Infections in immunocompromised hosts

Immunocompromised patients don't have the ability to respond normally to an infection due to an impaired or weakened immune system. This inability to fight infection can be caused by a number of conditions including illness and disease (eg, diabetes, HIV), and treatments like chemotherapy and drugs taken to reduce organ rejection in transplant patients.

Invasive Fungal Infections (IFI), like Aspergillus, causes severe infection in people with acute leukaemia who are having chemotherapy and also transplant patients. This is despite improvements in antifungal therapy for the treatment of IFI. The major reason for this is that the current standard diagnostic tests of culture and biopsy lack the ability to make a diagnosis, either early or accurately. Thus other strategies such as the use of prophylaxis are needed.  Currently, 15% of those at high-risk develop Invasive Aspergillosis and 60-90% of those with Invasive Aspergillosis die.

The main reason for this high death rate is that our current diagnostic tests are not good at detecting infection or often only detect the infection at advanced stages when treatment is ineffective. Because of the limitations of current diagnostic tests the current practice is to give empiric antifungal therapy (EAFT) early to treat suspected Invasive Aspergillosis. However, studies have demonstrated that this therapy has only resulted in a minor reduction in the mortality rates and it also causes significant drug toxicity. It is a suboptimal treatment modality.

New tests have recently been developed to diagnose Invasive Aspergillosis. These tests are for the detection of an Aspergillus protein in blood and for the detection of Aspergillus DNA in blood. Available data suggests that these new tests make an early diagnosis and seem to be able to monitor responses to treatment. Dr Morrissey is involved in trials to determine whether the use of the new diagnostic tests to guide antifungal therapy will help improve the treatment of Invasive Aspergillosis, reduce drug toxicity and reduce the death rate in the high-risk patients as compared with the current standard method of diagnosis and treatment with EAFT.

Dr. Orla Morrissey’s research has focused on optimising the prevention, diagnosis and treatment of invasive infections that pose a significant threat to immunocompromised individuals.



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Hospital-acquired infections pose a significant risk to immunocompromised individuals. Professor Anton Peleg leads a research program that focuses on the mechanisms of pathogenesis of these important hospital-acquired pathogens.

For more information please visit the Hospital Acquired Bacterial Pathogens homepage.