Why are newborns prone to diseases?

Newborns are prone to diseases for several reasons. In the first few months of life, they have an immature immune system that makes them more susceptible to infections. They also lack immunity to many common pathogens, putting them at risk for contracting illnesses. Additionally, their physical barriers and normal flora are not yet fully developed, making it easier for pathogens to invade their bodies.

What is the neonatal period?

The neonatal period is defined as the first 28 days after birth. During this time, newborns are adjusting to life outside the womb and their bodies are still developing and maturing. Their immune systems are not yet fully functional, making them especially vulnerable to infections and diseases.

Transitioning from the sterile womb

Inside the mother’s womb, the fetus lives in a relatively sterile environment, protected from most pathogens. However, immediately after birth, the newborn is exposed to countless bacteria, viruses, and other microbes that can cause illness. No longer protected by the mother’s immune system and maternal antibodies received in utero, the newborn must rely on its own immature defenses.

Underdeveloped immune system

The neonatal immune system is functionally deficient compared to older infants and children. Newborns have very low numbers of T cells, weak antibody responses, and less developed physical barriers. Critical components like skin, mucous membranes, and gut flora are still maturing. This puts them at high risk for infections until their immune system strengthens over the first year of life.

Why are newborns more prone to infections?

Newborns are especially vulnerable to infections for several key reasons:

Immature skin barrier

Infants are born with thin, delicate skin that offers little protection against pathogens. The outermost layer of skin, the stratum corneum, develops gradually after birth. Disruptions in skin integrity provide easy access for bacteria to enter the bloodstream. This is why careful handwashing and aseptic technique are vital when handling newborns.

Underdeveloped gut flora

The gastrointestinal tract of a full-term newborn is essentially sterile at birth. Colonization by normal commensal bacteria begins immediately and intestinal flora develops over the first year of life. Until this microbial community is established, the GI tract has little defense against pathogenic bacteria. Formula-fed infants also lack the protective benefits of the mother’s breastmilk.

Minimal mucous membrane barriers

Mucous membranes lining the eyes, nose, mouth, and lungs are incomplete in newborns. Tiny erosions in these surfaces allow opportunistic pathogens to breach defenses and invade local tissue or enter the bloodstream. Respiratory syncytial virus (RSV) and Streptococcus pneumoniae take advantage of poor mucous membrane barriers in the lungs.

Reduced complement system activity

The complement system is part of the innate immune response and enhances the ability of antibodies and phagocytic cells to clear pathogens. However, complement proteins are present at much lower concentrations in newborns. With an impaired complement system, newborns cannot mount an effective response to many bacterial and viral infections.

Weak adaptive immunity

The adaptive immune system relies on T and B lymphocytes that emerge from primary lymphoid organs after birth. At one week of age, a newborn’s adaptive immunity is only around 30% of normal levels. By six months, adaptive function reaches 60% of normal capacity. Without robust T and B cell responses, newborns cannot fight infections through acquired immunity.

How do newborns acquire passive immunity?

To compensate for an inadequate immune system, newborns acquire temporary immunity passively from the mother during pregnancy and breastfeeding:

Transplacental transfer of IgG antibodies

IgG is the only antibody class that crosses the placenta from mother to fetus. Maternal IgG peaks at around 34-36 weeks gestation, providing protection against pathogens encountered by the mother. However, IgG levels drop steadily after birth, leaving newborns vulnerable again by 2-3 months old.

Secretory IgA antibodies in breastmilk

Secretory IgA is present in colostrum and breastmilk. It coats mucosal surfaces in the GI tract, protecting against enteric pathogens like rotavirus, E. coli, and Salmonella. However, IgA levels are low in colostrum and take weeks to build up. Exclusive breastfeeding is key to providing adequate mucosal protection.

Transfer of leukocytes, antibodies, and immune factors

Breastmilk provides live immune cells like neutrophils, macrophages, and lymphocytes that can help fight infection. Antimicrobial proteins like lactoferrin inhibit microbial growth. Cytokines and growth factors stimulate the infant’s immature immunity. However, the protection conferred by breastmilk wanes as solid foods are introduced.

What factors increase the risk of neonatal infections?

While all newborns are vulnerable, certain factors place some infants at even higher risk of developing infections:

Preterm birth

Babies born prematurely are highly susceptible due to even less developed immunity and barriers. The earlier the gestational age, the greater their risk. They are deprived of the maternal antibodies and immune protection that would have been conferred later in pregnancy.

Low birth weight

Low birth weight infants have exaggerated immaturity of immune function and permeability of epithelial barriers. Very low birth weights below 1500g are associated with the highest infection rates in the neonatal period.

Invasive procedures

Procedures like intubation, intravenous catheters, and ventilator support bypass natural body defenses and provide access for pathogens. Hospitalized infants requiring multiple interventions are at increased risk for hospital-acquired infections.

Lack of breastfeeding

Formula-fed infants do not receive protective maternal IgA, leukocytes, and immune factors. Suboptimal mucosal immunity in the GI tract leaves them highly susceptible to diarrhea and sepsis from gut bacteria.

Congenital immunodeficiencies

Rare genetic disorders like SCID and DiGeorge syndrome cripple immune function. Affected infants often present in the neonatal period with recurrent, life-threatening infections.

