Stability of neomycin resistance in Staphylococcus aureus.

A strain of Staphylococcus aureus isolated from the skin of a subject with eczema showed a loss in resistance to neomycin and tetracycline after treatment with neomycin was stopped. Seven out of 22 strains of neomycin-resistant Staph. aureus showed a loss in resistance to neomycin and streptomycin after storage in nutrient broth for 14 days at room temperature, and it seems probable that resistance in these unstable strains was controlled by extrachromosomal elements or plasmids. Strains of phage types 84/85 and 29/77 and related types were frequently isolated in general hospital wards and showed no loss in resistance on similar storage in nutrient broth. Five of the neomycin-unstable strains were isolated from patients with eczematous lesions. Multiple-resistant and antibiotic-sensitive strains of Staph. aureus of similar phage type were isolated from patients in a ward for patients with skin disease, and the possibility of transfer of resistance in vivo is discussed.

Wound infections acquired from a disperser of an unusual strain of Staphylococcus aureus.

Seven post-operative wounds were infected with a strain of Staphylococcus aureus, probably acquired from a theatre orderly who suffered from a dry generalized eczema. The orderly was a nasal and heavy skin carrier, and was shown to be a disperser of the epidemic strain. Infection was probably acquired from airborne contamination in the operating theatre, since the orderly did not scrub-up. The epidemic strain (phage type 80/81 at 1,000 routine test dilution) was sensitive to penicillin and resistant to tetracycline and novobiocin. Neomycin resistance was variable. This strain was found to lose resistance to neomycin when subcultured in the absence of the antibiotic.

In-use testing of disinfectants in hospitals.

One hundred and five samples of clear, soluble phenolic disinfectants were obtained from varying sites in the wards of six hospitals. The concentration of disinfectant in each sample was measured by a colorimetric method and bacterial contamination was measured by an ;in-use' test and a membrane filter technique. The concentrations of disinfectant in 24/105 (23%) samples were at the recommended level and 53 (50.5%) were below. Bacterial contamination with Gram-negative bacilli was found in 26/49 (53%) samples containing less than 0.8% of disinfectant and 5/86 (8.9%) samples containing more than 0.8%. The concentrations in two of the heavily contaminated samples were 1.5% and 1.6% respectively.

A membrane filter technique for testing disinfectants.

A membrane filter was used for assessing the surface disinfecting activity of phenolic disinfectants and a chloroxylenol disinfectant. The influence of the type of organism, inoculum size, and hardness of water was investigated. Pseudomonas aeruginosa was chosen for the standardized test. Disinfectant solutions were prepared in water of 300 ppm hardness and applied for two and a half minutes and eight minutes to the bacteria deposited from filtration of 1 ml of a suspension containing 10-6 bacteria. The membrane filter test has certain advantages over many tests, eg, all organisms surviving after treatment can be counted and residual disinfectant is easily removed.

Tests of disinfection by heat in a bedpan washing machine.

Tests of effectiveness of disinfection of metal and polypropylene bedpans were made in a washer fitted with a steam generator. Broth cultures of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, or Streptococcus faecalis (approximately 4 x 10(8) organisms) were sealed in lengths of capillary tubing and attached to the surface of the pans. In other tests, pans were contaminated with an artificial soil containing Str. faecalis (10(8) organisms/ml). In both series of tests, counts of surviving organisms were made at the end of the washing and disinfection cycle. The tests using capillary tubes showed that the Gram-negative bacilli were effectively killed, but not necessarily Gram-positive cocci. However, when incorporated in standard soil, Str. faecalis was killed or removed during the cycle. The results indicate that the disinfection process was effective for metal bedpans, but less so for polypropylene. Possible disadvantages and modification of the machine are suggested.

Resistotyping of Proteus mirabilis and a comparison with other methods of typing.

