In 1941 Smith1 reported two types of lymphocytic reaction of the blood occurring in childhood which he designated as acute and chronic infectious lymphocytosis. These could be differentiated hematologically from infectious mononucleosis and leukemia, with which they were most often confused. A relative and absolute increase in the number of lymphocytes was common to both forms of the disease, and well defined mature lymphocytes with deeply basophilic cytoplasm characterized the blood smear.
The acute form of the disease occurred infrequently and was associated with a striking leukocytosis of short duration without recognizable symptoms and with a minimum of physical signs. The chronic type was more frequently encountered and followed infections of the upper respiratory tract of varying severity and was accompanied by low grade fever which persisted for weeks or months. Associated symptoms frequently included anorexia, pallor, fatigability and abdominal pain which was usually referred to the region of
DUNCAN PA. ACUTE INFECTIOUS LYMPHOCYTOSIS. Am J Dis Child. 1943;66(3):267-271. doi:10.1001/archpedi.1943.02010210043004