Infection is most common in young women - from the mid-teens through the mid-20's - with the peak incidence occurring at age 19.

The peak incidence is between 50 and 55.

There is some difference in ages of the peak incidence for the different subtypes with considerable overlap as described below.

The peak incidence occurs between 30-50 years of age.

The peak incidence occurs in the second decade.

The peak incidence occurs between the ages of 45 and 70 years.

The peak incidence is in the fourth to sixth decades of life.

It is found in men of any age, with the peak incidence in men aged 35-45 years.

The peak incidence occurs in the 3rd and 4th decades of life.

This coincides with the peak incidence of sudden infant death syndrome.