Maternal and Perinatal Infection in Pregnancy: Bacterial




Key Abbreviations


Acute respiratory distress syndrome ARDS


Body mass index BMI


Centers for Disease Control and Prevention CDC


Central venous pressure CVP


Computed tomography CT


Group B Streptococcus GBS


Human immunodeficiency virus HIV


Listeria monocytogenes LM


Magnetic resonance imaging MRI


Methicillin-resistant Staphylococcus aureus MRSA


Nucleic acid amplification test NAAT


Polymerase chain reaction PCR


Premature rupture of the membranes PROM


Systemic immune response syndrome SIRS


Bacterial infections are the single most common com­plication encountered by the obstetrician . Some infections, such as puerperal endometritis and lower urinary tract infection, are of principal concern to the mother and pose little or no risk to the fetus or neonate. Others, such as listeriosis and toxoplasmosis, are of greatest threat to the fetus. Still others—such as group B streptococcal infection (GBS), pyelonephritis, and chorioamnionitis—may cause serious morbidity, even life-threatening complications, for both the mother and baby. The purpose of this chapter is to review in detail the major bacterial infections and the key protozoan infection (toxoplasmosis) that the obstetrician confronts in daily clinical practice.




Group B Streptococcal Infection


Epidemiology


Streptococcus agalactiae is a gram-positive encapsulated coccus that produces β-hemolysis when grown on blood agar. On average, about 20% to 25% of pregnant women in the United States harbor this group B Streptococcus (GBS) in their lower genital tract and rectum. GBS is one of the most important causes of early-onset neonatal infection. The prevalence of neonatal GBS infection now is about 0.5 per 1000 live births, and about 10,000 cases of neonatal streptococcal septicemia occur each year in the United States.


Neonatal GBS infection can be divided into early-onset and late-onset infection, and Table 54-1 summarizes characteristics of both. About 80% to 85% of cases of neonatal GBS infection are early in onset and result almost exclusively from vertical transmission from a colonized mother. Early-onset infection presents primarily as a severe pneumonia and overwhelming septicemia. In preterm infants, the mortality rate from early-onset GBS infection may approach 25%. In term infants, the mortality rate is lower, averaging about 5%. Late-onset neonatal GBS infection occurs as a result of both vertical and horizontal transmission. It is typically manifested by bacteremia, meningitis, and pneumonia. The mortality rate from late-onset infection is about 5% for both preterm and term infants. Unfortunately, obstetric interventions have proved ineffective in preventing late-onset neonatal infection. Therefore the remainder of this discussion focuses on early-onset infection.



TABLE 54-1

CHARACTERISTICS OF EARLY- AND LATE-ONSET NEONATAL GBS SEPSIS

























TYPE OF GBS SEPSIS TIMING % OF CASES RISK FACTORS INCIDENCE MORTALITY RATE
Early onset Within first week 85%


  • Gestational age <37 weeks



  • rupture of membranes



  • Longer duration of membrane rupture



  • Intraamniotic infection



  • Young maternal age



  • Black or Hispanic race



  • Prior delivery of an infant with GBS disease

0.34 to 0.37 cases per 1000 live births 2% to 3% (term infants); 20% to 30% (preterm infants)
Late onset After first week (up to 3 months) 15%


  • Gestational age <37 weeks



  • Black race



  • Maternal GBS colonization

0.3 to 0.4 cases per 1000 live birth 1% to 2% (term infants); 5% to 6% (preterm infants)

GBS, group B Streptococcus .


Major risk factors for early-onset infection include preterm labor, especially when complicated by preterm premature rupture of the membranes (PROM); intrapartum maternal fever (chorioamnionitis); prolonged rupture of membranes, defined as greater than 18 hours; previous delivery of an infected infant; young age; and black or Hispanic ethnicity. About 25% of pregnant women have at least one risk factor for GBS infection. The neonatal attack rate in colonized patients is 40% to 50% in the presence of a risk factor and less than 5% in the absence of a risk factor. In infected infants, neonatal mortality approaches 30% to 35% when a maternal risk factor is present but is less than 5% when a risk factor is absent.


