What does the presence of large numbers of atypical lymphocytes in a peripheral blood smear suggest?

The presence of large numbers of atypical lymphocytes in a peripheral blood smear is primarily associated with infectious mononucleosis. This condition is often caused by the Epstein-Barr virus (EBV) and is characterized by a specific immune response, leading to the appearance of atypical lymphocytes. These atypical lymphocytes are usually T-lymphocytes that have been activated in response to the viral infection, illustrating the body's immune reaction to the pathogen.

Infectious mononucleosis commonly presents with symptoms such as fatigue, fever, sore throat, and lymphadenopathy, which coincide with the patient's immune response and the resultant changes seen in blood tests. The atypical lymphocytes are a key laboratory finding that helps in the diagnosis.

While acute bacterial infections might lead to an increase in lymphocyte counts, they usually do not produce the same distinct atypical lymphocytes observed in viral infections like mononucleosis. Similarly, croup primarily involves the respiratory tract and does not present with atypical lymphocytes, and glandular fever is another term often used for infectious mononucleosis, further affirming the association of atypical lymphocytes with the latter condition. Thus, the significant presence of atypical lymphocytes specifically indicates an infectious monon