Final answer:
It is true that patients with infectious mononucleosis often develop a rash if exposed to ampicillin. This rash is due to the heightened levels of heterophile antibodies present with mononucleosis. However, testing positive for these antibodies does not make an EBV or CMV infection the definitive cause of the symptoms without considering other potential overlapping clinical signs and conditions.
Step-by-step explanation:
Infectious mononucleosis (IM), commonly associated with the Epstein-Barr virus (EBV), is known for several characteristic symptoms such as fever, sore throat, swollen lymph glands, and fatigue. One peculiar feature of IM is a reaction that occurs when patients with the infection are treated with certain antibiotics, particularly ampicillin. If patients with infectious mononucleosis are exposed to ampicillin, there is a high likelihood that they will develop a maculopapular rash. Therefore, it is true that infectious mononucleosis patients develop a rash if exposed to ampicillin.
However, a patient testing positive on an immunoassay for IM does not provide an absolute certainty that the patient is infected by EBV or CMV and that the infection is causing infectious mononucleosis. This uncertainty exists because of potential cross-reactivity with other conditions and the presence of early and broad specificity heterophile antibodies, which may also arise from other infectious diseases and certain autoimmune conditions. Additionally, the clinical signs of IM overlap with those of other illnesses, requiring a comprehensive evaluation to confirm the diagnosis.