Isolation cohorting and contact isolation

Patients may need source isolation because they are infected and hazardous to others, or they may need protective isolation because their susceptibility to infection is increased. Such precautions against infection are often costly in money and the time of skilled staff and may be exasperating impediments to routine clinical work (Bagshawe et al., 1978; Barrett et al., 1998). Single room isolation may also precipitate psychological distress, particularly in the elderly (Tarzi et al., 2001). Cross-infection on wards, however, is difficult to prevent by routine measures, particularly if there is a staphylococcal disperser present. Both carriers and infected patients may heavily contaminate their immediate environment and release airborne particles carrying staphylococci (Boyce et al., 1997). Such patients should be isolated in a single room, if possible (Ayliffe et al., 1998).

Isolation is not generally practised without other basic hygienic procedures, so its impact on reducing staphylococcal spread in a hospital has to be assessed as part of an infection control package (Ayliffe et al., 1998). Furthermore, there are few, if any, studies examining the cost benefits of isolation as the single, or predominant, activity in control of MRSA. There is plenty of evidence, however, that isolation can facilitate control of endemic MRSA, including outbreaks and this in itself suggests that significant savings can be made from physically separating MRSA patients from others (Murray-Leisure et al., 1990; Shanson et al., 1985). In contrast, increasing the proximity of patients by adding a fifth bed to four-bedded bays significantly heightens the risk of cross-infection with MRSA (Kibbler et al., 1998). This supports the finding that the relative risk of MRSA acquisition increases with the colonization pressure from imported cases (Talon et al., 2003).

Hospitals can establish the use of specialised units with designated staff for control purposes (Fitzpatrick et al., 2000). An eight-bedded isolation unit in one large hospital was built specifically to control MRSA. The number of infections was more than halved in 2 years and further reductions occurred during the following 4 years (Selkon, 1980). A decrease in the spread of MRSA by use of isolation units was also observed in several London hospitals in the 1980s (Bradley et al., 1985; Dacre et al., 1986; Duckworth et al., 1988; Shanson et al., 1985). In contrast, a statistical model predicts that the risk of MRSA acquisition would increase by 160% per year in the absence of a dedicated cohort facility (Talon et al., 2003).

Hospitals without plentiful isolation facilities, or when overwhelmed with MRSA patients, have to be inventive when faced with control issues. Cohorting known positive patients together in ward bays is an option; if basic infection control practices are reinforced regularly, and there is access to flexible domestic support, spread of MRSA can be curtailed (Duckworth et al., 1988). Risk assessment regarding both patient and ward environment are helpful when considering control scenarios (Ayliffe et al., 1998; Wilson and Dunn, 1996). The establishment of an isolation facility on a temporary basis, however, may be required if the number of cases suddenly increases (Bradley et al., 1985; Cox et al., 1995).

Contact isolation is another control option for MRSA patients (Cohen et al., 1991; Jernigan et al., 1995), with or without cohorting (Arnold et al., 2002; Murray-Leisure et al., 1990). A theoretical cost-benefit analysis demonstrated that contact precautions could decrease the total days of MRSA isolation by 42%, prevent 8-41 infections each year, and decrease hospital costs by over $20,000 (Jernigan et al., 1995). Even the cost of gowns used for contact precautions can be reduced following the introduction of a programme of active surveillance cultures and immediate contact isolation for new ICU admissions (Muto et al., 2003). In the first 3 months of this particular programme, the incidence rate of MRSA decreased from 5.4 per 1,000 patient-days to 1.6 per 1,000 patient-days, while overall gown use decreased by 40% (Muto et al., 2003).

Contact isolation does not always control hospital-acquired MRSA, however, particularly if there is understaffing, unidentified carriers, unusual modes of transmission, or high carriage rates among patients on admission (Herwaldt, 1999). Infection control staff need to identify the reasons for persistent transmission and target their interventions specific to local circumstances (Herwaldt, 1999). Control can be achieved through a multifaceted approach, even in endemic situations. Patient cohorting, respiratory or contact isolation precautions, use of an isolation ward, and a hand hygiene programme significantly reduced the transmission of MRSA in one acute hospital (Herwaldt, 1999). The proportion of MRSA isolates decreased from 32% to 22%, the number of MRSA carriers was halved in 1 year and the rate of MRSA infections decreased from 2% to 0.2%. Furthermore, vancomycin expenditure decreased from $32,000 to $12,500 a year, saving the hospital $19,500 (Herwaldt, 1999).

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