Maternal Complications


Several obstetric complications occur with increased frequency in pregnant women who are colonized with GBS. The organism is one of the major causes of chorioamnionitis and postpartum endometritis . It may cause postcesarean delivery wound infection , usually in conjunction with other aerobic and anaerobic bacilli and staphylococci. The organism also is responsible for approximately 2% to 3% of lower urinary tract infections in pregnant women. GBS urinary tract infection, in turn, is a risk factor for preterm PROM and preterm labor. For example, Thomsen and colleagues reported a study of 69 women at 27 to 31 weeks’ gestation who had streptococcal urinary tract infections. Patients were assigned to treatment with either penicillin or placebo. Treated patients had a significant reduction in the frequency of both preterm PROM and preterm labor.


Other investigations have confirmed the association between GBS colonization and preterm labor and preterm PROM. Women with the latter complication who are colonized with GBS tend to have a shorter latent period and higher frequency of chorioamnionitis and puerperal endometritis compared with noncolonized women.


Diagnosis


The gold standard for the diagnosis of GBS infection is bacteriologic culture. Todd-Hewitt broth or selective blood agar is the preferred medium. Specimens for culture should be obtained from the lower vagina, perineum, and perianal area using a simple cotton swab. In recent years, considerable research has been devoted to assessment of rapid diagnostic tests for the identification of colonized women. Table 54-2 summarizes the results of several investigations of rapid diagnostic tests. The information in this table is based on the review by Yancey and associates. These authors noted that, although the rapid diagnostic tests had reasonable sensitivity in identifying heavily colonized patients, they had poor sensitivity in identifying lightly and moderately colonized patients.



TABLE 54-2

RELIABILITY OF RAPID DIAGNOSTIC TESTS FOR GROUP B STREPTOCOCCI





































TEST PERFORMANCE
TEST SENSITIVITY (%) SPECIFICITY (%) PV + (%) PV (%)
Gram stain 34-100 60-70 13-33 86-100
Growth in starch medium 93-98 98-99 65-98 89-99
Antigen detection (coagglutination, latex particle agglutination, enzyme immunoassay) 4-88 * 92-100 15-100 76-99
DNA probe >90 90 61 94

* Sensitivities for identification of heavily colonized women ranged from 29% to 100%.


Specimens were grown in culture for 3.5 hours before the DNA probe was used.



Although the first-generation rapid diagnostic tests were not as valuable as originally hoped, Bergeron and colleagues reported exceptionally favorable results with a new polymerase chain reaction (PCR) assay for GBS. In a series of 112 patients, the authors documented a sensitivity of 97%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 99%. This PCR assay now is commercially available and offers clear promise as a rapid test for screening patients at the time of admission for labor. Ahmadzia and colleagues recently reviewed the diagnostic accuracy of intrapartum nucleic acid amplification tests (NAATs) for GBS and reported that the sensitivity ranged from 91% to 94%.


Prevention of Group B Streptococcal Infection


In the past 20 years, several strategies have been proposed for the prevention of neonatal GBS infection. Each strategy has had major imperfections. In 1996, however, the Centers for Disease Control and Prevention (CDC) published a series of recommendations that incorporated the major advantages of previous protocols and minimized some of the more problematic aspects of selected strategies. The initial CDC guidelines recommended either universal culturing of all patients at 35 to 37 weeks’ gestation and intrapartum treatment of all colonized women or selective treatment on the basis of identified risk factors. Subsequently, in a large population-based survey, Rosenstein and Schuchat assessed the theoretic impact of the CDC recommendations and showed that a strategy of universal culturing and treatment of all colonized patients would prevent 78% of cases of neonatal infection. In contrast, only 41% of cases were prevented when patients were targeted for prophylaxis just on the basis of risk factors. In addition, Locksmith and colleagues confirmed that universal culturing also was of value in decreasing the rate of maternal infection compared with a strategy of only treating on the basis of risk factors.


In 2010, the CDC issued its most recent guidelines for prevention of early-onset GBS infection. The newest guidelines recommend universal cultures in all patients as the optimal method of prevention. Cultures should be performed at 35 to 37 weeks’ gestation. All patients who test positive should receive intrapartum antibiotic prophylaxis with one of the regimens outlined in Figure 54-1 . Ideally, antibiotics should be administered at least 4 hours before delivery. DeCueto and coworkers demonstrated that the rate of neonatal GBS infection was reduced significantly when patients were treated for at least this long. In a subsequent investigation to assess timing of antibiotic prophylaxis, McNanley and associates showed that mean vaginal GBS counts decreased fivefold within 2 hours of antibiotic administration, fiftyfold within 4 hours, and almost a thousandfold within 6 hours.