Risk Factor Contribution to Infection Risk
Preterm birth Leaky epithelial barriers, deficient IgG transfer, poor leukocyte function
Low birth weight Extreme immaturity of both innate and adaptive immunity
Invasive procedures Bypass natural defenses, provide entry for pathogens
Lack of breastfeeding Absence of sIgA, leukocytes, immune factors in breastmilk
Congenital immunodeficiencies Crippled T/B cell function, inability to fight infections

What types of infections commonly affect newborns?

Some of the most common and serious infections facing newborns include:

Bloodstream infections

Bacterial pathogens like E. coli, Klebsiella, and Staphylococcus epidermidis can gain access through the GI tract, lungs, or skin and cause life-threatening sepsis. Newborns may present with fever, apnea, poor feeding, lethargy, hypotension, and multi-organ failure.


Bacteria including Group B Strep, E. coli, and Listeria monocytogenes directly infect the central nervous system. Newborns with meningitis rapidly develop fever, seizures, bulging fontanelle, nausea, and altered mental status. Delays in treatment can lead to permanent brain damage or death.


Respiratory syncytial virus (RSV), parainfluenza, adenovirus, and Gram-negative bacteria are common causes of neonatal pneumonia. Infected infants struggle with rapid breathing, cough, hypoxia, and life-threatening apnea.

Skin infections

Disruptions in skin integrity put newborns at risk for infections by Staphylococcus aureus, Group A Strep, and Candida. Infected areas are erythematous, warm, and tender. Bullous impetigo can rapidly progress to sepsis.


The umbilical stump is a portal of entry for bacteria during the first week of life. Streptococci, Staphylococci, and Gram-negative organisms cause redness, swelling, and purulent discharge at the cord site.


Chlamydia, gonorrhea, and Staphylococcus aureus are common causes of neonatal conjunctivitis. Infants present with bilateral eye discharge, lid swelling, and chemosis within the first month of life.

What common illnesses do newborns acquire from their mothers?

Newborns are exposed to infections in the genital tract during childbirth. Some common perinatal infections include:


Infants can acquire chlamydia during vaginal delivery, causing ophthalmia neonatorum and pneumonia in the first weeks of life. Systemic infection can manifest as fever, respiratory distress, and lymphadenopathy.


Neonatal gonococcal infections manifest as conjunctivitis, scalp abscesses, arthritis, and sepsis. Gonorrhea causes severe eye infections that can lead to blindness if not treated urgently.


Congenital syphilis occurs when T. pallidum is transmitted across the placenta. If untreated, complications like deafness, dental deformities, nerve damage, and bone lesions can occur.

Genital herpes

Neonatal herpes causes devastating CNS disease, disseminated infection, and high mortality if the infant is exposed during delivery through an infected maternal genital tract.


Without antiretroviral treatment, 15-30% of infants born to HIV-positive mothers will acquire HIV infection around the time of birth or during breastfeeding.

Hepatitis B

HBV transmitted during delivery or breastfeeding leads to chronic infection in 90% of infants. All babies should receive hep B vaccine at birth to prevent perinatal transmission.

Infection Mode of Perinatal Transmission Clinical Manifestations
Chlamydia Exposure during vaginal delivery Conjunctivitis, pneumonia
Gonorrhea Exposure during vaginal delivery Conjunctivitis, sepsis, arthritis
Syphilis Transplacental transmission Bone, nerve, organ damage
Genital herpes Contact with infected genital tract Disseminated infection, CNS disease
HIV Transplacental passage, breastfeeding Immunodeficiency, failure to thrive
Hepatitis B Exposure during vaginal delivery Chronic hep B infection

How are neonatal infections diagnosed?

Diagnosing infections in newborns can be challenging but may involve:

Blood cultures

Positive blood cultures are the gold standard for diagnosing neonatal sepsis. Serial cultures are often needed to identify the causative pathogen in a timely manner.

Spinal tap

Lumbar puncture analyzes CSF for bacteria, white cells, glucose and protein to diagnose meningitis. CSF culture is the definitive diagnostic.

Chest X-ray

Radiologic findings like infiltrates and consolidation support the diagnosis of pneumonia. Testing respiratory secretions can identify the infectious agent.

Surface cultures

Swabs of the eyes, umbilicus, rectum, and throat may reveal Chlamydia, GBS, or pathogen colonization preceding invasive infection.

Polymerase chain reaction (PCR)

PCR rapidly detects pathogen DNA from body fluids and is highly sensitive for infections like HSV, Zika, syphilis, and Chlamydia.

Complete blood count (CBC)

CBC provides a peripheral white blood cell count with differential to assess the presence and character of infection. Markers like immature neutrophils suggest a serious bacterial infection.

Acute phase reactants

Levels of CRP and procalcitonin are elevated within hours of a bacterial infection and point to sepsis when significantly above normal neonatal values.

Microscopic examination

Gram stain and direct visualization of body fluids can provide rapid preliminary identification of organisms. Urine microscopy helps diagnose UTI.


Newborns are prone to infections during the first weeks to months of life due to immature innate and adaptive immunity. Barrier functions like skin, GI mucosa, and lung epithelium are incomplete. Maternal IgG antibodies and breastmilk provide partial passive protection but cannot prevent all infections. Preterm and low birthweight infants are most vulnerable due to exaggerated immunologic and physical deficits. Prompt diagnosis through cultures, molecular testing, and imaging is essential to prevent serious complications of neonatal infections. Education on prevention and early treatment of perinatal infections is crucial to protecting vulnerable newborns. Continued research on boosting neonatal immunity could save countless young lives.

Leave a Comment