Human Age and Microorganisms

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Human Age and Microorganisms

LEARNING OBJECTIVES

After reading this chapter, the student will be able to:

• Identify the different effects microorganisms have on the different age groups

• Explain the different immune reactions that occur in the different age groups

• Describe the infections that typically can occur in pregnant women and ultimately can have an effect on fetal development

• Name and describe congenital infections, including causative agent, transmission, symptoms, and treatments

• Discuss the common microbial infections that affect infants and children

• Describe the microbial infections that commonly occur in young adults

• Illustrate the environmental exposures to microbes that are typical for young adults

• Describe the common microbial infections in the elderly and compare these with the other age groups

• Explain the immune system of the elderly and contrast it to the other age groups

• Portray factors that can influence the susceptibility to microbial infections and disease among the elderly

KEY TERMS

WHY YOU NEED TO KNOW

IMPACT

Science certainly has progressed and so has the understanding of human aging, and the factors involved in treating diseases and infections during development and aging. Some advances in areas of medical treatments have been presenting new sets of factors in dealing with age-related infection problems. Hormone therapy, particularly in women, is growing in usage to address problems involved in the aging process as it affects the reproductive and related systems. Although this therapy may attenuate the negative effects of changes such as menopause, it also leads to changes of the pH in organs of the reproductive system, which increases susceptibility to both bacterial and fungal infections such as vaginitis. Research has also revealed new disease and infection problems related specifically to youth. For example, it is now established that there is a direct connection between the consumption of honey and infant botulism. Research has found that an important factor contributing to this problem is the fact that the intestinal tract of infants lacks a normal microflora, which successfully competes against pathogens such as Clostridium botulinum. Without such bacterial competition in the digestive system of immature infants, C. botulinum is able to thrive in the intestine and produce its lethal toxin. It has now been suggested that infant botulism may be responsible for up to 10% of cases of sudden infant death syndrome (SIDS).

Perinatal

An infection caused by bacteria or viruses that can be passed from a mother to her baby via the placenta, either during pregnancy or delivery, is referred to as a perinatal infection. Maternal infections may cause complications at birth, but the mother may or may not experience symptoms of the infection during pregnancy. Many perinatal infections become evident only after birth.

Introduction

The placenta is a highly specialized (Figure 23.1) structure that generally is an effective barrier, protecting the fetus from microorganisms that may be present in the mother’s circulation or in the urogenital tract. Placental tissue normally separates maternal and fetal blood supplies so that no intermixing occurs. Unfortunately, some infectious organisms may penetrate this barrier and injure the developing embryo or fetus.

image
FIGURE 23.1 Schematic drawing of a placenta.
The placenta generally is an effective barrier between the maternal and fetal blood supplies, protecting the fetus from most microorganisms that may be present in the mother’s bloodstream.

Infections During Pregnancy

The length of pregnancy in humans is approximately 39 weeks and is called the gestation period, divided into three phases referred to as trimesters. The embryonic phase of development extends from fertilization to the end of the eighth week, and the developing individual is referred to as an embryo. From the eighth week until birth the developing infant is called a fetus. Neither an embryo nor a fetus has a developed immune system (see Chapter 20, The Immune System). IgM and IgA synthesis is limited until the second half of the pregnancy, IgG antibody synthesis is absent, and cell-mediated immune responses are absent or poorly developed. In other words, the embryo/fetus is completely dependent on its mother’s immune system. Immunosuppression in the mother will result in a potentially disastrous susceptibility of the unborn to infectious disease. Certain infections can be more common during pregnancy (Table 23.1) and others may recur (Table 23.2), all of which can present a particular risk to the woman and/or her unborn child.

TABLE 23.1

Infections That May Be More Common or Severe During Gestation

Infection Covered in Chapter(s): Comments
Urinary tract infections (UTIs) 15 Cystitis; pyelonephritis; atony of the urinary bladder, leading to less effective emptying/flushing
Malaria 14 Probably due to depressed cell-mediated immunity
Viral hepatitis 7 and 12 Probably due to additional stress on metabolic activities
Influenza 11 Higher mortality during pandemics; may be prevented by vaccination
Poliomyelitis 7 Paralysis more common
Coccidioidomycosis 11 Leading cause of maternal mortality in endemic areas in the southwestern United States and Latin America
Candidiasis 10 Vulvovaginitis
Listeriosis 12 Influenza-like disease can cause auto-abortions in pregnant women

