Infections during pregnancy

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Chapter 17 Infections during pregnancy

CHAPTER CONTENTS

Urinary tract infection 136

Asymptomatic bacteriuria 137
Pyelonephritis 137
Vaginal infections 137
Bacterial infections 137

Group B streptococcus 137
Gonorrhoea 138
Syphilis 138
Other infection 138

Toxoplasmosis 138
Viral infections 138

Rubella 138
Genital herpes 139
Hepatitis B 139
Hepatitis C 139
Cytomegalovirus infection (CMV) 139
Human immunodeficiency virus infection (HIV) 139
Chickenpox (varicella) 140
Infections in the tropics 140

Helminth infestations – hookworm disease 140
Malaria 140

With the exception of poliomyelitis, pregnancy does not alter a woman’s resistance to infection. The severity of any infection, however, correlates positively with its effect on the fetus. For example, the more severe the infection and the earlier in pregnancy it occurs, the greater is the risk of miscarriage or of intra-uterine death of the fetus.

Infections have an indirect and a direct effect on the fetus. The indirect effect operates by reducing the oxygenation of the placental blood, and by altering the nutrient exchange through the placenta. The direct effect depends on the ability of the invading organism to penetrate the placenta and infect the fetus. Viruses, being smaller than bacteria, are able to do this more easily. At first, the virus multiplies in the trophoblast and subsequently invades the fetus. Most viral infections do not affect the fetus unless the mother’s infection is very severe. Three exceptions to this are rubella, cytomegalovirus and herpes simplex infections. These infections may cause congenital defects. The clinical effects of infections are microcephaly, congenital heart disease, eye damage (such as cataract), deafness, hepatosplenomegaly (with jaundice), purpura and, later in childhood, mental handicap.

As maternal antibodies cross the placenta they offer the fetus a degree of immunity, except in the case of a primary infection. The fetus becomes immunologically competent from about the 14th week of gestation, but the efficacy of this protection is low until the second half of pregnancy.

URINARY TRACT INFECTION

Urinary tract infection is the most disturbing of the bacter-ial infections. It occurs because the urinary tract dilates owing to the relaxation of the muscles of the ureter and the bladder in pregnancy, with consequent urinary stasis.

Asymptomatic bacteriuria

The prevalence of asymptomatic bacteriuria (defined as more than 100 000 bacteria per mL of urine) in pregnancy is 6%, similar to that in non-pregnant sexually active women; 30% of pregnant women who have asymptomatic bacteriuria will develop symptomatic urinary tract infection. Unless the infection is treated these women have an increased risk of delivering a low-birthweight baby, delivering prematurely and having postpartum endometritis.

Because of this risk, pregnant women should be screened for asymptomatic bacteriuria in early pregnancy. A midstream specimen of urine is sent to a laboratory for culture. In 85% of cases Escherichia coli is isolated, and in the remainder a variety of microorganisms are found. As the procedure is costly, other procedures, such as dip slides covered with a culture medium and reagent strips, have been developed and are reliable screening methods.

Treatment of asymptomatic bacteriuria consists of prescribing amoxicillin 500 mg/clavulanic acid 125 mg or cefalexin 2 g as a single dose or in appropriate doses for 5–7 days. Seven days after the woman has finished the antibiotics, a midstream specimen of urine is re-examined. If the asymptomatic bacteriuria has not been eliminated, a longer course of antibiotics is prescribed. Regular follow-up urine cultures must be made, and recurrences treated.

Pyelonephritis

As mentioned above, about 30% of women who have untreated bacteriuria will develop pyelonephritis during pregnancy, as will 1% of women who do not have the condition. Pyelonephritis can cause premature rupture of the membranes and perinatal death

The infection occurs when bacteria, growing in the stagnant urine, spread from the bladder to the ureter and then to the renal pelvis. Haematogenous infection is very uncommon. Pyelonephritis usually begins after the 20th week of pregnancy. In mild cases the woman complains of tiredness and urinary frequency, and occasionally dysuria. More severe infections start suddenly, with chills and rigors, fever, and pain over one or both renal areas. The patient may rapidly become dehydrated. The diagnosis is confirmed by examining a midstream specimen of urine, having excluded other causes of abdominal pain such as acute appendicitis and abruptio placentae.

