Symptoms may begin a few days after you've eaten contaminated food, but it may take as long as two months before the first signs and symptoms of infection begin.
If the listeria infection spreads to your nervous system, signs and symptoms may include:
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Headache
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Stiff neck
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Confusion or changes in alertness
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Loss of balance
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Convulsions
Symptoms during pregnancy, for newborns
During pregnancy, a listeria infection is likely to cause only mild signs and symptoms in the mother. The consequences for the baby, however, may be devastating. The baby may die unexpectedly before birth or experience a life-threatening infection within the first few days after birth.
As in adults, the signs and symptoms of a listeria infection in a newborn can be subtle, but may include:
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Little interest in feeding
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Irritability
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Fever
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Vomiting
Causes
Listeria infections are caused by eating food contaminated with the bacteria Listeria monocytogenes, which can be found in:
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Soil
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Water
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Some wild and domestic animals
Humans are often exposed to listeria by consuming:
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Raw vegetables that have been contaminated from the soil or from contaminated manure used as fertilizer
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Infected animal meat
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Unpasteurized milk or foods made with unpasteurized milk
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Certain processed foods — such as soft cheeses, hot dogs and deli meats that have been contaminated after processing
Unborn babies can contract a listeria infection from the mother via the placenta. Breast-feeding is not considered a potential cause of infection.
Risk factors
Those at highest risk of a listeria infection include:
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Pregnant women and their babies. Pregnant women are significantly more susceptible to listeria infections than are other healthy adults. In fact, nearly one-third of listeria infections occur during pregnancy, according to the Centres for Disease Control and infection prevention (CDC). Although a listeria infection may cause only a mild illness in the mother, consequences for the baby may include miscarriage, stillbirth, premature birth or a potentially fatal infection after birth.
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People who have weak immune systems. This includes older adults and anyone who has AIDS, cancer, diabetes, kidney disease or other conditions that affect the immune system, as well as those who take medications to block rejection of a transplanted organ.
Complications
Most listeria infections are so mild they may go unnoticed. However, in some cases, a listeria infection can lead to life-threatening complications — including:
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A generalized blood infection (septicemia)
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Inflammation of the membranes and fluid surrounding the brain (meningitis)
Complications of a listeria infection may be most severe for an unborn baby. Early in pregnancy, a listeria infection may lead to miscarriage. Later in pregnancy, a listeria infection may lead to stillbirth, premature birth or a potentially fatal infection in the baby after birth — even if the mother becomes only mildly ill.
Infants who survive a listeria infection may experience long-term neurological damage and delayed development.
Adults over 60 can also be seriously affected by a listeria infection, and death rates may be as high as 10 to 20 percent for this age group.
Diagnosis
A blood test is often the most effective way to determine whether you have a listeria infection. In some cases, samples of spinal fluid, urine or the fluid that surrounds and protects a baby before birth (amniotic fluid) may be tested as well.
References
http://www.about-listeria.com/listeria_symptoms_risks/#.V1Aa3LTG71s
http://www.cdc.gov/listeria/
http://www.medicinenet.com/listeria/article.htm
http://emedicine.medscape.com/article/965841-overview
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