FIG 54-1


Recommended regimens for intrapartum antibiotic prophylaxis for prevention of early-onset group B Streptococcus (GBS) disease. IV, intravenously.


The new CDC guidelines also addressed issues that previously had been imprecisely defined. Colonized patients scheduled for a planned cesarean delivery do not require intrapartum prophylaxis. Patients who tested positive for GBS in a previous pregnancy should not be assumed to be colonized and should be retested with each pregnancy. This recommendation is supported by a later report from Edwards and coworkers. These authors noted that only 59% of patients who were culture positive in a previous pregnancy were positive in the current pregnancy. Conversely, however, patients who have GBS bacteriuria in pregnancy, even if treated, should be considered heavily colonized and should be targeted for intrapartum prophylaxis. Moreover, patients who had a previous infant with GBS infection also should be considered colonized and should be treated during labor. Table 54-3 outlines indications and nonindications for intrapartum prophylaxis against GBS.



TABLE 54-3

INTRAPARTUM ANTIBIOTIC PROPHYLAXIS TO PREVENT EARLY-ONSET GROUP B STREPTOCOCCAL DISEASE










INTRAPARTUM GBS PROPHYLAXIS INDICATED INTRAPARTUM GBS PROPHYLAXIS NOT INDICATED



  • Previous infant with invasive GBS disease



  • GBS bacteriuria during any trimester of the current pregnancy



  • Positive GBS vaginal-rectal screening culture in late gestation (35 to 37 weeks optimally) during the current pregnancy



  • Unknown GBS status at the onset of labor (culture not done, incomplete, or results unknown) and any of the following intrapartum risk factors :




    • Delivery at less than 37 weeks



    • Amniotic membrane rupture ≥18 hours



    • Intrapartum temperature ≥100.4° F (≥38.0° C)



    • Intrapartum NAAT positive for GBS




  • Presence of one of the above intrapartum risk factors, even if intrapartum NAAT is negative for GBS



  • Unknown GBS status at the onset of labor (culture not done, incomplete, or results unknown) and any of the following intrapartum risk factors :




    • Delivery at less than 37 weeks



    • Amniotic membrane rupture ≥18 hours



    • Intrapartum temperature ≥100.4° F (≥38.0° C)



    • Intrapartum NAAT positive for GBS





  • Colonization with GBS during a previous pregnancy



  • GBS bacteriuria during a previous pregnancy



  • Negative vaginal and rectal GBS screening culture in late gestation during the current pregnancy regardless of intrapartum risk factors



  • Cesarean delivery performed before onset of labor in a woman with intact amniotic membranes, regardless of GBS colonization status or gestational age


GBS, group B Streptococcus ; NAAT, nucleic acid amplification test.




Urinary Tract Infections


Acute Urethritis


Acute urethritis, or acute urethral syndrome, is usually caused by one of three organisms: coliforms (principally Escherichia coli ) , Neisseria gonorrhoeae, and Chlamydia trachomatis. Coliform organisms are part of the normal vaginal and perineal flora and may be introduced into the urethra during intercourse or when wiping after defecation. N. gonorrhoeae and C. trachomatis are sexually transmitted pathogens. Patients affected by urethritis typically experience frequency, urgency, and dysuria. Hesitancy, dribbling, and a mucopurulent urethral discharge also may be present. On microscopic examination, the urine usually has white blood cells, but bacteria may not be consistently present. Urine cultures may have low colony counts of coliform organisms, and cultures of the urethral discharge may be positive for gonorrhea and chlamydia . A rapid diagnostic test, such as a NAAT, is now the preferred method for identification of gonorrhea and chlamydia .


Most patients with acute urethritis warrant empiric treatment before the results of laboratory tests are available. Infections caused by coliforms usually respond to the antibiotics described later for treatment of asymptomatic bacteriuria and cystitis. If gonococcal infection is suspected, the patient should be treated with intramuscular ceftriaxone (250 mg in a single dose) plus 1000 mg oral azithromycin. If the patient is allergic to β-lactam antibiotics, an effective alternative is azithromycin 2000 mg orally in a single dose. This high dose of azithromycin is more likely to be associated with gastrointestinal side effects than more conventional lower doses. An alternative choice in the penicillin-allergic patient is ciprofloxacin 500 mg orally in a single dose. If chlamydial infection is suspected or confirmed, the patient should be treated with azithromycin 1000 mg in a single dose.


