Infection Control

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Infection Control

Objectives

1. Define and compare health care–associated infections and community-acquired infections.

2. List three factors determining the likelihood that a given patient would acquire a health care–associated infection.

3. State the most common types of health care–associated infections, and identify the risk factors that predispose patients to acquire each infection.

4. Explain the emergence of antibiotic-resistant microorganisms and their impact on health care.

5. Describe hospital infection control programs, and outline the structure and responsibilities of the infection control committee in a medical facility.

6. Identify means of transmission for microorganisms within a health care facility.

7. Interpret the role of the microbiology laboratory in an infectious outbreak.

8. Compare the two major ways to characterize strains involved in an outbreak.

9. Discuss techniques for isolation precautions used to prevent the spread of health care–associated infections.

10. Identify potential useful applications for surveillance cultures.

It is estimated that between 1.75 and 3 million (5% to 10%) of the 35 million patients admitted annually to acute-care hospitals in the United States acquire an infection that was neither present nor in the prodromal (incubation) stage when they entered the hospital. These infections are called health care–associated infections (HAIs). HAI has replaced old confusing terms such as nosocomial, hospital-acquired or hospital-onset infections. Treatment of HAI is estimated to add between $4.5 and $15 billion annually to the cost of health care and represents an enormous economic problem in today’s environment of cost containment. In addition, many of these infections lead to the death of hospitalized patients (patient mortality) or, at minimum, additional complications (patient morbidity) and further antimicrobial chemotherapy.

Some of the earliest efforts to control infection followed the recognition in the nineteenth century that women were dying in childbirth from bloodstream infections caused by group A Streptococcus (Streptococcus pyogenes) because physicians were spreading the organism by failing to wash their hands between examinations of different patients. Hand washing is still the cornerstone of modern infection control programs. Moreover, the first recommendations for isolation precautions in U.S. hospitals were published in the late 1800s, when guidelines appeared advocating placement of patients with infectious diseases in separate hospital facilities. By the late 1950s, the advent of HAI caused by Staphylococcus aureus finally ushered in the modern age of infection control. In the past four decades, we have learned that, in addition to hospitalized patients acquiring infections, health care workers are also at risk of acquiring infections from patients. Thus, present-day infection control programs have evolved to prevent the acquisition of infection by patients and caregivers.

In contrast, community-acquired infection is an infection contracted outside a health care setting or an infection present on admission. Community-acquired infections are often distinguished from HAIs by the types of organisms that affect patients who are recovering from a disease or infection. Community-acquired respiratory infections commonly involve strains of Haemophilus influenzae or Streptococcus pneumoniae and are usually more antibiotic sensitive.

The American Recovery and Reinvestment Act of 2009 was signed into law on February 17, 2009. The Recovery Act was designed to stimulate economic recovery in various ways including strengthening the nation’s health care infrastructure and reducing health care costs. Within the Recovery Act, $50 million was authorized to support states in the prevention and reduction of HAI. The HAI Recovery Act funds would be invested in efforts that support surveillance and prevention of HAIs, encourage collaboration, train the workforce in HAI prevention, and measure outcomes.

Incidence of HAI

The Centers for Disease Control and Prevention (CDC) has established the National Healthcare Safety Network (NHSN) program to monitor the incidence of HAI in the United States. Data collected in NHSN are used to improve patient safety at the local and national levels. In aggregate, the CDC analyzes and publishes surveillance data to estimate and characterize the national burden of health care–associated infections. Regardless of a hospital’s size or medical school affiliation, the rates of infections at each body site are consistent across institutions. The majority of HAIs are urinary tract infections (33%), followed by pneumonia (15%), surgical site infections (15%), and bloodstream infections (13%). The remaining 24% are other miscellaneous infections. Each HIA adds 5 to 10 days to the affected patient’s hospital stay. Of individuals with hospital-acquired bloodstream or lung infections, 40% to 60% die each year. Likewise, patients with indwelling urinary catheters have a threefold increased chance of dying from urosepsis—a bloodstream infection that is a complication of a urinary tract infection—than those who do not have one.

