Final answer:
Mr. Singh's diagnosis was confirmed through diagnostic tests including chest radiography, blood, urine, and sputum samples. The doctor cannot be certain about the infection causing infectious mononucleosis based solely on clinical signs and test results.
Step-by-step explanation:
Mr. Singh's diagnosis was ultimately confirmed through a combination of diagnostic tests and clinical signs. The physician ordered a chest radiography, blood, urine, and sputum samples to determine the cause of Mr. Singh's symptoms. These tests can help identify specific pathogens, such as the Epstein-Barr virus (EBV) or cytomegalovirus (CMV), that are associated with infectious mononucleosis. However, the doctor cannot be absolutely certain about the infection causing infectious mononucleosis solely based on clinical signs and the test results.