Treatment consists of correcting the dehydration and prescribing appropriate antibiotics, having tested for bacterial sensitivity. In most cases, a cephalosporin or amoxicillin is appropriate initial treatment. As some women with pyelonephritis are nauseated, the antibiotic may have to be given intravenously. Follow-up examinations of a midstream urine culture at 2-week intervals for the remainder of the pregnancy should be instituted. Some authorities recommend prophylactic antibiotics for the duration of the pregnancy.

VAGINAL INFECTIONS

Vaginal infections during pregnancy due to Candida spp., Trichomonas and bacterial vaginosis are discussed on pages 260–262. The diagnosis and treatment are the same as in pregnancy.

BACTERIAL INFECTIONS

Group B streptococcus

Colonies of group B streptococci (GBS) are harboured in the lower vagina and/or rectum of 18–27% of pregnant women.

If group B streptococcal infection is present during labour the bacteria may colonize the neonate. Over half of babies born through an infected vagina are colonized, and 2–5% of them develop early onset GBS neonatal sepsis. The mortality rate for premature affected infants is 25–30%, for those at term 2–8%, and neurological sequelae for the survivors of 15–30%.

Up to 80% of cases of early-onset disease are associated with obstetric risk factors: preterm delivery, prolonged rupture of membranes for more than 18 hours, maternal fever >38° during labour. Treatment of known carriers or those at high risk with penicillin during active labour reduces both neonatal and maternal morbidity.

Two approaches to selecting those for treatment are widely used: one treats on risk factors alone, the other takes a low vaginal and a rectal swab at 36 weeks’ and then treats those with positive isolates. Both regimens have been shown to be effective. See Box 17.1.

Box 17.1 Strategies to prevent early-onset group B streptococcus (GBS) neonatal sepsis

A Screen all women between 35–37 weeks with low vaginal and anorectal swab

If positive or previous baby with early onset GBS or GBS bacteriuria during index pregnancy:

• Give 1.2 g IV benzylpenicillin when in labour or ruptured membranes followed by 600 mg IV 4-hourly until delivered
• If allergic to penicillin give clindamycin 600 mg IV 8-hourly or erythromycin 500 mg 6-hourly

B Treat if positive risk factor(s)

• Premature labour before 37 weeks
• Previous early onset GBS disease
• When anticipate membranes will have been ruptured >18 hours before delivery
• Intrapartum fever ≥38.0°C
• GBS bacteriuria during pregnancy

Gonorrhoea

Depending on the population studied, between 1 and 6% of pregnant women are found to have gonorrhoea on culture studies using the Thayer–Martin medium. Many have no symptoms. In symptomatic gonorrhoea the woman complains of dysuria and a vaginal discharge which occurs within 5 days of sexual intercourse. If the symptoms suggest gonorrhoea, or if the woman’s sexual behaviour suggests that she may have gonorrhoea, cervical and urethral swabs should be taken and inoculated directly on to preheated plates of culture medium. In addition, vaginal swabs should be made for other vaginal infective organisms. The management of gonococcal infection is discussed on page 264.

Syphilis

The importance of syphilitic infection in pregnancy is that treponemes are able to penetrate the placenta after the 15th week of pregnancy and infect the fetus, resulting in congenital syphilis in 20–50% and perinatal death in 20–30%. If the fetus survives the initial infection, by the time of the birth it is in the second stage of syphilis.

For this reason every pregnant woman should be offered screening for syphilis using a reagin test (either the VDRL or the rapid plasma reagin (RPR) test), although the incidence of syphilis in most areas is less than 0.1%. The test should be made at the first antenatal visit and, in regions with a high prevalence, repeated at the 30th week of pregnancy. False positives may occur, and so a woman who has had a positive screening test is investigated using a procedure that detects specific antitreponemal antibodies in her serum (e.g. the Treponema pallidum haemagglutination test, TPHA; the fluorescent treponemal antibody test, FTA-ABS; or the T. pallidum immobilization test, TPI).