TABLE 23.2

Maternal Infections That May Recur During Pregnancy

Infection Covered in Chapter(s): Comments
Cytomegalovirus 7 Sheds from cervix, is present in mother’s milk
Herpes simplex virus 10 and 12 Increased replication in cervical region
Epstein-Barr virus 14 Virus sheds in oropharynx; antibody titers are increased
Polyomavirus 15 Virus appears in urine

The use of any medication during pregnancy and lactation carries a potential risk for causing birth defects to the developing fetus. For example, the measles-mumps-rubella (MMR) vaccine should not be administered during the first trimester of pregnancy because of an association with fetal defects. Pregnancy and lactation also pose problems in antibiotic treatment, because some of them may cross the placenta. The use of the antibiotic tetracycline by a pregnant woman may cause stained teeth in the child.

LIFE APPLICATION

Ten Tips to Help Prevent Infections During Pregnancy*

*From the Centers for Disease Control and Prevention (CDC) http://www.cdc.gov/Features/Pregnancy/.

Congenital Infections

A congenital disorder is any medical condition that is present at birth regardless of its origin and therefore includes a broad category with a variety of conditions. Congenital infections are intrauterine infections occurring during pregnancy when microorganisms enter the blood, subsequently establish an infection of the placenta, and then infect the fetus. These infections may result in the death of the fetus and, if the infection does not result in abortion, it may lead to congenital malformations.

Congenital Cytomegalovirus Infection

Cytomegalovirus (CMV) belongs to the family Herpesviridae and in humans it is commonly referred to as human herpesvirus 5. CMV is a common virus that infects most people at some time during their lives but generally does not cause recognizable illness. According to the Centers for Disease Control and Prevention (CDC, Atlanta, GA), between 50% and 80% of adults in the United States are infected with CMV by age 40 years. Although not highly communicable, it can be spread from person to person through close contact. The virus is present in urine, saliva, semen, and other bodily fluids. Transmission can also occur from an infected mother to her fetus, and CMV is the most common virus transmitted during pregnancy. Reports from the CDC state that:

• About 1 in 150 children is born with a congenital CMV infection

• Approximately 1 in 750 children is born with or develops a permanent disability due to a CMV infection

• Roughly 8000 children each year suffer permanent disabilities due to CMV

• More than 90% of infected newborns are asymptomatic at the time of birth

• About 5% to 15% of asymptomatic babies at birth will develop symptoms within the first 2 years of life. These symptoms may include hearing loss, low intelligence, microcephaly, and chorioretinitis.

• Symptomatic newborns show various severities of the illness. Manifestations include hepatosplenomegaly, jaundice, purpura, microcephaly, cerebral calcifications, and chorioretinitis. Central nervous system involvement is the most common demonstration of congenital CMV infections. Ocular and hearing defects are common, and others include microcephaly, periventricular calcification, severe psychomotor retardation, strabismus, seizures, and low birth weight.

Congenital Rubella

Congenital rubella is caused by the action of the rubella virus when a pregnant woman is infected during the critical time of fetal development, namely during the first trimester of pregnancy. The condition includes a group of birth defects that include but are not limited to:

An infected fetus generally produces its own IgM to the virus, which can be detected in the umbilical cord and in the blood of the infant. Some congenitally infected children will develop insulin-dependent diabetes later in life. The main risk factor for congenital rubella occurs when a pregnant woman who has not been vaccinated comes into contact with a person who has rubella (also called German measles; see Chapter 7, Viruses).

Congenital Syphilis

Congenital syphilis is caused by the spirochete Treponema pallidum and is passed from an infected mother to the child during fetal development or at birth. Approximately 50% of infected fetuses die shortly before or after birth. Symptoms in infected newborns may include the following:

When a pregnant woman is identified as being infected with syphilis, appropriate treatment regimens, including penicillin, can effectively prevent the development of congenital syphilis in the infant. Patients with penicillin allergies may be desensitized before starting the full treatment. Despite the fact that the disease can be cured with antibiotics if identified early, increasing rates of syphilis among pregnant women in the United States have been reported, resulting in an increased number of infants born with congenital syphilis.