Attack rates vary according to the type of hospital. Large, tertiary-care hospitals that treat the most seriously ill patients often have higher rates of HIA than do small, acute-care community hospitals; large medical school–affiliated (teaching) hospitals have higher infection rates than do small teaching hospitals. This difference in the risk of infection is probably related to several factors, including but not limited to the severity of illness, the frequency of invasive diagnostic and therapeutic procedures, and variation in the effectiveness of infection control programs. Within hospitals, the surgical and medical services have the highest rates of infection; the pediatric and nursery services have the lowest. Moreover, within services, the predominant type of infections varies—that is, surgical site infections are the most common on the surgical service, whereas urinary tract or bloodstream infections are the most common on medical services or in the nursery.

Types of HAI

The majority of HAIs are endogenous in origin—that is, they involve the patient’s own microbial flora. Three principal factors determine the likelihood that a given patient will acquire an infection:

In general, hospitalized individuals have increased susceptibility to infection. Corticosteroids, cancer chemotherapeutic agents, and antimicrobial agents all contribute to the likelihood of HAI by suppressing the immune system or altering the host’s normal flora to that of resistant microbes. Likewise, foreign objects, such as urinary or intravenous catheters, break the body’s natural barriers to infection. Nonetheless, these medications or devices are necessary to cure the patient’s primary medical condition. Finally, exerting influence over the virulence of the pathogens is not possible because it is not possible to immunize patients against HAI. Patients with serious community-acquired infections are frequently admitted to the hospital, and the disease may spread by either direct contact; by contact with contaminated food, water, medications, or medical devices (fomites); or by airborne transmission. Thus, the HAI may never be completely eliminated, only controlled.

Urinary Tract Infections

Gram-negative rods produce the majority of health care–associated urinary tract infections, and Escherichia coli is the number one organism involved. Gram-positive organisms, Candida spp., and other fungi cause the remainder of the infections. The risk factors that predispose patients to acquire a health care–associated urinary tract infection include advanced age, female gender, severe underlying disease, and the placement of indwelling urinary catheters.

Lung Infections

The most common HAI pathogens causing pneumonia include gram-negative rods, S. aureus, and Moraxella catarrhalis. Streptococcus pneumoniae and Haemophilus influenzae, which cause the majority of community-acquired pneumonias, are not important etiologic agents in hospital-acquired infections except very early during the hospital course (first 2 to 5 days); these infections probably represent infections that were already incubating at the time of the hospital admission. The risk factors that predispose patients to acquire a health care–associated lung infection include advanced age, chronic lung disease, large-volume aspiration (the microorganisms in the upper respiratory tract are coughed up and lodge in the lungs instead of being spit out or swallowed), chest surgery, hospitalization in intensive care units, and intubation (placement of a breathing tube down a patient’s throat) or attachment to a mechanical ventilator (which controls breathing).

Surgical Site Infections

Approximately 4% of surgical patients develop surgical site infections; 50% of these infections develop after the patient has left the hospital, so this number may be an underestimate. Gram-positive organisms (S. aureus, coagulase-negative staphylococci, and enterococci) cause the majority of these infections, followed by gram-negative rods and Candida spp. The risk factors that predispose patients to acquire a health care–associated wound infection include advanced age, obesity, infection at a remote site (that spreads through the bloodstream), malnutrition, diabetes, extended preoperative hospital stay, greater than 12 hours between preoperative shaving of site and surgery, extended time of surgery, and inappropriate timing of prophylactic antibiotics (given to prevent common infections before they seed the surgical site). Surgical wounds are classified as clean, clean-contaminated, contaminated, or dirty, depending on the number of contaminating organisms at the site. Bowel surgery is considered dirty, for example, whereas surgery for a total hip replacement is considered clean.

Central Line-Associated Bloodstream Infection

A central line-associated bloodstream infection (CLABSI) is a serious infection that occurs when microbes enter the bloodstream through a central line. A central line is a tube that health care providers place in a large vein in the neck, chest, or arm to give fluids, blood, or medications or to do certain medical tests quickly. CLABSIs result in thousands of deaths each year and billions of dollars in added costs to the U.S. health care system, yet these infections are preventable. The risk factors that predispose patients to acquire a CLABSI include age 1 year of age or younger or 60 years of age and older, malnutrition, immunosuppressive chemotherapy, loss of skin integrity (e.g., burn or decubiti [bedsore]), severe underlying illness, indwelling device (e.g., catheter), intensive care unit stay, and prolonged hospital stay.