Asymptomatic Bacteriuria and Acute Cystitis


The prevalence of asymptomatic bacteriuria in pregnancy is 5% to 10%, and most cases antedate the onset of pregnancy. The frequency of acute cystitis in pregnancy is 1% to 3%. Some cases of cystitis arise de novo, whereas others develop as a result of failure to identify and treat asymptomatic bacteriuria.


E. coli is responsible for at least 80% of cases of initial infections and about 70% of recurrent cases. Klebsiella pneumoniae and Proteus species also are important pathogens, particularly in patients who have a history of recurrent infection. Up to 10% of infections are caused by gram-positive organisms such as GBS, enterococci, and staphylococci.


All pregnant women should have a urine culture at their first prenatal appointment to detect preexisting asymptomatic bacteriuria. If the culture is negative, the likelihood of the patient subsequently developing an asymptomatic infection is less than 5%. If the culture is positive—defined as greater than 10 5 colonies/mL urine from a midstream, clean-catch specimen—prompt treatment is necessary to prevent ascending infection. In the absence of effective treatment, about one third of pregnant women with asymptomatic bacteriuria will develop acute pyelonephritis. In a recent report, treatment of asymptomatic bacteriuria was also associated with a reduction in the incidence of low-birthweight babies (relative risk [RR], 0.66; 95% confidence interval [CI], 0.49 to 0.89), but no difference in preterm delivery was seen.


Patients with acute cystitis usually have symptoms of frequency, dysuria, urgency, suprapubic pain, hesitancy, and dribbling. Gross hematuria may be present, but high fever and systemic symptoms are uncommon. In symptomatic patients, the leukocyte esterase and nitrate tests are usually positive. When a urine culture is obtained, a catheterized sample is preferred because it minimizes the probability that urine will be contaminated by vaginal flora. With a catheterized specimen, a colony count greater than 10 2 /mL is considered indicative of infection.


Asymptomatic bacteriuria and acute cystitis characteristically respond well to short courses of oral antibiotics. Single-dose therapy is not as effective in pregnant women as in nonpregnant patients. However, a 3-day course of treatment appears to be comparable to a 7- to 10-day regimen for an initial infection. Longer courses of therapy are more appropriate for patients with recurrent infections. Table 54-4 lists several antibiotics of value for treatment of asymptomatic bacteriuria and cystitis.



TABLE 54-4

ANTIBIOTICS FOR TREATMENT OF ASYMPTOMATIC BACTERIURIA AND ACUTE CYSTITIS







































DRUG (TRADE NAME) STRENGTH OF ACTIVITY ORAL DOSE COST
Amoxicillin Some Escherichia coli, most Proteus species, GBS, enterococci, some staphylococci 500 mg TID or 875 mg BID Low
Amoxicillin-clavulanic acid (Augmentin) Most gram-negative aerobic bacilli and gram-positive cocci 875 mg BID High
Ampicillin Some E. coli, most Proteus species, GBS, enterococci, some staphylococci 250-500 mg 4 times daily Low
Cephalexin (Keflex) Most E. coli, most Klebsiella and Proteus species, GBS, staphylococci 250-500 mg 4 times daily Low
Nitrofurantoin monohydrate macrocrystals—sustained-release preparation (Macrobid) Most uropathogens except enterococci and Proteus species 100 mg BID Moderate
Double-strength trimethoprim-sulfamethoxazole (Bactrim DS, or Septra DS) Most uropathogens except some strains of E. coli 800 mg/160 mg BID Low

BID, twice a day; DS, double strength; GBS, group B streptococci; TID, three times a day.


When sensitivity tests are available—for example, for patients with asymptomatic bacteriuria—they may be used to guide antibiotic selection. When empiric treatment is indicated, the choice of antibiotics should be based on established patterns of susceptibility. In recent years, 20% to 30% of strains of E. coli and more than half the strains of Klebsiella have developed resistance to ampicillin. Thus this drug should not be used when the results of sensitivity tests are unknown unless the suspected pathogen is enterococci, in which case ampicillin or amoxicillin is the drug of choice.


