Disinfection: is it time to reconsider Spaulding?

The Spaulding classification, originally proposed in 1957, is a widely used system for matching the disinfection and sterilization of surfaces, particularly those of re-usable medical/surgical devices, with available processes. It presents a ranking, from simple disinfection through to sterilization, that should be considered in the reprocessing of devices, based on the risks associated with their use, ranging from 'critical' (presenting a high risk), through 'semi-critical' to 'non-critical' (presenting a low risk). The different levels of disinfection are based on demonstrating antimicrobial activity against established marker micro-organisms representing a range of pathogens. Although this classification system is probably as valid today as it was in 1957, the understanding of microbiology and micro-organisms has changed. This article discusses some examples of disinfection studies with viruses, bacteria, protozoa and prions that challenge the current definitions and expectations of high-, intermediate- and low-level disinfection. In many of these examples, the test micro-organisms demonstrate atypical tolerance or resistance profiles to disinfection processes. In addition to laboratory-based studies, there is now clinical evidence for at least some of these micro-organisms that biocide resistance can lead to infection outbreaks due to unexpected disinfection failure. These reports should encourage the reader to challenge current dogma, and reconsider the expectations of disinfection and sterilization practices.

Assessment of methods of destruction of Syphacia muris eggs.

An investigation was performed to identify methods suitable for decontamination of equipment being transferred from a facility contaminated with Syphacia muris to a new facility. Perianal samples were taken on clear sticky tape from rats known to be infected with S. muris. Tapes and attached worm eggs were treated with ethylene oxide, formaldehyde fumigation, potassium peroxysulphate, chlorine dioxide and didecyl di-methyl ammonium chloride, chlorine dioxide, alcohol/chlorhexidine, 100 degrees C dry heat for 30 min, ultraviolet light (UV), or left for 4 weeks at room temperature. The subsequent viability of the eggs was compared to untreated control samples. Heat and ethylene oxide produced a 100% kill rate of S. muris eggs. Formaldehyde gas and chlorine dioxide treatments showed marked effectiveness, with the number of eggs killed at 94% and 96%, respectively, while the other agents showed less efficacy (36-78% eggs killed). The percentage of eggs not hatching in the controls was 21%. Since so few agents were effective against S. muris eggs, care should be taken when choosing a method for decontaminating a facility.

Resource assessment and clutch size in the bean weevil, Acanthoscelides obtectus.

Bean weevil (Acanthoscelides obtectus (Say)) females were found to use seeds (discrete resource patches) differentially when different sizes were offered in multiple-choice tests. Females, either as a group or as individuals, laid significantly (two to six times) more eggs on large seeds than on those of five times smaller mass. In contrast, seed shape (flattened or spherical) did not contribute to clutch-size adjustment. Thus, A obtectus females seem to measure only relative seed size when a comparison is possible. Nevertheless, females overload seeds with eggs and this can result in larval competition, so that, whereas resource size assessment and a robust egg-load adjustment indicate a trade-off between resource use and female fitness, it does not seem to provide much benefit for the progeny in stored dry beans. Several features, eg the use of oviposition markers and its consequences, may counterbalance the possible negative effects. It is assumed that, due to life cycle differences, females in the bean field may realise different fitness gains in comparison with those living in stores.