Congenital Toxoplasmosis

Toxoplasmosis is caused by the parasite Toxoplasma gondii. The organism can be found in raw meat, and is commonly found in cat litter and contaminated soil. The life cycle of Toxoplasma gondii is illustrated in Figure 23.2. Although toxoplasmosis is common in men and women, the infection during pregnancy can lead to congenital toxoplasmosis, which can damage the baby’s eyes, nervous system, skin, and ears. Clinical features in the infant include the following:

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FIGURE 23.2 Life cycle of Toxoplasma gondii.

Oftentimes there are no detectable abnormalities at birth, but health problems may become apparent in the second or third decade of life. To prevent toxoplasmosis pregnant women should avoid cleaning litter boxes, other areas that have contact with cat litter, and also should cook meat until it is well done. Cross-contamination should be avoided. Treatment is possible for the pregnant mother, usually with spiramycin, and fetal infections diagnosed during pregnancy can be treated with pyrimethamine and sulfadiazine. CDC recommendations to prevent congenital toxoplasmosis are shown in Box 23.1.

BOX 23.1   CDC Recommendations for the Prevention of Congenital Toxoplasmosis

Congenital HIV Infection

Clinical symptoms of congenital HIV infections include poor weight gain, susceptibility to sepsis, developmental delays, lymphocytic pneumonitis, oral thrush, enlarged lymph nodes, hepatosplenomegaly, diarrhea, and pneumonia. Some infants develop AIDS by age 1 year. Most infections occur during late pregnancy or during delivery; transmission rates can be reduced by lowering the HIV load by using antiretroviral drugs during pregnancy. Elective cesarean section and avoiding breastfeeding may also reduce the risk of infection. The medical and supportive services recommended by the U.S. Department of Health and Human Services after a child is born to an HIV-positive mother are listed in Box 23.2. In developing countries, about a quarter of infants born to HIV-positive mothers are infected.

BOX 23.2   Follow-up Care for Babies Born to HIV-positive Mothers

Vaginal Infections

A common vaginal infection known as bacterial vaginosis (BV) is an imbalance of the normal bacterial flora of the vagina (see Chapter 16, Infections of the Reproductive System). With BV, increased numbers of anaerobic organisms are found, including Gardnerella vaginalis, Mycoplasma hominis, and Bacteroides. Although these organisms are part of the normal vaginal flora, they do cause problems when they outnumber the normal Lactobacillus flora. Pregnant women with BV are more likely to give birth to a premature infant with a low birth weight than are women who do not have the vaginal infection.

Vaginal infections caused by the protozoan Trichomonas vaginalis also have been associated with preterm labor and preterm birth. The parasite is sexually transmitted and it has been suggested that the infection may spread from the vagina to the uterus. According to the CDC, the prescription drug metronidazole can be used in the treatment of trichomoniasis in pregnant women; however, some studies indicate an increase in preterm births after treatment. Trichomoniasis also changes the pH balance in the vagina, which then can lead to bacterial vaginosis.

Vaginal yeast infections caused by Candida albicans are fairly common during pregnancy, but the infection usually does not travel up to the uterus and therefore does not affect the unborn. Intravaginal treatment is generally preferred over oral treatment with fluconazole, because the orally administered drug will enter the bloodstream. Whereas a single dose of fluconazole does not appear to be a risk to the fetus, high continuous doses may cause birth defects.

Infants and Children

Although many infections and illnesses that occur in infants and young children are due to perinatal infections, others infections may be transmitted to the newborn infant during the first week or two after birth.

Immune System in Infants and Children

The immune system of a newborn is immature and often unable to escalate an effective immune response. At birth and for the next few months the infant is dependent on the passive antibodies received through the placenta before birth, and via colostrum and breastmilk after birth. Antibodies that can cross the placenta are IgGs. In addition to IgGs, colostrum and breastmilk also contain IgAs (see Chapter 20, The Immune System) together with a variety of white blood cells. These passive antibodies are the same as the ones circulating in the mother’s circulatory system, representing the mother’s immunity to her environment. Therefore, infants usually have antibodies against microbes in their own home. However, a mother with a compromised or weak immune system will pass fewer antibodies to her child, who will thus have fewer passive antibodies and thus a weaker immune system.

