Near-Patient Sampling to Assist Infection Control-A Case Report and Discussion

Abstract

Air sampling as an aid to infection control is still in an experimental stage, as there is no consensus about which air samplers and pathogen detection methods should be used, and what thresholds of specific pathogens in specific exposed populations (staff, patients, or visitors) constitutes a true clinical risk. This case report used a button sampler, worn or held by staff or left free-standing in a fixed location, for environmental sampling around a child who was chronically infected by a respiratory adenovirus, to determine whether there was any risk of secondary adenovirus infection to the staff managing the patient. Despite multiple air samples taken on difference days, coinciding with high levels of adenovirus detectable in the child's nasopharyngeal aspirates (NPAs), none of the air samples contained any detectable adenovirus DNA using a clinically validated diagnostic polymerase chain reaction (PCR) assay. Although highly sensitive, in-house PCR assays have been developed to detect airborne pathogen RNA/DNA, it is still unclear what level of specific pathogen RNA/DNA constitutes a true clinical risk. In this case, the absence of detectable airborne adenovirus DNA using a conventional diagnostic assay removed the requirement for staff to wear surgical masks and face visors when they entered the child's room. No subsequent staff infections or outbreaks of adenovirus have so far been identified.

Keywords: adenovirus; air sampling; airborne; face masks; infection control; limit of detection; personal protective equipment; respiratory; sensitivity; transmission.

Figure 1

Portable (wearable) SKC Button Sampler (left) connected to the AirChek XR5000 pump (right) as used for near-patient air sampling in this study. The manufacturer’s sampling rate was fixed at 4 L/min. (Available from http://www.skcltd.com/index.php/uncategorised-articles/212-bio-aerosol-sampling-products).

Figure 2

Patient room layout and air sampling sites and durations during various activities for the patient. Position 1—environmental air sampling; 2—during daily suctioning of the tracheostomy (worn by physiotherapist); 3—hand-held over tracheostomy site; 4—during an educational session (worn by educational facilitator); 5—overnight environmental air sampling. See main text (Section 4) for more details.

Figure 3

Variable AdV DNA levels in the routine patients nasopharyngeal aspirates (NPAs). Note that the date increases from left to right along the x-axis, and the y-axis (placed on the right-hand side to allow easier comparison with dates of sampling) shows the AdV DNA in copies/mL VTM. Air sampling was performed on the dates indicated by the vertical black arrows. Despite high NPA AdV DNA levels at times, no AdV DNA was detected in any of the air samples with the same routine commercial diagnostic respiratory PCR assay (spiked samples with positive AdV DNA extract showed no inhibition from the gel filter).