When choosing among the drugs listed in Table 54-4 , the clinician should consider several factors. First, the sensitivity patterns of ampicillin, amoxicillin, and cephalexin are the most variable. Second, these drugs—along with amoxicillin-clavulanic acid—also have the most pronounced effect on normal bowel and vaginal flora and thus are the most likely to cause diarrhea or monilial vulvovaginitis. In contrast, nitrofurantoin monohydrate has only minimal effect on vaginal and bowel flora. Moreover, it is more uniformly effective against the common uropathogens, except for Proteus species, than trimethoprim-sulfamethoxazole. Third, amoxicillin-clavulanic acid and trimethoprim-sulfamethoxazole usually are the best empiric agents for treatment of patients with suspected drug-resistant pathogens. However, sulfonamides should be avoided in the first trimester of pregnancy because of possible teratogenicity, and they should be avoided immediately prior to delivery because of concern about displacement of bilirubin from protein binding sites, with resultant neonatal jaundice (see Chapter 8 ).


For patients who have an initial infection and experience a prompt response to treatment, a urine culture for test of cure may not be clinically necessary or cost effective. Cultures during or immediately after treatment are indicated for patients who have a poor response to therapy or who have a history of recurrent infection. During subsequent clinic appointments, the patient’s urine should be screened for nitrites and leukocyte esterase. If either of these tests is positive, repeat urine culture and retreatment are indicated.


Acute Pyelonephritis


The incidence of pyelonephritis in pregnancy is 1% to 2%. Most cases develop as a consequence of undiagnosed or inadequately treated lower urinary tract infection. Two major physiologic changes occur during pregnancy that predispose to ascending infection of the urinary tract. First, the high concentration of progesterone secreted by the placenta has an inhibitory effect on ureteral peristalsis. Second, the enlarging gravid uterus often compresses the ureters, particularly the right, at the pelvic brim, thus creating additional stasis. Stasis, in turn, facilitates migration of bacteria from the bladder into the ureters and renal parenchyma ( Fig. 54-2 ).




FIG 54-2


Intravenous pyelogram in a pregnant woman shows marked dilation of the right ureter and mild dilation of the renal collecting system.


About 75% to 80% of cases of pyelonephritis occur on the right side, 10% to 15% are left sided, and a slightly smaller percentage are bilateral. E. coli is again the principal pathogen. K. pneumoniae and Proteus species also are important causes of infection, particularly in women with recurrent episodes of pyelonephritis. Highly virulent gram-negative bacilli such as Pseudomonas, Enterobacter, and Serratia are unusual isolates except in immunocompromised patients. Gram-positive cocci do not frequently cause upper tract infection. Anaerobes also are unlikely pathogens unless the patient is chronically obstructed or instrumented.


The usual clinical manifestations of acute pyelonephritis in pregnancy are fever, chills, flank pain and tenderness, urinary frequency or urgency, hematuria, and dysuria. Patients also may have signs of preterm labor, septic shock, and acute respiratory distress syndrome (ARDS). Urinalysis is usually positive for white blood cell casts, red blood cells, and bacteria. Urine colony counts greater than 10 2 colonies/mL in samples collected by catheterization confirm the diagnosis of infection.


Pregnant patients with pyelonephritis may be considered for outpatient therapy if their disease manifestations are mild, they are hemodynamically stable, and they have no evidence of preterm labor. If an outpatient approach is adopted, the patient should be treated with agents that have a high level of activity against the common uropathogens. Acceptable oral agents include amoxicillin-clavulanic acid 875 mg twice daily or double-strength trimethoprim-sulfamethoxazole twice daily for 7 to 10 days. Alternatively, a visiting home nurse may be contracted to administer a parenteral agent such as intravenous (IV) or intramuscular (IM) ceftriaxone 2 g once daily. Although an excellent drug for lower tract infections, nitrofurantoin monohydrate does not consistently achieve the serum and renal parenchymal concentrations necessary for successful treatment of more serious infections.


Patients who appear to be moderately to severely ill or who show any signs of preterm labor should be hospitalized for IV antibiotic therapy. They should receive appropriate supportive treatment and should be monitored closely for complications such as sepsis, ARDS, and preterm labor. One reasonable choice for empiric IV antibiotic therapy is ceftriaxone 2 g every 24 hours. Compared with a first-generation cephalosporin like cefazolin, ceftriaxone has expanded coverage against aerobic gram-negative bacilli and has the advantage of once-daily dosing. If the patient is critically ill or is at high risk for a resistant organism, a second antibiotic, such as gentamicin (7 mg/kg/ideal body weight every 24 hours) or aztreonam (500 mg to 1 g every 8 to 12 hours) should be administered, along with ceftriaxone, until the results of susceptibility tests are available.