Although there is some protection for an infant in its mother’s womb, which contains microbes to which she has developed antibodies, the infant will not be immediately protected against new exposures. The greatest danger of infectious diseases to an infant is caused by microbes against which the mother has no antibodies; she cannot therefore pass on passive immunity to her infant. The hospital environment often contains bacteria that have developed resistance against antibiotics (see Healthcare–associated [Nosocomial] Infections in Chapter 9, Infection and Disease), which can cause a tremendous problem if an infant becomes infected.

The immune system of an infant begins to synthesize IgM antibodies soon after birth in response to the antigenic stimulation of its new environment. About 6 days after birth, the serum concentration of IgM rises sharply and this rise continues until adult levels are reached at about 1 year of age. While maternal passive IgGs will decline during the first 6 months of life, the rate of infant IgG synthesis increases. Furthermore, vaccination is done to stimulate the infant’s immune system to certain infectious diseases. Vaccination schedules are available in all doctors’ offices. A vaccine can be against a particular microbe, its toxins, or against the symptoms of the disease. Certain vaccinations may be required in order for the child to enter a child care center or, later, school. During childhood children are exposed to a multitude of microorganisms, illnesses, and diseases and therefore actively develop a functioning immune system.

Common Microbial Infections in Infants and Children

Skin Infections

The skin becomes colonized by normal flora during birth. The normal skin flora of an individual is dependent on age. For example, micrococci are more prominent in infants and children than on the adult skin. Skin infections are common during the neonatal period and in preschool age children exposed to contagious organisms. For more details on infections of the skin refer to Chapter 10 (Infections of the Integumentary System, Soft Tissue, and Muscle).

• Deep folliculitis: This condition may be extensive, involving a wide area, especially the scalp in infants and young children.

• Staphylococcal scalded skin syndrome, caused by group II staphylococci, is more common in infants than in adults.

• Impetigo: Three different forms of impetigo are recognized on the basis of clinical, bacteriological, and histological findings. In infants the most common form is impetigo neonatorum, caused by Staphylococcus aureus. It is a highly contagious disease and a real problem in nurseries. The illness usually occurs between the fourth and tenth day after birth and if not immediately treated can result in an epidemic in nurseries. Impetigo is also common in older children and usually is not serious; however, if attending a child care center the child may receive antibiotic treatment to be able to return to the center, usually 24 hours after the start of antibiotic therapy.

Infections in Children

In their first 10 years of life children are constantly exposed to a variety of microbes, especially in day care centers and elementary school. The following is a limited list of common infections in children; a detailed listing and more information can be found on the CDC website: http://www.cdc.gov/ncidod/diseases/children/diseases.htm

• Sore throat (pharyngitis) caused by Streptococcus pyogenes, which can result in complications (see Streptococcal Infections in Chapter 11, Infections of the Respiratory System).

• Rheumatic fever is a childhood disease that does not stand alone. It is always preceded by another streptococcal infection (see Medical Highlights: Complications of Strep Throat [Rheumatic Fever] in Chapter 11).

• Scarlet fever, once a serious childhood disease, is now treatable (see Scarlet Fever in Chapter 11).

• Otitis media: Ear infections.

• Chickenpox: A disease caused by the varicella-zoster virus, causing an itchy skin rash (see Chapter 7, Viruses). Vaccination is available.

• Rubella: German measles is a viral respiratory infection and it is recommended by the CDC that children should be vaccinated (see Chapter 7).

• Common cold: Caused by human parainfluenza viruses (see Chapter 7).

• Mumps and measles: Both are vaccine-preventable diseases (see Chapter 7).

Young Adults

Most infections that occur in young adults can also occur in middle-aged and older adults. The infections listed in the following sections commonly occur during the college years.

Common Microbial Infections in Young Adults

Infectious Mononucleosis

Infectious mononucleosis is caused by the Epstein-Barr virus and often occurs in young adults, especially during the high school years. It is also called the “kissing disease” because it occurs predominantly in high school–aged children. Oftentimes the virus is transmitted by sharing of drinking glasses, bottles, or utensils. For more information refer to Infectious Mononucleosis and Life Application: “Kissing Disease” in Chapter 14, Infections of the Circulatory System.

