United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S2-86/027d May 1986
c/EPA Project Summary
The Lubbock Land Treatment
System Research and
Demonstration Project:
Volume IV.
Lubbock Infection Surveillance
Study (LISS)
D. E. Camann, P. J. Graham, M. N. Guentzel,
H. J. Harding, K. T. Kimball, B. E. Moore,
R. L. Northrop, N. L Altman, R. B. Harrist,
A. H. Holguin, R. L. Mason, C. Becker Popescu, and
C. A. Sorber
The Lubbock Infection Surveillance
Study (LISS) was conducted to monitor in-
fections and acute illness in the primarily
rural community surrounding the Lubbock
Land Treatment (Demonstration) System
(LLTS) at the Hancock farm near Wilson,
Texas. The LISS objective was to identify
possible adverse affects on human hearth
from slow-rate (sprinkler) land application
of wastewater which contained potentially
pathogenic microorganisms.
An epidemiological analytic cohort
study of 478 area residents and Hancock
farm workers was maintained during the
first 20 months of operation of the LLTS
(February 1982-October 1983) and during
the 20-month period immediately preced-
ing LLTS operation (June 1980-January
1982). Blood samples collected semian-
nually were analyzed for antibody titers to
14 enteroviruses, 3 adenoviruses, 2 reo-
viruses, rotavirus, Norwalk virus, hepatitis
A, Legionella, Entamoeba histolytica, and
influenza A. Routine fecal specimens were
collected regularly to isolate enteric
viruses and overt and opportunistic
bacterial pathogens. Electron microscopic
examination was performed to detect a
variety of other virus-like particles. Tuber-
culin skin tests were administered annually
to detect non-tuberculosis mycobacterial
infections. Illness information was pro-
vided by study participants on a weekly
basis. Concentrations of microorganisms
also were measured in the wastewater,
wastewater aerosol, and drinking water.
Dispersion modeling, participant activity
diaries, and a weekly log of extensive
wastewater contact were used to
calculate an aerosol exposure index of
relative cumulative exposure of each par-
ticipant to the wastewater aerosol within
each of the four major irrigation seasons.
Very high levels of bacteria and enteric
viruses were present in the sprayed
wastewater obtained via pipeline directly
from the Lubbock sewage treatment plant.
Enteroviruses were consistently found in
the wastewater aerosol in 1982.
Participants in the high and low expo-
sure groups were generally well balanced
with regard to age, gender, previous titer,
and time spent in Lubbock. However,
aerosol exposure was largely confounded
with patronage of a local restaurant and
use of evaporative cooler air conditioners.
Disease surveillance did not disclose any
obvious connection between the self-
reporting of acute illness and degree of
aerosol exposure.
Whenever a sufficient number of infec-
tions was observed during an irrigation
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season, this infection episode was anal-
yzed by four different methods: confirm-
atory statistical analysis, exploratory
logistic regression analysis, confidence
intervals of incidence density ratios, and
risk ratio scoring. The association of infec-
tion status with wastewater aerosol ex-
posure and other relevant factors was
investigated.
Comparison of crude seroconversion in-
cidence densities indicated that some ex-
cess risk of viral infection (risk ratio of 1.5
to 1.8) appeared to be associated with
level of aerosol exposure. A symmetric risk
ratio scoring approach provided evidence
of a dose-related stable association
(p =0.002) between the infection events
in the observed episodes of infection and
aerosol exposure. More than the expected
number of statistically significant associa-
tions of the presence of infection with
wastewater aerosol exposure were found
in the confirmatory analysis of independ-
ent infection episodes using Fisher's exact
test. Thus, three different statistical ap-
proaches provided similar evidence that
the rate of viral infections was slightly
higher among members of the study pop-
ulation who had a high degree of aerosol
exposure.
In the episode of poliovirus 1 sero-
conversions in spring 1982, some of the
infections were probably caused by
wastewater aerosol exposure because a
strong association existed and no alter-
native explanation could be identified.
Three distinct risk factors (poliovirus
immunization in spring 1982, low polio 1
antibody liter in January 1982, and a high
degree of aerosol exposure) were inde-
pendently associated with the poliovirus
1 seroconversions and each appears to
have been responsible for some of the
poliovirus 1 infections. Weak evidence of
association was found between aerosol
exposure and infection by other enteric
viruses (specific coxsackie B viruses and
echoviruses) which were simultaneously
recovered from the wastewater during the
summer irrigation season of 1982.
