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Bacterial Infections and Pregnancy

Practice Essentials

Bacterial infections can affect pregnant women from implantation of the fertilized ovum through the time of delivery and peripartum period. They may also affect the fetus and newborn. Many women with these infections are asymptomatic, necessitating both a high degree of clinical awareness and adequate screening.

Group B Streptococcus

Group B Streptococcus (GBS; Streptococcus agalactiae) is the most common cause of life-threatening infections in newborns and can also affect the mother. Features of GBS infection are as follows:

GBS can be found as part of normal vaginal, rectal, and oral flora

Intrapartum transmission occurs via ascending spread or at the time of delivery

In pregnant women, GBS causes cystitis, amnionitis, endometritis, and stillbirth; occasionally, GBS bacteremia leads to endocarditis or meningitis

In postpartum women, GBS can cause urinary tract infections (UTIs) and pelvic abscesses

In newborns, early-onset GBS infection occurs before age 7 days (mean age at presentation is age 12 hours) and primarily manifests as nonfocal sepsis, pneumonia, or meningitis

Late-onset disease in neonates occurs at age 7-89 days (mean age, 36 days), and nonfocal bacteremia and meningitis are the most common presentations

Babies who survive the initial insult face possible hearing or vision loss, learning disabilities, and other neurologic sequelae

CDC recommendations are as follows:

At 35-37 weeks’ gestation, all pregnant women should undergo screening with a vaginal and rectal swab for culture

The most specific site for culture is at the introitus, just inside the hymeneal ring and rectally beyond the sphincter; cervical, perianal, perirectal, or perineal specimens are not acceptable, and speculum should not be used for culture collection

If the culture result is positive, the woman should be treated during labor

If culture results are unknown at the time of delivery, a risk-based approach can be used, in which patients are deemed at high risk and receive treatment if they meet any of the following criteria:

Previously delivered infant with invasive GBS infection

GBS bacteriuria during current pregnancy

Delivery before 37 weeks’ gestation

Duration of ruptured membranes longer than 18 hours

Intrapartum temperature of more than 100.4°F (38°C)

High-risk women with negative screening culture results within 5 weeks of delivery do not require treatment.

Treatment is as follows:

During labor and until delivery, IV penicillin G or ampicillin.

In patients with known penicillin allergy, sensitivities of the GBS isolate should be sent, although IV cefazolin is the best choice in penicillin-allergic patients at low risk for anaphylaxis,; in those at high risk for anaphylaxis, IV clindamycin or erythromycin is an acceptable alternative

If susceptibility to clindamycin or erythromycin has not been established, IV vancomycin can be used

The neonate must be carefully observed for signs and symptoms of disease

Urinary tract infections

Asymptomatic bacteriuria develops in 10-15% of pregnant women and can lead to complications such as pyelonephritis and premature labor, so all pregnant women should undergo screening with urine culture at least once during early pregnancy and should be treated if the results are positive.
Significant bacteriuria is defined as >100,000 colony-forming units (CFU) of a single organism in a clean-catch specimen.

Treatment is as follows:

Initial antibiotic therapy may be empiric, followed by tailoring to the pathogen grown in the urine

Sulfonamides, amoxicillin, amoxicillin-clavulanate, cephalexin, and nitrofurantoin are acceptable

Sulfonamides in the last few weeks of gestation may lead to kernicterus and hyperbilirubinemia in the newborn

Trimethoprim is relatively contraindicated during the first trimester due to theoretical teratogenicity

Nitrofurantoin may cause hemolysis in patients or fetuses with G6PD deficiency

A 7-day regimen treats bacteriuria and acute cystitis; single-dose therapy is less effective

Recurrent UTIs may warrant postcoital prophylaxis with single-dose cephalexin or nitrofurantoin macrocrystal

Apart from the need to avoid certain antibiotics, treatment of pyelonephritis in pregnant women mirrors that in nonpregnant patients

Mild cases may be treated in an outpatient setting, but more severe cases may necessitate hospitalization and IV antibiotics plus IV hydration for nausea, vomiting, and dehydration

Women who have had acute pyelonephritis should be monitored frequently with repeat urine cultures; if close follow-up care is not practical, continuous suppressive therapy can be considered


Features of infection with Listeria monocytogenes are as follows:

Approximately one third of all reported cases of listeriosis occur during pregnancy, typically during the third trimester

Infection mainly follows ingestion of contaminated food, but rare cases following direct contact with infected animals and nosocomial transmission have been reported

The most common clinical presentation in pregnant patients with listeriosis is bacteremia, often asymptomatic; CNS Listeria infections are rare, unlike in other populations

Symptomatic pregnant patients often have a febrile illness similar to influenza with fever, muscle aches, and, occasionally, nausea or diarrhea during the bacteremic phase of the disease

Although maternal symptoms may be mild, listeriosis can lead to amnionitis and result in spontaneous septic abortion, premature labor with delivery of an infected baby, or even stillbirth

Fetal infection may manifest as septicemia, meningoencephalitis, or disseminated granulomatous lesions with microabscesses

Confirming a diagnosis of listeriosis requires a culture showing L monocytogenes in blood or CSF

Serologic testing is not reliable for diagnosis, and stool cultures are not sensitive or specific

Treatment is with IV ampicillin or penicillin; patients with beta-lactam allergy should be desensitized

Trimethoprim-sulfamethoxazole is the usual alternative for patients allergic to penicillin but can be problematic during the first or third trimesters


Features of syphilis are as follows:

Untreated primary or secondary syphilis in pregnancy leads to a fetal infection rate of almost 100%

