Case Studies - Hospital Acquired Infections

Hospital acquired infection (HAI) mainly occurs where a breakdown of infection control causes patient to patient transmission of an infectious disease. Drug resistant bacterial infections, such as methicillin resistant staphylococcus aureus and multi-drug resistant strains of mycobacterium tuberculosis (TB), are a particular problem. HAI adds to the suffering for patients and places an economic burden on the healthcare system. Recent data indicate 100,000 cases of HAI in England annually, costing the National Health Service around £1 billion per year. Not all HAI is preventable, but improvements in infection control could significantly reduce the incidence.

One of HSE's priorities is the provisional health services and HAI is of concern because exposure to infectious agents could place clinical staff as well as patients at risk. To reduce risks, methods are needed to identify and control the hazards posed by HAI.

HSE and the Hospital Infection Society asked HSL to undertake a study and this has involved an applied occupational hygiene assessment, advanced microbiological detection techniques, air flow measurement and computational modelling to determine the movement of potentially infectious agents in hospital environments.

Bronchoscopy rooms were chosen as a model, since the clinical techniques used can create aerosols of respiratory bacteria, including the causative agent of TB. The study aimed to determine the likelihood and extent of exposure to bacteria and how this related to patterns of work.

Initial studies in one major teaching hospital compared conditions in the endoscopy suite, and in particular the bronchoscopy room, before and after a three-yearly maintenance programme. Air sampling together with molecular-based microbiological detection techniques was applied. Ventilation measurements were also made, including tracer gas tests to establish leakage paths. A three-dimensional computer model of the room was constructed and computational fluid dynamic techniques were used to predict air flow patterns and the potential for spread of contaminants. The air flow measurements and air sampling data were used to validate the model.

Improvements to the ventilation system were suggested which would reduce the spread of potential pathogens. Other controls such as changing the working practices of clinical staff and use of personal protective equipment were recommended. Studies at two other hospitals have been completed and reports detailing the findings and recommendations have been published.

These studies demonstrate the way in which different scientific disciplines within HSL can be used in a concerted approach to problem solving.

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