The treatment is that described on page 259 for non-pregnant women. Follow-up serological tests are made monthly for 3 months, every 2 months for the next 6 months, and every 3 months for the next year.

As the signs of syphilis in a neonate are often equivocal and the serology is inaccurate, the infant of a woman who has been diagnosed as having syphilis while pregnant, and who has not had a complete course of treatment and follow-up, should be given a full course of antibiotic treatment (aqueous procaine benzylpenicillin 50 000 U/kg body weight daily for 10 days).

OTHER INFECTION

Toxoplasmosis

Toxoplasma gondii infects 2–10 pregnant women per 1000. In 90% there are no clinical signs. Infections acquired in pregnancy may lead to a miscarriage or congenital infection of the fetus, one fetus in four being affected. The risk of fetal disease is highest in the first trimester; most neonates infected in the third trimester are asymptomatic with delayed sequelae, including developmental delays. The eyes and the central nervous system may be severely damaged.

Screening tests for toxoplasma are available but are not cost-effective. If chosen they are best carried out before pregnancy, and seronegative women should be retested in each of the quarters of pregnancy.

Preventive measures taken by a pregnant woman are more cost-effective:

• A pregnant woman should avoid touching cat faeces.
• She should avoid touching her eyes or mouth while handling raw meat, wash her hands after handling it, and should only eat well-cooked meat.
• The woman should wash vegetables and fruit thoroughly before eating them and, if a gardener, should wear gloves.

A proven infection may be treated with pyrimethamine plus sulfadiazine, with supplementary folic acid to counteract their antifolate activity.

VIRAL INFECTIONS

Seven viral infections need some discussion.

Rubella

Rubella infection is widespread. By the age of 19 more than 85% of people have been infected, and nine out of 10 of those infected have lifelong immunity.

Should rubella occur in a non-immune woman in the first 14 weeks of pregnancy, viraemia and infection of the fetus are almost certain, and more than 40% of the infected fetuses will be damaged by the virus. The virus invades actively dividing cells and alters the genome. Infection in weeks 4–12 of pregnancy affects the lenses of the eyes (causing cataract) or the ears (causing deafness). Infection between the fifth and 12th weeks damages the chambers of the heart. As well as causing damage to specific organs, rubella infection may cause widespread cellular damage, leading to fetal growth restriction, thrombocytopenia, hepatosplenomegaly and vasculitis and, in particular, renal artery stenosis.

These problems could be avoided if all women were immunized against rubella between the ages of 11 and 13 using a live attenuated strain of the virus (the RA 27/3 strain). Programmes to accomplish this have been developed in many countries.

A woman should be tested for rubella antibodies either when she decides to become pregnant or at the first pregnancy visit. If this test is positive the woman is immune to rubella. A non-immune woman who is not pregnant may be offered vaccination but should avoid pregnancy for 3 months. If a pregnant woman is inadvertently vaccinated the risk of the baby being infected is extremely small: no cases of congenital rubella syndrome have been reported in these circumstances.

A problem arises when a pregnant non-immune woman develops a rubelliform rash (as in half of women the rash is not due to rubella), or if the woman has been in contact with a case of rubella. A serological test should be made as soon as possible, preferably within 15 days of the appearance of the rash or the contact. If the rubella IgG is positive the woman may be reassured that her baby is in no danger of being infected. If it is negative then a second test measuring the IgM levels should be taken 21 days later. If the woman seroconverts, the problems of congenital infection should be discussed with her and a therapeutic abortion is an option she may wish to consider.

Genital herpes

A general discussion on herpes simplex virus (HSV) can be found on this page. In pregnancy HSV may cross the placental barrier to infect the fetus, and is more likely to be found in primary than in recurrent infections. Overall the risk is low, only one fetus per 11 000 live births being infected. The transmission risk is greater during childbirth, particularly if the mother has her first attack (40–50% risk), compared with a risk of <5% for a recurrent infection.

