The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)spreads via respiratory droplets and can survive on many surfaces for long periods. This is a known risk factor for nosocomial spread since various surfaces in hospitals can be contaminated with the virus.
A new study published in the journal Science of The Total Environment in September 2020 reports that the virus can be detected rapidly using already available technology, which will help to monitor viral spread within healthcare facilities more closely and enable better control of the pandemic.
LAMP: Alternative to PCR
Earlier studies on hospital ward surface contamination relied on real-time reverse transcriptase-polymerase chain reaction (RT PCR). In the typical PCR set-up, the virus is first deactivated, the nucleic acid is extracted, and finally, the RNA present is amplified. However, the extraction step can cause a marked reduction of the nucleic acid, as well as demanding a very low limit of detection for the successful application of the technology. This is a time-consuming step, contributing to the total span of 2.5 to 4 hours required per batch.
The current method is more rapid to enable on-site detection. It is called loop-mediated isothermal amplification (LAMP) and has brought the detection time down to 45 minutes, and preventing damage to the RNA by avoiding extraction.
Rapid Detection of Virus
The researchers collected 31 surface contamination samples from different wards before the daily cleaning and disinfection routines. The center of research was the Chengdu Center of Disease Control (Chengdu CDC). Seven surfaces were designated, from bedrails to fingertip of ECG monitors and bathroom door handles. The sample collection took place on five days over March and April.
The LAMP kit used the N gene for detection. Instead of RNA extraction, the researchers added the sample elution into a simple reaction MIX preparation. The detection kit integrates the RNA releasing agents, thus speeding up the process. Either a standard isothermal amplification instrument with a FAM channel can be used, or a standard real-time PCR instrument. The detection limit was at 20 copies/reaction, which is adequate for detecting surface contamination.
The researchers obtained 49 positive results from 14 cases, with 2-6 sites of contamination per case. With 9 cases, no surface tested positive. Overall, more than 70% of surfaces were contaminated by the virus from confirmed COVID-19 cases, which indicates a strong chance of cross-infection by surfaces in isolation wards.
High-Risk Surfaces
Over 70% of positive cases showed contamination of the ECG fingertip, which showed a higher viral RNA as well. This may indicate that these are high-risk surfaces for viral spread, requiring extra cleaning. The second highest risk was with the bedrail, with 10 samples being positive, probably from contact with the patients themselves as they lie down or get up.
The researchers, therefore, defined these as ultrahigh-contamination risk surfaces, which should be cleaned more often. Other less common sources of contamination were the beeper and the room cupboard.
The researchers then analyzed the correlations between the sampling sites, finding the highest value to be between the cupboard and the bedrail. In other words, if the bedrail was positive, the cupboard was likely to be positive as well. Bedrails were also correlated with several other surfaces. In fact, bedrails were correlated with more surfaces than any other. This would indicate the necessity of positioning bedrails as the most frequent site for sampling in future studies of this kind. Moreover, the bedrail may be a mirror of the degree of contamination of room surfaces.
There were five positive tests from bathroom door handles, which were all from cases where the ECG fingertips were positive as well. Four of the positive handle results also had positive bedrail samples, and three had in addition, positive cupboard and light switch handles. This prompted the investigators to suggest a daily analysis of samples from these handles, since “A surface contamination sample from the door handle can be interpreted as an ultra-high risk label,” and should prompt increased attention to cleaning of that ward.
Implications
The results showed which areas of a ward or room housing a COVID-19 patient should be monitored regularly to pick up contamination. The study also shows that monitoring for the presence of the virus is essential for ward management. The sample from the bathroom door handle is an indicator for more rigorous cleaning. ECG monitor fingertips are also prime spots for contamination.
Three of the samples came from six surfaces each, from outside mainland China, and from patients with moderate symptomatic disease. Thus, the presence of symptoms might affect the extent of contamination and risk of infection, but further work is needed.
Isothermal amplification fluorescent instruments can be used for on-site analysis as they are more cost-effective and portable than the standard PCR instruments. This study, which is the “first on-site analysis of COVID-19 surface contamination in wards,” may act as a guideline for disease control and ward hygiene protocols.
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