Survival of surrogate coronaviruses in water (2009)

This study was motivated by previous reports that faecal contaminated liquid droplets are a potential vehicle for the spread of viruses such as SARS-CoV.

This study evaluated survival of two surrogate coronaviruses:

• transmissible gastroenteritis (TGEV) and
• mouse hepatitis (MHV)

The test waters used in this study included:

• Reagent-grade water, produced by treatment with reverse osmosis and ultraviolet light irradiation.
• Lake water (pH 7.5, turbidity 1.73 NTU) from a lake that serves as the drinking water source for the town of Chapel Hill, North Carolina (USA). This was obtained from the raw water inlet of the local drinking water treatment plant.
• Municipal wastewater, which was used to produce pasteurised settled sewage. This was obtained from a wastewater reclamation facility. Settled sewage is raw sewage that has undergone an initial settling step after entry into the plant to separate large solids from the liquid. The resulting liquid (pH 7.6, turbidity 17.6 NTU) was pasteurised in a waterbath at 70 °C for 3 h to inactivate other microorganisms that would interfere with cell culture infectivity assays of coronaviruses.

The authors reported that these coronaviruses remained infectious in water and sewage for days to weeks.

At 25 °C, time required for 99% (2 log₁₀) inactivation in sterile laboratory water was 22 days for TGEV and 17 days for MHV. Both surrogate coronaviruses were observed to be much more pesistent in the same grade water at colder temperature (4 °C).

More rapid inactivations were observed in lake water (compared to laboratory grade water) at both test temperatures.

In pasteurised settled sewage, times for 99% (2 log₁₀) inactivation at 25 °C were 9 days for TGEV and 7 days for MHV. At 4 °C, there was <1 log₁₀ infectivity decrease for both viruses after four weeks.

Water type, incubation time, and temperature were significant predictors of log₁₀ viral reduction kinetics.

The authors concluded that coronaviruses can remain infectious for long periods in water and pasteurized settled sewage, suggesting contaminated water is a potential vehicle for human exposure if aerosols are generated.

Thier final conclusion was that “the persistence of coronaviruses in water observed in this study suggests that if SARS-CoV should reemerge in human populations, water contaminated with these viruses may continue to pose an exposure risk even after infected individuals are no longer present“.

REFERENCE:

Casanova L, Rutala WA, Weber DJ and Sobsey MD (2009) Survival of surrogate coronaviruses in water. Water Research, 43(7), 1893-1898.

DOI: https://doi.org/10.1016/j.watres.2009.02.002