Once antibiotic therapy is initiated, about 75% of patients defervesce within 48 hours. By the end of 72 hours, almost 95% of patients are afebrile and asymptomatic. The two most likely causes of treatment failure are a resistant microorganism and obstruction. The latter condition is best diagnosed with computed tomography (CT) scan or renal ultrasonography and typically results from a stone or physical compression of the ureter by the gravid uterus.


Once the patient has begun to defervesce and her clinical condition has improved, she may be discharged from the hospital. Oral antibiotics should be prescribed to complete a total of 7 to 10 days of therapy. Selection of a specific oral agent should be based on considerations of efficacy, toxicity, and expense. A repeat urine culture should be obtained after therapy is completed to ensure that the infection has been adequately treated.


About 20% to 30% of pregnant patients with acute pyelonephritis develop a recurrent urinary tract infection later in pregnancy. The most cost-effective way to reduce the frequency of recurrence is to administer a daily prophylactic dose of an antibiotic such as nitrofurantoin monohydrate 100 mg. Patients receiving prophylaxis should have their urine screened for bacteria at each subsequent clinic appointment. They also should be questioned about recurrence of symptoms. If symptoms recur, or the dipstick test for nitrite or leukocyte esterase is positive, a urine culture should be obtained to determine whether retreatment is necessary.




Upper Genital Tract Infections


Chorioamnionitis


Chorioamnionitis—or amnionitis, intraamniotic infection—may present with fever and fetal tachycardia. Because both the mother and infant may experience serious complications when chorioamnionitis is present, prompt diagnosis is imperative.


Epidemiology


Chorioamnionitis occurs in 1% to 5% of term pregnancies. In patients with preterm delivery, the frequency of clinical or subclinical infection may approach 25%. Although chorioamnionitis may result from hematogenous dissemination of microorganisms, it more commonly is an ascending infection caused by organisms that are part of the normal vaginal flora. The principal pathogens are Bacteroides and Prevotella species, E. coli , anaerobic gram-positive cocci, GBS, and genital mycoplasmas.


Several clinical risk factors for chorioamnionitis have been identified. The most important are young age, low socioeconomic status, nulliparity, extended duration of labor and ruptured membranes, multiple vaginal examinations, and preexisting infections of the lower genital tract (e.g., bacterial vaginosis and GBS infection). Antibiotic use in preterm PROM is associated with a statistically significant reduction in chorioamnionitis. In term PROM, consideration should also be given to minimizing use of vaginal digital examinations intrapartum once membrane rupture has occurred, as well as antibiotic prophylaxis, especially when latency greater than 12 hours is expected (see Chapter 30 ).


Diagnosis


In most situations, the diagnosis of chorioamnionitis can be established on the basis of the clinical findings of maternal fever and maternal and fetal tachycardia in the absence of other localizing signs of infection. In more severely ill patients, uterine tenderness and purulent amniotic fluid may be identified. The disorders that should be considered in the differential diagnosis of intrapartum fever include respiratory tract infection, pyelonephritis, viral syndrome, and appendicitis, but chorioamnionitis should always be the principal consideration.


Laboratory confirmation of the diagnosis of chorioamnionitis is not routinely necessary in term patients who are progressing to delivery. However, in preterm patients who are being evaluated for tocolysis or corticosteroids, laboratory assessment may be of value in establishing the diagnosis of intrauterine infection. In this clinical context, amniotic fluid should be obtained by transabdominal amniocentesis. Table 54-5 summarizes the abnormal laboratory findings that may be present in infected patients.



TABLE 54-5

DIAGNOSTIC TESTS FOR CHORIOAMNIONITIS




































TEST ABNORMAL FINDING COMMENT
Maternal white blood cell count (WBC) ≥15,000 cells/mm 3 with preponderance of leukocytes Labor and/or corticosteroids may also result in elevation of WBC count.
Amniotic fluid glucose ≤10 to 15 mg Correlation is excellent with positive amniotic fluid culture and clinical infection.
Amniotic fluid interleukin-6 ≥7.9 ng/mL Correlation is excellent with positive amniotic fluid culture and clinical infection.
Amniotic fluid leukocyte esterase ≥1 + reaction Correlation is good with positive amniotic fluid culture and clinical infection.
Amniotic fluid Gram stain Any organism in an oil immersion field Identification of particularly virulent organisms, such as group B streptococci, is possible; however, the test is very sensitive to inoculum effect. In addition, it cannot identify pathogens such as mycoplasmas.
Amniotic fluid culture Growth of aerobic or anaerobic microorganism This test is the gold standard, although results are not immediately available for clinical management.
Blood cultures Growth of aerobic or anaerobic microorganism Cultures will be positive in 5% to 10% of patients; however, they will usually not be of value in making clinical decisions unless the patient is seriously ill, at increased risk for bacterial endocarditis, immunocompromised, or has a poor response to the initial treatment.


