Infections occur at all ages but are a great cause for concern in newborns because newborns, especially premature ones, have an underdeveloped immune system and are more susceptible to infection. Although certain protective antibodies pass from the mother to the fetus through the placenta (the organ that provides nourishment to the fetus), the levels of antibodies in the fetus's blood may not be high enough to fight an infection.
Fetuses and newborns can acquire an infection in the following ways:
An infection in the fetus, which can occur any time before birth, results from an infection in the mother. Sometimes doctors and the mother know she has an infection, but sometimes they do not. The mother's infection is passed to the fetus through the placenta.
Common infections that are passed on via the placenta include rubella, toxoplasmosis, cytomegalovirus, Zika virus infection, and syphilis. Human immunodeficiency virus (HIV) infection and hepatitis B virus infection may also sometimes be passed on via the placenta. There are also many rarer infections that can infect the fetus before birth.
An infection can be acquired during birth if the baby passes through an infected birth canal or if an infection moves up from the vagina if delivery is delayed after the membranes have ruptured.
An infection acquired after birth occurs when a newborn has close contact with an infected mother directly or through breastfeeding. An infection acquired after birth can also occur if newborns have contact with infected health care practitioners, family, or visitors in the hospital (see Hospital-Acquired Infections in Newborns) or at home.
Infections in newborns are usually caused by bacteria or viruses and less commonly by fungi or parasites. Bacteria include group B streptococci, Escherichia coli (E. coli), Listeria monocytogenes, gonococci, and chlamydiae. Viruses include herpes simplex viruses (HSV), human immunodeficiency virus (HIV), cytomegalovirus (CMV), and hepatitis B virus (HBV).
Some infections that can affect people of all ages cause particular problems when they occur in a fetus or newborn. Some of the more serious infections in newborns include the following:
See Candidiasis (Yeast Infection) for infection caused by the fungus Candida.
Doctors suspect an infection based on the newborn's symptoms or abnormalities (such as birth defects) and on the results of a physical examination.
Doctors also do blood tests and test samples of the newborn's blood, spinal fluid, urine, saliva, or tissues to determine which organism is causing the infection. The mother may also be tested.