Sexually Transmitted Infections

Sexually transmitted infections (STIs) are also referred to as sexually transmitted diseases (STDs). There are about 19 million new STIs in the United States each year and almost 50% of these occur among young adults between the ages of 15 and 24 years. Despite awareness efforts, the United States has the highest rates of STIs among developed countries. Common STIs on college campuses are as follows:

Most college students are or have been sexually active, and many have had multiple partners, increasing the risk for STIs. The rates of chlamydia, gonorrhea, and HPV are highest among female adolescents. For information about specific sexually transmitted infections please refer to Chapter 17, Sexually Transmitted Infections/Diseases.

MEDICAL HIGHLIGHTS

HIV Infections in Adolescents and Young Adults

The U.S. Department of Health and Human Services expressed rising concern about the occurrence and effects of HIV/AIDS in the United States among adolescents and young adults between the ages of 13 and 24 years. In 2004 the CDC reported 40,049 cumulative cases of AIDS among individuals in this age group. More than 10,000 adolescents and young adults with AIDS have died since the beginning of the epidemic. Because of the average interval between the infection and the development of AIDS, which is 10 years, most adults with AIDS were likely infected as adolescents or young adults. Most of these young HIV-infected individuals are exposed to the virus through sexual intercourse. In addition, there are an increasing number of children who were infected as infants and are now surviving adolescence.

Environmental Exposures Typical for Young Adults

During adolescence many individuals become sexually active, exposing themselves to sexually transmitted microorganisms. Many of these microbes will cause infection and show symptoms, and some of them will be asymptomatic (see Chapter 17, Sexually Transmitted Infections/Diseases).

Many young adults also will attend college or join the military, where they usually are in close quarters, which can be breeding grounds for various microorganisms, some of them potentially pathogenic. After finishing college individuals enter the work force, where they are again exposed to new microbes—the immune system being challenged and actively producing antibodies (see Active Immunity [Humoral] in Chapter 20, The Immune System). Another possible exposure to new microbial environments is encountered during the travel many young adults undertake, including international destinations.

LIFE APPLICATION

“New Teachers”

A good example of young adults being exposed to a “new” microbial environment is teachers—including those in day care centers, preschool, elementary school, and beyond. Especially when dealing with young children, these individuals are exposed to every cold and childhood disease. No wonder new teachers are sick a lot of the time. The good news is that after a few years of teaching a young instructor’s healthy immune system usually produces immunity to many of these microbes, and the teacher will not get sick as often, even if all the children in the classroom are.

Older Adults

The United States population is rapidly aging, leading to the publication of “The State of Aging and Health in America 2007,” a report released by the CDC and the Merck Company Foundation in March 2007. According to the report, by 2030 the number of Americans age 65 years and over will be more than 71 million, encompassing about 20% of the U.S. population. This will provide a challenge to the healthcare system to preserve the health of this elderly population. Besides other health challenges for an aging body, it is important to understand that microbes will interact differently in the elderly than in a young adult.

Immune System in Older Adults

Aging brings a decline in immune function, which leads to increased vulnerability to infectious disease as well a delay in recovery after an illness. This progressive dysfunction of the immune system is called immune senescence. The changes are generally slight and most people do not notice them. Older people most often notice changes when their immune system is less able to fight infections, when infections linger or become severe. For example, people who were infected with tuberculosis during adolescence or early adulthood may not have symptoms until old age, when the immune system is weakened.

The aging immune system is also often less able to differentiate between the body’s own cells and foreign substances, and may start attacking some of the body’s own cells. This can result in autoimmune disorders (see Chapter 20, The Immune System), which become more frequent during aging. The immune system is responsible for the destruction of cancer cells, invading microbes, and other foreign substances. The aging immune system is less capable of doing so, which may explain the increased incidence of cancer in the older population. Because of the reduced activity of the immune system, allergic reactions also decline.

Common Microbial Infections in Older Adults

Infectious diseases are a serious concern in the elderly population. It is estimated that infectious diseases are responsible for one third of all deaths in individuals 65 years of age and older. This is in part due to the decline in the immune system response, as well as to the problem of early detection, because the signs and symptoms of an infection are different in the elderly population. Among younger adults the classic indications of infection are fever and leukocytosis, which are present less frequently or not present at all in older infected adults. It has been reported that 60% of older adults with serious infections do develop leukocytosis, but the absence does not necessarily rule out an infection. In addition, frail elderly people generally have a poor temperature body response and elevations in body temperature of only 1.1° C from their normal baseline should be considered a febrile (feverish) response. Therefore, slight increases in body temperature likely indicate a microbial infection, which may even be life-threatening. Some of the most common infections include the following:

