Although the name sounds similar, parainfluenza viruses do not cause the flu. This different group of viruses is responsible for a range of respiratory illnesses, including colds, pneumonia, bronchitis, and croup. There are four types of parainfluenza virus. Infections of each present a little differently, and some are more severe than others. Interestingly, each follows a predictable seasonal pattern.

Parainfluenza Types 1 and 2

Parainfluenza type 1 is a leading cause of respiratory infections in children younger than 3. Parainfluenza type 2 causes similar infections that tend to be less severe. Children develop a stronger immunity to these types around age 2 or 3.

These parainfluenza types affect adults differently than children. Studies on adults involving experimental infections demonstrate that symptoms of a type 1 infection last about four days, while symptoms from a type 2 infection last about six. Both can cause nasal discharge lasting as long as two weeks.

young woman blowing her nose


Parainfluenze Types 3 and 4

Parainfluenza type 3 can cause severe respiratory illness in infants and the immunocompromised. Type 3 tends to be more prominent in older toddlers. One survey demonstrated that the rate of infection with type 3 parainfluenza for children around 2-years old is 60 percent. By age 4, this increases to 80 percent.

Type 4 is not as common and may cause mild to severe respiratory infections.

little girl on couch blowing her nose



Interestingly, parainfluenza infections follow a predictable pattern. Type 1 is most prominent from September to December in odd-numbered years. Type 3 parainfluenza infections occur yearly, usually from April to June; however, in even-numbered years when type 1 is not circulating, type 3 infections continue over into the fall and may surge again in November and December. Type 2 parainfluenza infections are most common in October through December, whereas type 4 peaks in the fall of odd-numbered years.

mother checking forehead of sick little boy



Parainfluenza commonly causes respiratory illnesses in infants, young children, older adults, and those with weakened immune systems, but anyone can experience this type of infection. Symptoms of parainfluenza include nasal congestion, cough, fever, sore throat, wheezing, and sneezing. In most cases, they appear within a week of exposure and may last a few days or up to two weeks.

mother caring for sick child wrapped in blanket



Parainfluenza is transmitted through large aerosols or aerosol spread. The infection spreads when an infected person coughs, talks, and sneezes, exposing healthy people to the virus. Parainfluenza can also live on porous surfaces for up to 10 hours, and infection can result from coming into contact with the virus and then touching the eyes, nose, or mouth.

man blowing his nose during an office meeting



There is no vaccine for parainfluenze, though researchers have been trying to develop one. The best way to avoid a parainfluenza infection is to avoid large crowds during outbreaks and maintain good hand hygiene. Hospitalized immunocompromised individuals require enhanced infection control measures during known outbreaks, including limiting visitors and patient-to-patient contact. Caregivers should mask to prevent spreading the virus, and careful cleaning and hygiene should be maintained.

mom helping her young daughter wash her hands


Asthma and COPD

Parainfluenza infections can exacerbate chronic respiratory conditions and cause severe respiratory symptoms. In one small study of a group of adults with asthma exacerbations, 60 percent had a parainfluenza infection. Another study of COPD patients showed that a virus was detected in 25.7 percent of exacerbations. Combined, parainfluenza 4 and 3 make up the fourth most prevalent virus. Rhinovirus is number one.

little girl outdoors using her asthma inhaler


Diagnosis and Treatment

In most cases, determining the specific virus causing an infection is not necessary unless there is a question of bacterial involvement, and the doctor is considering antibiotics.

A physical exam may show a red throat, swollen glands, and wheezing or crackling in the lungs. Further testing is not normally needed, but in severe infections, a chest x-ray, CT scan, blood cultures, and blood counts can provide a complete picture of the illness and help drive treatment.

doctor in hospital examining chest x-ray


Croup and Bronchiolitis

Two of the most common complications in children with parainfluenza are croup and bronchiolitis. Croup is most often associated with Parainfluenza 1 and 2 and may present with fever, a barking cough, and inflammation that could lead to airway obstruction. Bronchiolitis occurs in infants and young children and is more often associated with parainfluenza 3. It begins with a fever and nasal congestion and spreads to the lungs, causing rapid, labored breathing and a cough. Recovery can take as long as three weeks.

mother holding sick toddler in her lap



Pneumonia is one of the main complications of parainfluenza, especially for older children and adults. Parainfluenza types 1 and 3 are more likely to lead to pneumonia, though any type can cause it. Type 3 causes as many as 12 percent of pneumonia hospitalizations with children, type 1 as many as 6 percent, according to some studies.

Of all hospitalized patients infected with parainfluenza, pneumonia was most common in patients older than 15 years. Symptoms include fever and cough, and chest x-rays may show consolidation or white sections that can help in diagnosis.

doctor checking headbeat and breathing of coughing child


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