How long do nosocomial pathogens persist on inanimate surfaces? A systematic review

BACKGROUND: Inanimate surfaces have often been described as the source for outbreaks of nosocomial infections. The aim of this review is to summarize data on the persistence of different nosocomial pathogens on inanimate surfaces. METHODS: The literature was systematically reviewed in MedLine without language restrictions. In addition, cited articles in a report were assessed and standard textbooks on the topic were reviewed. All reports with experimental evidence on the duration of persistence of a nosocomial pathogen on any type of surface were included. RESULTS: Most gram-positive bacteria, such as Enterococcus spp. (including VRE), Staphylococcus aureus (including MRSA), or Streptococcus pyogenes, survive for months on dry surfaces. Many gram-negative species, such as Acinetobacter spp., Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, Serratia marcescens, or Shigella spp., can also survive for months. A few others, such as Bordetella pertussis, Haemophilus influenzae, Proteus vulgaris, or Vibrio cholerae, however, persist only for days. Mycobacteria, including Mycobacterium tuberculosis, and spore-forming bacteria, including Clostridium difficile, can also survive for months on surfaces. Candida albicans as the most important nosocomial fungal pathogen can survive up to 4 months on surfaces. Persistence of other yeasts, such as Torulopsis glabrata, was described to be similar (5 months) or shorter (Candida parapsilosis, 14 days). Most viruses from the respiratory tract, such as corona, coxsackie, influenza, SARS or rhino virus, can persist on surfaces for a few days. Viruses from the gastrointestinal tract, such as astrovirus, HAV, polio- or rota virus, persist for approximately 2 months. Blood-borne viruses, such as HBV or HIV, can persist for more than one week. Herpes viruses, such as CMV or HSV type 1 and 2, have been shown to persist from only a few hours up to 7 days. CONCLUSION: The most common nosocomial pathogens may well survive or persist on surfaces for months and can thereby be a continuous source of transmission if no regular preventive surface disinfection is performed

4-Switch extended commutation cell

The extended commutation cell (ECC) is a four-port, four-switch cell that allows for bidirectional energy transport in two orthogonal directions throughout the cell. By cascading multiple cells, a multilevel converter can be constructed with a high number of levels. The voltage across each cell capacitor can be adjusted independently of the load, resulting in high flexibility in output levels. Improved fault tolerance is also provided

Comparison between dissipative snubber and passive regenerative snubber cells as applied to isolated DCM SEPIC converters

This paper presents the comparison between dissipative RCD and passive regenerative snubber cells for isolated SEPIC converters. The passive cell is \u3cbr/\u3eintended to improve the converter’s efficiency by transferring the energy stored in the transformer leakage inductance to the converter output. The analysis for both snubbers are detailed including design guidelines. In order to validate the regenerative proposal and compare its feasibility, experimental verification is performed for both snubbers on a 100 W, 100 V input and 50 V output voltage SEPIC converter operating in DCM

Flexbattery

A power conversion and energy storage device is provided that includes port A, port B, port C, port D, an internal battery cell Bt1 having a negative pole connected to port C and a positive pole connected to port D, internal nodes N1 and internal node N2, an inductor L1 having a negative terminal connected node N1 and a positive terminal connected to node N2, a switch S1 configured to open or close an electrical connection between port A and the node N1, a switch S3 configured to open or close an electrical connection between port C and node N1, a switch S2 configured to open or close an electrical connection between port B and node N2, and a switch S4 configured to open or close an electrical connection between port D and node N2, where a modular battery unit is formed

Load current corrected capacitor voltage control in eight-level DC-AC converter using extended commutation cells

The extended commutation cell is a four-port, four-switch cell that allows for bidirectional energy transport in two orthogonal directions throughout the cell. By cascading multiple cells a multilevel converter can be constructed with a high number of levels. The voltage across each cell capacitor can be adjusted independently of the load, resulting in high flexibility in output levels. This paper presents an improved method for capacitor voltage control, based on a system model and the measured output current. The proposed method is analyzed and verified on a 4.4 kW eight-level dc-ac converter. The obtained reduction in capacitor voltage ripple is more than 75%

Robust control of extended commutation cell based converters

An extended commutation cell (ECC) is a four-port four-switch power processing cell that allows for bidirectional energy transport in two orthogonal directions throughout the structure. By cascading multiple cells a high-quality output voltage waveform can be constructed with a high number of levels. In this paper a model of the internal energy flow, together with a robust control structure is proposed. The proposed structure is analyzed, simulated and experimentally verified on an eight-level inverter prototype of 4.4 kW

Robust control of extended commutation cell based converters

An extended commutation cell (ECC) is a four-port four-switch power processing cell that allows for bidirectional energy transport in two orthogonal directions throughout the structure. By cascading multiple cells a high-quality output voltage waveform can be constructed with a high number of levels. In this paper a model of the internal energy flow, together with a robust control structure is proposed. The proposed structure is analyzed, simulated and experimentally verified on an eight-level inverter prototype of 4.4 kW

Passive regenerative and dissipative snubber cells for isolated SEPIC converters: analysis, design, and comparison

An isolated converter such as SEPIC has high voltage stress on the main switch due to transformer leakage inductance. To solve this issue active or passive clamp action is necessary. The common passive solution based on an RCD snubber is simple but impractical when the value of the leakage inductance is significant. On the other hand, passive regenerative solutions generally compromise the isolation, making the search for a suitable snubber a challenge. In this paper, an effective passive regenerative snubber cell for isolated SEPIC converters operating in DCM or CCM is presented. It is intended to improve the converter efficiency by transferring the energy stored in the transformer leakage inductance to the output. The analysis is presented in detail for DCM and extended to CCM together with a practical design procedure. In order to compare with the RCD, the analysis and design of a conventional cell are presented as well. To validate the proposal and quantify its feasibility, experimental results are performed for both dissipative and regenerative snubbers on a 100 W, 100 V input and 50 V output voltage converter operating first in DCM and later in CCM

Flexible multilevel converters using four-switch extended commutation cells

The extended commutation cell is a 4-port, 4-switch cell that allows for bidirectional energy transport in two orthogonal directions throughout the cell. By cascading multiple cells a multilevel converter can be constructed with a high number of levels. The voltage across each cell capacitor can be adjusted independently of the load, resulting in high flexibility in output levels. In this paper the general theoretical analysis for this cell, including the necessary design tools is detailed. Experimental results of a 2-cell 8-level dc-ac converter are given. The outcomes are in good agreement with the analysis and simulation results