It is important to recognize inadequate handwashing and the contaminated hand as the major factor responsible for the transmission of resistant pathogens in the hospital setting. One must not, however, unduly downplay the role of other vehicles in such transmission. It is often difficult to demonstrate the importance of environmental contamination in causing nosocomial infections, but there are sufficient examples in the literature of such occurrences to remind us that in certain settings environmental contamination clearly does lead to infection. Shared equipment such as electric thermometers (33), stethoscopes (34), endoscopes (35), breast pumps (36), and respiratory equipment (37) have all been implicated as vehicles for transmission of resistant pathogens. Similarly, plumbing fixtures have been responsible for outbreaks of resistant Pseudomonas aeruginosa (38) and Enterobacter cloacae (39) nosocomial infections, and contamination of an antiseptic containing soap led to an outbreak of Serratia marcescens infections in a neonatal intensive care unit (40).
Animate reservoirs may also play a role in the transmission of resistant bacteria, causing both endemic and epidemic nosocomial infections. The gastrointestinal tracts of both patients (41-44) and employees (41) have been identified as important reservoirs for resistant pathogens in hospital outbreaks. In the case of Clostridium difficile, asymptomatic colonization as well as symptomatic disease of the gastrointestinal tract remains the major reservoir of these organisms in endemic, hyperendemic, and outbreak settings (45,46). Colonized as well as symptomatic patients heavily contaminate multiple surfaces in their environment, as well as the hands of a substantial percentage of the health care workers caring for them.
Patients with chronic colonization of the urinary tract may be a source for nosocomial infections with resistant Gram-negative bacilli (47). Patients who have infected or colonized bum wounds with multiply resistant S. aureus (MRSA) heavily contaminate their immediate environment (48,49), leading to cross-infections in other patients in the unit. Similarly patients having pneumonia with MRSA can heavily contaminate their surroundings (14). While health care worker colonization with MRSA is infrequently a source of patient infections, certain health care workers do seem to have a tendency toward shedding the organism into the environment and transmitting the resistant bacteria to patients (50,51). Such transmission appears to be more likely when the health care worker has an upper respiratory tract infection or chronic dermatitis.
The epidemiology of resistant microorganisms in the hospital environment involves the complex interplay of antibiotic use; the clustering of ill, immunocompromised patients; and both animate and inanimate vehicles and reservoirs. While the precise origin of these microbes is often not identified, it is clear that excessive antibiotic use creates the environment that promotes their amplification, with such use being greatest in the intensive care unit. As antibiotic use may vary widely between different specialties within the same institution, it should not surprise us that different resistance patterns, and different species of resistant organisms, may be seen in differing areas of the hospital. Under the selection pressure of excessive antibiotic use resistant organisms may reach quite high levels in reservoirs such as the gastrointestinal tract, the urinary tract, and the mucous membranes. Patients so colonized may be totally unrecognized by their care givers, allowing for the heavy contamination of the surrounding inanimate environment. The hands of health care workers caring for these patients may become contaminated by direct patient contact or by contact with the contaminated environment. As hand washing practices in the absence, or often in the presence, of isolation precautions are often not optimal (2), the hands of health care workers, contaminated with highly resistant pathogens, readily transmit these organisms to other patients on the unit. It is for these reasons that many feel that any control strategies for containing antimicrobial-resistant pathogens in the hospital setting must include good infection control technique (11,12,21).
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