An epidemiological survey of methicillin-resistant Staphylococcus aureus in a tertiary referral hospital.

Over a 30-month period from July 1995 to December 1997, new detections of methicillin-resistant Staphylococcus aureus (MRSA) were prospectively studied in a tertiary referral hospital. The aims of the study were to determine the incidence of colonization of patients admitted to each of the hospital's 39 clinical units and ascertain where each patient had become colonized. Epidemiological information (time to detection, ward movement, admission to other hospitals, data on MRSA isolations in hospital wards) and phage typing were used by the hospital's infection control unit to make this determination. Routine containment procedures included cohorting, flagging and triclosan body washes. Surveillance cultures were collected infrequently. Patients known to be colonized with MRSA were excluded from orthopaedic and haematology wards. During the study period, 995 patients were found to be newly colonized. The incidence of colonization varied from nil to 72 per 1000 admissions, being highest in the main intensive care unit and in services which frequently used that unit. The incidence of colonization in elective orthopaedic surgery (< 1 per 1000) and haematology (3 per 1000) was very low. Determining the place where patients acquired MRSA was made difficult by the high frequency of endemic phage types and frequent patient transfer between wards. Epidemiological data suggested that the main intensive care unit and surgical wards nursing patients with colorectal, urological and vascular diseases were the places where most patients became colonized. MRSA was never acquired by patients nursed in wards which practised an exclusion policy towards patients known to be colonized with MRSA. Our data suggest that in tertiary referral hospitals, where MRSA is not only endemic but frequently imported from other hospitals, it is possible to establish areas where MRSA is never acquired.

A prospective survey of current methicillin-resistant Staphylococcus aureus control measures.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is now endemic in tertiary referral hospitals among the developed world. By prospective survey, the effect of two measures aimed to reduce the spread of MRSA was determined. First, a surgical ward with persistently high levels of MRSA detection was cleaned and renovated. Second, the medical records of all MRSA-colonized patients were electronically flagged, facilitating immediate application of control measures on readmission. METHODS: Data were collected for 995 newly colonized patients admitted between 1 July 1995 and 31 December 1997. Methicillin-resistant Staphylococcus aureus detection was determined before and after implementation of the interventions, along with the likely place of MRSA acquisition and the monthly incidence of MRSA detection for all inpatients. Chi-squared testing with odds ratios and 95% confidence intervals determined associations between the effect of control measures studied and MRSA detection rates. RESULTS: New MRSA detection was 21.6 per 1000 admissions before refurbishment compared with 20.4 per 1000 admissions to the surgical ward after refurbishment. New MRSA detection averaged 6.4 per 1000 hospital admissions before the introduction of record flagging and patient cohorting, compared with 6.2 per 1000 admissions after. CONCLUSION: Neither ward refurbishment, nor introduction of flagging, significantly reduced rates of colonization during the study period. In hospitals that receive MRSA-colonized patients and provide intensive care facilities, spread of MRSA is a major problem. Effective containment demands separate wards for MRSA-colonized and non-colonized patients. The need for such containment should be considered in design of the modern hospital.

Phages for methicillin-resistant Staphylococcus aureus: an international trial.

An internationally agreed and validated set of phages is used worldwide for the typing of strains of Staphylococcus aureus of human origin. However, because of the sometimes reduced susceptibility of methicillin-resistant strains (MRSA) to these phages, some of the national typing centres use locally isolated and characterized sets of experimental phages. In this trial, 42 such phages were distributed to 6 centres and tested against 744 isolates of MRSA with the intention of defining a phage set to augment the international set. The use of these experimental phages increased the percentage typability from 75% with the international set to 93% and the number of identifiable lytic patterns from 192 to 424. A subset of 10 experimental phages was selected. When this subset was compared with the experimental panel, the typability rate was 91% and 370 distinct patterns were obtained. This subset of phages has been distributed for international trial.

Strains of methicillin-resistant Staphylococcus aureus isolated in Australian hospitals from 1986 to 1990. Australian Group for Antimicrobial Resistance.

Major teaching hospitals in each state of Australia participated in five annual surveys (1986 to 1990) of clinically significant isolates of Staphylococcus aureus. All isolates of methicillin-resistant S. aureus (MRSA) were phage typed with the Basic International Set and an Australian experimental set of typing phages. One or two predominant strains were isolated in individual states during each of the survey periods. Less than 3% (33 of 1243) of MRSA isolates were not typable and more than 86% (1070 of 1243) belonged to strains that were isolated on at least five occasions during a single survey period. Strains of phage types 83A/85/95/90/88@47T/90A/87M/13M and 85/90/88@47T/90A/87A were the most prevalent, but each was identified in only four of the five surveys. Isolates of phage type (83A/85/95) weak/88@87M persisted throughout the survey period.

Impact erosion of the primordial atmosphere of Mars.

Abundant geomorphic evidence for fluvial processes on the surface of Mars suggests that during the era of heavy bombardment, Mars's atmospheric pressure was high enough for liquid water to flow on the surface. Many authors have proposed mechanisms by which Mars could have lost (or sequestered) an earlier, thicker atmosphere but none of these proposals has gained general acceptance. Here we examine the process of atmospheric erosion by impacts and show that it may account for an early episode of atmosphere loss from Mars. On the basis of this model, the primordial atmospheric pressure on Mars must have been in the vicinity of 1 bar, barring other sources or sinks of CO2. Current impact fluxes are too small to erode significantly the present martian atmosphere.