The disease can cause stillbirth; late abortion; or neonatal disease, death, or latent infection

In primary syphilis, a hard, painless red ulcer typically forms on the vulva, cervix, or vagina

Secondary syphilis predominantly manifests as a nonpruritic rash that may involve the palms and soles; fever, lymphadenopathy, and joint pain are less common manifestations of secondary syphilis

The latent stage causes no symptoms and is still transmissible to the fetus

Tertiary syphilis can result in cardiovascular or gummatous disease

Neurosyphilis can occur at any stage, resulting in CNS or ophthalmic presentations

Serologic tests should be performed at the initial prenatal visit in all pregnant women; patients considered to be at high risk should have repeat testing at 28 weeks’ gestation and at delivery

Nontreponemal antibody test results (eg, RPR, VDRL) are often false-positive in pregnant women; therefore, positive findings should be confirmed with specific antitreponemal antibody tests such as the microhemagglutination assay– T pallidum (MHA-TP) and the fluorescent treponemal antibody absorption test (FTA-ABS)

Once syphilis is diagnosed, consider other sexually transmitted diseases, especially HIV

Treatment is with a single dose of 2.4 million units of IM benzathine penicillin for primary, secondary, and early latent syphilis, but some experts recommend a second dose of benzathine penicillin G 1 week after the initial dose, especially in the third trimester or in patients with secondary syphilis

In late latent syphilis, treatment consists of 3 doses of benzathine penicillin, each one week apart; if results of subsequent quantitative VDRL or an equivalent test show a 4-fold increase, re-treat the patient and perform a lumbar puncture to rule out neurosyphilis

Pregnant women who are allergic to penicillin must be desensitized and then treated with penicillin

Jarisch-Herxheimer reactions in pregnancy may involve uterine contractions, preterm labor, and premature delivery


Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease in the United States and continues to be a major cause of complications in pregnancy and disease transmission in newborns. Features of Chlamydia infection are as follows:

Approximately 75% of women with C trachomatis infection are asymptomatic

C trachomatis can cause endometritis, cervicitis, acute PID, and acute urethral syndrome in all women and chorioamnionitis, postpartum endometritis, and gestational bleeding in pregnant women

The usual mode of transmission to the fetus is vertical during the second stage of labor

In neonates, C trachomatis infection commonly causes conjunctivitis (ophthalmia neonatorum) and pneumonia

All pregnant women should undergo Chlamydia screening early in pregnancy; pregnant women younger than 25 years and high-risk patients should be screened again in the third trimester

Patients diagnosed with chlamydial infection in the first trimester should be retested 3-6 months later

According to the CDC, the following are the accepted screening methods

A nucleic acid amplification test (NAAT) performed on urine or an endocervical swab specimen

An unamplified nucleic acid hybridization test, an enzyme immunoassay, or direct fluorescent antibody test performed on an endocervical swab specimen

Culture performed on an endocervical swab specimen

Treatment is as follows:

Azithromycin (first-line recommended therapy)

Amoxicillin (alternative agent)

Erythromycin (second-line agent because of compliance-limiting GI adverse effects)

Tetracyclines and fluoroquinolones are contraindicated in pregnant women

Retest treated women 3 weeks after therapy to ensure therapeutic cure


Features of Neisseria gonorrhoeae infection are as follows:

Gonococcal infections are second only to chlamydial infections in the number of cases of bacterial STDs

Gonococcal infections cause no symptoms in approximately 50% of patients

Pregnancy is a predisposing factor to the development of disseminated gonococcal infection, which classically presents as an arthritis-dermatitis syndrome

Newborns exposed to gonorrhea during vaginal delivery can develop an acute conjunctivitis (ophthalmia neonatorum), sepsis, arthritis, and/or meningitis

The American College of Obstetricians and Gynecologists recommends screening (via endocervical culture) in high-risk pregnant women on their first antenatal visit

The CDC recommends screening all pregnant women “at risk for gonorrhea,” with rescreening in the third trimester for those at continued risk

The recommended screening method remains endocervical culture; alternatives include the NAAT and the nucleic acid hybridization test

Culture, nucleic acid hybridization, and NAAT tests can all be used for diagnosis

The treatment of choice for uncomplicated cervicitis is single-dose IM ceftriaxone and oral azithromycin

Bacterial vaginosis

Bacterial vaginosis is a clinical syndrome caused by excessive growth of bacteria that may normally be present in the vagina. Features of bacterial vaginosis are as follows:

The etiology is polymicrobial in nature; with a pH of more than 4.5, Gardnerella vaginalis and anaerobes become the prominent associated organisms

Women with bacterial vaginosis may be asymptomatic or may report an abnormal vaginal discharge with an unpleasant, fishlike odor, especially after sexual intercourse

The discharge is generally white or gray, and women may experience burning during urination or itching around the vagina

Infection can lead to premature labor unresponsive to tocolytic therapy

Infection can be transmitted via the placenta to the fetus and can cause intrauterine fetal death

A diagnosis of bacterial vaginosis can be confirmed via clinical or Gram stain criteria. When using the clinical criteria, 3 of the following 4 conditions should be present:

A homogeneous, white, noninflammatory discharge that smoothly coats the vaginal wall

Clue cells (ie, vaginal epithelial cells that have a stippled appearance due to aggregates of coccobacilli)

Vaginal fluid pH of more than 4.5

A positive whiff test result (ie, a fishy odor to the vaginal discharge before or after the addition of 10% potassium hydroxide solution)

Oral metronidazole or clindamycin is recommended; clindamycin cream should be avoided during the second half of pregnancy

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