The article, titled “Negative-pressure ICU rooms and pulmonary aspergillosis: room conversion matters,” highlights a critical distinction between purpose-built negative-pressure rooms and conventional rooms that have been retrofitted for air pressure control. The authors argue that the physical configuration of the room, rather than the pressure direction alone, determines the safety of the environment for patients susceptible to airborne pathogens.
The correspondence responds to a multicenter observational study by Kreitmann et al., which investigated the relationship between negative-pressure ICU rooms and COVID-19-associated pulmonary aspergillosis, or CAPA. Kreitmann et al. analyzed a cohort of 1,233 mechanically ventilated patients from 75 ICUs. Their findings suggested that exposure to negative-pressure rooms was associated with a lower 60-day cumulative incidence of probable invasive pulmonary aspergillosis, as defined by FUNDICU criteria. However, the authors of the correspondence emphasize that this observational association does not establish a protective effect of negative pressure, a limitation acknowledged by the original researchers.
The central argument of the correspondence rests on the authors’ own experience during the first wave of the COVID-19 pandemic. Following this conversion, six of 26 patients developed probable or proven pulmonary aspergillosis, while two additional patients were colonized with Aspergillus fumigatus. Simultaneously, A. fumigatus was recovered from air samples in several affected rooms, indicating a significant environmental presence of the fungus.
Upon investigation, the authors hypothesized that the conversion from positive to negative pressure had modified airflow pathways within the ICU. Specifically, they proposed that the pressure change may have mobilized contaminated dust from plenum spaces above false ceilings, facilitating the entry of fungal spores into patient rooms. After implementing surface disinfection and adjusting room pressure toward neutral or slightly positive values, airborne A. fumigatus concentrations decreased and subsequently became undetectable. Although antifungal prophylaxis was also administered to remaining patients, which precludes attributing the absence of further cases solely to pressure adjustment, the temporal correlation suggests a link between room conversion and fungal exposure.
The apparent discrepancy between the authors’ experience and the findings of Kreitmann et al. may stem from the definition of a “negative-pressure room.” A room specifically designed to operate under negative pressure differs fundamentally from a conventional ICU room converted from positive to negative pressure, particularly when the latter lacks an anteroom or appropriate pressure zoning. Such conversion may alter pre-existing airflow pathways and draw air from surrounding spaces into the patient room. The resulting environmental risk depends not only on the direction of the pressure gradient but also on room configuration, airtightness, air-exchange rates, filtration, exhaust systems, and potential fungal reservoirs.
Supporting this distinction, observations by Biebelberg et al. in two academic hospitals with similar infection control practices showed that hospital-acquired Aspergillus rates among patients with COVID-19 were higher in the hospital with greater use of negative-pressure rooms. After the use of negative-pressure rooms was reduced, rates declined and became similar among the two hospitals. Although these findings do not establish a causal relationship, they suggest that the conditions under which negative pressure is implemented may influence environmental fungal exposure. Schaffzin et al. further emphasized that air balance alone is insufficient to characterize a negative-pressure environment, highlighting air-exchange rates, filtration, exhaust, airtightness, and room configuration as integral components of a properly designed airborne infection isolation room.
In their reply, Biebelberg et al. acknowledged that applying negative pressure to rooms that did not meet all criteria for such isolation rooms may have drawn environmental pathogens into patient rooms without adequately removing them. The correspondence notes that Kreitmann et al. acknowledged the lack of detailed measurements of room pressure, ventilation, and filtration performance in their study. Anteroom configuration was also not reported, meaning that patients classified as exposed to negative pressure may have experienced substantially different aerobiological conditions across participating centers.
Diagnostic intensity also plays a crucial role in interpreting these findings. Mycological investigations were performed less frequently in patients exposed to negative-pressure rooms in the Kreitmann et al. cohort. Bronchoalveolar lavage with mycological testing was performed in 5.8% of patients in the negative-pressure group compared with 22.3% in the neutral-pressure group. Similarly, serum galactomannan testing was performed in 14% versus 26%, respectively. The authors explicitly acknowledge that these differences may have led to underdiagnosis and differential case detection. The correspondence agrees that this limits the interpretation of the lower incidence of probable invasive pulmonary aspergillosis in the negative-pressure group, as the diagnostic yield was not standardized across the two groups.
Statistical significance also varied with the diagnostic definition used in the Kreitmann et al. study. Although a lower incidence of probable invasive pulmonary aspergillosis according to FUNDICU criteria was observed in patients exposed to negative-pressure rooms, no significant association was found for putative invasive pulmonary aspergillosis according to the AspICU algorithm or for the combined endpoint of putative invasive pulmonary aspergillosis and Aspergillus colonization. However, the effect estimates for these secondary outcomes were in the same direction as those for probable invasive pulmonary aspergillosis, suggesting a consistent trend despite the lack of statistical significance for the broader definitions.
The findings of these studies may therefore be more complementary than contradictory. The association observed by Kreitmann et al. does not resolve whether risk differs between purpose-built and converted rooms. The experience of the correspondence authors and the observations of Biebelberg et al. raise a different question: whether converting rooms not originally designed for negative pressure may create unintended airflow pathways and increase exposure to environmental Aspergillus.
Thus, the relevant question may not simply be whether an ICU room is under negative pressure, but whether it was designed to operate safely under these conditions. Future studies should assess room architecture, anteroom configuration, pressure gradients, ventilation, and filtration characteristics, alongside standardized mycological and environmental surveillance.
Subject of Research: The impact of ICU room pressure conversion on pulmonary aspergillosis risk
Article Title: Negative-pressure ICU rooms and pulmonary aspergillosis: room conversion matters
Article References: Ichai, P., Saliba, F., Coilly, A., & Jeblaoui, A. (2026). Negative-pressure ICU rooms and pulmonary aspergillosis: room conversion matters. Critical Care, 30(1), Article 527. https://doi.org/10.1186/s13054-026-06371-5
Image Credits: AI Generated
DOI: 10.1186/s13054-026-06371-5
Keywords: pulmonary aspergillosis, negative pressure rooms, ICU infection control, airflow dynamics, Aspergillus fumigatus, room conversion, airborne pathogens, FUNDICU criteria, AspICU algorithm, serum galactomannan, bronchoalveolar lavage, hospital epidemiology, ventilation systems, fungal reservoirs, pressure gradients, anteroom configuration, environmental surveillance, mycological testing, invasive pulmonary aspergillosis, air-exchange rates
