HAA meaning in Community ?

In medicine, histiocytosis is an excessive number of histiocytes (tissue macrophages), and the term is also often used to refer to a group of rare diseases which share this sign as a characteristic. Occasionally and confusingly, the term "histiocytosis" is sometimes used to refer to individual diseases.

According to the Histiocytosis Association of America, 1 in 200,000 children in the United States are born with histiocytosis each year. HAA also states that most of the people diagnosed with histiocytosis are children under the age of 10, although the disease can afflict adults. The disease usually occurs from birth to age 15.

Histiocytosis (and malignant histiocytosis) are both important in veterinary as well as human pathology.