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ORIGINAL PAPER
Survival of Coronaviruses in Water and Wastewater
Patricia M. Gundy ÆCharles P. Gerba Æ
Ian L. Pepper
Received: 1 October 2008 / Accepted: 13 November 2008 / Published online: 3 December 2008
ÓSpringer Science+Business Media, LLC 2008
Abstract The advent of severe acute respiratory syn-
drome and its potential environmental transmission
indicates the need for more information on the survival of
coronavirus in water and wastewater. The survival of rep-
resentative coronaviruses, feline infectious peritonitis
virus, and human coronavirus 229E was determined in
filtered and unfiltered tap water (4 and 23°C) and waste-
water (23°C). This was compared to poliovirus 1 under the
same test conditions. Inactivation of coronaviruses in the
test water was highly dependent on temperature, level of
organic matter, and presence of antagonistic bacteria. The
time required for the virus titer to decrease 99.9% (T
99.9
)
shows that in tap water, coronaviruses are inactivated faster
in water at 23°C (10 days) than in water at 4°C
([100 days). Coronaviruses die off rapidly in wastewater,
with T
99.9
values of between 2 and 4 days. Poliovirus
survived longer than coronaviruses in all test waters, except
the 4°C tap water.
Keywords Survival Water Wastewater Coronavirus
SARS
Introduction
The 2003 epidemic of severe acute respiratory syndrome
(SARS) resulted in over 8,000 cases worldwide with a
mortality rate of approximately 10% (Manocha et al. 2003;
Centers for Disease Control 2004). The last known
outbreak occurred in a research lab in Beijing in 2004. The
cause of this disease was identified as a novel human
coronavirus with probable origins in civets and a possible
reservoir in bats (Guan et al. 2003; Lau et al. 2005; Wang
et al. 2006). Coronaviruses are enveloped, single-stranded
RNA viruses that range from 60 to 220 nm in size. They
can infect birds and mammals, including humans, and are
transmitted through aerosols or the fecal-oral route. The
rapid spread of coronaviruses during outbreaks suggests the
primary mode of transmission of human coronaviruses is
respiratory droplets; however, there is no direct evidence to
support this (Belshe 1984). Since coronavirus infection in
humans up to this point has been characterized as a mild,
self-limiting condition, there is limited information on its
transmission potential through the environment.
The SARS epidemic had potential links to water and
wastewater given that the March 2003 outbreak at the high-
rise housing estate in Hong Kong involving over 300
people was linked to a faulty sewage system (Peiris et al.
2003). The fact that SARS-CoV can replicate in the enteric
tract (Leung et al. 2003) makes it a possible enteric path-
ogen, and the incidence of diarrhea ranging from 8 to 73%
in SARS cases (SARS Epidemiology Working Group
2003) causes concern about its potential environmental
transmission. Leung et al. (2003) also reported that viral
cultures from SARS patients recovered higher yields from
the small intestine than the lung tissues, which are the
target organs of this virus. Infectious virus has been cul-
tured from stools of SARS patients up to 3 weeks post
infection (Chan et al. 2004; Liu et al. 2004). The advent of
SARS and the question of its transmission indicate the need
for more information, specifically the survival of corona-
virus in water and wastewater. This study compared the
survival of representative coronaviruses and poliovirus 1 in
tap water and wastewater.
P. M. Gundy (&)C. P. Gerba I. L. Pepper
Department of Soil, Water and Environmental Science,
University of Arizona, 1177 E. 4th St. Room 429,
P.O. Box 210038, Tucson, AZ 85721, USA
e-mail: pgundy@ag.arizona.edu
123
Food Environ Virol (2009) 1:10–14
DOI 10.1007/s12560-008-9001-6
Materials and Methods
Feline infectious peritonitis virus (FIPV) (ATCC-990), an
enteric feline coronavirus, was propagated and assayed in
the Crandell Reese feline kidney cell line (CRFK) (ATCC-
94). Human coronavirus 229E (HCoV) (ATCC-740), a
respiratory virus, was propagated and assayed in the fetal
human lung fibroblast, MRC-5 cell line (ATCC-171).
