Listeria (Listeriosis)

Diagnosis

How do I know if I have Listeriosis?

If you develop fever and chills while pregnant or if you are very sick with fever and muscle aches or stiff neck, consult your doctor immediately. A blood or spinal fluid test (to look for the bacteria) will show if you have listeriosis.

Clinical Diagnosis

Listeria is found in the environment and all people are exposed to it regularly. Therefore, there is no clinical value in performing laboratory testing on asymptomatic patients, even if high risk.

For symptomatic patients, diagnosis is confirmed only after isolation of Listeria monocytogenes from a normally sterile site, such as blood, CSF (in the setting of nervous system involvement), or amniotic fluid/placenta (in the setting of pregnancy). Stool samples are of limited use and are not recommended. 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. You can expect that that the cultures will take 1-2 days for growth. Importantly, a negative culture does not rule out infection in the presence of strong clinical suspicion. Serological tests are unreliable, and not recommended at the present time.