Resistotyping of P. mirabilis using 10 compounds is reported. The method was tested for reproducibility and specificity and results were compared with those obtained by serological, bacteriophage, and proticine typing methods and the Dienes test. The possible relationship between resistance to the chemicals used in the test and antibiotics was also studied.The method was found to be simple, reproducible, show good specificity, and compare favourably with other typing methods. No linkage between resistance to the chemicals and antibiotic resistance was detected.

Antibiotic-resistant Staphylococcus aureus in dermatology and burn wards.

Staphylococcus aureus isolated between 1967 and 1975 from the nose and skin lesions of patients in dermatology wards and from the burns of patients in a burns unit in Birmingham showed a high incidence of multiple antibiotic-resistant strains in both environments. Over 20% of the strains isolated from patients on admission to the dermatology wards were multiresistant. Resistance to benzylpenicillin, tetracycline, erythromycin, and fusidic acid was common in the dermatology wards; a smaller proportion of strains were resistant to lincomycin, and few (since 1972 none) were resistant to methicillin; resistance to novobiocin and chloramphenicol was uncommon. In the burns unit, fusidic acid resistance was uncommon, but resistance to benzylpenicillin, tetracycline, erythromycin, novobiocin, neomycin, methicilin, and lincomycin was common. Several of the antibiotics to which resistance was common in the burns unit were rarely if ever used there; strains resistant to these antibiotics probably remained common in the ward through the frequent use of other antibiotics, especially erythromycin, to which these strains were also resistant.

A test for 'hygienic' hand disinfection.

A standardised test procedure is described in which finger-tips are inoculated with broth cultures of organisms (Staphylococcus aureus, Staphyloccocus saprophyticus, Escherichia coli, and Pseudomonas aeruginosa): counts are made from washings of hands after disinfection with various antiseptic-detergents, alcoholic solutions, or unmedicated soap. 70% alcohol, with or without chlorhexidine, was the most effective preparation. The two antiseptic detergents showed variable results, but against Gram-negative bacilli neither was significantly more effective than plain soap. Some tests were also made on the death rate of organisms dried on the skin without disinfection.

Bacteriological sampling of postmortem rooms.

Thirty hospital and coroners' postmortem rooms in the West Midlands were visited over two years. The design, environmental facilities, and hygienic practices were investigated and air exchange rates were measured. Microbiological samples were taken from the environment and from gloves, hands, and protective clothing of staff. Glove punctures were also recorded and a plastic isolator evaluated. Bacterial counts in the air were low and related more to the number of people in the room than to the air exchange rate. There was little evidence of the production of aerosol containing bacteria, although splashing occurred while intestines were being washed out. Surfaces often remained contaminated with Gram negative bacilli after cleaning but numbers were considerably reduced on drying. Decontamination of instruments was satisfactory. A wide range of disinfectants and concentrations was used, but none showed evidence of contamination. Gloves were heavily contaminated after use, and occasionally the hands of the wearer after removal of the gloves. Washing the hands effectively removed residual transient organisms, irrespective of the agent used. The incidence of glove punctures was higher among technicians (38%) than pathologists (12%). The plastic isolator reduced smells and limited environmental contamination but visibility and acceptability were poor. The results of the study suggest that there is little evidence of risk of infection to staff, providing basic hygienic precautions are taken, but consideration should be given to the prevention of glove punctures.

A surface test for virucidal activity of disinfectants: preliminary study with herpes virus.

A test was developed to assess the surface activity of disinfectants against dried viral preparations. In this preliminary study a variety of disinfectants was tested against herpes virus. The results showed that 2% alkaline glutaraldehyde and 70% ethanol or isopropanol were effective in 1 min. Hypochlorite solutions (2500 ppm av. Cl2) were effective in 5 min, but povidone-iodine (10%) was slower in action and a clear soluble phenol showed uncertain activity at 5 and 10 min. High concentrations of alcohols (above 95%), two quaternary ammonium compounds and 0.5% aqueous chlorhexidine showed little activity in 10 min.

An outbreak of candidiasis in a special care baby unit: the use of a resistogram typing method.

