Brief Report A 2-year comparative study of mold and bacterial counts in air samples from neutral and positive pressure rooms in 2 tertiary care hospitals Laura Ryan FRCPath a,b, *, Niall O’Mara MB BAO BCh, Pg Dip Ed c , Sana Tansey MSc a , Tom Slattery MSc c , Belinda Hanahoe MSc a , Akke Vellinga MSc, PhD d , Maeve Doyle MD c , Martin Cormican MD a,d a Department of Microbiology, Galway University Hospital, Galway, Ireland b Department of Microbiology, University Hospital Waterford, Waterford, Ireland c Department of Medicine, University Hospital Waterford, Waterford, Ireland d School of Medicine, National University of Ireland, Galway, Ireland Key Words: Positive pressure room neutral pressure room positive pressure ventilated lobby mold air sample Immunocompromised patients are at risk of invasive fungal infection. These high-risk patients are nursed in protective isolation to reduce the risk of nosocomial aspergillosis while in hospital—ideally in a pos- itive pressure single room with high-efficiency particulate air filtration. However, neutral pressure rooms are a potential alternative, especially for patients requiring both protective and source isolation. This study examined mold and bacterial concentrations in air samples from positive and neutral pressure rooms to assess whether neutral pressure rooms offer a similar environment to that of positive pressure rooms in terms of mold concentrations in the air. Mold concentrations were found to be similar in the positive and neutral pressure room types examined in this study. These results add to the paucity of literature in this area. © 2017 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved. Aspergillus spp are ubiquitous fungi, many of which cause human infections, particularly in immunocompromised patients. 1 Many guidelines recommend that patients at high risk of infection with Aspergillus spp be nursed in a positive pressure high-efficiency par- ticulate air (HEPA)–filtered room for the duration of their neutropenic period, as one of the measures to try to reduce the risk. 2-5 Recom- mended threshold levels of Aspergillus spp are <1 and <5 colony forming units (CFU)/m 3 in HEPA-filtered air and in a ward with no filtration, respectively. 3 Positive pressure ventilated lobby (neutral pressure) rooms are specifically designed to keep the room at neutral pressure relative to the corridor outside. HEPA-filtered air is sup- plied in the lobby at positive pressure to both the room and the corridor and air extraction is via an en suite toilet. This type of room has many other specific design parameters which must be met for it to function correctly, including a pressure stabilizer above the door between the patient room and the lobby, and a transfer grille on the lower section of the en suite door. 5 The room has been vali- dated from an engineering perspective only as being appropriate for source isolation and protective isolation. 6 This room type is po- tentially suitable for an immunocompromised patient with an airborne infection, but it has not yet been clinically validated as pro- viding both source and protective isolation. 3 There are very little data available to document the relative performance of any neutral pressure room (positive pressure ventilated lobby design or other- wise) in reducing exposure to fungal elements and specifically Aspergillus spores; therefore, the aim of this study was to compare concentrations of mold and bacteria in air sampled from positive and neutral pressure rooms. METHODS Air samples of defined volume were collected on a monthly basis over consecutive 1-year periods at each of 2 hospitals, at times when there was construction work on-site. In total, 216 air samples were collected over 24 months (Table 1). At the first hospital, samples were collected from 12 areas, including 2 positive pressure rooms, 2 neutral pressure rooms, 2 unventilated rooms, and the corridor directly outside each of the 6 rooms (2 samples per month, 144 in total). Samples were collected once per month from October 2014- September 2015. At the second hospital, samples were collected from one of each room type and the corridor directly outside, once per * Address correspondence to Laura Ryan, FRCPath, Department of Microbiology, University Hospital Waterford, Ardkeen, Waterford, Ireland. E-mail address: ryanlaurab@gmail.com (L. Ryan). Conflicts of interest: None to report. ARTICLE IN PRESS 0196-6553/© 2017 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved. https://doi.org/10.1016/j.ajic.2017.10.019 American Journal of Infection Control ■■ (2017) ■■-■■ Contents lists available at ScienceDirect American Journal of Infection Control journal homepage: www.ajicjournal.org American Journal of Infection Control