The following information highlights some of the differences seen among six viral groups that commonly cause colds.

Rhinoviruses

'Rhin' is Greek for nose. Rhinoviruses (of which there are more than 100 types) are the most common cause of colds. Colds caused by rhinoviruses are generally mild and rarely lead to hospitalization except in situations where there are other underlying conditions. They are the most frequent trigger of acute asthma exacerbations in older children and a common cause for hospitalization in children and adults who suffer from asthma.

The viruses spread easily in nasal secretions and saliva. When they enter the nose (i.e. through rubbing with a contaminated hand), they attach to the cells inside the nose and begin to multiply within the first fifteen minutes, sometimes resulting in symptoms within 8 to 10 hours.

The viruses can last up to four days on contaminated surfaces and a few hours on skin. The best prevention is hand washing, keeping contaminated surfaces clean and when possible, avoiding contact with people who have a cold.

Coronaviruses primarily infect animals and birds. Only 5 types of coronaviruses are known to infect humans. However, they are the second leading cause of colds in humans and are primarily seen in the winter and early spring. Symptoms are generally mild and go away on their own.

Coronaviruses became better known after the SARS (Severe Acute Respiratory Syndrome) outbreak in 2002-2003. The virus responsible for SARS caused lower respiratory tract infections as well as upper respiratory tract infections. Some coronaviruses cause diarrhea and in rare cases have resulted in encephalitis.

Respiratory Syncytial Virus (RSV)

The respiratory syncytial virus causes colds with moderate to severe symptoms. Symptoms generally last from 8 to 15 days. The virus can survive for a few hours on environmental surfaces such as (countertops, stair rails, escalator rails, shopping cart handles, door knobs etc). However it is readily destroyed by soap and water and disinfectants.

Infections are usually experienced as community outbreaks once yearly in the late fall, winter or early spring, with outbreaks lasting an average of 4-6 months.

RSV is also the most common cause of lower respiratory tract infections (bronchiolitis and pneumonia) in infants and children under one year of age. It results in hospitalization in .5-2% of these cases, with the majority being under six months of age. 2

Human Parainfluenza Viruses (HPIV) (Common cold and croup)

There are four HPIV viruses that cause the common cold. Symptoms may take 1 to 7 days to develop; as a result, it is easy for those who have the virus to spread the illness before they know they have been infected.2 The viruses can survive for a few hours on environmental surfaces (i.e. crib rails and countertops), and can be readily destroyed through washing with soap, water and disinfectants.

HPIV is the second leading cause of lower respiratory tract infections in young children, the elderly and people with compromised immune systems. HPIV-1 is the leading cause of croup in children. HPIV-2 can also cause croup but is less common. HPIV-3 is more often associated with bronchiolitis and pneumonia (which are lower respiratory tract infections). HPIV-4 is rarely detected, possibly because it causes only mild illness.2

Adenoviruses

There are 49 different types of adenoviruses. They can cause the common cold, croup, bronchitis and other illnesses such as gastroenteritis, conjunctivitis, cystitis, and rash. Those that cause respiratory infection are more common in the late winter, spring and early summer, although infections can occur at any time throughout the year. Symptoms are generally mild and seldom require treatment.

Unfortunately, the adenovirus is unusually stable in the environment and can be spread easily in swimming pools that are not adequately chlorinated.

Enteroviruses "Summer cold"

Enteroviruses infect millions of people in the United States each year. They are spread through the fecal-oral route and get their name from entero meaning 'gut/intestine.' Regular hand washing and cleansing of all contaminated surfaces can effectively reduce the spreading of these diseases. Good hygiene is especially important in infant and child care centers and pediatric wards of hospitals.

Two enteroviruses that commonly cause cold symptoms are the coxsackieviruses and echoviruses. Cold symptoms from these viruses are generally mild and are sometimes accompanied by a rash. Coxaskieviruses are the most common cause of hand, foot and mouth disease.

On rare occasions enteroviruses can cause more serious illnesses, such as myocarditis (an infection involving the heart), viral meningitis (infection involving the lining around the brain) or encephalitis (an infection involving the brain). They are also believed to play a role in the development of juvenile diabetes.

A well known crippling enterovirus is the polio virus. Infections from the polio virus began to dramatically drop in 1954 with the development of a polio vaccine. However, the disease continues to infect approximately ¼ million people per year in developing countries.