An outbreak of candida infections involving 12 neonates in a special care baby unit is reported. An investigation of colonization of all the babies in the unit was made together with the sampling of the environment and hands of staff. Resistogram typing of isolates indicated the presence of several strains with probable cross-infection. Transmission was possibly by the hands of staff, but multiple antibiotic therapy may have played a role in the increased incidence of infection in the unit.

Risk of airborne transmission in an operating theatre containing four ultraclean air units.

This study shows that a single, large, operating theatre (barn) containing four ultraclean operating units (cabins), was highly effective in reducing the number of airborne bacteria in the operating fields providing all occupied ultraclean cabins were functioning correctly. The air flows and bacterial counts during operations within the cabins met the current standard for ultraclean systems (HTM 2025 1994) and there was no evidence of mixing of air between cabins. It is, however, recommended that air flows are regularly checked for compliance with the standard. If failure occurs in any single ultraclean unit, surgery in that cabin should cease as contaminated air may enter from the barn and surrounding cabins. Routine microbiological sampling should not be necessary providing there is no evidence of filter leakage. An operating theatre with several ultraclean operating tables in a single room would appear to be a viable proposition for the future. Considerable savings are likely in revenue costs as much of the air is reused and support services are shared.

Virucidal activity of disinfectants: studies with the poliovirus.

The activity of various disinfectants against poliovirus (Sabin 1 an) was assessed using surface and suspension tests. The surface test showed that 2% glutaraldehyde and high concentrations of hypochlorites (9200 ppm avCl2) were effective (i.e. greater than or equal to 4 log10 reduction) against a dried virus suspension in 1 min. Diluted aldehydes ('Sporicidin' and 'Gigasept'), lower hypochlorite concentrations (1000 ppm avCl2) and peroxides (3%) were less effective while 70% ethanol showed variable results; 70% isopropanol was ineffective in 10 min. In the suspension tests hydrogen peroxide (3% and 6%) and 70% ethanol were ineffective in 1 min.

Evaluation of the Steris System 1 Peracetic Acid Endoscope Processor.

An automated endoscope sterilizing machine, the Steris System 1 Processor, was tested for bactericidal and sporicidal efficacy. The disinfectant, peracetic acid, was diluted to 0.2% within an enclosed system. The exposure time to the disinfectant was 12 min and the overall cycle time ranged from 25-38 min, mean 29 min. Preliminary suspension tests, with and without yeast or serum, showed a log10 reduction of > 5 with Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis in 5 min with 0.2% peracetic acid. After a routine cycle in the machine, endoscopes contaminated with the same organisms showed no growth. Two of 24 spore strips, containing 10(6) B. subtilis showed a small number of survivors (less than 10 per strip). No significant damage to the endoscope was observed although the number of cycles tested was small (i.e. 31). The advantage of the system is that staff are not directly exposed to the agent, but the costs per cycle are higher than glutaraldehyde, since peracetic acid is not renewed. Unlike other automated processors the Steris machine has no cleaning cycle.

A mathematical model for assessing risk of postoperative wound infection.

A mathematical model for predicting the risk of acquisition of postoperative wound infection in individuals or groups of patients is described. It is based on data from prevalence surveys of 41 hospitals and includes 1980 wounds. The factors included in the model, i.e., age, sex, length of pre-operative stay, type of operation, wound drainage, number of occupied beds in ward, and special factors, e.g., diabetes, steroid therapy, were obtained by stepwise regression analysis of the original data. Most of the ward facilities and practices were excluded as non-significant. The model has been modified for use with incidence studies and its accuracy confirmed in a further 1331 patients by comparing predicted and recorded infection rates.

Comparison of automated systems for the cleaning and disinfection of flexible fibreoptic endoscopes.

