Parainfluenza Virus Clinical Presentation

Human parainfluenza viruses (HPIVs) have been associated with every type of upper and lower respiratory tract illness. However, all HPIV types strongly correlate with specific clinical syndromes, age, and time of year. Lack of epidemiological data on HPIV-4 has so far prevented a clear understanding of the true clinical significance of the virus. The incubation period of HPIV infection generally lasts 1-7 days. Weinberg et al (2009) found that HPIV accounted for 6.8% of all hospitalizations for fever, acute respiratory illnesses, or both in children younger than 5 years.^[4]

• Croup: Croup is a generic term that encompasses a heterogeneous group of illnesses that affect the larynx, the trachea, and the bronchi. It affects about 3% of children in a given year, usually between ages 6 months and 3 years.^[5] HPIV-1, HPIV-2, and HPIV-3 are the most frequent causes of croup, accounting for almost 75% of all cases. HPIV-1 is the most common and is estimated to cause 18% of all croup cases. Symptoms of croup include fever, hoarse barking cough, laryngeal obstruction, and inspiratory stridor.
• Bronchiolitis: All 4 types of HPIV can cause bronchiolitis, but HPIV-1 and HPIV-3 have been reported most commonly. Each of these 2 groups appears to cause 10-15% of bronchiolitis cases in nonhospitalized children. The peak incidence of bronchiolitis occurs during the first year of life (81% of cases during this period) and then dramatically declines until it virtually disappears by school age. Predominant symptoms include fever, expiratory wheezing, tachypnea, retractions, rales, and air trapping.
• Pneumonias: HPIV-1 and HPIV-3 each cause about 10% of outpatient pneumonia cases, but, similar to bronchiolitis, HPIV-3 causes a larger percentage of cases in hospitalized patients. HPIV-2 and HPIV-4 can both cause pneumonia, but the incidence of disease is not well described. HPIV-1 infection has been associated with secondary bacterial pneumonias in elderly persons. Symptoms of pneumonias include fever, rales, and evidence of pulmonary consolidation.
• Tracheobronchitis: More than 25% of the agents identified to cause tracheobronchitis have been HPIVs. (HPIV-3 is more commonly associated with tracheobronchitis than HPIV-1 or HPIV-2.) Tracheobronchitis is the most common feature seen in persons with HPIV-4 infections.
• Other infections: HPIVs routinely cause otitis media, pharyngitis, and conjunctivitis coryza, and these can occur singly or in combination with a lower respiratory tract infection. HPIV-3 is the most frequently reported HPIV associated with otitis media.
• Infections in immunocompromised patients: The increasing number of patients who receive intense immunosuppression after undergoing transplantation of bone marrow and solid organs has highlighted the role of HPIVs as potential opportunistic pathogens. HPIV-2 causes giant cell pneumonia in persons with severe combined immunodeficiency diseases (SCIDs), and HPIV-3 has been found in persons with SCIDS and acute myeloid leukemia (AML) and in patients who have undergone bone marrow transplantation (BMT). The natural history of HPIV in patients infected with HIV is generally less severe than that in transplant recipients.

A broad range of findings is observed and may include fever, nasal congestion, pharyngeal erythema, nonproductive to minimally productive cough, inspiratory stridor, rhonchi, rales, and wheezing.

• The epiglottis is sometimes grossly swollen and reddened because of viral infection. Severe airway obstruction may ensue, requiring emergency tracheotomy.
• In serious cases, children should be quickly hospitalized (generally within 3-24 h). In immunocompromised hosts, upper respiratory tract symptoms are similar to those observed in healthy hosts, but the incidence of lower respiratory tract symptoms and sinusitis is much higher. In these groups, especially bone marrow transplant recipients, lower respiratory tract infection can lead to respiratory failure and death.

HPIV infection is acquired through inhalation of infected droplet nuclei or indirectly through contact with infected secretions. The incubation period is generally 2-6 days. See Pathophysiology.