To summarize the literature regarding susceptibility of pregnant women to infectious diseases and severity of resulting disease, we conducted a review using a PubMed search and other strategies. Studies were included if they reported information on infection risk or disease outcome in pregnant women. In all, 1454 abstracts were reviewed, and a total of 85 studies were included. Data were extracted regarding number of cases in pregnant women, rates of infection, risk factors for disease severity or complications, and maternal outcomes. The evidence indicates that pregnancy is associated with increased severity of some infectious diseases, such as influenza, malaria, hepatitis E, and herpes simplex virus (HSV) infection (risk for dissemination/hepatitis); there is also some evidence for increased severity of measles and smallpox. Disease severity seems higher with advanced pregnancy. Pregnant women may be more susceptible to acquisition of malaria, HIV infection, and listeriosis, although the evidence is limited. These results reinforce the importance of infection prevention as well as of early identification and treatment of suspected influenza, malaria, hepatitis E, and HSV disease during pregnancy. 1. Introduction Pregnancy is often thought to be associated with increased susceptibility to infection. For example, during the 19th and early 20th century, pregnancy was thought to have a deleterious effect on the course of tuberculosis, so much so that therapeutic abortion was recommended in pregnant women with tuberculosis [1]. However, during the second half of the 20th century, after radiography became available, it became clear that the extent of disease, radiographic pattern, and individual susceptibility were more important than pregnancy itself in determining the course and prognosis of the disease. After the advent of effective chemotherapy, pregnant women with tuberculosis have the same generally good prognosis as nonpregnant women. In the 1950s, the transplant immunologist Peter Medawar proposed that during pregnancy there is a general maternal immune suppression in order to assure tolerance of the semiallogeneic fetus [2–4]. Our understanding of the immune alterations that occur during pregnancy has evolved considerably since Medawar’s time to include more complex theories of immune alteration. There is evidence that adaptive immune responses are weakened, potentially explaining reduced viral clearance [4–7]. Evidence also suggests a boosted innate response [4, 6, 8], which may represent a compensatory immune mechanism to protect the pregnant
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