Airborne Transmission Of Infection Research Articles

An alternative approach to delivering safe, sustainable surgical theatre environments

Outcomes are reported from an antimicrobial-resistance research initiative into the infection control offered by downward laminar-flow ventilation in hospital operating theatres. Pre-cooled air is forced down onto the patient with the intention of diverting airborne pathogens from the surgical wound. The concept was commercialised in the early 1970s as the Ultra Clean Ventilation (UCV) system, a commonly applied contemporary solution. Data collected by the authors in unoccupied UCV theatres in a recently completed acute hospital indicate that as the warming air descends into the occupied zone, it may be subject to recirculation within the suite of spaces. This phenomenon is confirmed by the authors’ experimental modelling. Increasing the residence time of microorganisms will increase the probability of surgical site infection (SSI). An alternative is proposed: an upflow displacement ventilation scheme in combination with a localised source of filtered air to ventilate the wound as required. Likely ventilation flows are modelled experimentally and compared with those of the downdraught-ventilated UCV type. The alternative arrangement appears to provide comparable risk of SSI, while requiring less energy to drive the ventilation system. The concept is developed into a novel surgical theatre proposal in which background airflows are driven by natural buoyancy. <em><strong>Policy relevance</strong></em> It is doubtful that the UCV configuration for surgical theatres fulfils its original design intent. New evidence contributes to an evolving concern that the system may not eliminate the risk of SSIs of airborne origin. If airborne transmission of infection in surgery is, in practice, a very minor concern, as some surgeons believe the resource-intensive UCV configuration is unnecessary. At a global scale, surgical equity is not served by the complexity, capital and operating costs of this model with its high maintenance burden. The alternative upflow-ventilated surgical theatre described, being a configuration rather than a product, could be created by using locally available construction.

Effects of temperature, humidity, air quality and anthropic activities on the transmission of SARS-CoV-2: a systematic review protocol

IntroductionThe current global pandemic of the virus that emerged from Hubei province in China has caused coronavirus disease in 2019 (COVID-19), which has affected a total number of 900 036...

Engineering control of respiratory infection and low-energy design of healthcare facilities

Indoor microorganisms and infection have become an emerging direction in indoor air quality research science. Airborne droplet nuclei can serve as carriers of respiratory infectious diseases. The study of expiratory droplets and their exposure control has received particular attention since the 2003 severe acute respiratory syndrome epidemics and the 2009 influenza pandemics. Little is known about how effective the commonly used indoor environment control strategies are for infection control. Significant questions also exist on the ventilation requirements for airborne infection control. There is a broad range of relevant important issues, including the exposure risk, and effective control methods in various indoor settings, such as hospitals, homes, schools, and offices. What is known is that the minimum required ventilation rate for infection control in hospitals can be much higher than the general health and comfort requirement in homes and offices. This has resulted in significant energy-efficiency issues in healthcare facilities. This review considers the current knowledge on airborne transmission of infection and the potential implications of a move to low-energy design, particularly in hospitals, on the risk of infection. The review outlines active research and development on reducing hospital energy use while improving infection control and discusses the potential for conducting “clinical trials” to gain the necessary evidence to support changes in hospital ventilation design.

Airborne transmission of disease in hospitals

Hospital-acquired infection (HAI) is an important public health issue with unacceptable levels of morbidity and mortality, over the last 5 years. Disease can be transmitted by air (over large distances), by direct/indirect contact or a combination of both routes. While contact transmission of disease forms the majority of HAI cases, transmission through the air is harder to control, but one where the engineering sciences can play an important role in limiting the spread. This forms the focus of this themed volume. In this paper, we describe the current hospital environment and review the contributions from microbiologists, mechanical and civil engineers, and mathematicians to this themed volume on the airborne transmission of infection in hospitals. The review also points out some of the outstanding scientific questions and possible approaches to mitigating transmission.

