A baby can also be infected during the last trimester of pregnancy or during birth, and become ill in the first three weeks of life. The symptoms generally appear about 3 weeks after exposure but may appear as soon as 3 days or as long as 70 days after exposure. Infection can also be transmitted from a pregnant woman to her baby in the womb or during birth. The organism enters the body through the mouth, but then tends to affect the central nervous system. Healthy people may consume contaminated foods without getting ill.
Infected humans can shed the organism in stool for several months.
Mothers of infected newborn infants may shed the bacteria in vaginal discharges and urine for 7-10 days after delivery. The bacteria are not easily passed from one person to another, however, so this disease is not considered to be very contagious. Penicillin or ampicillin used alone or with other medications are used to treat listeriosis. Antibiotics may be given to infected pregnant women to prevent illness in the baby. Thoroughly cook meats and poultry.