These findings suggest that:

• A woman with a history of genital herpes need have no anxiety that her baby will be infected and may expect to be delivered vaginally, unless a recurrence of the infection or a new infection occurs during the pregnancy.
• If a first infection or a recurrence of genital herpes occurs during the pregnancy, but has healed by the time labour starts, the woman may give birth vaginally.
• If herpetic lesions are present when the membranes rupture or labour starts, a caesarean section should be performed to avoid the risk that the baby will acquire a herpetic infection during the passage through the birth canal.

The strategy of taking endocervical swabs for viral culture every 2 weeks from the 34th week of pregnancy can be abandoned, as positive HSV-infected swabs do not predict the risk of the infant being exposed to herpes infection during birth. The infant only needs treatment with aciclovir if it is clinically ill or has positive viral cultures. Severe neonatal HSV infection carries a 30% risk of neonatal death and neurological damage occurs in 40% of the survivors.

Hepatitis B

Less than 0.5% of women in the developed nations are hepatitis B carriers but, in contrast, up to 30% of migrants from parts of Africa and east and southeast Asia have hepatitis B surface antigen (HBsAg) in their blood and are potentially infectious to healthcare workers, who may be infected by contact with blood and other body secretions. Many units now screen all pregnant women for hepatitis B. Precautions are taken when caring for such women in childbirth, and most hospitals have developed appropriate protocols.

It is also known that the hepatitis B virus is readily transmitted to the baby, probably during the birth. Babies at particularly high risk are those whose mothers have HBcAg as well as HBsAg in their blood. If not treated, many of the babies will develop hepatocellular carcinoma in adulthood. This can be avoided to a large extent if babies at high risk are given hepatitis B immunoglobulin together with hepatitis B vaccine 10 μg at birth, and two further injections of the vaccine at the ages of 1 and 6 months. Many centres offer hepatitis B vaccination to all children.

Hepatitis C

Hepatitis C infection is usually contracted from needle sharing (50–70% of IV drug users are hepatitis C positive), from contaminated blood transfusions or from contaminated instruments, e.g. tattooing or body piercing. In Australia the prevalence of hepatitis C is 13/1000. The risk of vertical transmission to the fetus is 3–7%, but if associated with HIV infection and a high viral load can reach 25%.

Currently there are no effective management strategies to reduce transmission, including caesarean section and the avoidance of breastfeeding. Fetal scalp electrode application and fetal scalp blood sampling should be avoided. The antiviral agents (interferon and ribavirin) used to treat hepatitis C in the non-pregnant are teratogenic. If identified, women should be referred for specialist assessment and treatment after delivery, and the baby followed up so that it can also be treated if its HCV RNA serology stays positive after 12–18 months.

Cytomegalovirus infection (CMV)

Over half of all pregnant women show serological evidence of previous CMV infection. One per cent of women may become infected with CMV during pregnancy, most of whom are asymptomatic. The infection is associated with an increased perinatal mortality, and 3–7% of the infants have congenital abnormalities.

Screening has proved to be of no value – there is no vaccine available.

Human immunodeficiency virus infection (HIV)

Although in western countries most cases of HIV infection occur in homosexual or bisexual men, intravenous drug users who share needles are increasingly being infected, as are some heterosexual men and women who do not abuse drugs. In sub-Saharan Africa and south and southeast Asia many heterosexual women and men are HIV positive and the numbers are increasing. Infected women who become pregnant have a 30% risk of transmitting the virus to the fetus, and all infected fetuses will be antibody positive and develop AIDS. There is a strong argument that screening for HIV infection should be offered to all pregnant women, particularly as the use of antiretroviral drugs antenatally and intrapartum, delivery by caesarean section and bottle feeding can significantly reduce the risk of vertical transmission of the disease to 2%.

