How are children affected by infectious disease?

Definition

Infectious diseases are an unavoidable fact of life. Infections
are caused by microorganisms that are found in the environment or that are passed
from one person to another, and children are particularly susceptible to these
organisms for a number of reasons. Most of these infections are mild, resolving
with the help of the child’s immune system and, in some cases,
treatment with antimicrobial medications, such as antibiotics.

Not all microbes (bacteria, viruses, fungi, and parasites) cause disease. Many
are normal inhabitants (called normal flora) and coexist on the skin and inside
the body of children and adults. Microbes serve important functions, such as
preventing the growth of dangerous pathogens (organisms that cause
illness) and manufacturing essential vitamins, such as vitamin K, which are not
produced by the human body.

At birth, the immune system of the child is immature and cannot work at full
strength. While in utero, the growing fetus depends on the pregnant woman (or
girl) for much of its immune function. Antibodies and other immune factors
cross the placenta to provide protection and are boosted during breast-feeding.
The newborn immune system will not catch up for several months and will not be
fully mature until the child is fourteen years of age.

The small child is immunologically naïve, and repeated exposure to microbes, including pathogens (disease-causing organisms), helps the child build a strong immune system; this exposure also makes infection a frequent cause of visits to the family doctor or pediatrician. Risk of infection is also increased for young children because babies and toddlers tend to put things in their mouths and pay little, if any, attention to hygiene. Children in group settings, such as child care and school, easily pass infection to other children.

Childhood infections, whether caused by bacteria, viruses, or other organisms,
take many forms and can affect many parts of the body. Among the most classic
infections are those, such as rubella and measles, that
cause skin rash and fever. Others, like the common cold,
which can occur an average of six to eight times per year in the young child,
affect the respiratory tract and other body systems.

The prevention of childhood infection is based in part on the development of
vaccines and immunization. Many diseases that were
once considered major killers of children are now well controlled. Some of these
diseases remain significant threats in developing countries. Recurrent outbreaks
of vaccine-preventable illnesses point to the ongoing and critical need for
widespread immunization.

Other ways to provide a boost to the immune system include good nutrition, adequate sleep, and careful hygiene and food preparation practices. The overuse of antibiotics is a serious concern too, as overuse leads to new strains of antibiotic-resistant organisms and, thus, weakened immunity.

The Immune System

Immunity is the ability of the body to resist infection. The child’s immune system will develop to become an intricate system of organs, cells, and proteins that work to protect against foreign invaders such as bacteria, viruses, fungi, and parasites. The immune system is unique in that its parts are not physically connected to each other and are scattered through the body. The system includes the thymus gland, the spleen, the appendix, lymphoid tissue and lymph nodes, and bone marrow. The job of this loosely connected system is to produce white blood cells, antibodies, and other factors that seek out and destroy organisms and abnormal cells that cause disease, and to do so without harming the body’s healthy tissue.

Critical cells of the immune system include neutrophils, monocytes, macrophages, T
lymphocytes, and B lymphocytes. These cells develop from stem cells in the growing
embryo beginning at about five weeks gestation. By birth, the cells are getting
ready to respond to foreign invaders, but this response will still be developing.
The newborn depends on passive immunity that is acquired from the pregnant female through
the placenta or through breast-feeding after birth. This type of immunity lasts
six to eight months only and then begins to wane.

Infants begin to make their own antibodies at an increased rate soon after
birth, when their environment presents many new antigens
(molecules that induce the production of antibodies). The serum concentration of
antibodies reaches adult levels by the end of the child’s first year and peaks at
age seven or eight years.

The immune system works by responding to an organism or substance that enters the body. The cells “see” the invader and produce specific antibodies and proteins to attack it. Later, if the body is presented with the same invader, it is primed to prevent illness. In this case, the child (or adult) has developed active immunity.

Active immunity may arise naturally or through immunization. For example, when
a child contracts an infection such as chickenpox, which is caused by the
varicella virus, the immune system develops antibodies to fight it. After several
days of illness, the virus is defeated and the child recovers. The primed immune
cells and antibodies specific to varicella remain, and if the child is exposed
again, no illness will result.

A vaccine that protects against chickenpox exists. It consists of an attenuated (weakened) form of the virus that cannot cause full-blown disease and that tricks the body into mounting an immune response. Later exposure to the live virus will not cause disease. This is the basic mechanism of childhood immunization.

