Management of shunt infection.

SIR,-In your issue of 23 September (p. 776) it is stated that a positive toxoplasmosis dye test is regarded as possibly significant when the patient's serum remains capable of preventing the uptake of dye by Toxoplasma gondii at a dilution of 1 in 256 or more in cases of retinal disease. It is important to realize that almost all cases of retinitis in early adult life are due to recurrences of congenital infection, and as such may not be accompanied by high dye test titres. Taken in conjunction with the typical fundus appearance of a recurrence of chorioretinitis adjacent to an old scar, a positive dye test in a dilution of 1 in 4 or more is strongly suggestive of toxoplasmosis. Higher titres may of course occur but are not obligatory to sustain the diagnosis. We have found that immigrants from West Africa and the West Indies with recurrences of congenital infection tend to have higher dye test titres than those usually found in the indigenous population of this country.' Lymphadenopathy due to toxoplasmosis is the result of recent infection and higher titres of antibody are therefore to be expected. Such patients very rarely have chorioretinitis.-I am, etc.,