The classic obstetric infection is postpartum endometritis. The postpartum patient develops fever that may be associated with abdominal pain, uterine tenderness, malaise, or foul-smelling discharge. In most cases the patient is started on antibiotics without obtaining cultures (16). Endometritis can occur after either vaginal delivery or cesarean section but is more common after cesarean section. Infection has been reported to occur after fewer than 3% of vaginal deliveries and 5% to 95% of cesarean sections (2,16,19). The variation in infection rates results from the variation in risk factors in the population studied and patient’s management. Endometritis after cesarean section occurs earlier than after vaginal delivery, as shown by hospital readmissions for postpartum endometritis. Most women who were readmitted for endometritis had delivered vaginally (20).

Endometritis may be caused by either a single bacterial species or multiple microorganisms (21). Common etiologic agents include the gram-positive cocci, such as streptococci and enterococci; gram-negative bacilli, such as E. coli, K. pneumoniae, and P. mirabilis; and anaerobes, such as Bacteroides bivius and peptostreptococci (16,21,22). Some studies have distinguished between early and late postpartum endometritis (23,24); late infection is a milder disease that occurs after vaginal delivery. It has been suggested that genital Mycoplasma and Chlamydia are important etiologic agents in late endometritis.

The most important risk factor for postpartum endometritis is cesarean section, and the risk of infection is greatest when it is a nonelective procedure after rupture of the membranes and the onset of labor (16,19,25). General anesthesia, long duration of surgery, intraoperative problems, and poor surgical technique may all be risk factors. Currently patients undergoing both elective and nonelective cesarean sections are routinely given prophylactic antibiotics as they are shown to decrease postpartum endometritis and wound infections by 50% to 75% (26). Administration of intravenous antibiotics is done before skin incision as it has been shown to be more effective than administration at cord clamping, the previous practice (27,28). In vaginal deliveries, prolonged rupture of the membranes, midforceps delivery, and soft tissue trauma increase the risk. With many other risk factors for postpartum endometritis, it is difficult to separate out relative risks, because the factors are interrelated. This applies to risk factors such as prolonged labor, frequent vaginal examinations, and internal monitoring. Host factors that increase risk include bacterial vaginosis, human immunodeficiency virus (HIV) infection, anemia, low socioeconomic status, maternal age, and obesity (25,29,30).

Infection of the endometrium may extend into the myometrium and parametrial tissue, causing abscess formation
or sepsis. Septic pelvic thrombophlebitis (SPT) should be suspected in a patient who does not respond to antibiotic therapy (31). If the workup fails to identify another infection, computed tomography should be performed to look for pelvic thrombophlebitis. Past treatment included the addition of heparin to broad spectrum antimicrobial therapy. However, a large randomized trial of SPT showed no benefit from adding heparin to antimicrobial therapy when compared to those receiving antimicrobial therapy alone (32).

Evaluation of the febrile postpartum patient should include a relevant history and physical exam along with laboratory studies: complete blood count, chest X-ray, urine culture, and blood cultures. Leukocytosis is usually present but may also be seen in the noninfected postpartum patient. Uterine cultures are often not done because of the difficulty in interpreting the results. Because the microorganisms recovered are usually part of the normal maternal flora, these may either represent contamination during specimen collection or be the cause of endometritis. Unless a blood culture is positive, there is no way to confirm that the isolates are significant. However, good aerobic and anaerobic cultures do show the range of potential pathogens and detect infections caused by unusual pathogens such as the rare group A β-hemolytic streptococci (GABHS) infection. Uterine cultures can be collected with a cotton swab (33).

Episiotomy infections are uncommon and usually not serious, but severe complications such as necrotizing fasciitis can develop (34,35). Episiotomy sites should be examined carefully to detect infection early and infections should be treated to prevent complications.