Management


Both the mother and infant may experience serious complications when chorioamnionitis is present. Bacteremia occurs in 3% to 12% of infected women. When cesarean delivery is required, up to 8% of women develop a wound infection, and about 1% develop a pelvic abscess. Fortunately, maternal death due to infection is exceedingly rare.


Of neonates delivered to mothers with chorioamnionitis, 5% to 10% have pneumonia or bacteremia. The predominant organisms responsible for these infections are GBS and E. coli . Meningitis occurs in less than 1% of term infants and in a slightly higher percentage of preterm infants. Mortality due to infection ranges from 1% to 4% in term neonates but may approach 15% in preterm infants because of the confounding effects of other complications such as hyaline membrane disease, intraventricular hemorrhage, and necrotizing enterocolitis.


To prevent maternal and neonatal complications, parenteral antibiotic therapy should be initiated as soon as the diagnosis of chorioamnionitis is made, unless delivery is imminent. Three separate investigations have demonstrated that mother-infant pairs who receive prompt intrapartum treatment have better outcomes than patients treated after delivery. The principal benefits of early treatment include decreased frequency of neonatal bacteremia and pneumonia and decreased duration of maternal fever and hospitalization.


The most extensively tested IV antibiotic regimen for treatment of chorioamnionitis is the combination of ampicillin (2 g every 6 hours) or penicillin (5 million U every 6 hours) plus gentamicin (1.5 mg/kg every 8 hours or 5 to 7 mg/kg/ideal body weight every 24 hours). The latter regimen of gentamicin is the most cost-effective. These antibiotics specifically target the two organisms most likely to cause neonatal infection: GBS and E. coli . With rare exceptions, gentamicin is preferred to tobramycin or amikacin because it is available in an inexpensive generic formulation. Amikacin should be reserved for immunocompromised patients who are particularly likely to be infected by highly virulent, drug-resistant aerobic gram-negative bacilli. In patients who are allergic to β-lactam antibiotics, clindamycin (900 mg every 8 hours) should be substituted for ampicillin.


If a patient with chorioamnionitis requires cesarean delivery, a drug with activity against anaerobic organisms should be added to the antibiotic regimen. Either clindamycin (900 mg) or metronidazole (500 mg) is an excellent choice for this purpose. Failure to provide effective coverage of anaerobes may result in treatment failures in 20% to 30% of patients.


Extended-spectrum cephalosporins, penicillins, and carbapenems also provide excellent coverage against the bacteria that cause chorioamnionitis. Dosages and dose intervals for several of these agents are listed in Table 54-6 . As a general rule, these drugs are more expensive than the generic combination regimens outlined earlier.



TABLE 54-6

SINGLE AGENTS OF VALUE IN TREATMENT OF CHORIOAMNIONITIS AND PUERPERAL ENDOMETRITIS


































































DRUG DOSAGE AND DOSE INTERVAL RELATIVE COST TO THE PHARMACY *
Extended-Spectrum Cephalosporins
Cefepime 2 g every 12 hours Intermediate
Cefotaxime 2 g every 8-12 hours Intermediate
Cefotetan 2 g every 12 hours Low
Cefoxitin 2 g every 6 hours Intermediate
Ceftizoxime 2 g every 12 hours Intermediate
Extended-Spectrum Penicillins
Ampicillin-sulbactam 3 g every 6 hours Low
Mezlocillin 3 to 4 g every 6 hours Intermediate
Piperacillin 3 to 4 g every 6 hours Intermediate
Piperacillin-tazobactam 3.375 g every 6 hours Intermediate
Ticarcillin–clavulanic acid 3.1 g every 6 hours Low
Carbapenem
Ertapenem 1 g every 24 hours High
Imipenem-cilastatin 500 mg every 6 hours High
Meropenem 1 g every 8 hours High

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Mar 31, 2019 | Posted by in OBSTETRICS | Comments Off on Maternal and Perinatal Infection in Pregnancy: Bacterial
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