Residual Bactericidal Action of Wool Blankets Laundered with Formaldehyde: A Hospital Trial

Abstract

A hospital trial of wool blankets laundered with a 0*38'$(0 (w/v) solution of formaldehyde in the last but one rinse showed evidence of residual bactericidal action of the blankets. On removal from the beds after a fortnight's use, dirty treated blankets contained down to one tenth of the number of bacteria present on dirty untreated blankets. There were also fewer dirty treated than control blankets on which coagulase positive bacteria could bo detected. Chemical tests showed that the formaldehyde content of the blankets built up to c. 1%. No complaints were received of odour from the blankets.LABORATORY TESTS on formaldehyde laundered wool blankets, infected with micrococci mixed with cotton powder, indicated considerable residual bactericidal action under dry conditions (Dickinson & Wagg, 1967). Ward trials by Alder (pers. comm.) showed residual action by treated wool blanket samples, judged by the total bacterial count obtained from a percussion sampling method. For instance, blanket pieces that had been laundered 6 times with formaldehyde without intermediate use yielded < 60% the number of bacteria obtained from untreated pieces after several days' exposure on an occupied hospital bed. Moreover, there was no adverse patient reaction in ward trials with formaldehyde treated whole blankets.It seemed desirable therefore to investigate the effect of instituting a regular regime of formaldehyde laundering of wool blankets used on beds in a hospital ward.As judged by maceration, the total counts on the treated blankets, immediately after removal from the beds, were always lower than those on similarly used, but untreated, wool blankets. The control blankets were being subjected to regular disinfection by high temperature laundering, and the count from the treated blankets was sometimes only 1110th that from the controls, the effect becoming generally greater as the number of launderings increased. Counts by a percussion sampling technique showed a similar trend, but the numerical differences were smaller. From the second cycle onwards, the number of formaldehyde treated blankets on which coagulase positive organisms could be detected was always less than the number of control blankets.