Pneumonia

Although pneumonia (see also Chapter 11, Infections of the Respiratory System) occurs in people of all ages, it occurs more commonly in older people, where it tends to be more serious. Pneumonia is one of the most common and also significant health problems in the elderly, especially those hospitalized or residing in other healthcare facilities. It is often the terminal event after a prolonged serious illness and is the leading infectious cause of death in this age group. The major risk factor for developing pneumonia in this age group is the presence of another serious illness, or it can be a result of a previous illness such as influenza. In 30% to 50% of cases the infectious agent is not identified; the most common identifiable organisms causing the illness are listed as follows:

• Streptococcus pneumoniae causes pneumococcal pneumonia and is the most common bacterial cause of community-acquired pneumonia in the elderly. Individuals 65 years of age and older are three to five times more likely to die of this condition than are younger individuals. Drug-resistant strains cause drug-resistant Streptococcus pneumonia (DRSP) disease, with the elderly being highly susceptible (see Drug-resistant Streptococcus pneumoniae Disease in Chapter 11, Infections of the Respiratory System).

• Haemophilus influenzae account for 8% to 20% of pneumonias in the elderly, most frequently in those with chronic bronchitis.

• Legionella spp.: The susceptibility to these organisms increases with age.

• Gram-negative bacilli are more common in institutional settings and include Klebsiella, Pseudomonas aeruginosa, Enterobacter spp., Proteus spp., Escherichia coli, and others. Gram-negative bacilli often colonize in the pharynx of seriously ill patients and account for approximately 40% to 60% of all culture-diagnosed pneumonias.

• Anaerobic bacteria cause 20% of community-acquired infections and 31% of nosocomial cases of pneumonia in the elderly. These microbes usually cause illness among the elderly on aspiration, especially by those with conditions that cause altered consciousness due to medications and medical conditions. The organisms involved may be Fusobacterium nucleatum, peptostreptococci, peptococci, and Bacteroides fragilis.

• Viral causes of pneumonia include influenza and parainfluenza viruses, respiratory syncytial virus, and occasionally adenoviruses.

Influenza

Influenza is caused by one of the influenza viruses and affects the entire body, but its most evident effect is on the airways (see Chapter 11, Infections of the Respiratory System). Influenza affects persons of all ages but is particularly serious in the elderly. In a typical year the illness leads to more than 20,000 deaths, with older people accounting for more than 80% of these. Influenza vaccination is recommended for all older persons. Pneumonia and severe bronchitis commonly accompany influenza in the older population, and the rate of severity increases with age. Pneumonia may be due to primary influenza, other viral infection (e.g., the common cold), or secondary bacterial infection.

Skin Infections

Aging leads to changes in the skin and its appendages. These changes include dryness, atrophy, and decline in cell replacement, barrier function immunologic responsiveness, thermoregulation, and many more. These changes can cause a variety of skin infections including herpesvirus infections (e.g., varicella-zoster virus and herpes simplex virus [HSV]), cellulitis, erysipelas, necrotizing fasciitis, impetigo, folliculitis, furunculosis, candidiasis, and a variety of rashes. For more detailed information about the various skin infections please refer to Chapter 10, Infections of the Integumentary System, Soft Tissue, and Muscle.

HEALTHCARE APPLICATION
Pneumonias in the Elderly*

Organism Comments Treatment
Streptococcus pneumoniae Community-acquired; person-to-person contact or inhalation Penicillin, first-generation cephalosporin, a macrolide, a fluoroquinolone
Haemophilus influenzae Mostly in patients with chronic bronchitis; transmitted by aerosol Cefuroxime, third-generation cephalosporins, trimethoprim-sulfamethoxazole, levofloxacin
Legionella spp. Susceptibility increases with age; Legionnaire’s disease Erythromycin with or without rifampin, newer macrolide, a fluoroquinolone
Pseudomonas aeruginosa Institutional setting; colonizes the posterior pharynx of seriously ill patients Antipseudomonal penicillin or ceftazidime plus an aminoglycoside
Anaerobic bacteria Community-acquired and nosocomial; usually the result of aspiration Penicillin or clindamycin
Influenza A virus Influenza—most important cause of pneumonia in the elderly Amantadine or rimantadine and an antibiotic

*Also see Healthcare Application: Pneumonias in Chapter 11, Infections of the Respiratory System.

