Tuesday, 17 January 2012

Invasive Aspergillosis Outbreak in Intensive Care Unit - Contaminated Air Identified As Cause

Though it may appear to be obvious few studies have convincingly demonstrated that the source of an outbreak of invasive aspergillosis is unclean air in the hospital environment. It is not generally enough to show that  there are spores present in the air of a hospital as spores can also be present prior to the entry of a patient into the hospital, in their airways, on their clothes or in their food

In this study patients undergoing open heart surgery in a dedicated unit suffered an outbreak (December 2006 to April 2008) with seven becoming infected during this time and mortality was high (86%). The authors were able to look at the monthly surveillance records for the air in the heart surgery unit over this time and correlate the species found in the air with those found to be infecting the patients.

Aspergillus fumigatus was the main infecting species (6/7) and no spores were found during the periods prior to and after the outbreak. However during the outbreak a series of six abnormal air tests were recorded showing from 50 to 400 viable A. fumigatus spores per cubic metre of air in the intensive care units where patients spent time recovering from surgery - there was clearly a correlation between the presence of these spores in the air of ICU and the seven cases of invasive aspergillosis. The air in the operating theatres was clean throughout this time.

However there was still the problem of proving whether or not these spores caused the infections - perhaps the infecting spores were present prior to the operations?

To address this problem the authors have genotyped the strains of A.fumigatus found in the air of ICU and compared them with those found growing in infected patients and found them to be the same strains in half the patients - strongly indicating that in at least half of the cases the source of the infection was indeed the spores found in the air of ICU.

This is strong evidence for the importance of maintaining clean air for patients throughout their time in hospital after major surgery, during the operation and afterwards.

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