Detection of fungal contamination: surface sampling with a dusting cloth improves quantitative recovery of aspergilli.

Background. The health-care facility environment can be implicated in disease transmission in immunocompromised patients. Exposure of such patients to moulds can result in fatal infections. Incidence of hospital -acquired aspergillosis can be minimized by adherence to ventilation standards for specialized care environments, appropriate maintenance and careful cleaning of patient environment. Mycological control is also recommended in protective environments or operating rooms mainly during building renovation, by air sampling but also surface sampling, an efficient method to detect minor fungal contamination. Objective. To make surface sampling easier and to reduce surveillance costs, we developed a simple technique using sterile dusting paper cloths. To validate this method, we used an experimental protocol to evaluate ability of the system to capture fungal conidia, in comparison with two other methods, Rodac Contact plates and cotton pads. Materials/method. Aspergillus niger was chosen as organism test. A reference suspension of conidia (0.5 McFarland) was prepared with serial dilutions (1/30, 1/40, 1/50, 1/100) to contaminate sterile stainless steel plates (n=18), each 30 by 30 cm. Each one was divided into 16 smaller squares: 0.5 ml of the suspension was placed in the centre of each square and allowed to dry. Thus, 288 square surfaces were contaminated. From 96 of these, Rodac plates were used to harvest the spores; from another 96 the cotton pads were used, and from the last 96 the dusting cloths were used and inseminated in Petri plates. The remaining stainless steel plates were used to repeat the experiment (dilutions 1/40 and 1/50) with agar neutralised with lecithin and polysorbate 80. All the plates were incubated at 37°C for 18 h. For the statistical analyses, the data were transformed using the natural logarithm. Multiple log-linear regression was used to estimate the differences between the 3 methods, between the 4 dilutions, and the effect of neutralisation. Results. The mean number of colonies was approximately the same for each method at dilution 1/100. At dilutions 1/50, 1/40 and 1/30 the mean number of colonies is much higher for the cotton pads and dusting cloths than for Rodac. The multiple regression showed that neutralization reduces the number of colonies by 12% (not significant P=0.07). In comparison with dilution 1/50, the number of colonies recovered at dilutions 1/40 and 1/30 were slightly increased, by 13% and 6% respectively (not significant P=0.09 and P=0.52). However, in comparison with Rodac plates, both cotton pads and dusting cloths identified many more of colonies, 5 times as many and 6 times as many respectively (highly significant P<0.00005). Conclusions. This method using dusting cloths for surface sampling is able to take samples on every type of surface (smooth, mesh, flat, curved) and to have all information about contamination taking only one sample from the area (air ventilation outlets, filters, patient’s bed, scialitic lamp..). We showed that this device improves quantitative recovery of A. niger from stainless steel surfaces. Although these results are preliminary, we think that this sampling method could contribute an easy, sensitive and inexpensive approach to environmental control.