False-positive epidemic infectious mononucleosis.

Investigation of four alleged infectious mononucleosis (IM) epidemics revealed that each resulted from either misuse or misinterpretation of mononucleosis slide tests. Even though such tests are a valuable, rapid adjunct to the diagnosis of IM, they must be carefully done with fresh reagents, using both positive and negative controls, and must be interpreted in the light of clinical findings and blood cell morphology.