However, it could not be determined
whether aerosol exposure or identified
alternative explanations were the actual
risk factor(s) in these enteric viral infec-
tions. The association of viral infections
with aerosol exposure shows a dose
effect, since the study population was
exposed to more enteroviruses via the
wastewater aerosol in 1982 than in 1983.
This Project Summary was developed
by ERA'S Health Effects Research
Laboratory, Research Triangle Park. NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Background
Land Application and Potential
Infectious Disease Hazards
Land application of wastewater can be
an attractive alternative to traditional
waste disposal practices. It avoids con-
tamination of surface waters, provides ad-
ditional waste treatment, returns nutrients
to the soil, and reuses the water. The
policy of the U.S. Environmental Protection
Agency (EPA) is to "press vigorously for
publicly-owned treatment works to utilize
land treatment processes to reclaim and
recycle municipal wastewater." Applicants
for federal construction grants (Section
201) must show in their requests that they
have considered the application of
wastewater to land as an alternative.
Financial incentives are provided to en-
courage land application as stated in the
Clean Water Act of 1977. Slow rate ap-
plication of wastewater to land by spray
irrigation has been and continues to be
one of the most popular application
methods. With EPA encouragement, it is
likely that the practice of applying
wastewater to land by sprinkler irrigation
according to EPA design criteria will
become more prevalent as a means of final
treatment and disposal.
Along with its considerable benefits,
land application of wastewater entails the
potential risk of infection from exposure
to microorganisms in the wastewater. A
variety of agents of human disease, in-
cluding many overt and potentially
pathogenic microorganisms, may survive
treatment processes, and thus could
theoretically pose a threat. There are
various environmental pathways by which
these agents in the wastewater and the
aerosol produced by its sprinkler applica-
tion might be introduced and initiate infec-
tion in susceptible exposed individuals.
Farmers will come in direct contact with
the wastewater and its sprayed mist in the
course of their work with the irrigation
system. Agents in the wastewater aerosol
can be transported by the wind and might
be inhaled or ingested in exposed food
while still viable and infective. Other
potential environmental pathways include:
1) ingestion of wastewater-contaminated
ground water used as the domestic water
supply, 2) dust storms in which waste-
water-irrigated surface soils are entrained
by strong winds, 3) insect vectors (e.g.,
flies attracted by the wastewater lagoons),
4) rodents (e.g., feed or food stuffs con-
taminated by fecal droppings or urine from
field mice,infected by wastewater spray,
which may be spending the winter in farm-
houses and barns), and 5) fomites (e.g.,
wastewater-contaminated work shoes,
clothing, hands, or doorknobs). Once
introduced into the local population, the
infectious agents might be transmitted by
contact between infected and susceptible
individuals.
Recent Literature
An Israeli study in 1976 cautioned that
the infectious disease hazards associated
with irrigation of partially treated
wastewater are greater than previously
assumed. Existing illness records were
analyzed in a retrospective study of enteric
diseases among communal agricultural
settlements (kibbutzim) in Israel. The
incidence rates of enteric illness for kib-
butzim utilizing wastewater for spray
irrigation were compared with other kib-
butzim practicing no form of wastewater
irrigation. Two- to four-fold increases in the
incidence of shigellosis, salmonellosis,
infectious hepatitis, and typhoid fever
were reported for the kibbutzim utilizing
wastewater, whereas the incidence of
other diseases not normally associated
with sewage were similar in both groups.
A subsequent retrospective study of Israeli
kibbutzim in 1983 identified serious defi-
ciencies in the data of the original study,
including misclassification of some kibbut-
zim regarding wastewater reuse, uncer-
tainties about periods of irrigation, and the
inadequacy of the communicable disease
reports used as the basis for the study. In-
deed, the subsequent study failed to find
evidence of excess risk associated with
wastewater irrigation except in kibbutzim
in a "switch" category (i.e., in kibbutzim
practicing two consecutive years of
wastewater irrigation followed by the
same period without irrigation or vice ver-
sa). In this category, a significantly in-
creased risk of total enteric disease was
noted only for the 0-4 age group during
periods of wastewater irrigation.
