Monitoring COVID-19 transmission risks by RT-PCR tracing of droplets in hospital and living environments

Abstract

SARS-CoV-2 environmental contamination occurs through droplets and biological fluids released in the surroundings from patients or asymptomatic carriers. Surfaces and objects contaminated by saliva or nose secretions represent a risk for indirect transmission of COVID-19. We assayed surfaces from hospital and living spaces to identify the presence of viral RNA and the spread of fomites in the environment. Anthropic contamination by droplets and biological fluids was monitored by detecting the microbiota signature using multiplex RT-PCR on selected species and massive sequencing on 16S-amplicons. A total of 92 samples (flocked swab) were collected from critical areas during the pandemic, including indoor (3 hospitals and 3 public buildings) and outdoor surfaces exposed to anthropic contamination (handles and handrails, playgrounds). Traces of biological fluids were frequently detected in spaces open to the public and on objects that are touched with the hands (>80%). However, viral RNA was not detected in hospital wards or other indoor and outdoor surfaces either in the air system of a COVID-hospital, but only in the surroundings of an infected patient, in consistent association with droplets traces and fomites. Handled objects accumulated the highest level of multiple contaminations by saliva, nose secretions and faecal traces, further supporting the priority role of handwashing in prevention. In conclusion, anthropic contamination by droplets and biological fluids is widespread in spaces open to the public and can be traced by RT-PCR. Monitoring fomites can support evaluation of indirect transmission risks for Coronavirus or other flu-like viruses in the environment.

Testing at scale during the COVID-19 pandemic

“…In the early stages of the COVID-19 pandemic, the routes of SARS-CoV-2 transmission were unclear, and viral particles that land on objects and surfaces ( fomites ) were considered to pose a risk of indirect transmission 88 . Testing of hospital and public surfaces close to infected patients detected the presence of viral RNA, and countries such as China implemented testing of frozen food imports 89 , 90 . However, ongoing environmental testing and epidemiological studies suggest that this mode of transmission is uncommon, and that viral transmission is instead primarily caused by contaminated respiratory droplets and aerosols 91 .…”

Laboratory diagnosis of emerging human infections by SARS-COVID-19: Prevalence and challenges

“…The virus can infect the gastrointestinal system and be shed in large numbers in the feces; potentially contaminating the wastewater. Untreated urban wastewater; including settled particles and sludge, may be sensitively identified for SARS-CoV-2 RNA (Piana et al, 2021). The increase in concentration of the SARS-CoV-2 RNA in raw wastewater is linked to the increase in the reported COVID-19 cases, according to the retrospective investigations.…”