Human parainfluenza viruses (HPIVs) are one of the common pathogens causing acute respiratory infections in infants, young children, and adolescents. HPIVs infection is usually self limiting, but sometimes it can lead to serious clinical consequences and even death. Although both HPIVs and influenza viruses can cause acute respiratory infections, they are completely different viruses, and receiving influenza vaccines cannot prevent HPIVs infection. At present, there are no specific antiviral drugs and vaccines available for the treatment and prevention of HPIVs infection, so maintaining good hygiene habits and paying attention to personal hygiene is crucial. 1、 What is human parainfluenza virus? HPIVs are single stranded RNA viruses of the family Paramyxoviridae isolated from clinical specimens of infants and young children with acute respiratory infections in the 1950s. There are four serotypes, including HPIV1, HPIV2, HPIV3, and HPIV4. Among them, HPIV1 and HPIV3 belong to the respiratory virus genus, while HPIV2 and HPIV4 belong to the mumps virus genus. On a global scale, HPIVs are the second largest viral pathogen causing acute respiratory infections in children after human respiratory syncytial virus, causing a serious disease burden in both developed and developing countries. 75% -80% of children under 5 years old have been infected with HPIVs, with HPIV3 having the most severe disease burden. 2、 What are the clinical manifestations of HPIVs infection? All four serotypes of HPIVs can cause upper and lower respiratory tract infections, but the clinical severity of HPIV infection in different serotypes is closely related to factors such as infection age and infection time. About 40% of HPIVs infections can cause acute laryngotracheobronchitis (Croup) in infants and young children, with fever, barking cough, throat sounds, and hoarseness as the main clinical symptoms. After the first infection with HPIVs, most people mainly experience respiratory clinical manifestations including rhinitis, pharyngitis, laryngitis, bronchiolitis, bronchiolitis, and pneumonia, often accompanied by fever symptoms. In addition to respiratory symptoms, HPIVs infection can also cause complications in other systems, including sinusitis, otitis media, myocarditis, pericarditis, meningitis, Guillain Barr é syndrome, acute disseminated encephalomyelitis, etc. 3、 How is the human parainfluenza virus transmitted? The incubation period of HPIVs infection is about 3-6 days, starting from the initial site of infection in the nose and oropharynx, and then spreading to the lower respiratory tract. After 2-5 days of infection, the virus replication reaches its peak. HPIVs are mainly transmitted through respiratory droplets and close contact. The HPIVs virus exists in respiratory secretions and spreads through coughing and sneezing, forming droplets in the air. Secondly, transmission can be carried out through close contact, such as direct contact or handshake, or touching the surface of an object carrying the HPIVs virus, and then touching human parts such as the mouth, nose, or eyes. Therefore, HPIVs are easily spread within households, and outbreaks occur in enclosed areas such as kindergartens, hospitals, and other places. 4、 Is HPIVs infection seasonal? Four serotypes of HPIVs can occur throughout the year and are prevalent in different seasons. HPIV1 and HPIV2 infections usually occur alternately, with HPIV1 infection mainly occurring in autumn and early winter, while HPIV2 infection often occurs in autumn with a one-year interval, but its detection rate is relatively low; HPIV3 infection is the most common, usually prevalent in spring and summer each year; HPIV4 infection usually has no significant seasonality, is mostly sporadic, and rarely causes serious clinical symptoms. 5、 What are the preventive measures for HPIVs? Breastfeeding in the first few months after birth can protect infants from HPIVs infection, possibly due to the presence of antibodies against HPIVs infection in breast milk. In addition, daily hygiene measures can also reduce the risk of HPIVs infection, such as paying attention to personal hand hygiene; Do not touch your eyes, nose, mouth, or other parts with your hands after coming into contact with public goods; Open windows frequently and maintain indoor ventilation; When going to crowded or poorly ventilated places, wear masks scientifically. Patients infected with HPIVs should avoid close contact with others, cover their mouth and nose when coughing or sneezing, keep objects and surfaces clean and disinfected, and wear masks. (Lai Xin She)