Definition
The elderly population, which includes persons who are sixty-five years of age or older, makes up about 13 percent of the total population of the United States and is expected to grow to about 20 percent of all Americans by the year 2030. Infectious diseases are the cause of one-third of all deaths in the elderly. The most common infectious diseases among older people can be categorized as follows: urinary tract infections (UTIs), respiratory tract infections (RTIs), skin and soft tissue infections (SSTIs), and gastrointestinal tract infections (GTIs).
Risk Factors, Etiology, and Pathogenesis
As a person ages, his or her immune system weakens and becomes less effective (immunosenescence). Studies have shown that increasing age is associated with a decline in the number of (or with functional alterations in) CD8+ cells, naive T cells, and B cells, all of which are involved in fighting infections. Other causes may include the impact of other diseases (comorbidities) and a decline in bodily functions. Malnutrition may also play a role, as approximately 10 to 25 percent of elderly persons have nutritional deficiencies and up to 50 percent of the elderly who are hospitalized have some kind of caloric or micronutrient deficiency. Malnutrition is a risk factor for infection, and infection can lead to malnutrition, particularly in the geriatric population.
UTIs are the most common infection in the elderly. Although urine is normally sterile, older persons are more likely to have bacteria in their urine (bacteriuria), with a prevalence of 15 to 30 percent in men and 25 to 50 percent in women. Factors contributing to this increased bacterial colonization include reduction in bladder capacity, decreased urinary flow, incomplete voiding, prostatic disease in men, and prolapsed bladder and lower estrogen levels in women.
An indwelling urinary catheter, common among institutionalized and elderly persons, is another risk factor for UTIs, as catheters contain stagnant urine in a warm environment, which promotes the growth of microorganisms. Thinning of the urinary epithelium also contributes to increased bacterial colonization, particularly in women, as does a higher vaginal pH and deficiencies in vaginal and periurethral antibodies that occur with age. Regular urination and strong urinary flow are protective against infectious bacteria, but the aging bladder is less able to sense the need to void. Urinary flow rates are slower in the elderly, and the elderly are more likely to experience incomplete bladder emptying.
Escherichia coli is the main pathogen responsible for UTIs in women, but about one-third of elderly persons have polymicrobial infections, which are rarely seen in younger persons. Infection with multiple organisms is more common in catheterized persons.
RTIs such as pneumonia and influenza are
the second-most common infections in the elderly. Older people are at increased
risk relative to younger people because they frequently have deficiencies in
protective airway reflexes (such as coughing) and mucus clearance. Decreased
elasticity of the alveoli (air sacs in the lung), poorer lung capacity, smoking,
and preexisting conditions such as chronic obstructive pulmonary disease
(COPD) and congestive heart failure are also common risk
factors for lung infections. The elderly are also more prone to active
tuberculosis
(TB) infections. Latent (inactive) TB is prevalent in all
ages, but decreasing immune function with age can lead to the infection becoming
active.
The epithelial cells of the skin, bladder, bronchus, and digestive system form a physical barrier to
bacteria, fungi, and viruses that may become compromised with age. For example,
the skin becomes thinner, dryer, and more easily breached, leading to a higher
risk of skin infections. Skin also loses collagen over time, affecting the
ability to resist trauma. Epidermal renewal time (the time it takes the body to
make all new skin cells) increases from twenty days in younger adults to thirty
days in older people, delaying wound healing and making wounds more likely to be
colonized by microorganisms. Cellulitis, a bacterial infection often
seen in the legs, is much more common in the elderly, especially those with
diabetes. Shingles are caused by the reactivation of the varicella
zoster virus (chickenpox), which is dormant after the initial infection (usually
in childhood) but can flare up in old age.
GTIs, including gastroenteritis and colitis, are also more common in older adults. Predisposing factors include pH changes in the stomach, decreased intestinal movement, and changes in the composition of the gut bacteria. The risk of gastrointestinal infections is also affected by the presence of Helicobacter pylori , which is found in 40 to 70 percent of elderly people. H. pylori causes chronic gastritis in about one-third of those infected, which can lead to lower acid levels in the stomach and a higher risk of infections from other pathogens. Treatment with antibiotics and proton pump inhibitors can change the composition of the stomach’s normal bacteria, which can lead to susceptibility to infectious organisms such as Clostridium difficile.
