Listeriosis laboratory tests

Overview
Diagnosis is confirmed only after isolation of Listeria monocytogenes from a normally sterile site, such as blood, or from amniotic fluid or the placenta in the setting of pregnancy. Listeria monocytogenes can be isolated readily on routine media, but care must be taken to distinguish this organism from other Gram-positive rods, particularly diphtheroids. Selective enrichment media improve rates of isolation from contaminated specimens. Serological tests are unreliable, and not recommended at the present time.

Diagnosis
Laboratory tests may be done to detect the bacteria in amniotic fluid, blood, feces, and urine. A CSF culture may be performed.Note: There is no way, without testing, to know if meningitis is due to listeria or another cause.

Resources
CDC Listeriosis Diagnosis