A comparison of four cleaning and disinfection machines is described. These varied considerably in design and function and although no single machine possessed all the preferred characteristics, cleaning and disinfection, particularly between patients, was substantially improved. Before purchasing a machine it is recommended that the user ensures that it is convenient to operate, effective in removing soil and bacteria, and adaptable to the range of fibrescopes used within the unit. Infections are often caused by Gram-negative bacilli which are particularly difficult to remove manually from moist narrow channels of the fibrescope and perfusion of all channels including the air channel, is, therefore, recommended. Thorough cleaning and disinfection will not only reduce the likelihood of infection but will also reduce channel blockages and the general deterioration of the fibrescope.

Contamination of protective clothing and nurses' uniforms in an isolation ward.

Staphylococcus aureus was frequently isolated, usually in small numbers, from cotton gowns (12.6 per cent), plastic aprons (9.2 per cent) and nurses' uniforms (15 per cent). Gram-negative bacilli were infrequently isolated. Contamination of the protective clothing did not increase when used over periods of up to 11 days. Fewer organisms were recovered from the front of nurses' uniforms when plastic aprons instead of gowns were worn, but gowns provided better shoulder protection. However, no differences were observed in isolations of Staph, aureus or Gram-negative bacilli from these sites.

A test procedure for evaluating surgical hand disinfection.

A technique for assessing the immediate and prolonged efficacy of surgical scrubs and alcoholic hand rubs is described. A mean baseline count is obtained from all volunteers and logarithmic reductions in resident skin flora immediately after one or more applications, and after wearing gloves for 3 h, are measured. Loose-fitting surgical gloves are used for sampling resident flora. Preparations were applied using a standard technique for 2 min, apart from one test with 70% isopropanol (IPA) in which the application time was 30 s. Two studies are described, one of which compared four chlorhexidine scrubs, and the second 70% IPA, 7.5% povidone-iodine scrub, 2% triclosan cleanser and unmedicated bar soap. In spite of their constituent similarity, the four chlorhexidine scrubs varied considerably in efficacy and user acceptability. A 2 min application of 70% IPA was the most effective treatment, and gave log10 reductions of 1.65 for immediate and 1.58 for prolonged effect. This was marginally more effective than a 30 s application, but the difference was not significant. 'Hibiscrub' was the most effective aqueous formulation and gave reductions of 1.01 for immediate effect and 1.16 for prolonged effect. The test described could be used by reference centres and manufacturers to assess the efficacy of new and existing surgical hand disinfection formulations.

Bacterial contamination and frequency of changing ventilator circuitry.

A questionnaire sent to 40 intensive care units showed that ventilator circuits were changed every 24 h in 62% and every 48 h in 20% of the units. A similar survey in 40 special-care baby units showed that only 9.7% changed circuits daily and the majority were changed weekly (38.7%) or between patients (38.7%). A prospective study of bacterial contamination of circuits in adult patients showed that when water humidification was used, 28/72 samples from inspiratory and 31/72 from expiratory tubing were contaminated with Gram-negative bacilli. None of 48 sets of tubing was contaminated when a heat-moisture exchanger was used and only one expiratory tube was contaminated in tubing from 45 neonates using a water humidifier. Gram-negative bacilli were isolated from the mouths of 21/36 adults and 6/12 neonates, and also from 6/17 hands of staff after changing circuits. It is suggested that circuits with water humidification may be changed every 48 h in adult patients, and between patients or weekly in neonatal units or between patients if a heat-moisture exchanger is used. Handwashing after removal of a circuit is of major importance in the prevention of spread of infection.

A test for the assessment of 'hygienic' hand disinfection using rotavirus.

A standardized test procedure is described in which finger tips are inoculated with bovine rotavirus. The level of virus recovered after disinfection of artificially contaminated hands with various disinfectant detergents, alcoholic solutions and alcoholic formulations was determined. The method was found to be easy to perform and reproducible. The most efficient method for removal of virus from fingertips was found to be treatment with alcoholic solutions or products. Soap and water and disinfectant detergents were found to be a much less effective method of removing virus from contaminated hands.