Infectious Diseases

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Author: Margaret Alic
Editor: Jacqueline L. Longe
Date: 2009
Document Type: Disease/Disorder overview
Pages: 7
Content Level: (Level 4)

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Page 1032

Infectious diseases


Infectious diseases are caused by microbes—primarily bacteria, viruses, protozoa, and fungi—that can be passed to or among humans by various means.


Infectious diseases are a major cause of illness and death in older people and may exacerbate other medical conditions. Pneumonia, influenza (flu), and septicemia are among the top ten causes of death in older adults. Pneumonia is a lung infection caused by bacteria, viruses, or fungi. Influenzas are respiratory illnesses caused by highly contagious viruses. Septicemia, also called blood poisoning, occurs when a microorganism enters the bloodstream and causes infection throughout the body. Septicemia can damage the circulatory system, cause severe low blood pressure, and lead to infections in other organs such as the lungs or brain.

Other infectious diseases that are particularly dangerous in older people include:

  • food poisoning caused by the bacterium Escherichia coli (E. coli)
  • tuberculosis (TB), in seniors usually resulting from reactivation of a latent infection by Mycobacterium tuberculosis
  • chickenpox caused by the Varicella zoster virus
  • West Nile virus infection
  • acquired immunodeficiency syndrome (AIDS) caused by the human immunodeficiency virus (HIV).

Other common infectious diseases in older adults include:

  • colds
  • bronchitis, an inflammation of the main air passages to the lungs usually resulting from a respiratory virus infection
  • urinary tract infections, usually involving the bladder or kidneys
  • infections of the skin and soft tissues, often called cellulitis
  • bacterial infections of the gut, including diverticulitis, appendicitis, infectious diarrhea, gall bladder infection, or abdominal abscesses
  • gastroenteritis, an intestinal infection
  • bacterial infections of the bones and joints
  • infectious endocarditis, an inflammation of the heart valves
  • bacterial meningitis, which causes inflammation of the membranes lining the brain
  • shingles or herpes zoster, a reactivation of the virus that causes chickenpox
  • Lyme disease, caused by the bacterium Borrelia burgdorferi.

Another way to classify the infections caused by microbial diseases is based on the onset and duration of the illness. Infections fall into three general categories:

  • Acute infections, including influenza and many forms of pneumonia, developing within hours or days. The illness may last from hours to a couple of weeks and may range from mild to life-threatening.
  • Chronic infections, such as some forms of bone infection, typically lasting from weeks to years. Chronic infection can sometimes develop from acute infection or may develop very slowly.
  • Latent infections, such as certain forms of tuberculosis, can remain hidden in the body for many years without causing symptoms. These germs may become active, cause symptoms, and be transmissible to others months or years after the initial infection occurred.



Infectious diseases are responsible for more deaths worldwide than any other cause, and seniors Page 1033  |  Top of Articleare particularly susceptible, in large part due to age-related changes in the immune system. The majority of elderly people have 30 to 50% less immunity than the young or middle-aged, a condition called immunosenescence. With age, specific types of immune cells become less able to produce antibodies to fight infection. In addition the skin and mucous membranes lining the gastrointestinal, respiratory, and urinary tracts become less effective barriers to infectious organisms entering the body. Nevertheless some older people have immune responses that are almost as effective as those of much younger people.

The effectiveness of the immune response also depends on overall health and is adversely affected by such factors as the following:

  • poor nutrition
  • smoking
  • alcohol consumption
  • environmental pollutants
  • the presence of another disease, referred to as comorbidity
  • medications used to treat a concurrent disease

Other factors that can increase the susceptibility of older adults to infectious diseases include:

  • stress
  • age-related changes in the lungs—especially the collapse of small airways and stiffening of lung tissue—that increase the risk of respiratory infection
  • inability to cough strongly enough to clear the airways of phlegm and mucus
  • difficulty swallowing, which increases the risk of inhaling or aspirating foods or liquids
  • a reduced response to vaccines against pneumonia and flu
  • an inability to completely empty the bladder, leaving urine in which bacteria can grow
  • changes in urine or prostate secretions that affect their antibacterial properties
  • common skin conditions such as blisters and pressure ulcers
  • general immobility, as may occur after a stroke or surgery
  • exposure to infectious organisms, such as in a hospital or nursing home
  • use of catheters or other tubes, such as for kidney dialysis, that remain in the body for long periods.