Emergence of Antibiotic-Resistant Microorganisms

The organisms that cause HAIs have changed over the years because of selective pressures from the use (and overuse) of antibiotics (see Chapter 11). Risk factors for the acquisition of highly resistant organisms include prolonged hospitalization and prior treatment with antibiotics. In the pre-antibiotic era, most HAIs were caused by S. pneumoniae and group A Streptococcus (Streptococcus pyogenes). In the 1940s and 1950s, with the advent of treatment of patients with penicillin and sulfonamides, resistant strains of S. aureus appeared. Then, in the 1970s, treatment of patients with narrow-spectrum cephalosporins and aminoglycosides led to the emergence of resistant aerobic gram-negative rods, such as Klebsiella, Enterobacter, Serratia, and Pseudomonas. During the late 1970s and early 1980s, the use of more potent cephalosporins played a role in the emergence of antibiotic-resistant, coagulase-negative staphylococci, enterococci, methicillin-resistant S. aureus (MRSA), and Candida spp. The 1990s witnessed the emergence of beta-lactamase–producing, high-level gentamicin-resistant, and vancomycin-resistant enterococci (VRE). The twenty-first century has seen the emergence of vancomycin-resistant Staphylococcus aureus (VRSA).

Patients’ normal flora will change quickly after hospitalization from viridans streptococci, saprophytic Neisseria spp., and diphtheroids to potentially resistant microorganisms found in the hospital environment. The colonized nares, skin, gastrointestinal tract, or genitourinary tract can later serve as reservoirs for endogenously acquired infections. Moreover, if patients colonized with resistant microorganisms return to nursing homes in the community harboring these organisms, they can also transfer them to other patients. This further increases the pool of patients who harbor multidrug-resistant organisms when they, in turn, are hospitalized. These new patients recontaminate the hospital environment and serve as potential reservoirs for spread to additional patients.

Hospital Infection Control Programs

Hospital infection control programs are designed to detect and monitor HAIs and to prevent or control their spread. The infection control committee is multidisciplinary and should include a microbiologist, an infection control practitioner (often a nurse with special training), a hospital epidemiologist (usually an infectious disease physician), and a pharmacist. The infection control practitioner collects and analyzes surveillance data, monitors patient care practices, and participates in epidemiologic investigations. Daily review of charts of patients with fever or positive microbiology cultures allows the infection control practitioner to recognize problems with HAIs and to detect outbreaks as early as possible. The infection control practitioner is also responsible for the education of health care providers in techniques, such as hand washing and isolation precautions, that minimize the acquisition and spread of infections.

It is the infection control practitioner’s job to identify all cases of an outbreak. The investigation of the cluster of cases during a particular outbreak involves its characterization in terms of commonalities, such as location in the hospital (nursery, intensive care unit), same caregiver, or prior respiratory or physical therapy. Risk factors—including underlying diseases, current or prior antimicrobial therapy, and placement of a urinary catheter—are also assessed. This information helps the infection control committee determine the reservoir of the organism in the hospital—that is, the place where it exists and the means by which the organism is transmitted from its reservoir to the patient.

Microorganisms are spread in hospitals through several modes:

Once the reservoir is known, the infection control practitioner can implement control measures, such as reeducation regarding hand washing (in the case of spread by health care workers) or hyperchlorination of cooling towers in the case of legionellosis.

Role of the Microbiology Laboratory

The microbiology laboratory supplies the data on organism identification and antimicrobial susceptibility profile that the infection control practitioner reviews daily for evidence of HAI. Thus, the laboratory personnel must be able to detect potential microbial pathogens and then accurately identify them to species level and perform appropriate susceptibility testing. The microbiology laboratory staff should also monitor multidrug-resistant organisms by tabulating data on antimicrobial susceptibilities of common isolates and studying trends indicating emerging resistance. Significant findings should be immediately reported to the infection control practitioner. If an outbreak is suspected, the laboratory works in tandem with the infection control committee by (1) saving all isolates, (2) culturing possible reservoirs (patients, personnel, or the environment), and (3) performing typing of strains to establish relatedness between isolates of the same species. Microbiology laboratories are also obligated by law to report certain isolates or syndromes to public health authorities. For example, Table 79-1 lists organisms to be reported to state health authorities in Texas. Other states have similar criteria.

TABLE 79-1

Examples of Notifiable Infectious Conditions in Texas*

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Diseases to Be Reported Immediately by Telephone/Fax† Diseases to Be Reported within 1 Working Day Diseases to Be Reported within 1 Week Diseases to Be Reported Quarterly
Anthrax Brucellosis

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