Viability of MS2 and Phi6 Bacteriophages on Carpet and Dust

Respiratory viral illnesses are commonly spread in the indoor environment through multiple transmission routes, including droplets, aerosols, and direct/indirect contact. Indoors, resuspension of dust from flooring is a major source of human exposure. However, it is critical to determine viral persistence on dust and flooring to better characterize human exposure. The goal of this work is to determine viral viability on two carpet types (cut and looped) and house dust over time and after four different cleaning methods. MS2 and Phi6 bacteriophages were used to represent non-enveloped and enveloped viruses, respectively. These viral surrogates were placed in an artificial saliva solution and nebulized onto carpet or dust. Viability was measured at various time points (0, 1, 2, 3, 4, 24, and 48 hours) and after cleaning (vacuuming, hot water extraction with stain remover, steam, and a disinfection spray). Viability decay was modeled as first-order. MS2 bacteriophages showed slower viability decay rates in dust (-0.11 hr-1), cut carpet (-0.20 hr-1), and looped carpet (-0.09 hr-1) compared to Phi6 (-3.36 hr-1, -1.57 hr-1, and - 0.20 hr-1 respectively). The difference between phages was statistically significant in dust and cut carpet (p<0.05). Viral RNA demonstrated minimal degradation that in most cases was not statistically different from zero over the 48 hours measured (p>0.05). Viable viral concentrations were reduced to below the detection limit for steam and disinfection for both MS2 and Phi6 (p<0.05), while vacuuming and hot water extraction with stain remover showed no significant changes in concentration from uncleaned carpet (p>0.05). This study used viral surrogates and did not model risk of viral transmission via dust. Overall, these results demonstrate that MS2 and Phi6 bacteriophages can remain viable in carpet and dust for several hours to days, and cleaning techniques with heat and disinfectants may be more effective than standard vacuuming for viral removal. Future work should model risk from exposure via dust and flooring for various viruses such as influenza, SARS-CoV-2, and RSV. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=99 SRC="FIGDIR/small/444479v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@1cc0ad9org.highwire.dtl.DTLVardef@dc440corg.highwire.dtl.DTLVardef@f787dcorg.highwire.dtl.DTLVardef@f8bda3_HPS_FORMAT_FIGEXP M_FIG C_FIG

Indoor dust as a matrix for surveillance of COVID-19 outbreaks

Ongoing disease surveillance is a critical tool to mitigate viral outbreaks, especially during a pandemic. Environmental monitoring has significant promise even following widespread vaccination among high-risk populations. The goal of this work is to demonstrate molecular SARS-CoV-2 monitoring in bulk floor dust and related samples as a proof-of-concept of a non-invasive environmental surveillance methodology for COVID-19 and potentially other viral diseases. Surface swab, passive sampler, and bulk floor dust samples were collected from rooms of individuals infected with COVID-19, and SARS-CoV-2 was measured with quantitative reverse transcription polymerase chain reaction (RT-qPCR) and two digital PCR (dPCR) methods. Bulk dust samples had geometric mean concentration of 159 copies/mg-dust and ranged from non-detects to 23,049 copies/mg-dust detected using ddPCR. An average of 88% of bulk dust samples were positive for the virus among detection methods compared to 55% of surface swabs and fewer on the passive sampler (19% carpet, 29% polystyrene). In bulk dust, SARS-CoV-2 was detected in 76%, 93%, and 97% of samples measured by qPCR, chip-based dPCR, and droplet dPCR respectively. Detectable viral RNA in the bulk vacuum bags did not measurably decay over 4 weeks, despite the application of a disinfectant before room cleaning. Future monitoring efforts should further evaluate RNA persistence and heterogeneity in dust. This study did not measure virus viability in dust or potential transmission associated with dust. Overall, this work demonstrates that bulk floor dust is a potentially useful matrix for long-term monitoring of viral disease outbreaks in high-risk populations and buildings. ImportanceEnvironmental surveillance to assess pathogen presence within a community is proving to be a critical tool to protect public health, and it is especially relevant during the ongoing COVID-19 pandemic. Importantly, environmental surveillance tools also allow for the detection of asymptomatic disease carriers and for routine monitoring of a large number of people as has been shown for SARS-CoV-2 wastewater monitoring. However, additional monitoring techniques are needed to screen for outbreaks in high-risk settings such as congregate care facilities. Here, we demonstrate that SARS-CoV-2 can be detected in bulk floor dust collected from rooms housing infected individuals. This analysis suggests that dust may be a useful and efficient matrix for routine surveillance of viral disease outbreaks.