Using basic environmental sampling and laboratory techniques aided by chromogenic culture media, we identified ESBL reservoirs (sinks) and plausible transmission vehicles (medical equipment, infant formula, hands of caregivers/healthcare workers, insects) in this NICU environment. This strategy was a simple and cost-efficient method to assess ESBL bioburden and may be feasible for use in other settings to support ongoing infection control assessments and outbreak investigations.
The identification of sinks as stable reservoirs for ESBL in this setting was anticipated; the moist and warm environments created by plumbing traps provide ideal conditions for biofilm formation . Furthermore, eradication of ESBL from plumbing traps using conventional remediation techniques is challenging and therefore allows for long-term survival of bacterial communities . Additionally, the stable contamination of sink grids, basins, tap handles, and some backsplashes demonstrated in this study illustrates the retrograde model of bacterial dispersal from wastewater previously postulated by in situ studies . The fact that some healthcare workers’ hands demonstrated Pseudomonas spp. post-handwashing which were not present prior to handwashing is concerning for acquisition from the sink environment (although could be explained by variability of swab technique). Following these results, the importance of using ABHR for all hand hygiene (including after washing with soap and water) was re-emphasized to all staff and caregivers.
The recognition of sinks as environmental reservoirs for ESBL has led some intensive care units (ICUs) to adopt “water free” care, moving sinks away from the immediate patient care environment, with corresponding declines in patient colonization rates for pathogens of interest . In settings where these changes may not be feasible, interim measures targeting transmission vehicles are appropriate. In this study, we identified medical equipment, formula, insects, and hands of healthcare workers and caregivers as potential transmission vehicles that might move pathogenic organisms from a fixed location to the patient. Infection control teams should engage with doctors, nurses, and cleaning staff to ensure shared medical equipment is adequately disinfected in between uses, according to equipment package inserts or best practices, such as the U.S. Centers for Disease Control and Prevention’s “Environmental Cleaning in Healthcare Facilities in Resource-Limited Settings” . Preparation of shared powdered infant formula sources should be carefully monitored and, if possible, carried out in accordance with World Health Organisation’s guidelines for safe preparation, storage and handling of powdered infant formula .
We found that insects within the patient care environment were often colonized with potentially pathogenic organisms. While insect infestations are not typically reported as contributing to either endemic or outbreaks of healthcare-associated infections, the importance of vector control in the patient care environment cannot be over-emphasized. For example, cockroaches have been implicated in outbreaks of neonatal K. pneumoniae infections , and ESBL colonization of fruit flies is well-documented . In our study setting, LED-light insect traps have proved to be an effective measure, along with window screens, at reducing the presence of insects in the patient care environment.
There are several limitations to this study, both in its technical and conceptual approach. First, environmental sampling was conducted at a single centre, and findings may not be generalizable to other units, depending on local climate, patient census, and cleaning practices. These point prevalence surveys were conducted in a ward that was actively used for patient care and the timing of sample collection had to adjust to the demands of patient care. Our sampling events were not coordinated with cleaning times, so we are unable to determine the extent to which current cleaning practices were effective in reducing the burden of contamination. We attempted to overcome this limitation by performing multiple sampling events and categorizing single contaminations as “transient” and repeated contaminations as “stable”. Our use of “semi-sterile” techniques could have resulted in some false-positive results due to inadvertent contamination, but again we sought to counteract these limitations through the use of serial sampling. Although the chromogenic media chosen purports inhibition of all non-ESBLs, including those producing ampC beta lactamases, the possibility of false positive results have been noted by other studies . Thus, an overestimation of ESBL bioburden remains until isolates are confirmed using standard antimicrobial sensitivity methods.
Sampling bias may have influenced our findings on the prevalence of hand carriage of potential pathogens by caregivers and healthcare workers. For example, those confident with their hand hygiene practices may have been more willing to participate, leading to an under-estimation of the true contamination rate.
This study took place in the midst of the COVID-19 pandemic, when heightened efforts to mitigate hospital transmission of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) were in place. In comparison to pre-pandemic practices, hand hygiene was enforced more strictly and soap and ABHR were more readily available. These important measures may have contributed to an overall decreased bacterial bioburden, particularly on the hands of healthcare workers and caregivers.
We are unable to confirm that the identified environmental contamination contributed to concurrent clinical infections. In future studies, whole genome sequencing can help to establish true transmission pathways.
Despite these limitations, this simple environmental sampling technique might be a feasible way in which neonatal and other high-risk units facing hyper-endemic rates of ESBL infections can better understand the nature of contamination and transmission dynamics in their unit. Further, it might help catalyse the implementation of infection control measures targeting defined reservoirs and suspected transmission pathways. The temporal link between increased recovery of Acinetobacter spp. from the environment and increased incidence of Acinetobacter infections hospital-wide is an anecdote of the importance of timely and reliable environmental sampling as an important outbreak response tool. This sampling method may also be pivotal in trialling and measuring the impact of novel remediation and prevention strategies. For example, neonatal units who have identified sinks as stable ESBL reservoirs should consider removing sinks and implementing “water-free” care for ICU patients , placing sink covers , or implementing anti-microbial alloys, such as copper, which has been shown to reduce microbial burden in NICUs . This environmental sampling technique can be used to test microbial burden before and after implementation of these infection control interventions and track bioburden overtime.