Poliovirus 1 LSc-2ab (PV-1), a human enteric virus known
to be very stable in the environment, was propagated and
assayed in the Buffalo green monkey kidney (BGM) cell
line. Infected cells were frozen and thawed three times at
-20°C to release virus after cytopathogenic effects (CPE)
were observed in the monolayer. This was followed by
centrifugation at 1000gfor 10 min to remove cell debris,
addition to the virus suspension of 9% polyethylene glycol
(MW 8000) and 0.5 M sodium chloride, and stirring
overnight at 4°C. After centrifugation at 10,000gfor
30 min, the pellet was resuspended in 0.01 M phosphate
buffered saline (PBS; pH 7.4) (Sigma, St. Louis, MO) to
5% of the original virus suspension volume. The coro-
naviruses were then titered and stored at -80°C. The
poliovirus was further purified by extraction with equal
volumes of Vertrel XF (Dupont, Wilmington, DE), emul-
sified and centrifuged at 7,500gfor 15 min, and
subsequently the top aqueous layer was collected, titered,
and stored at -80°C.
Tap water samples were collected from a cold tap faucet
in the laboratory. The source is groundwater with water
quality parameters: pH 7.8, 297 mg/l dissolved solids, and
0.1 mg/l total organic carbon. The water was allowed to
run for 3 min before collection of the sample. Virus sur-
vival was determined in both nonfiltered tap water and tap
water passed through a 0.2-lm pore size filter to remove
bacteria. Tap water (30 ml) was added to sterile 50 ml
polypropylene centrifuge tubes, to reduce loss of virus by
adhesion to the container. Sterile sodium thiosulfate was
added to a final concentration of 33 lg/ml to dechlorinate
the water. After vortexing, virus was added to each tube to
a final concentration of 10
5
TCID
50
/ml. Again the tubes
were vortexed and a sample was immediately taken (zero
time point). The tubes of tap water were then stored at
either 4°C or room temperature (23°C). The tubes stored at
room temperature were covered in aluminum foil to pre-
vent exposure to light. Tubes were sampled after 1, 3, 6,
10, 15, and 21 days and the samples frozen at -80°C until
they were assayed on cells.
Samples of primary and activated sludge (secondary)
effluent were collected in sterile polypropylene bottles
from the Roger Road Wastewater Treatment Plant in
Tucson, AZ, USA. Primary effluent was collected after
settling and secondary effluent was collected prior to
chlorination. Typical wastewater quality parameters for
this facilities primary effluent are biological oxygen
demand (BOD) and suspended solids of 110–220 mg/l.
Secondary effluent at Roger Road typically reflects a 90–
95% reduction in both BOD and suspended solids from the
primary effluent. The effluent (30 ml) was added to sterile
50 ml polypropylene centrifuge tubes. Primary effluent
was filtered through a 0.2-lm pore size filter before addi-
tion of the virus and was also tested unfiltered. Secondary
effluent was only tested unfiltered. Virus was then added to
each tube to a final concentration of 10
5
TCID
50
/ml. The
tubes were vortexed and a sample was immediately taken
(time zero). The tubes were then covered and held at room
temperature (23°C). Samples were collected after 1, 2, 3, 6,
10, 15, and 21 days and the samples frozen at -80°C until
assay.
Viruses were enumerated on cell cultures using either
the plaque assay or TCID
50
technique. PV-1 was titered in
6-well plastic cell culture plates by the plaque assay
method (Payment and Trudel 1993). This is a direct
quantitative method with a minimum detection limit of
10 pfu/ml. Each dilution was plated in duplicate wells.
