Clinical Overview of Human Parainfluenza Viruses

Overview

HPIVs are enveloped RNA viruses that belong to the Paramyxoviridae family. There are four types (1 through 4) and two subtypes (4a and 4b) of HPIVs. The clinical and epidemiological features for each HPIV type can vary.

Types

There are four types of HPIVs and two subtypes that circulate at different times of the year. The incubation period, the time from getting infected with HPIV to symptom onset, is generally 2 to 6 days.

1. HPIV-1 infections often cause croup in children. They can cause upper and lower respiratory illness and cold-like symptoms. There are usually more cases in the fall.
2. HPIV-2 infections can also cause croup in children. They can cause upper and lower respiratory illness and cold-like symptoms. HPIV-2 infections are more common in the fall. They are less frequently detected than HPIV-1 and HPIV-3.
3. HPIV-3 infections are more often associated with bronchiolitis and pneumonia. They usually occur in spring and early summer months. However, HPIV-3 infections can occur throughout the year, particularly when HPIV-1 and HPIV-2 are not in season.
4. HPIV-4 (subtypes 4a and 4b) infections are diagnosed less often because of infrequent testing. They may cause mild to severe respiratory tract illness, including bronchiolitis and pneumonia. Seasonal patterns are not as well characterized but seem to occur in fall and winter each year.

All HPIVs can worsen chronic lung conditions, such as asthma.

Symptoms and illness

Symptoms

HPIV can cause upper respiratory symptoms that may include:

• fever

• runny nose

• cough

• sneezing

• sore throat

Other symptoms of HPIV illness may include:

• ear pain

• irritability
• decreased appetite

Serious illness in children

HPIVs can cause more serious illness in children, including:

• croup (infection of the vocal cords [larynx], windpipe [trachea], and sometimes into the larger airways into the lungs [bronchi])

• bronchitis (infection of the main airways that connect the windpipe to the lungs)

• bronchiolitis (infection in the smallest airways in the lungs)

• pneumonia (infection of the lungs)

• worsening of underlying lung conditions, such as asthma

Symptoms of more serious illness in children may include:

• barking cough

• hoarseness

• stridor (noisy or high-pitched sound with breathing)

• wheezing

Illness in adults

HPIVs commonly cause upper respiratory infections in adults. More severe illness, such as bronchitis and pneumonia may occur, especially in older adults and people with weakened immune systems.

Symptoms in adults may include:

• fever

• runny nose

• cough

• sore throat

Reinfections

Most children ages 5 years and older have antibodies against HPIV-3, and approximately 75% have antibodies against HPIV-1 and HPIV-2. This shows that children are generally infected at a younger age with HPIVs.

However, people can get multiple HPIV infections in their lifetime. These reinfections usually cause mild upper respiratory tract illness with cold-like symptoms.

Transmission

HPIVs are usually spread by direct contact with infectious droplets or by spread of droplets when an infected person breathes, coughs, or sneezes.

HPIVs may remain infectious in expelled droplets for over an hour and on surfaces for a few hours depending on environmental conditions.

People are most contagious during the early stage of illness.

Prevention and treatment

Currently, there is no vaccine to prevent HPIV infection. However, researchers are trying to develop vaccines. Also, there is no specific antiviral treatment for HPIV illness. Most HPIV illnesses are mild and typically require only treatment of symptoms.

In hospital settings, healthcare providers should follow contact precautions, such as handwashing and wearing protective gowns and gloves. For more information, see CDC's 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings.

Resources

Human Parainfluenza Surveillance, National Respiratory and Enteric Virus Surveillance System (NREVSS)

Pediatric Acute Respiratory Illness (ARI) Interactive Dashboard