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. 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). Microorganisms are spread in hospitals through several modes: • Direct contact—for example, in contaminated food or intravenous solutions • Indirect contact, for example, from patient to patient on the hands of health care workers (MRSA, rotavirus) • Droplet contact—for example, inhalation of droplets (>5 µm in diameter) that cannot travel more than 3 feet (pertussis) • Airborne contact—for example, inhalation of droplets (>5 µm) that can travel large distances on air currents (tuberculosis) • Vector-borne contact—for example, disease spread by vectors, such as mosquitoes (malaria) or rats (rat-bite fever); this mode of transmission is rare in hospitals in developed countries 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. 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* Hemolytic-uremic syndrome (HUS) Hepatitis B, D, E, and unspecified (acute) Hepatitis B (chronic) identified prenatally or at delivery Hepatitis C (newly diagnosed infection) Human immunodeficiency virus (HIV) infection Salmonellosis, including typhoid fever Spotted fever group rickettsioses Streptococcal disease, invasive (group A or B or S. pneumoniae)
Infection Control
Emergence of Antibiotic-Resistant Microorganisms
Hospital Infection Control Programs
Role of the Microbiology Laboratory
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
Acquired immunodeficiency syndrome (AIDS)
Vancomycin-resistant Enterococcus (VRE)
Botulism, food-borne
Hepatitis A (acute)
Amebiasis
Penicillin-resistant Streptococcus pneumoniae
Diphtheria
Q fever
Botulism, infant
H. influenzae, type b invasive infections
Rubella (including congenital)
Campylobacteriosis
Measles (rubeola)
Tuberculosis
Chancroid
Meningococcal infections, invasive
Tularemia
Chlamydia trachomatis infections
Pertussis
Vibrio infection, including cholera
Creutzfeldt-Jakob disease
Plague
Cryptosporidium infections
Poliomyelitis, acute paralytic
Cyclospora
Rabies in humans
Dengue
Severe acute respiratory syndrome (SARS)
Encephalitis (specify etiology)
Smallpox
Ehrlichiosis
Viral hemorrhagic fevers
Escherichia coli O157:H7
Yellow fever
Gonorrhea
Vancomycin-resistant Staphylococcus aureus (VRSA)
Hansen’s disease (leprosy)
Vancomycin-resistant coagulase-negative Staphylococcus spp.
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