Parainfluenza refers to a group of viruses called human parainfluenza viruses (HPIVs). There are four viruses in this group. Each one causes different symptoms and illnesses. All forms of HPIV cause an infection in either the upper or lower respiratory area of a person's body.
Symptoms of HPIVs are like those of the common cold. When cases are mild, the viruses are often misdiagnosed. Most healthy people infected with an HPIV recover with no treatment. However, a person with a weakened immune system is at risk for developing a life-threatening infection.
Read more at: https://www.healthline.com/health/cold-flu/parainfluenza#:~:text=Parainfluenza%20refers%20to%20a%20group,area%20of%20a%20person's%20body.