Other factors that increase the risk of infectious diseases among the elderly
include a higher likelihood of being bedridden, which increases the risk of
pressure ulcers and subsequent skin infections, and more frequent
institutionalization and hospitalization, which increase the risk of nosocomial
(hospital-acquired) infections and higher exposure to pathogens in confined
settings. In addition, older people are more likely to have comorbid conditions
such as diabetes, cancer, and heart disease; both the diseases and their
treatments (for example, chemotherapy) can weaken the immune system and lead to a
higher risk for infections.
Symptoms
Older people often do not have the same symptoms associated with infections that younger people do. For example, the classic symptoms of infection include fever, inflammation, pain, chills, and vomiting. However, elderly people with infections often have nonspecific symptoms such as delirium, confusion, fatigue, loss of appetite, decline in function, mental status changes, incontinence, falls, or subnormal temperature. This atypical presentation can potentially lead to a delay in diagnosis and treatment, especially because the same symptoms are also present in noninfectious diseases in the elderly. The average body temperature for older adults is often lower too, meaning that if a baseline temperature is unknown, a fever may be missed. In an institutional setting, cognitive comorbidities increase the risk of a missed infection. For example, about one-half of nursing home residents have dementia and are unable to describe symptoms at all.
UTIs generally cause symptoms such as an urgent need to urinate, increased frequency of urination, and pain. Fever may also be present. However, these symptoms may be hidden by preexisting incontinence. In some cases, delirium, confusion, and rapid functional decline are the main symptoms of a UTI, and these infections may even manifest with respiratory symptoms such as cough or shortness of breath. Diagnosis relies on symptoms, urinalysis, and urine culture, although elderly persons with symptomatic UTIs may have lower bacterial counts than younger persons: Although 105 or more colony-forming units (CFU) per milliliter (mL) of urine is the standard definition, bacterial counts in the elderly may be only 102 to 103 CFU/mL.
RTIs can affect the nose, throat, airways, and lungs and are typically associated with cough, fever, weakness, sore throat, irritability, difficulty breathing, and aches and pains. Often, any type of RTI is attributed to the flu, because the different types of infections are difficult to distinguish; other types of infections have not been studied as thoroughly. In persons with COPD, even a simple cold can cause an acute exacerbation, leading to hospitalization and even death.
SSTIs such as cellulitis generally present with redness, warmth, and swelling.
The primary symptom associated with shingles is pain, and even after the infection
clears, persons frequently experience postherpetic neuralgia, or nerve pain,
which can last up to one year or longer.
GTIs are typically associated with gastrointestinal pain, diarrhea, fever, cramping, nausea, and vomiting. Diarrhea may be bloody in the case of E. coli infections but typically is not bloody among persons infected with C. difficile. As with other infectious diseases, GTIs may be hard to distinguish from other conditions in the elderly, including incontinence, irritable bowel, or medication-induced diarrhea. Initial infection with H. pylori is associated with nausea, upper abdominal pain, vomiting, and fever lasting anywhere from three days to two weeks; after the original infection subsides, the bacteria tend to colonize the gastrointestinal tract, triggering subsequent gastritis episodes, unless treated.
Prevention and Treatment
UTIs may be prevented through personal hygiene, avoidance of catheterization wherever possible, and possibly certain nutritional approaches such as cranberry juice. Although asymptomatic bacteriuria is very common, the guidelines of the Infectious Diseases Society of America do not recommend screening for or treating the condition because of a lack of proof that doing so prevents future UTIs or reduces morbidity; in addition, overtreatment for asymptomatic infections may contribute to antibiotic resistance. In persons with symptomatic UTIs, existing catheters are removed and the infection is treated with an oral antibiotic specific to the pathogen involved. If the infection is serious, intravenous antibiotic therapy may be required. Polymicrobial infections may require a broad-spectrum antibiotic.
The most reliable ways to prevent RTIs include smoking cessation and vaccination. In addition, vigilance on the part of health care providers and caregivers is required, because symptoms can be subtle, particularly for TB. Vaccines for both pneumonia and influenza are available and recommended for all adults age sixty years and older. The United States has one of the highest rates of influenza and pneumonia vaccination in elderly persons in the world, at about 80 percent for flu and 70 percent for pneumonia, although the rate is still less than the government target of 90 percent.
