Cytomegalovirus (CMV)

• Primary (acute) infection is often asymptomatic. If symptomatic it causes a mononucleosis-like illness, with fever and feeling generally unwell, usually without localising symptoms.
• In those with normal immune systems it is self-limiting and doesn’t need specific treatment.
• It can cause more serious illness in people with severe immune compromise, and also congenital infections in pregnancy. Seek specialist advice in these situations.
• Reactivation or reinfection can occur, but are not of clinical significance in otherwise healthy people and are very difficult to diagnose.

Unlike EBV (glandular fever), it is uncommon to see exudative tonsillitis (sore throat), and lymphadenopathy is also less common. Rash is seen in around one third of patients.

Laboratory confirmation of CMV infection is not necessarily required in non-pregnant people.

• Mimics to consider: Primary HIV infection, syphilis, viral hepatitis (if significant LFT derangement), bacteraemia e.g. endocarditis.
• Lymphocytosis with mononuclear predominance, atypical lymphocytes on blood film, and some degree of liver test derangement are consistent with, but not specific for, CMV.

Request CMV serology              

CMV IgG indicates infection at some point in time (can be acute or past infection)

• Excellent sensitivity – negative result excludes CMV infection (unless tested within the first 2-3 weeks of symptoms)
• Excellent specificity – positive result confirms infection at some stage

CMV IgM is used to diagnose primary (acute) infection

• Good sensitivity – negative result makes primary infection unlikely
• Poor specificity – positive result doesn’t necessarily indicate acute infection

IgM can remain positive for many months after resolved primary infection, or reappear with other unrelated illnesses. The combination of compatible symptoms, atypical lymphocytosis and a positive CMV IgM makes the diagnosis probable (but not definite)

CMV PCR/viral load:

• This is reserved for specialist use and specific situations, usually in severely immunocompromised patients and is not used for diagnosis of primary CMV.