Pyjamas and sheets as a potential source of nosocomial pathogens

It is recognised that the most important and frequent mode of transmission of nosocomial infections is through direct contact between a susceptible host and an infected or colonised person. Direct contact is mainly attributed to healthcare workers who do not wash their hands effectively before attending patients. Additionally, susceptible hosts may be infected indirectly via intermediate objects, such as contaminated instruments, needles, dressings, or gloves. 1 Gastmeier P. Stamm-Balderjahn S. Hansen S. et al. Where should one search when confronted with outbreaks of nosocomial infection?. Am J Infect Control. 2006; 34: 603-605 Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar A healthcare worker who touches pathogens on contaminated surfaces can then transport these pathogens to patients by the contact route. Indeed, the sources of contamination in 21.1% of 1561 nosocomial outbreaks studied have been attributed to contaminated surfaces. 1 Gastmeier P. Stamm-Balderjahn S. Hansen S. et al. Where should one search when confronted with outbreaks of nosocomial infection?. Am J Infect Control. 2006; 34: 603-605 Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar Importantly, most common nosocomial pathogens may persist on surfaces for months and can thereby be a continuous source of transmission. 2 Kramer A. Schwebke I. Kampf G. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect Dis. 2006; 6: 130 Crossref PubMed Scopus (1516) Google Scholar Another form of contact spread is via endogenous transmission of the patient's own flora from one part of the host's body to another. 3 Kropec A. Huebner J. Riffel M. et al. Exogenous or endogenous reservoirs of nosocomial Pseudomonas aeruginosa and Staphylococcus aureus infections in a surgical intensive care unit. Intensive Care Med. 1993; 19: 161-165 Crossref PubMed Scopus (48) Google Scholar Recently, the notion that airborne transmission of bacteria contributes significantly to hospital-acquired infections is gaining recognition. 4 Beggs C.B. The airborne transmission of infection in hospital buildings: fact or fiction?. Indoor Built Environ. 2003; 12: 9-18 Crossref Scopus (147) Google Scholar Although a better understanding of how nosocomial pathogens are transmitted and more rigorous infection control measures are being implemented, it is clear that the current modalities to reduce nosocomial infections are not sufficient, as the rates of nosocomial infections, especially those caused by antibiotic-resistant bacteria, are increasing alarmingly worldwide.

The airborne transmission of infection between flats in high-rise residential buildings: Particle simulation

Several case clusters occurred in high-rise residential buildings in Hong Kong in the 2003 SARS (the severe acute respiratory syndrome) epidemic, which motivated a series of engineering investigations into the possible airborne transport routes. It is suspected that, driven by buoyancy force, the polluted air that exits the window of the lower floor may re-enter the immediate upper floor through the window on the same side. This cascade effect has been quantified and reported in a previous paper, and it is found that, by tracer gas concentration analysis, the room in the adjacent upstairs may contain up to 7% of the air directly from the downstairs room. In this study, after validation against the experimental data from literatures, Eulerian and Lagrangian approaches are both adopted to numerically investigate the dispersion of expiratory aerosols between two vertically adjacent flats. It is found that the particle concentration in the upper floor is two to three orders of magnitude lower than in the source floor. 1.0 μm particles disperse like gaseous pollutants. For coarse particles larger than 20.0 μm, strong deposition on solid surfaces and gravitational settling effect greatly limit their upward transport.

Hospital infection past and present

Why does so much hospital infection still exist despite the attention that it attracts? There were about 9·6 million UK National Health Service (NHS) hospital admissions in 2002–03. 5–10% of inpatients acquire an infection during their stay, and thus about 0·5–1·0 million hospital infections occur each year in the UK alone. Graham Ayliffe and Mary English offer a fascinating account of how the relation between hospitals and infection has altered through the centuries, mainly because of the realisation that many diseases were not a result of bad air (miasma). Although we now understand routes of cross-infection and have preventive strategies for most of these, understanding how beliefs and approaches to hospital infection have changed is instructive for challenges that still exist. In Roman times, hospital orderlies were known as nosocomi, the word deriving from Latin and Greek words for hospital. It is appropriate that in modern times nosocomial (meaning hospital acquired) is so closely linked to an old name for health-care workers. Health-care workers remain inadvertently responsible for most cases of cross-infection, either directly or indirectly via their hands. Airborne transmission of infection is now an uncommon cause of most hospital-acquired infections, but miasmas were widely espoused from the 6th to the 19th centuries as the way in which disease was spread. Ironically, however, there are examples of infections that may be transmitted by aerosols, which continue to confound us. Why have hospitals been over-run by outbreaks of viral gastroenteritis for much of the past 2years? How did severe acute respiratory syndrome spread so dramatically in modern well equipped hospitals? How would we cope with new cases of smallpox? As Ayliffe and English point out, it is still unknown how some of the last cases of hospital-acquired smallpox were contracted. The prevention and control of hospital infection must be underpinned by surveillance, which was pioneered in the USA, notably by the work of Robert Haley in the 1970s. These studies showed that intensive surveillance, feedback to clinicians, and a control prog-ramme could cut rates of hospital infection by about a third. Clinician feedback is fundamental to sharing the responsibility for controlling hospital infection. The US Communicable Disease Center established the National Nosocomial Infections Scheme, which runs to this day and has been copied in many countries. The UK Department of Health has recognised that standardised surveillance methods that are affordable and yet based on Haley's principles are one way forward. These allow comparison of infection rates or proxy measurements between units, but clearly case mix and unit type must be borne in mind; meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia rates are now one of the performance indicators for NHS trusts. This book has many evocative photographs and illustrations. One of these, a Nightingale ward in 1900, reminds me of the picture on my office wall. My grandmother and other nursing staff replete in their starched uniforms are grouped around the ward. Both photographs ooze cleanliness and order, but both are filled with empty beds. The high number and turnover of patients is a major modern day obstacle to ensuring good infection-control practice. Ayliffe and English note that persuading staff to do the basics now seems to be as difficult as it was for Ignaz Semmelweis. Unfortunately, Semmelweis, dismayed by the reluctance of his peers to believe his exhortations about the need to wash their hands to control the spread of puerperal sepsis, was eventually committed to a sanatorium in Vienna, where he died of septicaemia in 1865. Shortly after Semmelweis died, Joseph Lister's first paper on antisepsis was published. In 1999, a UK NHS Executive Health Service Circular instructed health-care providers to strengthen the prevention and control of communicable disease and infection-control processes. Specifically they were asked to “put infection control and basic hygiene where they belong, at the heart of good management and clinical practice with appropriate resources”: fine words, but actions speak louder than words.

