Clinical Information on Listeriosis – August 28, 2008

Dear Colleagues,

As the current nationwide listeriosis outbreak unfolds, we have been receiving a number of calls about the clinical management of patients. While the assessment and management of undifferentiated patients will be determined by your clinical judgment, we hope this memo will provide some practical information for you. This information, prepared in collaboration with Middlesex-London Health Unit and consultation with Ministry officials will be available on our web site at Ottawa.ca/health under Physicians and Health Professionals located on the left sidebar.

Who is at risk of serious illness due to listeriosis?

Please consider listeriosis in patients who:

• have symptoms that may include fever, myalgia, nausea, diarrhea and/or neurological symptoms including fever, headache, stiff neck, loss of balance or convulsions. Listeria infection in the newborn often manifests like group B streptococcal disease, typically with either an early onset sepsis syndrome (transmitted in utero) or a late onset meningitis (~2 weeks postpartum, often transmitted during delivery).
• have a history of eating meat that has been part of the national recall within 70 days of developing symptoms. It can take from 3 days to 70 days after eating contaminated food for listeriosis to develop, although symptoms usually occur 3 to 4 weeks after exposure.
• are elderly, pregnant or immuno-compromised with symptoms. If a pregnant woman has listeriosis, even if the illness is mild, the infection may affect the fetus leading to miscarriage, preterm delivery, fetal death or infection of the newborn.
• In healthy, non-pregnant individuals, listeriosis is usually a self-limiting illness not requiring treatment.

Testing

Individuals who have eaten suspect food only require laboratory testing if they have a fever or symptoms of meningitis and invasive disease. Specimens for Listeria monocytogenes should not be collected on asymptomatic patients.

To confirm diagnosis, routine blood cultures (aerobic and anaerobic) should be ordered. The Ontario Public Health Laboratory (OPHL) recommends two cultures taken from different sites (for example, one from each arm) drawn at the same visit. A third set of blood cultures should be drawn, if and only if endocarditis is suspected. This can be ordered through any local lab. Please label the requisition with “Suspected listeriosis”. Cultures are repeated after 48 hours if the previous cultures are negative and there is on-going concern of invasive infection with Listeria monocytogenes. You will find detailed information on testing on our website. Cultures generally take 6 days before a result is available. Cultures of other sites can also yield the bacteria (eg. CSF, meconium, amniotic fluid, gastric washings, placental tissue and other infected tissue specimens such as joint, pleural and pericardial fluid). If Listeria grows on the culture, OPHL will do further genotyping of the isolates. This is to determine if the case of listeriosis is linked to the outbreak.

If a patient has diarrhea, stool culture may help to establish another cause for the diarrhea. While not routine, if you require a stool culture of Listeria, a special arrangement must be made with the Medical Microbiologist at OPHL

Treatment

Treatment should be tailored to specific clinical circumstances. Prophylaxis in people who are not symptomatic is not recommended.

Prompt treatment in pregnancy can improve the outcome for the baby.

The treatment of choice for severe infections is usually ampicillin and an aminoglycoside (usually gentamicin). In immunocompetent hosts, ampicillin alone can be given once a favourable response has occurred or for patients with mild infections. For penicillin-allergic patients, the alternative regimen is trimethoprim-sulfamethoxazole. Cephalosporins are not active against Listeria monocytogenes.

For invasive infections without associated meningitis, treatment for 10 to 14 days is reportedly usually sufficient. For meningitis caused by Listeria monocytogenes, 14 to 21 days of treatment is generally recommended. Longer courses are needed for patients who are severely ill or who have endocarditis or rhomboencephalitis.

Clinical counselling

• Please advise patients to discard any meat that has been recalled including items that may still be in the freezer. Reassure them that even though large quantities of meat were recalled, it is likely that only a small portion was actually contaminated. Refer them to Ottawa.ca/health to find the listing for the recalled meat.
• If the person has eaten a potentially contaminated product and does not have any symptoms, there is no need to have any tests or treatment, even if the person is in a high-risk group.
• Pregnant women with a history of symptoms compatible with listeriosis, now resolved, should be evaluated given the increased risk to the fetus.
• If you strongly suspect the person may have listeriosis, please advise your patient that listeriosis is a reportable disease, and a report to Ottawa Public Health will occur.
• Refer patients to the Ottawa Public Health web site at Ottawa.ca/health for more information.

If you have any further questions, please contact Ottawa Public Health at 613-580-6744, ext. 15414 or ext. 23748. Alternatively, and after hours, please call 3-1-1 and ask for the Ottawa Public Health Manager on call.

Your continued assistance in this matter is greatly appreciated.

Isra G. Levy, MB BCh, MSc, FRCPC, FACPM

Medical Officer of Health