The use of plastic isolators and of an ‘air curtain’ isolator for protection of patients against infection was studied in a burns unit.
Preliminary bacteriological tests showed that very few airborne bacteria gained access to a plastic ventilated isolator; even when the filter and pre-filter were removed from the air inflow, settle-plate counts inside the isolator were much lower than those in the open ward, but the difference was smaller in tests made with an Anderson air sampler, which showed also that fewer large bacteria-carrying particles appeared inside the isolator than outside it. An open-topped isolator allowed virtually free access of bacteria from ambient air. The numbers of airborne bacteria inside an air curtain were appreciably lower than the counts of airborne bacteria in the open ward, but not as low as those in the plastic ventilated isolator.
Controlled trials of isolators were made on patients with fresh burns of 4–30 % of the body surface; the patients were given no topical chemoprophylaxis against Staphylococcus aureus or Gram-negative bacilli. Patients treated in plastic isolators showed a significantly lower incidence of infection with Pseudomonas aeruginosa than those treated in the open ward; this protective effect was shown by isolators with or without filters or with an open top. Ventilated isolators, which protected patients against personal contact and airborne infection, gave a limited protection against multi-resistant ‘hospital’ strains of Staph. aureus, but no such protection was given by an open-topped isolator, which protected only against personal contact infection, or by air curtains, which protected only against airborne infection; the air curtain gave no protection against Ps. aeruginosa, and there was no evidence of protection by any isolator against Proteus spp. and coliform bacilli.
Both the controlled trials and evidence from the bacteriology of air, hands, fomites and rectal and nasal swabs taken on admission and later, supported the view that Ps. aeruginosa is transferred mainly by personal contact, Staph. aureus probably by air as well as by contact and coliform bacilli mainly by self infection with faecal flora, many of which are first acquired from the hospital environment in food or on fomites.
The use of plastic isolators is cumbersome, and of limited value except in the control of infection with Ps. aeruginosa. For this reason and because of the effectiveness of topical chemoprophylaxis such isolators are unlikely to have more than an occasional use in the treatment of burns. Though air curtains greatly reduce airborne contamination, their use in a burns unit does not appear to protect patients against infection when the alternative (and, for Ps. aeruginosa, more important) routes of contamination by personal contact and fomites are left open.