The presence of other diseases or physical conditions, such as kidney or heart disease, can greatly reduce the body's ability to fight infections. Chronic obstructive lung disease decreases mucus clearance from the airways, increasing the risk of pneumonia. Nerve damage and slow wound healing associated with diabetes increase the risk of serious infection, especially in the limbs. Complications from surgery and surgical wounds—and hospitalization itself—increase the risk of infection.


The microbes that cause many infectious diseases, such as common cold and flu viruses and M. tuberculosis, can be transmitted through the air from the coughs or sneezes of an infected person. Other infectious diseases are transmitted by close personal contact, including kissing, sexual intercourse, or accidental transfer from feces to hand to mouth. Some organisms can be transmitted by handshaking or touching a contaminated surface. Some infectious diseases—including salmonella enterocolitis (an infection of the intestine), and severe acquired respiratory syndrome (SARS), a serious viral pneumonia—can be transmitted either directly or indirectly from animals, including household pets. Other diseases, such as Rocky Mountain spotted fever or malaria, are transmitted through the bite of a vector, such as a mosquito, flea, or tick, or via contaminated food or water. International travel can expose people to infectious diseases from other parts of the world. People can carry infectious organisms and transmit them even without having symptoms of disease.


People aged 65 and older, especially women and the very elderly, account for more than half of all cases of pneumonia in the United States. Influenza, which infects 5 to 20% of the U.S. population annually, results in some 200,000 hospitalizations and 36,000 deaths each year, primarily in older adults. Septicemia is a common cause of hospitalizations among older adults and is the sixth leading cause of death among black women aged 85 and older.

Pneumonia and other infectious diseases are very common in hospitals and nursing homes. Older adults are particularly susceptible to hospital infections from open wounds and tubes inserted in the body. The incidence of serious infections by group B Stretococcus (strep) bacteria increases with age, especially in those with other medical conditions such as bedsores, diabetes, liver disease, or a history of stroke or cancer.

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Strep B infections often occur in older adults after a trauma or surgery.

About 1.7 billion people worldwide, including 16 million Americans, are infected with M. tuberculosis, the leading cause of death from a single infectious organism. In the United States 25% of all active cases of TB are in adults aged 65 and older, and up to 50% of older nursing-home residents have a positive reaction to a TB test, indicating previous exposure. Most of these people were infected in the early 1900s when it is estimated that 80% of the population was exposed to TB by the age of 30.

Initially HIV infections in older people were limited to those who had received transfusions with infected blood. However, the number of older Americans who are contracting HIV through sexual activity is increasing as of 2008, and many older adults remain unaware of the risk of HIV infection. About 10% of all new AIDS diagnoses in the United States are in older people, and in 2004 people aged 50 and over accounted for almost 20% of newly diagnosed cases. Older people with HIV are at particular risk of complications, due to immuno senescence.

Urinary tract infections affect more than 10% of older adults each year. Urinary tract infections are much more common in women than in men. Between 15% and 40% of older women have bacteria in their urine without symptoms of illness.

Older adults are at risk for bone and joint infections because conditions such as arthritis, gout, or artificial joints cause tissue damage. Bacteria can reach the bones and joints through the blood, from wounds, or from nearby infected tissues. Bacteria from pressure ulcers or diabetic foot infections are also common sources of bone and joint infections, particularly among nursing-home residents.

Infectious endocarditis is particularly common in the first two months after surgical implantation of an artificial heart valve. Bacteria can attach to the diseased or artificial valves and spread to the heart lining, the blood, and other organs.

Gastroenteritis and shingles are particularly common among nursing-home residents. Shingles affects at least one million Americans annually, most of them over age 60.

Causes and symptoms

Infectious diseases in seniors often follow other illnesses that have compromised the immune system.

