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Objective To evaluate the evidence for the effectiveness of isolation measures in reducing the incidence of methicillin resistant Staphylococcus aureus (MRSA) colonisation and infection in hospital inpatients.

Methicillin-resistant Staphylococcus aureus (MRSA) represents a serious threat to the health of hospitalized patients. Attempts to reduce the spread of MRSA have largely depended on hospital hygiene and patient isolation. These measures have met with mixed success: although some countries have almost eliminated MRSA or remained largely free of the organism, others have seen substantial increases despite rigorous control policies. We use a mathematical model to show how these increases can be explained by considering both hospital and community reservoirs of MRSA colonization. We show how the timing of the intervention, the level of resource provision, and chance combine to determine whether control measures succeed or fail. We find that even control measures able to repeatedly prevent sustained outbreaks in the short-term can result in long-term control failure resulting from gradual increases in the community reservoir. If resources do not scale with MRSA prevalence, isolation policies can fail ''catastrophically.''

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The characteristics of bursts of spectral type II are studied in a sample of 65 bursts. Approximately half the bursts show harmonic structure and about half are compound type III-type II events. Band splitting, the doubling of both the fundamental and second harmonic bands, is also relatively common. A rather less common feature is the appearance of herring-bone structure in which the slowly drifting band of the type II burst appears to be a source from which rapidly drifting elements diverge towards lower and higher frequencies.Statistics are given of the rate of occurrence of the bursts, their frequency range, the rate of frequency drift, and the harmonic ratio There is a greater tendency for the geomagnetic field to be disturbed in the few days following a type II burst than there is after large flares which are not accompanied by type II bursts, or after large radio bursts of spectral type III. Statistically the greatest disturbance occurs after about two days, implying a mean speed of travel of about 1000 km/sec.

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SummaryWhen an aerial is used to survey the distribution of radio brightness over the sky, the observed distribution is smoother than the true distribution; the broader the beam of the aerial, the greater the smoothing. It is shown that the aerial does not register those spatial Fourier components of the true distribution having frequencies beyond a cut-off determined by the aerial aperture. Components of lower frequency are registered but their relative strengths are altered.Two important consequences follow. (i) There are invisible distributions which produce no response when scanned by the aerial. Consequently there is not a unique solution to the problem of correcting for aerial smoothing. The established method of correcting by successive smoothing, leads to the principal 8olution, in which Fourier components accepted by the aerial have been restored to their full values, but the components rejected by the aerial are still not represented. (ii) In conducting a survey it is sufficient to observe at discrete intervals. The measuring points must be closer together than half the period of the Fouri,er component at cut-off. For an aperture of width w, this peculiar interval is equal to fA/w (radians).