Lymphocytosis is most commonly associated with a normal or a decreased total WBC count. The most common etiology is viral infection. The lymphocytosis seen in the majority of viral infections is actually a relative type due to a decrease in granulocytes while total (absolute) lymphocyte numbers remain constant. The same phenomenon is found in Addison’s disease and in drug-induced agranulocytosis. A real (absolute) lymphocytosis with leukocytosis occurs in pertussis, infectious lymphocytosis, lymphocytic leukemia, and in some infants with adenovirus infection. Infectious mononucleosis, adult cytomegalovirus infection, and sometimes hepatitis virus infection are associated with absolute lymphocytosis and atypical lymphocytes; there may be leukopenia in the early stages, which is followed by leukocytosis. Toxoplasmosis sometimes produces absolute lymphocytosis. One report indicates that severe trauma may be associated with absolute lymphocytosis that changes to lymphopenia accompanied by increased granulocytes within 24 hours.