Discussion

Indoor air quality in hospitals is an important factor in the control of healthcare-associated respiratory infections, especially in immunocompromised hosts. ^{Reference Cho, Myong and Kim5} Types and amount of fungi released from above-ceiling activity in healthcare facilities varies by location and cannot be predicted. Aspergillus, for instance, remains the most common construction-related pathogen; it can remain aerosolized for extended periods and travel long distances. ^{Reference Chang, Ananda-Rajah and Belcastro6} The MDCC significantly reduced the potential for aerosolization of pathogenic fungi, especially in above-ceiling spaces with high levels of fungi. The highest concentration of fungi we identified was collected inside the MDCC (38 CFU/m³) compared to outside (1 CFU/m³) and near the exhaust (0 CFU/m³) (Fig. 3). Sampling occurred in the burn intensive care unit that housed patients at high risk for respiratory infections.

Fig. 3.

Fungal growth (at day 7) from samples collected in and around a mobile dust-containment cart (MDCC) during above-ceiling work in a burn intensive care unit.

The correlation coefficient for CFU and particle count was +0.48, indicating a moderate relationship between fungal CFU and particle count, even though our ultrafine particle counter measures particles <1 μm and most molds are larger in the range of 2–20 μm. Previous researchers have detected a strong correlation between fungal counts and particle counting in the same size range of our work, <1 μm and a weak correlation in the larger size range of most fungi (ie, 5, 10, and 25 μm). ^{Reference Armadans-Gil, Rodríguez-Garrido, Campins-Martí, Gil-Cuesta and Vaqué-Rafart7,Reference Wong, Mohamed and Nazri8} Some sampling locations had low particle counts but high numbers of fungal colonies and vice versa. Because of the inconsistent correlations, the use of a particle counter for a single point-prevalence sampling as a substitute for fungal activity is inappropriate.

Microbial air sampling and particle counts collected near the HEPA-filtered air exhaust were not statistically different from samples taken before work began (ie, controls). We sampled this location based on a report that 73% of 85 portable HEPA devices failed to provide HEPA level performance. ^{Reference Newcomer, LaPuma, Brandys and Northcross9} Although the MDCC HEPA filtration systems were performing effective filtering, there was no practical way to assess filter failure other than observing dust exhaust expulsion from the MDCC. Therefore, routine maintenance and a regular filter replacement schedule is critical given the amount of pathogenic fungi that could potentially be ejected into a patient care area from a failed HEPA filtering device.

Our study has several limitations. All 3 MDCCs were the same manufacturer model, although other manufacturers use a similar design. Different models may function better or worse depending on features such as a more robust HEPA system or no HEPA filtration. We had a single microbial air sampler and single particle counter, which required sequential sampling of the above-ceiling work instead of capturing simultaneous measurements. To account for this sequential sampling, we alternated the order for the outside and exhaust sampling on several occasions, and order did not appear to be related.

In conclusion, this evaluation provides quantitative evidence that MDCCs, when used correctly, are effective barriers for reducing the risk of potential pathogenic exposures during above-ceiling activities in areas with critically ill and immunocompromised patients. The use of particle counters in lieu of microbial air sampling can provide quick results but is not an accurate substitute for fungal counts and should be considered only one of several methods to evaluate construction barrier effectiveness.