Conditions can sometimes place added burdens on the immune system, making the job of fighting infection much more difficult. Some children are born with immune deficiencies or acquire them after birth. These children cannot mount a normal immune response and may be more susceptible to common infections. Children treated with cancer or organ transplant medications, and those on steroids, may become immune suppressed. Medical devices such as catheters and tubes that enter the body provide a direct path for invaders and often lead to infection. Over-prescription of antibiotics can kill normal protective flora and leave room for the overgrowth of pathogenic species that may become resistant to antibiotics.

Common Infections

As soon as a child is born, his or her body is exposed to microbes that can cause infection. Some of these cause illness, while others do not, and the reasons are not always known. It is clear, however, that infection is a normal part of childhood, and most children will have several infections each year. These infections include colds and other respiratory infections, ear infections, infections of the gastrointestinal tract, and nonspecific viral infections that cause a fever and rash.

The incubation period is the time it takes for a child to become ill after
infection. The incubation period can be as short as one day for the common cold or
for viral diarrhea or as long as two weeks for chickenpox. It typically takes
several years for the human immunodeficiency virus (HIV) to
cause disease (such as those related to acquired immunodeficiency syndrome, or
AIDS).

Not all infections are contagious (spread from child to child). Ear infections and bladder infections are caused by microbes that gain access to collections of fluid (mucus and urine, respectively) and are not passed from one child to another. Diarrhea and colds, on the other hand, can spread quickly. When and for how long a child is contagious varies with the infection and the child. Young children may be contagious for a longer period than older children.

It is useful to categorize common childhood infections by the part of the body affected. Respiratory infections can cause a wide range of symptoms. Some are mild (such as runny nose, sneezing, and cough) while others are more severe and include wheezing and respiratory distress. Severity may depend on the age and health of the child and on the virulence of the organism. Some of these more severe respiratory infections include bronchiolitis (infection of the small airways), croup, the common cold, flu, pneumonia, and whooping cough.

The primary symptom of a skin infection is a rash, which is the
result of the organism’s direct invasion of the skin itself. These infections can
be caused by viruses, bacteria, fungi, and parasites and include yeast diaper
rash, ringworm, scabies, cold sores, impetigo, warts, and head lice.

Intestinal infections cause nausea and vomiting, diarrhea, and cramping pain.
They are either food-borne or are transmitted through direct contact between
children. These infections include (by organism) rotavirus,
Clostridium difficile, Cryptosporidium,
pinworm, Escherichia coli,
Salmonella, and Staphylococcus species.
Infectious diarrhea is the primary cause of child morbidity and mortality in the
developing world.

Head, ear, nose, and throat infections cause diverse symptoms depending on the
area of the body affected. Ear infections are second only to the common cold in
causing a visit to a doctor. Pinkeye, thrush (yeast infection of the mouth), strep
throat, and mononucleosis are common and easily treatable. Meningitis is
an infection of the tissues surrounding the brain. Symptoms can be serious and
difficult to treat.

Urinary tract infections are more common in girls than in boys because of the
anatomy of the female urinary tract. The short urethra, in proximity to the
bacteria of the vagina and anus, makes infection more likely. Cystitis is
an infection of the bladder and is the most common type of urinary tract
infection. Pyelonephritis is an infection of the kidneys and can be
more serious.

Childhood infections can also be organized by the type of organism involved.

Viral infections. Viral infections are the most common
cause of childhood illness. Many of the classic childhood infections are viral,
including measles (rubeola), rubella, chickenpox (varicella), croup
(parainfluenza), hand, foot, and mouth disease (enterovirus), respiratory
syncytial virus infection, roseola, the cold, and the flu. Some of these are
preventable with vaccines and others resolve on their own without treatment.
Antibiotics do not treat viral infections.

Bacterial infections. Bacteria causes many infections, including
those of the ear and the urinary tract, some pneumonias, some forms of meningitis,
sinusitis, impetigo, strep throat, tetanus, whooping cough (pertussis), and cat
scratch fever. Bacterial infections can be treated with antibiotics.
Antibiotic-resistant strains of several types of bacteria have emerged because of
the over-prescription of antibiotics and because of its overuse in the food
supply.

Yeast and other fungi. Yeast and other fungi are microbes that
commonly infect the skin, hair, and nails. Fungal
infections can be more serious in children who are
immunosuppressed. Thrush (yeast), ringworm (tinea), and athlete’s foot (tinea) are
types of fungal infection. They can be treated with topical or systemic antifungal
medications (or both).

Parasitic infections. Parasitic infections are quite common
worldwide. They cause life-threatening diarrheal and blood diseases
(cryptosporidiosis, giardiasis,
and malaria) in the developing world and more superficial
infections (scabies and pinworm) elsewhere. They can be treated with
antimicrobial medications when available.