A more serious problem is SSI of a cesarean section. SSIs are reported to occur in about 3% to 4% of cesarean section patients, including both incisional and organ and space infections (2,36). Recently, this rate has declined, perhaps as a result of administering perioperative antibiotics just prior to incision (37). SSIs are usually caused by maternal flora in the endometrium but, as with any other SSI, can be caused by microorganisms from exogenous sources (18,38). In the latter cases, S. aureus is the most frequent cause of infection. Although the pathogenicity of genital mycoplasma in SSIs has not been proved, a study reported these to be the most common bacteria isolated in infected postcesarean surgical sites (38). SSIs should be cultured before antibiotic therapy is begun (see also Chapter 21).

Urinary tract infections are a common problem in pregnancy and during the postpartum period (39). Risk factors for postpartum infections include urinary retention from anesthesia, trauma during delivery, and the need for catheterization. Urine cultures of the febrile patient with urinary tract symptoms should always be collected, although midstream samples may be contaminated by vaginal discharge. In those cases, the results are interpreted in the context of the clinical findings and the response to empiric antibiotic therapy. The major preventable risk factor in the postpartum period is catheterization. Catheterization is indicated for urinary retention but should be done only as needed (40), with the catheter removed as soon as possible. Another risk factor for postpartum urinary tract infection is bacteriuria during pregnancy. Pregnancy is one of the few conditions for which treatment of asymptomatic bacteriuria is indicated (41). Detection and treatment of bacteriuria in pregnant women may decrease postpartum urinary tract infections.

Intrauterine infection during pregnancy, such as postpartum endometritis, is usually caused by ascending infection from vaginal flora and is caused by similar bacteria (16,42,43). Most infections are also polymicrobial, and the major risk factor is prolonged rupture of the membranes. Infection is rare in women with intact membranes. Other risk factors are similar to those for postpartum endometritis: duration of labor, number of vaginal examinations, internal monitoring, and possibly bacterial vaginosis. A variety of other obstetric procedures may introduce infection, including amniocentesis, chorionic villus sampling, and percutaneous umbilical blood sampling.

Because fever can be the only presenting sign, initial diagnosis may be difficult. Specific diagnosis requires examination of amniotic fluid by gram stain, culture, and amniotic fluid glucose level (44). Healthcare-associated chorioamnionitis can be suspected in patients who become febrile after vaginal examinations, internal fetal monitoring, or other such procedures, but there is no standardized definition for healthcare-associated infection. Once the diagnosis is suspected, the patient should be started on broad spectrum antibiotic therapy, including anaerobic coverage, and delivered as soon as possible.

In a study of obstetric patients who were contacted after discharge from the hospital, mastitis was the most common infection reported (45). Very few breast infections were seen during hospitalization, because mastitis and breast abscess usually occur several weeks into the postpartum period. A slight fever can develop early with breast engorgement, but it is transient. Later in the postpartum period, infectious mastitis must be distinguished from milk stasis and noninfectious inflammation (46). Infection is associated with higher fevers, erythema, and unilaterality.

The most common cause of breast infection is S. aureus (47). Epidemics of staphylococcal mastitis occurred in the past but have not been reported in recent years. Therefore, the traditional classification of infectious mastitis into sporadic and epidemic forms is seldom useful. Both types are usually caused by S. aureus. Increasing numbers of cases due to community-acquired MRSA are also being reported (48). Predisposing factors for mastitis include the lack of nipple care, poor feeding technique, and inadequate emptying of the breasts. Infection can be confirmed by gram stain and culture and responds to antistaphylococcal antibiotics and, if needed, surgical drainage. Continued breast drainage is important and can be accomplished by continued nursing, if appropriate, or pumping and discarding milk.

Approximately one third of Listeria monocytogenes infections occur in pregnant women. Listeria can cause a febrile illness in obstetric patients and may rarely result in severe diseases such as meningitis (49), miscarriage, or premature delivery. It can be transmitted to the neonate and cause severe disease. Contaminated food, particularly soft cheeses, cold meats, and hot dogs, can infect the obstetric patient. Transmission of Listeria to neonates in the delivery room has been reported on several occasions (50,51). Routine blood cultures should be obtained from febrile patients, providing a diagnosis and allowing directed antibiotic therapy.