What is the SINGLE most appropriate causative organism?

A 34 year old homosexual man attends clinic with a history of weight loss and progressive visual deterioration. A funduscopic examination reveals retinal haemorrhages and yellow-white areas with perivascular exudates. What is the SINGLE most appropriate causative organism?
A. Mycobacterium avium
B. Herpes simplex virus
C. Haemophilus influenzae
D. Cytomegalovirus
E. Pneumocystis jiroveci

The hint here is the homosexual man. For a very inappropriate reason, question writers tend to use the phrase homosexual to hint to you for the possibility of AIDS like in this case. The combination of weight loss is another clue towards the diagnosis of HIV. One of the rare manifestations of cytomegalovirus includes retinitis. It is usually seen in an immunocompromised host (e.g. a positive HIV patient) like in this stem. Although it is rare, retinitis is still the most common manifestation of CMV disease in patients who are HIV positive. Retinal haemorrhage is a recognized association with cytomegalovirus retinitis Cytomegalovirus retinitis Presentation: - Decreased visual acuity, floaters, and loss of visual fields on one side - Examination shows yellow-white cloudy retinal lesions. Lesions may appear at the periphery of the fundus, but they progress centrally. - It begins as a unilateral disease, but in many cases it progresses to bilateral involvement Remembering the findings of the examination of the eye for cytomegalovirus retinitis is less important as the question writers would have to give a history of HIV for this to be cytomegalovirus retinitis. In view of that, if a patient with positive HIV attends with visual deterioration, cytomegalovirus should be at the top of your differential.