Preventing Infection

Many of the important infections of childhood are preventable with immunization
and with improved hygiene. Vaccines used in immunization stimulate the immune
system to respond to small doses of a killed or weakened microbe as if it were a
real infection, thus helping the body develop immunity to the disease. Vaccines
have been so effective at controlling disease, particularly in the developed
world, that it is easy to forget the harm caused by the infections they prevent.
Many of these diseases are still present, especially in the developing world, and
outbreaks are common. Unvaccinated children are at risk of catching preventable
disease, and they also put others at risk.

An example of an outbreak in the developed world is the 2010 epidemic of
pertussis infection (whooping cough) in the United States.
Thousands of cases were identified nationwide, and several children died in
California alone. It is believed that infants who were not immunized or who were
under-immunized were infected by their adult caretakers and by older children, who
tend to get a milder form of the disease. The Centers for Disease Control and
Prevention (CDC) recommends that persons who are frequently
around young children, especially infants, receive boosters.

The concept of community (or herd) immunity is important in health policy. Children who are not immunized are partially protected against vaccine-preventable disease by being surrounded by immunized people. This community immunity is especially important in the protection of children who have immune deficiencies or who are immunosuppressed and cannot receive vaccinations.

Some parents have concerns about vaccine safety, causing them to delay or deny immunization for their children. While no vaccine is 100 percent safe (or 100 percent effective), and all medicines have risks and side effects, serious physical reactions to vaccination are rare. Preventable childhood infection is a greater risk.

The widespread use of improved hygiene also lowers the risk of infection. Respiratory hygiene, including using tissues or coughing or sneezing into one’s elbow; isolation during respiratory illness; and frequent, thorough handwashing can help limit the spread of colds and the flu. Other preventive measures include careful food preparation that includes the washing of fruits and vegetables, disinfectant use on preparation surfaces and utensils, and thorough cooking of raw foods, particularly meats and eggs, to a temperature high enough to kill microbes. These measures are essential to the prevention of food-borne illnesses and diseases.

Impact

Infection is the leading cause of death in children worldwide and the leading cause of childhood illness in the United States. Public health policy aimed at reducing infant and childhood mortality will depend on increased attention to the prevention and control of infection, particularly in the developing world, where HIV infection, AIDS, diarrheal disease, and malaria account for almost one-half of all deaths. Ongoing research into new vaccines to prevent these diseases will play a critical role in the prevention of childhood (and adult) diseases.

Bibliography

Behrman, Richard E., Robert M. Kliegman, and Hal B. Jenson, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia: Saunders/Elsevier, 2007. Text covering all disorders in children with authoritative information on genetics, endocrinology, etiology, epidemiology, pathology, pathophysiology, clinical manifestations, diagnosis, prevention, treatment, and prognosis.

Fisher, Margaret C. Immunizations and Infectious Diseases: An Informed Parent’s Guide. American Academy of Pediatrics, 2006. A pediatrician explains childhood infection and its prevention.

Kimball, Chad T. Childhood Diseases and Disorders Sourcebook: Basic Consumer Health Information About Medical Problems Often Encountered in Pre-adolescent Children. Detroit: Omnigraphics, 2003. Offers basic facts about common illnesses, serious diseases, and chronic conditions in children. Discusses frequently used diagnostic tests, surgeries, and medications. Also examines long-term care for seriously ill children.

Long, Sarah S., Larry K. Pickering, and Charles G. Prober, eds. Principles and Practice of Pediatric Infectious Diseases. 3d ed. Philadelphia: Churchill Livingstone/Elsevier, 2008. An excellent text focusing on children and infectious diseases and conditions.

Martin, Richard J., Avroy A. Fanaroff, and Michele C. Walsh, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 2 vols. 8th ed. Philadelphia: Mosby/Elsevier, 2006. This classic reference work includes discussions of the practice of neonatal-perinatal medicine and the development and disorder of organ systems.

Murphy, Kenneth, Paul Travers, and Mark Walport. Janeway’s Immunobiology. 7th ed. New York: Garland Science, 2008. A thorough and comprehensive review of the human immune system.

Pickering, Larry K., et al., eds. Red Book: 2009 Report of the Committee on Infectious Diseases. 28th ed. Elk Grove Village, Ill.: American Academy of Pediatrics, 2009. The bible on infections of children and the official source for American Academy of Pediatrics policy.

Plotkin, Stanley A., Walter A. Orenstein, and Paul A. Offit. Vaccines. 5th ed. Philadelphia: Saunders/Elsevier, 2008. An excellent discussion of the role of vaccines in the prevention of disease. The book begins with a history of immunization practices, and each subsequent chapter deals with a specific disease and the role and history of vaccine production in its prevention.