HIV infection has no adverse effect on pregnancy, nor has the pregnancy any adverse effect on the progress of HIV infection. As the HIV infects the amniotic fluid as well as the women’s blood, full infectious disease control precautions should be taken by attendant medical staff during labour and childbirth. Delivery by caesarean section reduces the risk of transmission to the baby by 50%; vaginal delivery may be considered if the viral load is <1000 copies per mL. Coexisting STIs, chorioamnionitis and ruptured membranes for more than 4 hours quadruple the risk for the baby. If vaginal delivery is undertaken then invasive procedures such as fetal scalp electrodes, scalp blood sampling and episiotomies should be avoided, the baby should be washed as soon as possible, and given AZT (azathioprine) within 8 hours of delivery and for the next 6 weeks. In communities where access to triple therapy is limited a single dose of nevirapine 200 mg at the onset of labour reduces the vertical transmission. The decision on whether or not to breastfeed will depend on the risk of other infections due to suboptimal hygiene in the preparation of formula feeds.

Chickenpox (varicella)

Varicella infection is common, over 80% of pregnant women testing positive for IgG antibodies to the varicella zoster virus (VZV). Primary infection can result in serious complications for both mother and baby, because during pregnancy the maternal immune system is less efficient. Pneumonia occurs in 10% of women and can result in death. If the infection occurs in the first trimester, 0.4% and in the second trimester 2% of the fetuses are infected, and the viral vesicles can cause a wide spectrum of abnormalities, including limb hypoplasia, microcephaly, cortical atrophy, cataracts, psychomotor retardation, convulsions and intrauterine growth restriction. If the maternal infection becomes apparent 7 days before or 7 days after delivery, the baby is at risk of developing disseminated varicella infection, as maternal antibody production will not yet be adequate.

If there is doubt about the diagnosis or previous history of infection, maternal blood should be taken for anti-VZV, IgG and IgM antibodies. If there is a high risk of maternal or fetal complications, the mother should be given 12.5 units per kg of VZV immunoglobulin (VZIG) intramuscularly within 96 hours of exposure. For severe maternal infection, aciclovir 10–15 mg/kg should be given every 8 hours. An infected infant may be given VZIG and aciclovir.

Many communities offer varicella zoster vaccination, and this should be considered for women who are seronegative before they conceive.

INFECTIONS IN THE TROPICS

Helminth infestations – hookworm disease

Endemic infections by helminths are almost universal among rural dwellers in the tropics and subtropics, and the most serious of these is hookworm disease. Two types of hookworm are found, Ancylostoma duodenale and Necator americanus. In the gut the worms attach to the villi by suckers, and feed on blood obtained from the villi; after passing through their bodies this blood is excreted into the lumen of the bowel. The blood loss due to hookworm is related closely to the hookworm load, and varies from 2 to 90 mL/day. Hookworm infestation is a cause of iron deficiency anaemia, and this is particularly serious in pregnancy. Treatment consists of eliminating the worms by administering bephenium hydroxynaphthoate (Alcopar) in a dose of 5 g daily for 3 days, and treating the anaemia with iron.

Malaria

Exacerbation of malaria, or relapse in a partially immune woman, is particularly common during pregnancy, and each attack may precipitate abortion or the onset of premature labour. The fetus is protected by the placenta in most cases, although large numbers of immobilized parasites may be found in the placenta, particularly if the infection is by Plasmodium falciparum. Occasionally, in non-immune patients, congenital transmission of malaria occurs.

Pregnant women travelling to an area where malaria is endemic should take prophylactic antimalarial drugs. If the strains of P. falciparum in the area are chloroquine resistant, problems arise. The alternative drugs, Fansidar and Maloprim, affect folic acid synthesis and may induce a fatal Stevens–Johnson syndrome. They should be avoided. If the risk of chloroquine resistance is low, chloroquine and proguanil should be given. If the risk of chloroquine resistance is high, a pregnant woman should postpone her visit until she has given birth.

Any pregnant woman developing a high fever in a malarial area should be suspected of having the infection, and if this is confirmed by finding parasites in a thick blood film, treatment is given with chloroquine 600 mg (base) initially, followed 8 hours later by 300 mg, and 300 mg daily for the next 3 days.

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