A study of coagulase-negative staphylococci isolated from clinically significant infections at an Australian teaching hospital.

Some 151 isolates of coagulase-negative staphylococci isolated from patients at an Australian teaching hospital were characterized by biochemical analysis, antibiotic sensitivity patterns and slime production. S. epidermidis was the predominant species (64%) isolated from clinically significant infections, and all S. epidermidis isolates from true bacteremias produced slime. Forty-nine per cent were resistant to methicillin and 61% to gentamicin. S. haemolyticus isolates from clinically significant infections also showed antibiotic resistance and 80% were resistant to more than five antibiotics. The importance of coagulase-negative staphylococci as pathogens in this large teaching hospital was confirmed.

Observations on the resistance to drying of staphylococcal strains.

Death rates have been determined for staphylococcal strains dried on cotton blanket material and stored at room temperature in the dark and in the light. Methicillin-resistant Staphylococcus aureus (MRSA) strains that produced a golden pigment and had a wide distribution within the hospital survived for longer periods than MRSA strains that produced little pigment and had a restricted local distribution. Death rates of methicillin-sensitive strains of S. aureus at day 7 were similar to those of the general epidemic MRSA strains, and there was no significant difference between the death rates at day 7 of the local epidemic MRSA strains and the coagulase-negative strains.

The Large Crater Origin of SNC Meteorites.

A large body of evidence strongly suggests that the shergottite, nakhlite, and Chassigny (SNC) meteorites are from Mars. Various mechanisms for the ejection of large rocks at martian escape velocity (5 kilometers per second) have been investigated, but none has proved wholly satisfactory. This article examines a number of possible ejection and cosmic-ray exposure histories to determine which is most plausible. For each possible history, the Melosh spallation model is used to estimate the size of the crater required to produce ejecta fragments of the required size with velocities >/=5 kilometers per second and to produce a total mass of solid ejecta consistent with the observed mass flux of SNC meteorites. Estimates of crater production rates on Mars are then used to evaluate the probability that sufficiently large craters have formed during the available time. The results indicate that the SNC meteorites were probably ejected from a very large crater (> 100 kilometers in diameter) about 200 million years ago, and that cosmic-ray exposure of the recovered meteorites was initiated after collisional fragmentation of the original ejecta in space at much later times (0.5 to 10 million years ago).

Phage-typing patterns and lysogenicity of methicillin-resistant strains of Staphylococcus aureus from Sydney, Australia, 1965-85.

Methicillin-resistant strains of Staphylococcus aureus isolated at the Royal Prince Alfred Hospital since 1965 were differentiated by phage-typing and by their lysogenic status. Most of these strains were isolated during two periods, 1965-72 and 1976-85. Nearly all of the strains isolated in the first period had one of four phage-typing patterns. Strains with each typing pattern carried two prophages; these eight phages were all different, as characterised by serological grouping and lytic spectrum. Lysogenisation of the non-lysogenic strain 1489 with each of these phages narrowed its phage-typing pattern; the typing pattern of the double lysogens was generally similar to and occasionally identical with that of the host strain that had yielded the pair of phages. In the second period, strains with one of five other phage-typing patterns predominated. Representatives of each of these carried the lysogenic phage C. The first methicillin-resistant strain carrying this phage had been isolated in 1974. The current methicillin-resistant S. aureus strains thus appear to form a distinct group that can be differentiated from those seen in earlier years.

Lysogenicity of methicillin-resistant strains of Staphylococcus aureus.

The lysogenic status of 23 strains of methicillin-resistant Staphylococcus aureus, isolated at the Royal Prince Alfred Hospital, Sydney, since 1980, was studied. Twenty strains, belonging to the four predominant phage types isolated in this hospital, carried the same lysogenic phage which we have designated C. Three other phages were isolated from five strains belonging to phage type 84/85/90. The presence of phage C had little effect on the phage-typing pattern of the strains. Similarly, lysogenization with the other three phages did not result in a significant change in phage-typing patterns. However, when strain 1489, isolated in 1969, was lysogenized with these three phages, there was a change in phage-typing pattern. Lysogenization of this strain with phage 47T resulted in a marked loss of sensitivity to both group-I and group-III phages. The lysogenic status of these methicillin-resistant strains of S. aureus was compared with that of strains isolated between 1967 and 1970. There was no evidence that the strains isolated recently were either related to, or derived from, the earlier ones.

Strain differentiation in methicillin-resistant Staphylococcus aureus.

Three different systems were used to test 236 isolates of methicillin-resistant Staphylococcus aureus in an attempt to ascertain if more than one strain is responsible for the current problem of cross-infection by this organism in N.S.W. hospitals. The biochemical tests used were of little assistance. Phage typing, using the Basic International Set of typing phages at 100 x routine test dilution (RTD), provided evidence of the presence of several different strains. Phage type 83A/85/95/90/88 was the typing pattern of the predominant strain and the nest most frequent group was not typable. These results were often difficult to read. Five new phages were therefore isolated and found to be valuable as they produced easily identifiable patterns at RTD.