A nosocomial, or hospital-acquired, infection is a new infection that develops in a patient during hospitalization. It is usually defined as an infection that is identified at least forty-eight to seventy-two hours following admission, so infections incubating, but not clinically apparent, at admission are excluded. With recent changes in health care delivery, the concept of "nosocomial infections" has sometimes been expanded to include other "health care–associated infections," including infections acquired in institutions other than acute-care facilities (e.g. nursing homes); infections acquired during hospitalization but not identified until after discharge; and infections acquired through outpatient care such as day surgery, dialysis, or home parenteral therapy.
Early studies reported at least 5 percent of patients became infected during hospitalization. With the increased use of invasive procedures, at least 8 percent of patients now acquire nosocomial infections.
The most frequent types of infection are urinary-tract infection, surgical-wound infection, pneumonia, and bloodstream infection (see Table 1). These infections follow interventions necessary for patient care, but which impair normal defenses. At least 80 percent of nosocomial urinary infections are attributable to the use of an indwelling urethral catheter. Surgical-wound infection follows interference with the skin barrier, and is associated with the intensity of bacterial contamination of the wound at surgery. Nosocomial pneumonia occurs most frequently in intensive-care-unit patients with endotracheal intubation on mechanical ventilation—the endotracheal tube bypasses normal defenses of the upper airway. Finally, primary nosocomial bloodstream infection occurs virtually only with the use of indwelling central vascular catheters, and correlates directly with the duration of catheterization.
|Frequency of most common nosocomial infections|
|SOURCE: Mayhall, ed.|
|Urinary tract infection||2.34/100 admissions||5.3-10.5/1,000 catheter days|
|Surgical site infection||4.6-8.2/1,000 discharges||2.1-7.1% of wounds|
|Pneumonia||0.5-1.0/100 admissions||9-47% ventilated patients 1-3%/ventilator day|
|Central vascular line||—||1.4% of central catheters 1.7/1,000 catheter days|
The clinical status of the patient is important in the development of infection. Many hospitalized patients, such as leukemia patients or transplant patients, have profoundly impaired immunity due to both their disease and therapy. These patients are highly susceptible to infection, frequently with organisms that do not cause infection in normal persons. Patients with neurologic problems may have swallowing difficulties due to aspiration of bacteria from the mouth or stomach, which can lead to pneumonia. Patients who have received antimicrobials may develop nosocomial infectious diarrhea caused by Clostridium difficile.
The hospital environment may also contribute to infections. Repeated outbreaks of Legionnaire's disease caused by organisms in a hospital's potable water or in air conditioning cooling towers have occurred. Increases in Aspergillus spores in the air during hospital construction cause fungal pneumonia in some immunocompromised patients, with a mortality rate of over 50 percent. Bacterial contamination of sterile intravenous fluids or equipment has repeatedly caused outbreaks of nosocomial infections. Finally, patients may acquire tuberculosis or chicken pox from other patients.
NATURE AND DIMENSION OF PUBLIC HEALTH PROBLEM
The high frequency of nosocomial infections places a substantial burden on individual patients and on the health care system. There is increased morbidity, including delayed wound healing, delayed rehabilitation, increased exposure to antimicrobial therapy and its potential adverse effects, and prolonged hospitalization. The average prolongation of stay is 3.8 days for urinary infection, 7.4 days for surgical-site infection, 5.9 days for pneumonia, and 7 to 24 days for primary bloodstream infection. Some infections, such as infection occurring in a hip or knee replacement, result in prolonged or even permanent disability and require repeated rehospitalization and reoperation. Nosocomial infections also cause mortality. The case-fatality rate for patients with ventilator-associated pneumonia is 42 percent, with an attributable mortality of 15 to 30 percent. For nosocomial bloodstream infection, the case fatality rate is 14 percent, with an estimated attributable mortality of 19 percent.
Nosocomial infections are costly. The direct costs of hospital-acquired infections in the United States is estimated to be $4.5 billion per year. In England, the cost for one health unit is estimated to be 3.6 million pounds per year. Prolongation of stay necessitated by nosocomial infection limits access of other patients to hospital resources, and contributes to overcrowding on wards and in emergency departments.
Nosocomial infections also contribute to the emergence and dissemination of antimicrobial-resistant organisms. Antimicrobial use for treatment or prevention of infections facilitates the emergence of resistant organisms. Patients with infection with antimicrobial-resistant organisms are then a source of infection for other hospitalized patients. Some bacteria, such as methicillin-resistant Staphylococcus aureus, may subsequently spread to the community.
CONTROL AND PREVENTION
Prevention of nosocomial infections requires a systematic, multidisciplinary approach. This is usually achieved under the leadership of an institutional infection-control program. The principle activities of such a program include surveillance, outbreak management, policy development, expert advice, and education. An optimal program may decrease the incidence of nosocomial infections by 30 to 50 percent.
Surveillance of nosocomial infections, by itself, may decrease the incidence. When each surgeon is provided with their own wound-infection rates and with other surgeons' rates for comparison, the institutional surgical-wound infection rate decreases. Outbreak control includes early identification of potential outbreaks, as well as evaluation and intervention if an outbreak is identified. Continuing education of hospital staff about the importance of, and their role in, preventing nosocomial infections is necessary. The infection-control program also provides expert consultation to other hospital programs such as occupational health, clinical microbiology, and pharmacy.
Institutional policies and practices must be developed and adhered to. In particular, optimal handwashing and glove use must be facilitated and reinforced, as transmission of organisms between patients occurs primarily on the hands of staff members. Isolation guidelines to identify and segregate patients who have an increased risk of transmitting infection to other patients or staff are also essential. Other important policies include: for urinary infection, the use and care of the indwelling catheter; and for surgical wound infection, optimal surgical technique including preoperative preparation and prophylactic antimicrobials. Many national or local standards and regulations will also prevent nosocomial infection, and institutions must be in compliance. These regulations cover hospital construction, municipal water supply, laundry management, food handling, waste disposal, sterilization and other reprocessing procedures, as well as standards for pharmacy and microbiology laboratory practice.
An effective infection-control program requires dedicated staff with appropriate training and sufficient resources. The number of personnel is determined by the size and complexity of the facility. Infection-control practitioners, usually from a nursing background, are responsible for program activity. In larger hospitals, program leadership is provided by a physician with training in epidemiology and infection control. Smaller facilities may obtain such expertise by contractual arrangement with outside experts. Oversight of the infection-control program is usually provided by a multidisciplinary infection-control committee. The program director, however, should report directly to senior hospital management to ensure optimal program effectiveness.
LINDSAY E. NICOLLE
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