Although the preventive efficacy of the influenza and pneumonia vaccines is lower in older persons, vaccination has been shown to reduce the severity of cases in terms of length of hospital stays and in terms of mortality, when they do occur. Some health care institutions are now instituting standing orders for vaccinations for the elderly, a strategy that takes the physician out of the equation and allows pharmacists, nurses, and physician assistants to provide routine vaccinations after a simple screening. Treatment for RTIs varies from simple bed rest to complex antiviral or antibiotic regimens lasting weeks.
SSTIs are best prevented through awareness and through good hygiene by both older people and their caregivers. Pressure ulcers may be prevented through regular repositioning of persons restricted to their bed, using supportive devices and surfaces, and keeping skin hydrated. Diabetics and people with poor circulation, who are at higher risk of cellulitis, can wear supportive stockings and keep the lower extremities elevated whenever possible to prevent swelling. A vaccine is approved for herpes zoster, indicated for all adults age sixty years and older, regardless of their history of zoster infection. The vaccine has been shown to be both effective and cost-effective in the elderly.
GTIs are best prevented through scrupulous personal hygiene, proper food-safety measures, and avoidance of antibiotics and proton pump inhibitors unless necessary. Institutional settings should ensure against transmission from infected persons, including visitors and staff, to healthy residents. Risk-based food-safety programs and ongoing food safety education for staff are necessary. Treatment for GTIs includes hydration and supportive care and the discontinuation of any antibiotic that may have caused the problem. Treatment with antidiarrheal agents is not recommended in infections related to C. difficile or E. coli. Oral metronidazole or vancomycin may be used to treat C. difficile infections. Alcohol-based hand sanitizers are not effective at killing C. difficile, so soap and water should be used if that is the infectious agent. Treatment regimens for H. pylori infections may include proton pump inhibitors, amoxicillin, clarithromycin, and metronidazole.
Impact
Infectious diseases are major causes of death, disability, morbidity, cost, and health-services utilization in the elderly. The infectious disease hospitalization rate in the United States increased by about 12 percent from 1998 to 2006 and is about four times higher among the elderly than among younger adults.
UTIs accounted for 13 percent of infections in 2011, according to the Multistate Point-Prevalence Survey of Health Care–Associated Infections, published in the New England Journal of Medicine. Among institutionalized elderly persons, prevalence ranges from 0.1 to 2.4 cases per 1,000 resident days, and 12 to 30 percent of residents have a minimum of one UTI every year.
RTIs such as pneumonia, influenza, and chronic bronchitis are the fourth-leading cause of death in this age group, after heart disease, cancer, and stroke. In 2012, the elderly accounted for about 35 percent of all inpatient stays in the United States, totaling close to $160 billion in costs. Pneumonia was the second-most common reason for admission in this age group (after congestive heart failure). Among those age sixty-five years and older, there were nearly 600,000 discharges costing more than $5 billion for influenza and pneumonia in 2008. COPD, which is an umbrella diagnosis that includes chronic bronchitis and emphysema and is generally related to smoking, is found in approximately 10 percent of all adults and is more common in older persons. According to a 2014 study published by Respiratory Research and another by the World Health Organization, in 2010, in the United States, COPD was the cause of 1.5 million emergency department visits, 700,000 hospitalizations, and 134,700 deaths. Most were a result of acute exacerbations of the disease, which are caused by viral, bacterial, or fungal infections in about two-thirds of cases. People age sixty-five years and older make up more than 50 percent of cases of active TB in the United States, and nursing home residents have higher infection rates than do community-dwelling older people.
Bacterial, viral, and fungal SSTIs that are common in the elderly include shingles (herpes zoster), cellulitis, pressure ulcers, scabies, and chronic fungal infections of the nails (onychomycosis). Other SSTIs that have a higher incidence in older people include necrotizing fasciitis, methicillin-resistant Staphylococcus aureus infections of the skin, and surgical site infections. In 2010, the incidence of herpes zoster is 3.25 per 1,000 person years; approximately two-thirds of people age seventy years and older have a minimum of one skin problem.
GTIs caused by H. pylori are common in elderly persons, and if left untreated, chronic infection with H. pylori can lead to gastritis, gastric ulcers, and even stomach cancer, which is the second-most frequent cause of cancer-related death worldwide. The incidence and severity of C. difficile-associated diarrhea has increased since the 1970s, when it was first identified, so that it is now endemic to hospitals and long-term care facilities. An antibiotic-resistant strain has been identified and is associated with a high rate of recurrent infection.
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