Bacterial pneumonia often follows an infection such as the flu that damages the lungs. Common causes of septicemia include:

  • strep and other bacteria that cause pneumonia or other infections of the respiratory system, urinary tract, or skin
  • Salmonella
  • medical devices such as catheters that provide bacteria an entry point into the body
  • surgically implanted prosthetic devices, including artificial joints, pacemakers, heart valves, and eye lenses. Bacteria can reach the prosthesis during surgery or later through the blood or nearby infection and grow on the implanted device.

The most common causes of urinary infections in older people are urinary catheters and conditions such as fecal incontinence that allow gut organisms to enter the urinary tract. In older men prostate disease and difficulty emptying the bladder are the primary causes of urinary tract infections.

Older adults do not necessarily exhibit typical signs of infection. The most common symptom of a serious infection is fever; however, as many as 50% of older people do not have a fever even with a serious infection such as pneumonia. This is probably due to an age-related loss in the ability to regulate body temperature and to the generally lower body temperature of older people. The definition of a fever in a person over 75 should be lowered by about one half of a degree. In addition the fever response to infection and inflammation, as with other stress responses, may lessen with age. Therefore, in older adults the symptoms of infection may be general or unusual:

  • a sudden loss in wellbeing or function for no apparent reason
  • loss of appetite
  • falling
  • confusion

Symptoms of infectious disease that require a physician's attention include:

  • a cough lasting more than a week
  • difficulty breathing
  • fever
  • a rash, particularly if accompanied by fever
  • swelling
  • Page 1035  |  Top of Articlevomiting
  • open sores or pus draining from anywhere in the body
  • episodes of rapid heartbeat
  • change in urination habit or in the appearance or odor of the urine


Some infectious diseases can be diagnosed by a medical history and physical exam. Rapid blood, urine, or x-ray tests may provide helpful information. However, the most definitive tests for infection are bacterial cultures, in which a sample of blood, urine, sputum, spinal fluid, tissue, drainage from a wound, or a swab from the throat or other body part is placed in special material at the laboratory. These tests usually require one or more days to complete. Bacteria that grow usually signify the presence of infection and are tested to determine sensitivity to antibiotics. Viral and fungal infections can be diagnosed by more complicated types of cultures or other tests.

Blood tests can detect signs of inflammation, such as a high white blood cell count. However, many conditions can cause such results and older people may not have elevated white blood cells in response to infection. Other diagnostic tools include:

  • x rays
  • ultrasound
  • body scans
  • biopsies, in which a piece of tissue is removed for examination


Some infectious diseases, such as colds, are treated by bed rest and drinking plenty of liquids and are allowed to run their course, although symptoms may be treated with cold medications.

Bacterial infections are usually treated with antibiotics. Intravenous antibiotics may be administered for severe infections. However, the increase in drug-resistant bacteria due to the overuse of antibiotics is a worldwide health problem, especially in hospitals. Active TB requires months of treatment with multiple drugs. Infections associated with implanted medical devices may require removing the device before antibiotic treatment. Certain gastrointestinal, soft tissue, and bone and joint infections, and infectious endocarditis may require surgical treatment.

Fungal infections of the skin and nails may be treated with topical or oral medicines. Many topical antifungal medications are sold over-the-counter as treatment for athlete's foot. Oral antifungals usually require a prescription.

Nutrition/Dietetic concerns

It has been estimated that about half of adults over age 65 do not ingest the calories, vitamins, and minerals needed to maintain a healthy immune system to fight infection. This tendency is particularly true for nursinghome residents. However, older adults living independently may also be malnourished, particularly if they are depressed, have poorly controlled diabetes, side effects from medications, or medical conditions that interfere with appetite or metabolism. Although a 2007 study found that multivitamin and mineral supplements may not reduce the risk of infection among older nursing-home residents, other studies have found that nutritional supplements—particularly those containing antioxidants, B vitamins, selenium, and zinc—benefit both the immune system and the general health of those aged 65 and over.


Seniors are much more likely than younger people to die of an infectious disease. Of the at least 45,000 Americans who die of pneumonia or flu each year, 90% are 65 or older. The first wave of SARS was fatal in more than 50% of victims over age 65. Septicemia also has a poor prognosis in older adults, even with proper treatment, and the death rate from invasive strep B infections is 15–25% for adults aged 65 and over.

