CONICET | Buscador de Institutos y Recursos Humanos

In industrial clean rooms or in high complexity health care facilities, environmental air microbiological load (AML) is a key parameter that needs to be carefully controlled. Since the airborne nature of the interhuman COVID-19 transmission was established, AML control measures have become more extensively adopted, even in places like classrooms or public transports. In order to check effectiveness of germ depletion measures, passive or active sampling methods are currently employed in order to determine the number of culturable microorganisms remaining in the air before and after a given treatment. In our country, active microbial samplers are costly because they need to be imported. Therefore, we design, construct and test a cost-effective portable agar impact active sampler device. In this kind of AML samplers, microorganisms present in the environmental air are conducted by negative pressure and impacted into a surface of solid PCA agar media (φ90 mm) that is later incubated at 35◦C for 36 hs giving a value of colony forming units per volumetric unit (CFU/m3). The LUMI-Wiro prototypes 1.0 and 2.0 were based on a published computer-aided design (CAD) from which key internal aerodynamic pieces were geometrically refined in order to optimize the sampling process adapting it to our cylindrical casing design. Our system employs a small fan turbine with an arduino microcontroller in order to sample a programmable air volume, typically 3 m3 in 9 min. Air flow at entry and exit was calibrated with a digital anemometer. Upper, lower and internal parts were polymer 3D printed and screwed to the casing. For portability, a rechargeable 12 V battery was incorporated. For durability, in the ultimate version the casing was made of heat painted steel instead of plastic pipe. After lab testing, both prototypes were evaluated in several real life scenarios including a double floor autobus, a ballroom and an intensive care unit. These field experiments were conducted before and after the application of increasing doses of upper room UVC irradiation (low pressure Hg lamps, 254 nm), and with different numbers of people inhabiting the enclosure. LUMI-Wiro 1.0 and 2.0 demonstrate to be sensitive enough to detect a significant AML reduction as soon as 20 min after germicidal lamps ignition and show good correlation with passive gravitational sampling performed in parallel. We conclude that this device is able to accomplish the same task as the commercial products being at least five fold cheaper.

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