Coronaviruses, which do not form plaques in cell culture,
were titered in 24-well plastic cell culture plates by the
tissue culture infectious dose 50% technique (TCID
50
)
(Payment and Trudel 1993). This technique determines the
dilution at which 50% of the wells show CPE. Taking the
inverse log of this dilution gives a titer of the virus per ml
TCID
50
. The minimum detection for this method was 3.7
viruses per ml. Each dilution was plated in a minimum of 8
wells. Any samples that were not from test waters filtered
prior to adding virus had to be filtered before assaying on
cell culture to eliminate bacterial contamination. The
0.2 lm low protein binding Millex filters (Millipore,
Billerica, MA) with polyethersulfone (PES) membrane
were prepared by passing 3% beef extract (Becton Dick-
inson, Sparks, MD) at pH 7 through to block sites that
might adsorb virus. All experiments were performed in
triplicate.
Results and Discussion
Table 1shows the survival in days of the three viruses in
the test waters. The log reduction of each virus was cal-
culated by the formula ‘‘log
10
N/N
0
’’ where Nis the titer of
the virus at the specified day and N
0
is the virus titer at time
0. The slope of the linear regression was used to determine
the survival; the time required for the virus titer to decrease
99% and 99.9% (expressed as T
99
and T
99.9
respectively).
Factors that can influence virus survival in water include
temperature, organic matter, and aerobic microorganisms
(John and Rose 2005; Melnick and Gerba 1980; Sobsey
and Meschke 2003). The most critical influence on virus
Food Environ Virol (2009) 1:10–14 11
123
survival is temperature. It has been shown that virus sur-
vival decreases with increasing temperature, mainly caused
by denaturation of proteins and increased activity of
extracellular enzymes (Hurst et al. 1980; John and Rose
2005). The results of the tap water study verify that this is
the case with coronavirus. By testing filtered tap water, we
reduced or eliminated the influence of particulate organic
matter and bacteria. At room temperature it required only
10 days to result in a 99.9% reduction of coronavirus in
filtered tap water, while at 4°C this level of virus inacti-
vation would require over 100 days. The survival of PV-1
in tap water at 4°C was similar to the coronavirus, but at
room temperature (23°C) this virus survived six times
longer in both the filtered and unfiltered water. The sur-
vival of the three study viruses in tap water at room
temperature (23°C) and 4°C are shown in Figs. 1and 2,
respectively. The increase in virus titer over time from the
initial titer in the 4°C water can be attributed to the
tendency of viruses to form aggregates that then disag-
gregate, not from viral replication in the sample.
The presence of organic matter and suspended solids in
water can provide protection for viruses that adsorb to these
particles but at the same time can be a mechanism for
removal of viruses if the solids settle out. The level of
organic matter and suspended solids in the test waters
increased from tap water to secondary effluent to primary
effluent. Coronavirus inactivation was greater in filtered tap
water than unfiltered tap water. Furthermore, HCoV sur-
vived longer in unfiltered primary effluent over the filtered.
