Introduction

Infection is still a significant cause of abortion, fetal malformation, prematurity, infant death and long-term morbidity, especially in sick and preterm babies (Newell & Darling 2008). Normally the fetus is protected from infection during pregnancy (congenital infection) by the cervical mucus plug, intact amniotic sac and placenta, all of which act as a barrier to most bacterial conditions; but certain viruses and protozoa, because of their small molecular size, can cross the placenta, causing teratogenic (fetal malformation) effects and infections (Box 47.1).

The fetus can also acquire infection around the time of birth (perinatal infection) due to exposure to maternal infection in the birth canal or birth trauma that causes abrasion of newborn skin, giving a potential portal of entry for infection. In the neonatal period (postnatal infection) infection may be acquired from the mother, other babies, hospital equipment; inadequate handwashing by health professionals, carers and parents; and droplet infections via the respiratory route. Puncturing the skin, such as during the Guthrie blood spot test, also provides a potential portal of entry for infection, and, in certain circumstances, infection can be acquired through breastfeeding.

Bacterial infections include those caused by group B streptococcus (GBS) and Listeria monocytogenes and sexually transmitted diseases such as chlamydia, gonorrhoea and syphilis. Viral infections include cytomegalovirus (CMV), herpes simplex virus (HSV), rubella, hepatitis, varicella–zoster and human immunodeficiency virus (HIV). Toxoplasmosis is a protozoal infection and candidiasis a fungal infection.

The effect of fetal infection depends upon the nature of the organism and the stage of gestation. For example, exposure to rubella in the first trimester of pregnancy is associated with a high risk of serious congenital defects, whereas exposure in late pregnancy poses little risk. In contrast, genital herpes infection in early pregnancy poses little risk, but if acquired at birth there is a high risk of neonatal infection. Exposure to primary CMV infection in pregnancy gives a risk of adverse neonatal outcome at any stage of pregnancy, but infection acquired during birth or in the postnatal period through breastfeeding is not associated with adverse neonatal outcome (Newell & McIntyre 2000).

Some infections have long-term sequelae which may not become apparent for months or even years. For example, the ophthalmic damage caused by chlamydia becomes apparent in the neonatal period but the pneumonia associated with chlamydia infection usually occurs months after delivery; deafness associated with congenital CMV, toxoplasmosis, syphilis and rubella infection often does not become apparent until later in childhood; and hepatitis B and C infection may result in an initial infection but chronic hepatitis develops later and after hepatitis B infection cirrhosis and carcinoma of the liver do not occur for several decades (Newell & McIntyre 2000).

Antenatal screening for infection

Currently, all women in early pregnancy in the UK are offered screening for syphilis, HIV, hepatitis B and rubella (UKNSC/HPA 2007). Women who present in labour without having received any antenatal care should be offered screening for these four infections in labour.

At initial booking, midwives must ensure sensitive questioning reveals any risk factors for infections. Immigrants and refugees from different countries may not have had rubella vaccinations or may come from areas with a high incidence of tuberculosis or HIV. Vaccination programmes address some conditions, such as hepatitis B and rubella, and research into vaccines for other pathogens, such as HIV and GBS, continues.

Newborn immunity

Both preterm and term infants are vulnerable to infection because they are naturally immunodeficient at birth. Also, because the immune system is not exposed to common organisms until birth, there is an initial delayed or diminished response to any invading organisms (Blackburn 2007).

Newborn term infants do have some degree of natural immunity at birth due to the following:

• Maternal immunoglobulin G (IgG): which crosses the placenta during the third trimester (it is the only immunoglobulin with a small enough molecular size to do this). Because there is no transfer of IgG until after 32 weeks’ gestation, very preterm infants are even more vulnerable to infection, and they are more likely to have invasive procedures, longer hospital stays and numerous caregivers.

• IgM: is not passed transplacentally, but small amounts are synthesized by the fetus. It takes approximately 2 years to attain adult IgM levels; this makes babies more susceptible to Gram-negative organisms, causing gastrointestinal infections.

• IgA: although this is relatively deficient at birth, because IgA molecules are too big to be transferred across the placenta, serum levels rise following birth, giving some protection against respiratory and gastrointestinal infections. Breast milk, particularly colostrum, is rich in secretory IgA and interferon, which significantly enhances the baby’s resistance to enteric infections (Kelly & Coutts 2000). Several studies show that breast milk may actively stimulate the newborn immune system (Oddy 2001).

• Breast milk also contains IgD, lactoferrin, Lactobacillus bifidus and lysozyme, an anti-infective agent. These help to ensure the gut is colonized with relatively harmless Gram-positive bifidobacteria, as opposed to coliforms and enterococci found in formula-fed infants (Dai & Walker 1999). Lactoferrin affects iron absorption, depleting Escherichia coli of the iron it needs to replicate.

• Lymphocytes are produced in the thymus gland, which is fairly large at birth. The quantity and quality of neutrophils in the neonate are relatively low compared with older babies. Breastfeeding, particularly in the early weeks, can improve these levels, as breast milk is especially rich in neutrophils and macrophages (white blood cells) (see Ch. 43).

The complement system

The complement system is a major component of innate immunity. Complement consists of a series of plasma proteins and their fragments that, when activated, enhance other components of the immune system. For example, the effect of complement on the cell membrane of invading organisms enables their destruction by other defence mechanisms of the body (Blackburn 2007). Breast milk contains some components of the complement system but the overall action of complement is limited at birth.

Prevention of infection

Midwives must be vigilant in recognizing risk factors and early symptoms of maternal and neonatal infection. To do this effectively requires multidisciplinary working to prevent, diagnose and promptly treat infection in the mother, baby and, if necessary, the midwife.

The midwife needs to educate women to be aware of sources of potential infection that may affect her and/or her child and ensure that any infection during pregnancy is managed and treated promptly. As well as maternal transmission of infection, organisms can be introduced during invasive antenatal procedures, such as amniocentesis. Intrauterine pneumonia is the commonest effect, but it depends on the pathogens introduced. Strict aseptic techniques must be assured.

Newborn infants in maternity units are at risk of cross-infection and frequent, effective handwashing remains the single most important method of preventing the spread of infection (NPSA 2010: see website). Other strategies include newborn ‘rooming in’ with the mother, encouraging breastfeeding to increase immune protection, using individual equipment for each baby, and, if necessary, isolation of an infected infant. Visitors should be discouraged from sitting on beds and from visiting if they have an infection or feel unwell.

To avoid exposure to bloodborne infections, such as hepatitis B and HIV, midwives must integrate into their practice the Department of Health universal precautions (DH 1998) to reduce exposure to blood and other body fluids and tissue that may contain bloodborne pathogens. Universal precautions include covering any skin cuts/lesions with a waterproof dressing, wearing rubber gloves and other protective clothing as appropriate, avoiding needlestick injuries and disposing safely of sharps (needles) and other instruments and waste, and vaccination against hepatitis B.