Older adults usually respond as well as younger people to anti-retroviral drugs that prevent symptoms of AIDS. However, older people with untreated HIV tend to deteriorate very rapidly. Other infectious diseases can damage organs and cause various other complications. Although the shingles rash usually goes away on its own in two to four weeks, for about one in five, the severe pain continues, a condition known as postherpetic neuralgia.


Hand washing is one of the easiest and most effective ways to prevent infectious disease. Scrubbing the hands vigorously with soap and water for 15 seconds will wash away many disease-causing organisms, including cold viruses and Staphylococcus and strep bacteria. It is particularly important to wash the hands:

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  • before preparing or eating food
  • after coughing or sneezing into the hand
  • after using the toilet
  • after changing a diaper

Septicemia can be prevented by cleanliness and sterile techniques, such as cleaning the area with iodine before inserting an intravenous line. Patients should insist that doctors, nurses, and other healthcare workers wash their hands before touching them.

Other preventions against infectious disease include:

  • cooking meat thoroughly
  • avoiding unpasteurized juices
  • washing cuts immediately with soap and water
  • cleansing skin that is not exposed to the air, such as the groin and under the breasts
  • seeing a dentist regularly and replacing toothbrushes every three months.


Many infectious diseases can be prevented with vaccines. Most adult Americans are immune to the infectious diseases that they had as children. However, since childhood diseases can be far more serious in older people, adults who did not have diseases such as measles or chickenpox in childhood should be vaccinated against them. Adults should also be vaccinated regularly against tetanus and diphtheria. Before traveling abroad Americans should receive vaccines against infectious diseases that are common in areas they will visit.

It is recommended that all adults aged 50 and older get annual flu vaccinations in October or November before the height of the flu season. A 2006 study found that higher doses of the vaccines are safe for older adults, significantly increase antibodies against the flu virus, and afford additional protection against the disease. People over age 64 should also get a one-time vaccination against Streptococcus pneumoniae, which often causes pneumonia and meningitis in older adults. This vaccine can be given at any time of the year. A single-dose shingles vaccine became available in 2006 and is recommended for adults aged 60 and over.


Antibiotics are sometimes prescribed as a preventative against bacterial infections such as TB. People testing positive for TB for the first time are usually treated with isoniazid for nine months as a preventative therapy. Those at high risk for infectious endocarditis or for infection from certain implanted devices are sometimes given antibiotics before dental cleanings or medical procedures to prevent bacteria from entering the blood and infecting the heart or medical device. Antiviral medications are effective in preventing some viral infections.

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  • How will my disease be diagnosed?
  • Can I transmit this disease to others?
  • What precautions should I take to prevent transmitting this disease?
  • What is the treatment for this disease?
  • How should I take my medications?
  • What are the side effects of the medications?
  • Will these medications interact with others that I am taking?
  • What else can I do to recover faster?
  • What is the prognosis?

Caregiver concerns

Caregivers can help prevent the spread of infectious diseases by washing their hands frequently and fully cooking food. Older people with dementia or other mental loss may not wash properly or refrigerate their food or may do other things that increase the risk of infectious disease. They may forget to take their medications, take the wrong ones or in the wrong dosage, or take them at the wrong time. This can cause an infection to linger or for other complications to develop. Antibiotics should be taken with plenty of water and with or without food, depending on the specific drug. It is very important that the entire course of antibiotics be taken, even if the patient feels better.

Older adults with mental difficulties may have trouble communicating symptoms of infection. Caregivers should take the following steps:

  • watch for signs and symptoms of infection, such as fever, chills, cough, change in urination habit, and especially a change in the ability to engage in normal activities
  • Page 1037  |  Top of Articlereduce fevers with acetaminophen and cold washcloths to the forehead after calling a doctor
  • encourage intake of fluids by frequently offering small amounts of clear liquid, ice cubes, or popsicles.

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Comorbidity—Simultaneous presence of more than one—usually independent—medical conditions.