The Airborne Transmission of Infection in Hospital Buildings: Fact or Fiction?

Airborne transmission is known to be the route of infection for diseases such as tuberculosis and aspergillosis. It has also been implicated in nosocomial outbreaks of MRSA, Acinetobacter spp. and Pseudomonas spp. Despite this there is much scepticism about the role that airborne transmission plays in nosocomial outbreaks. This paper investigates the airborne spread of infection in hospital buildings, and evaluates the extent to which it is a problem. It is concluded that although contact-spread is the principle route of transmission for most infections, the contribution of airborne micro-organisms to the spread of infection is likely to be greater than is currently recognised. This is partly because many airborne micro-organisms remain viable while being non-culturable, with the result that they are not detected, and also because some infections arising from contact transmission involve the airborne transportation of micro-organisms onto inanimate surfaces.

Mousepox in inbred mice innately resistant or susceptible to lethal infection with ectromelia virus. IV. Studies with the Moscow strain.

The pathogenesis and transmission of infection with the Moscow strain of ectromelia virus were studied in inbred mice. BALB/cAnNcr had high morbidity and mortality and C57BL/6Ncr (B6) mice had high morbidity and low mortality. Virus was detected in B6 mice for 2 weeks after subcutaneous (s.c.) inoculation and infected mice developed lesions compatible with acute mousepox. B6 inoculated by footpad transmitted infection to cagemates for up to five weeks and soiled cages that had housed infected mice were infectious for three weeks. S.c.-inoculated B6 mice also transmitted by contact for 2 weeks. Transmission was attributed to oronasal excretion of virus. Airborne transmission of infection between adjacent cages occurred at a low rate. Ectromelia virus-free progeny were derived from previously infected dams. These studies indicate that the highly virulent and infectious Moscow strain of ectromelia virus caused self-limiting infection in inbred mice and that direct contact is the most efficient means of transmission. These findings support the concept that mousepox can be contained by husbandry practices that minimize or eliminate the spread of infection by direct contact or fomites.

The effect of air ionization on the air-borne transmission of experimental Newcastle disease virus infections in chickens

The effect of artificial air-ionization on air-borne transmission of Newcastle disease virus (NDV) infection in chickens was studied in an isolated system consisting of two side-by-side cages with solid walls and a wire-gauze roof. During a 3-week observation period more than 90% of the uninoculated indicator chickens, housed in one of the cages, contracted the virus shed to the air by the NDV-inoculated, diseased birds in the neighbouring cage. This air-borne transmission of NDV was completely prevented by increasing the ion concentration in the test room by a constant negative corona discharge above the wire-gauze roof. On the other hand, spreading of the infection within a group of chickens housed in a single cage was not affected by air ionization. These and other results suggest that artificial air-ionization may protect animals from certain air-borne infections by interfering with microbial aerosol formation and/or by facilitating their decay.