Healthcare quality experts talk about

the Swiss Cheese model of error – for an error or an infection to occur, the chain of infection must somehow penetrate all of the defence systems, and, ideally, we will interpose all possible defence systems to protect ourselves and our patients. The problem is that each defence costs something in terms of first cost, complexity, and operational cost, and there is a necessary limit to what can practically be done. Engineered systems pose an interesting problem, as they can be seen as a better defence than human activity, because humans are well known for being less than perfect. This assumption has some validity, but also raises at least the possibility of over- reliance on such systems so that they become more dangerous when they fail.

Research There is little definitive research available that absolutely establishes the value for any particular levels of ventilation, air changes, filtration, etc. in a particular application. In 2009, the World Health Organization

(WHO) published its Natural ventilation for infection control in health-care settings. That publication notes that preventing the spread of airborne infectious disease, from both infectious patients, and high-risk procedures which can spread pathogens through droplet nuclei over short distances, requires ‘administrative controls environmental and engineering controls – patient room with special air handling and ventilation, and PPE – the use of particulate respirators by health-care workers whenever possible’. The WHO Guidelines suggest the adequacy of natural ventilation in certain circumstances for such applications. A multidisciplinary systematic review

suggested that ventilation rate and air flow patterns contribute directly to the airborne spread of infectious agents. However, the minimum ventilation rate for effective airborne transmission control is unknown at present. A study conducted in 1990 by Malter,

Marthi, Fieland and Ganio for the American Society for Microbiology showed that the survival of some aerosolise bacteria is greater in relatively

high humidity, low temperature environments when the bacteria were contained in small droplets. Generally, temperatures above 75˚F decrease survival of all airborne bacterial species, where effects of RH are more complex. Attempting to deal with the lack of

data, The American Society of Heating, Refrigeration, Air Conditioning, and Environments (ASHRAE), The Facility Guidelines Institute (FGI), and the American Society for Healthcare Engineering (ASHE) have hired a team of researchers to determine the extent to which the US Standards, embodied in ASHRAE Standard 170, are supported, contradicted, or have no support. However, in general, most international

ventilation standards have proceeded based on a mix of assumptions, experience, and hope.

International ventilation strategies Regulation writers around the world struggle to find science on which to base their requirements. The IFHE is a body of hospital engineering societies from around the world, sharing best thinking and best practices. Our observation is that many people in many countries struggle with these issues, usually in vain, and usually referencing one another. Lacking good information, most regulation writers create regulations that

The world needs better data to determine how much ventilation, air changes, filtration, air distribution, pressure relationships, humidity and temperature control – and in what combination, and how much and under what circumstances – matter


are some function of (country wealth, fear, local community risk, assumptions about local clinical practices, experience and personal prejudice, and historical practices). Many countries, striving towards

world-class facilities, start by looking to those of the United States. In general, the US, having a relatively high per capita wealth, has some of the most stringent prescriptive ventilation standards in the world. Many of the precise numbers embodied in these regulations are thought to be at least somewhat arbitrary, but regulators there feel safer sticking with what they know. At the same time, the ASHRAE regulators are taking the courageous step of assessing the evidence that substantiates or contradicts their regulations, aiming to ultimately produce some of the most credible regulations in the world. Having said that, rates of hospital-

acquired infection in the US are generally better than those in other parts of the world (4.5% in the US vs. 7.1% in Europe vs. 15.5% in middle to low income countries). All the same, there are hospitals in low-income countries that have better outcomes than the best US hospitals, even in hospitals using thatched roofs and natural ventilation. If that is true, are US norms, coming at the cost that they do, and with the impact that they might have, truly ‘world class’? Taking another example. A decade

ago, the author toured, and extensively interviewed Infection Control officers of the Riks Hospital in Oslo, Norway. Staff co-located patients together, if they were from Norway. If, however, the patient was not from Norway, or if the patient had travelled outside of Norway within a few months, the hospital isolated that patient for sufficient time to ensure that the patient did not suffer from C. difficile or MRSA. The levels of community risk were so low that the hospital did not need to


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