E. coli—Escherichia coli; a bacterium that usually resides harmlessly in the lower intestine but can spread to cause infection elsewhere; also, some infectious strains produce a toxin that causes intestinal illness.

Endocarditis—Inflammation of the lining of the heart or the heart valves that can be caused by an infectious microorganism.

Herpes zoster—Shingles; an acute nerve inflammation resulting in a rash and pain, caused by the reactivation of latent chickenpox virus in the body.

Immunosenescence—Loss of immune system function with age.

Influenza—Flu; any of several highly contagious respiratory diseases caused by strains of three different species (A, B, or C) of orthomyxoviruses.

Meningitis—A bacterial or viral infection that causes inflammation of the membranes surrounding the brain and spinal cord.

Pneumonia—A lung disease usually caused by an infectious bacterium, virus, or fungus.

Salmonella—A genus of bacteria that causes food poisoning, acute gastrointestinal inflammation, typhoid fever, and septicemia.

Septicemia—Blood poisoning; an infection of the bloodstream by a virulent bacterium, virus, or fungus, causing acute systemic illness.

Shingles—Herpes zoster; an acute nerve inflammation resulting in a rash and pain, caused by the reactivation of latent chickenpox virus.

Staphylococcus—Staph; a genus of bacteria that causes various diseases, including food poisoning, skin infections, and endocarditis.

Streptococcus—Strep; a genus of bacteria that causes various diseases; Group B strep organisms cause pneumonia, septicemia, and meningitis.



Anderson, Mary Ann. Caring for Older Adults Holistically, 4th ed. Philadelphia: F. A. Davis, 2007.

Lerner, Brenda Wilmoth, and K. Lee Lerner. Infectious Diseases: In Context. Farmington Hills, MI: Thomson Gale, 2008.


Arnst, Catherine. “Roll Up Your Sleeve, Gramps; A Graying Population May Create a Huge Market for Vaccines that Buttress Aging Immune Systems.” Business Week no. 4055 (October 22, 2007): 90.

Kendall, Patricia A., et al. “Food Safety Guidance for Older Adults.” Clinical Infectious Diseases 42, no. 9 (May 1, 2006): 1298–1304.

Langkamp-Henken, Bobbi, et al. “Nutritional Formula Improved Immune Profiles of Seniors Living in Nursing Homes.” Journal of the American Geriatrics Society 54, no. 12 (December 2006): 1861–1870.

Liu, Barbara A., et al. “Effect of Multivitamin and Mineral Supplementation on Episodes of Infection in Nursing Home Residents: A Randomized Placebo Controlled Study.” Journal of the American Geriatrics Society 55, no. 1 (January 2007): 35–42.


“Aging in the Know: Infectious Diseases.” The AGS Foundation for Health in Aging. May 23, 2005 [cited March 31, 2008].

“Beyond Newborns and Mothers—Some Facts About Group B Strep Disease in the Rest of the Population.” Group B Strep Prevention. October 4, 2006 [cited March 31, 2008]. .

“Fight Flu and Pneumonia.” Health Information. June 20, 2007 [cited March 31, 2008]. .

“NAIAD Study Finds Higher Dose of Flu Vaccine Improves Immune Response in the Elderly.” NIH News. May 22, 2006 [cited March 31, 2008]. .


AGS Foundation for Health in Aging, Empire State Building, 350 Fifth Ave., Suite 801, New York, NY, 10118, (212) 755-6810, (800) 563-4916, (212) 832-8646, .

Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA, 30333, (404) 498-1515, (800) 311-3435, .

National Institute of Allergy and Infectious Diseases, 6610 Rockledge Dr., MSC 6612, Bethesda, MD, 20892-6612, (301) 496-5717, (866) 284-4107, (301) 402-3573, .

Margaret Alic Ph.D.

Source Citation

Source Citation   (MLA 8th Edition)
Alic, Margaret. "Infectious Diseases." The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers, edited by Jacqueline L. Longe, vol. 3, Gale, 2009, pp. 1032-1038. Gale Ebooks, Accessed 17 Sept. 2019.

Gale Document Number: GALE|CX3232000354

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