Factors Influencing Susceptibility to Microbial Disease

Biological, cultural, and social factors all influence the susceptibility to infection among the elderly. Biological factors include the decline in defense mechanisms, thinning of the skin, reduced activity of sweat glands, decreased urine flow, and others. All these factors make it easier for microorganism to cause infection and disease. Other factors that increase susceptibility to infections are chronic disease such as heart disease and diabetes.

Elderly individuals in the developed world have more access to good healthcare and therefore are less susceptible to microbial diseases than those in underdeveloped countries. Different lifestyles and behavioral practices also play a major role in the susceptibility of the elderly to infectious diseases. Social factors that play a role in the susceptibility to infectious diseases in the United States include the increasing age of the population, resulting in the increased incidence of some age-related diseases which in turn will increase the susceptibility to infections in this population. Many of the older population spend more time in the hospital/healthcare environment or in nursing homes, thus making them more susceptible to nosocomial infections.

Summary

• Microorganisms affect the various human age groups in different manners because of a variety of factors, one of the most important ones being the functional capacity of the immune system.

• Microbial infections that can be passed on from a mother to a child either during pregnancy or during birth are referred to as perinatal infections. Many of them will become evident after birth.

• A congenital disorder is any medical condition that is present at birth, regardless of the origin. Congenital infections, on the other hand, are intrauterine infections that occur during pregnancy when microorganisms enter the blood, infect the placenta, and ultimately the fetus.

• Many infections and illnesses in infants are due to perinatal infections, but others may be transmitted to the newborn during the first week or two after birth.

• The immune system of the infant is immature and its defense against microorganisms depends on passive antibodies received from the mother during pregnancy and lactation.

• Young children during their day care, preschool, and elementary school years are exposed to a multitude of microbes, infections, and diseases, all of which stimulate the maturation of the immune system. Vaccination also plays an important role in this process.

• Although most infections that occur in young adults can also occur in middle-aged and older adults, certain infections such as mononucleosis and sexually transmitted infections occur more commonly in adolescents and college-aged individuals.

• In general, the immune system of young adults can respond to all the microbes it has previously been exposed to. However, once entering college, the military, or the work environment new microbial environments will challenge the immune systems of young adults to make more antibodies.

• The population aged 65 years and over is constantly increasing in the United States as well as in the rest of the world. Various infectious diseases are of great concern in this population.

• A progressive decline or dysfunction in the aging immune system is referred to as immune senescence, and is responsible for the increased incidence of severe infectious disease in the elderly. The severity of infections often increases with increasing age.

Review Questions

1. The highly specialized structure that protects the fetus from microorganisms is the:

2. Congenital CMV infections are caused by:

3. The most common virus transmitted during pregnancy is:

4. A fetus infected with rubella virus produces which of the following antibodies that can then be detected in the umbilical cord?

5. The type of antibody that can cross the placenta is:

6. Staphylococcal scalded skin syndrome is most common in:

7. Infectious mononucleosis most often occurs in:

8. Almost half of all the STIs diagnosed in the United States are among:

9. Infectious diseases in the adult population are responsible for about one third of all deaths in individuals over the age of:

10. All the following infections may recur during pregnancy except:

11. A bacterial or viral infection that can be passed from a mother to her child before or during birth is called a(n) __________ infection.

12. Impetigo neonatorum is caused by __________.

13. Infectious mononucleosis is caused by __________.

14. Chlamydia commonly occurring in young adults is a(n) __________ disease.

15. The decline in the functioning of the immune system during aging is referred to as __________.

16. Discuss congenital CMV infections and give three statistics about the infection in the United States.

17. Describe the measures the CDC has recommended to avoid congenital toxoplasmosis.

18. Name the most commonly occurring sexually transmitted infections on U.S. college campuses.

19. Name and discuss the most common microbial infections that occur in the elderly population.

20. Differentiate between the immune systems of the infant, young adult, and older individual.

Related posts:

Pharmacology Infections of the Reproductive System Infections of the Respiratory System Infections of the Integumentary System, Soft Tissue, and Muscle Infections of the Circulatory System Cell Structure and Function