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Environmental Analysis

Opportunistic fungal pathogen screen [OFPS]

Published: July 8th, 2009

Revised: March 7th, 2023

Serious infections caused by filamentous or dimorphic fungi are rare in immunologically normal people and normally only caused by one of several pathogenic species. In people with varying degrees of immune dysfunction, however, serious fungal infections are common, and may be caused by a much larger set of fungi many of which are not pathogenic under normal circumstances. These fungi are sometimes called “opportunistic pathogens”, in reference to their proclivity to invade tissues given the opportunity presented by immune compromise. While not typically a problem in the broad community, opportunistic fungal pathogens can be important agents of serious and even fatal disease in health care institutions.

Culture-based methods are the current gold-standard for the detection of opportunistic fungal pathogens, and 1 CFU/m³ has been advised as an action limit (Mayhall 2003, p 706). This test is read rapidly (after 48 hr of incubation). It relies on culture-dependent evaluation of the presence of the most commonly occurring airborne agents of opportunistic fungal disease. Results are reported on the same day that the samples are read.

Taxa included

  • Aspergillus species complexes (including A. flavus, A. fumigatus, Aspergillus nidulans, A. niger, A. terreus, and A. ustus)
  • Dematiaceous fungi with opportunistic potential (including Curvularia species and relatives, Cladophialophora species, Exophiala species and others)
  • Fusarium species complexes (including F. solani, F. dimerum, F verticillioides, and F. oxysporum)
  • Paecilomyces species (including P. variotii and Purpureocillium lilacinus species complexes)
  • Phaeoacremonium species
  • Phialemonium species
  • Scedosporium species (including S. apiospermum and S. prolificans species complexes)
  • Thermotolerant zygomycetes (including Absidia, Cunninghamella, Mucor, Rhizomucor and Rhizopus species)
  • Trichoderma species (including T. citrinoviride/ longibrachiatum complex)
  • Yeasts (including Trichosporon, Candida and Cryptococcus species)

Field sample collection

  1. This test requires the use of an instrument that permits a high sampling flow rate. Instruments including the RCS High Flow, the Andersen N6 and the SAS sampler are suitable, however validation studies have so far only been completed on the Andersen N6. The test requires the collection of a total of 1 cubic metre of air on tandemly collected samples which together are considered as a single sample for the purposes of evaluating the airborne fungal concentration against the target action level of 1 CFU/m³. A proprietary sampling medium is used for this test, which we are pleased to provide to clients.
  2. Prior to use, the sampling head and exterior of the device should be disinfected with 70% isopropyl alcohol and allowed to dry. This treatment will help to prevent carry-over contamination from previous usages. As well, a clearly-defined sampling plan should be constructed before beginning sampling.
  3. Verify that the expiration date on the sampling medium is current, and that there is no evidence of damage to the surface of the collection medium (e.g. drying or cracking, colour changes, small glistening, pasty or fuzzy dots that might be microbial colonies, or free water on the medium surface)
  4. Insert the sampling medium into the air sampler following manufacturer’s recommendations. Wear latex or nitrile gloves during this process to prevent handling contamination.
  5. Turn the sampler or sampling pump on to initiate air flow. A maximum air volume of 200 L on a single sample should be collected in as many tandem samples are required to sample an overall volume of 1,000nbsp;L of air. All other aspects of this test are similar to IAQ analysis, fungal culture [FC-A]
  6. After the sampling period has concluded, carefully remove the sampling medium from the device, taking care not to touch the surface of the medium. For Petri plate media, replace the lid and secure it around the edge with tape or Parafilm. Ensure that you use a water-impermeable marker to label the strip, since the strip cannot be identified if the markings become accidentally wetted. Preprinted self-adhesive stickers work well for sample labeling purposes. Be sure to note the order in which samples were collected, and the sample sets that comprise a single collection.
  7. Place samples in a reclosable clean plastic bag and keep in darkness until receipt at the laboratory. Do not store or ship samples on freezer packs, since this leads to condensation on the agar surface which can lead to the formation of spurious satellite fungal colonies, artifactually inflating the count. Samples need to be protected from abrupt temperature changes during shipment, so it is a good idea to keep them in an insulated box during sampling. The bag containing sample media may be wrapped in bubble wrap or paper and packed into a box or sturdy envelope for shipping. Samples must be received at the laboratory no later than 24 hr post sampling. Please ensure that you use a reliable courier service to meet these requirements. In the past we have experienced numerous problems with Purolator in this regard, and we recommend our clients to use FEDEX for the shipment of time critical samples.

Laboratory code: OFPS

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