What viral serological test should be performed on a 25-year-old male with symptoms similar to chronic fatigue syndrome when other tests are negative?

The recommendation to perform a viral serological test for cytomegalovirus (CMV) in this scenario is based on the association of CMV with symptoms that can mimic chronic fatigue syndrome. CMV is a member of the herpesvirus family and is known to cause a variety of health issues, particularly in individuals with weakened immune systems. However, it can also present nonspecifically in otherwise healthy individuals, leading to fatigue, malaise, and other systemic symptoms.

In the context of the patient's symptoms, as well as the absence of positive results from other tests, testing for CMV would be appropriate. This is partly due to the prevalence of CMV in the population; many adults are carriers of the virus and may experience reactivation, particularly under stress or immunological stress, which can present as chronic fatigue.

Other viral tests listed, such as those for echovirus, respiratory syncytial virus, and measles virus, are less fitting given the context. Echovirus generally affects the gastrointestinal and respiratory systems in younger children, respiratory syncytial virus primarily impacts infants and young children, and measles virus would typically present with distinct symptoms including a rash and is less likely to be a contributor to a chronic fatigue presentation. Thus, focusing on CM