What is the likely etiology for close poly and lymphocyte presence in a 14-year-old's CBC?

The presence of close poly (polymorphonuclear neutrophils) and lymphocytes in the complete blood count (CBC) of a 14-year-old is most commonly associated with a viral infection. This immune response is typical because viral infections often lead to an increase in lymphocytes, which are a type of white blood cell vital for combating viral pathogens. In addition, the presence of polymorphonuclear neutrophils also indicates an inflammatory response, which can sometimes occur in viral infections even though they are predominantly associated with bacterial infections.

Leukemia would typically present with an abnormal number and types of white blood cells, including immature forms, rather than showing a clear pattern of both increased polys and lymphocytes. While certain bacterial infections, like Haemophilus influenzae and Bordetella pertussis, can elevate these cell types, they usually present with unique clinical symptoms and laboratory findings that would help differentiate them from a viral etiology.

In summary, the combination of increased polys and lymphocytes is indicative of a viral infection, making this the most likely etiology in this scenario.