This suggests that higher solids do provide protection for
coronaviruses in water. For PV-1, however, filtration made
very little difference in its survival in tap water. In the
primary effluent, PV-1 survived three times longer in the
filtered primary effluent than the unfiltered. It is important
to note that there was a substantial decrease in titer of the
coronaviruses between the time of addition to the waste-
water and the immediate retrieval for testing (zero time
Table 1 Survival in days
a
of study viruses
b
in tap water and wastewater
Virus Tap water
filtered 23°C
Tap water
unfiltered 23°C
Tap water
filtered 4°C
c
Primary effluent
filtered 23°C
Primary effluent
unfiltered 23°C
Secondary
effluent
T
99
T
99.9
T
99
T
99.9
T
99
T
99.9
T
99
T
99.9
T
99
T
99.9
T
99
T
99.9
HCoV 6.76 10.1 8.09 12.1 392
d
588
d
1.57 2.35 2.36 3.54 1.85 2.77
FIPV 6.76 10.1 8.32 12.5 87.0
d
130
d
1.60 2.40 1.71 2.56 1.62 2.42
PV-1 43.3
d
64.9
d
47.5
d
71.3
d
135
d
203
d
23.6
d
35.5
d
7.27 10.9 3.83 5.74
a
The slope of the linear regression was used to determine the survival; the time, in days, for the virus titer to decrease 99% and 99.9%, expressed
as T
99
and T
99.9
, respectively
b
Human coronavirus 229E (HCoV), feline infectious peritonitis virus (FIPV), poliovirus 1 (PV-1)
c
HCoV was unfiltered
d
Projected values
-5
-4
-3
-2
-1
0
0 5 10 15 20 25
Days
Log10 N/N0
HCoV
FIPV
PV-1
Fig. 1 Average log
10
reduction (average log
10
N/N
0
where Nis titer
of virus at specified day and N
0
is titer of virus at time 0) of study
viruses [human coronavirus 229E (HCoV), feline infectious perito-
nitis virus (FIPV), poliovirus 1 (PV-1)] in dechlorinated, filtered tap
water at room temperature (23°C)
-4
-3
-2
-1
0
1
0 5 10 15 20 25
Days
HCoV*
FIPV
PV-1
Log10 N/N0
Fig. 2 Average log
10
reduction (average log
10
N/N
0
where Nis titer
of virus at specified day and N
0
is titer of virus at time 0) of study
viruses [human coronavirus 229E (HCoV), feline infectious perito-
nitis virus (FIPV), poliovirus 1 (PV-1)] in dechlorinated, filtered tap
water at 4°C. *Unfiltered
12 Food Environ Virol (2009) 1:10–14
123
point). The titer of the coronaviruses immediately decreased
99.9% upon addition to the wastewater, while the PV-1 titer
only dropped 10%. This decrease may be due to the pres-
ence of solvents and detergents in wastewater that would
compromise the viral envelope and ultimately inactivate the
virus. This may also indicate that coronaviruses adsorb
more readily than PV-1 to solids in the wastewater. The
hydrophobicity of the viral envelope makes coronaviruses
less soluble in water and could therefore increase the ten-
dency of these viruses to adhere to the solids. Wastewater
samples had to be filtered to prevent bacterial contamina-
tion of the cell monolayer, which would remove solids and
any solids-associated viruses as well.
The presence of predatory microorganisms, such as
protozoa, can increase the inactivation rate of virus in water,
as well as the action of proteases and nucleases (Gerba et al.
1978; John and Rose 2005). The level of bacteria and solids
is both higher in primary effluent compared to secondary
effluent. All three test viruses were able to survive longer in
the unfiltered primary effluent than the unfiltered secondary
effluent, though for FIPV this was negligible. Again, this
suggests that solids-associated viruses in wastewater are
protected from predation and inactivation. However, the
coronaviruses were below the minimum detection limit
after 3 days, whereas PV-1 was detectable after 21 days.
Results for the average log reduction for the study viruses in
wastewater are listed in Table 2.
Conclusion
The results of this study indicate that coronaviruses are
much more sensitive to temperature than PV-1 and that
there is a considerable difference in survivability between
PV-1 and the coronaviruses in wastewater. This may be
due in part to the fact that enveloped viruses are less stable
in the environment than nonenveloped viruses. Coronavi-
ruses die off very rapidly in wastewater, with a 99.9%
reduction in 2–3 days, which is comparable to the data on
SARS-CoV survival (Wang et al. 2005a,b). Survival of the
coronaviruses in primary wastewater was only slightly
longer than secondary wastewater, probably due to the
higher level of suspended solids that offer protection from
inactivation. PV-1 survived substantially longer than cor-
onaviruses, requiring 10 days for a comparable reduction
in primary wastewater and 5 days in secondary wastewater.
This study demonstrates that the transmission of coronav-
iruses would be less than enteroviruses in the aqueous
environment due to the fact that coronaviruses are more
rapidly inactivated in water and wastewater at ambient
temperatures.
Acknowledgment This work was supported by a grant from the
University of Arizona National Science Foundation Water Quality
Center.
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