How best to assess for coronavirus: Wastewater or surfaces?

Posted Nov 18, 2020 by Tim Sandle
While there has been considerable interest concerning the spread of coronavirus by wastewater and using this method to track community spread, a new study puts across the view that surfaces provide a better indicator of viral spread.
Scientist Peter Tsai recommends leaving the mask out for seven days before reuse
Scientist Peter Tsai recommends leaving the mask out for seven days before reuse
A new study titled “Longitudinal monitoring of SARS-CoV-2 RNA on high-touch surfaces in a community setting“, has been issued. Given there have been very few studies about the survival of the coronavirus on surfaces issued recently, the new study becomes one of interest. This perhaps indicates that surfaces are less likely to be a source of transmission for SARS-CoV-2, compared with air.
The new study has examined several high-touch surfaces in a community setting and found that around 8 percent were positive. This seems to tally with other literature.
To gather the data, the researchers (from Tufts University) performed swab sampling of high-touch non-porous surfaces in a Massachusetts town during a COVID-19 outbreak from April to June 2020. The surfaces sampled included crosswalk buttons, trash can handles, and door handles of certain business like a grocery store or a bank, areas that are used by a high volume of people.
The data indicated that the estimated risk of infection from touching a contaminated surface was low (at less than 5 in 10,000). For the researchers, this suggests fomites play a minimal role in SARS-CoV-2 community transmission.
While the presence of the virus on surfaces was assessed as low, the researchers make an argument that surfaces might even be a better leading indicator of community spread than wastewater although these seems to run counter to those studies looking at wastewater that appear to offer evidence that assessing wastewater is a useful indicator of community spread. For example, a U.S. study showed how wastewater samples can be examined in a straightforward manner ("First detection of SARS-CoV-2 RNA in wastewater in North America: A study in Louisiana, USA").
The analysis of the wastewater samples involved concentrating the samples via ultrafiltration together with an adsorption–elution method using electronegative membranes and then using two reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assays to identify the virus.
The reason why the weight is put on surfaces is because any increases from the relatively low levels could a sign of worsening conditions. This is on the basis of the study finding that the percentage of positive samples in one postal district peaked roughly 7 days before a spike in COVID-19 cases in the same district.