Two prospective epidemiologic studies
were conducted among residents around
activated sludge sewage treatment plants
near Chicago, Illinois, using the family-
based virus watch approach. Both studies
included a health watch of participating
households that involved health diaries,
serology, and clinical specimen isolations.
Neither study detected any obvious ad-
verse health effects in residents potentially
exposed to wastewater aerosols from aer
ation basins.
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Occupational health effects of waste-
water and wastewater aerosols have also
been investigated. A study of Muskegon
County, Michigan, workers exposed to
wastewater spray irrigation failed to show
any differences in illness or viral isolation
rates between the workers and a control
group. Although antibody titers to cox-
sackievirus B5 were significantly higher in
spray irrigation nozzle cleaners, serocon-
versions were not documented. Likewise,
a prospective seroepidemiologic study of
municipal sewer and sewage treatment
workers and controls in three American
metropolitan areas failed to support a
significant risk associated with exposure
to the wastewater. However, inexperi-
enced workers reported significantly
higher rates of gastrointestinal illness, and
the level of antibody to certain viruses ap-
peared to be related to level of exposure
to wastewater aerosols. In Sweden, an in-
creased incidence of acute febrile illness
was found among workers exposed to
sludge dust (probably due to endotoxins)
and also increased incidence of gastro-
intestinal symptoms among sewage treat-
ment workers.
None of these studies has investigated
the effects on nearby residents' health of
sprinkler irrigation of wastewater over a
known broad range of wastewater quali-
ty. The Lubbock Infection Surveillance
Study (LISS) was designed to observe any
association of the potential infectious
disease effects with exposure to sprayed
wastewater.
The Lubbock Land Treatment
System (LLTS) Expansion
A major new land treatment system was
constructed as a demonstration project to
apply wastewater from Lubbock, Texas, by
sprinkler irrigation at the Hancock farm
near Wilson, Texas, (see Figure 1). The
design and operation of this large
demonstration project provided for collec-
tion of research data under a wide range
of quality of the wastewater that was used
for irrigation. The first four major irrigation
periods after the LLTS expansion com-
menced operation in February 1982 were
monitored. The quality of the applied
wastewater was substantially different in
each of the four periods. The original spray
nozzles directed the wastewater upward,
which enhanced the creation and drift of
aerosols. Thus, the LISS investigated the
risk of wastewater exposure ranging from
conditions representative of established
guidelines (fecal coliforms <1000
MPN/100 mL) to those which explored the
relative safety factor of the guidelines.
Key:
Pipeline
SeWRP
Hancock Farm
Figure 1. Wastewater irrigation system.
The LISS was one of several areas of
research which were conducted simul-
taneously at the land treatment demon-
stration site. The chemical, biological and
physical conditions of the ground water,
soils, and crops were characterized prior
to and during the wastewater irrigation.
The effects of hydraulic, nutrient, and salt
mass loading were assessed on the per-
colate and on the crops and soil.
The Lubbock Infection
Surveillance Study (LISS)
The LISS was conducted to monitor in-
fections in the community surrounding the
new land treatment demonstration sys-
tem. This prospective observational study
Scale
5
JO km
has attempted to determine the associa-
tion, if any, between the occurrence of
infectious diseases in residents and
workers and their exposure to the
wastewater and aerosols produced by
wastewater spray irrigation. The initial two
years of operation of the LLTS expansion
at the Hancock farm were investigated.
LISS involved a 4-year health watch of
nearby residents and microbiological
monitoring of the wastewater and its
aerosol. This site is unique in that a typical
rural community with no prior wastewater
exposure was challenged by the enteric
agents active in a much larger urban com-
munity (Lubbock). Persons residing around
the Hancock site may have been exposed
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to infectious agents indigenous in the Lub-
bock population but not circulating in the
study area. Thus, many in the study pop-
ulation may have been relatively suscept-
ible to the pathogens in the wastewater.
A health watch of the rural community
was maintained before, during, and after
periods of wastewater spray irrigation. The
health watch focused on infections de-
tected serologically and through isolates
recovered from routine fecal specimens. To
enhance the likelihood of interpreting
observed episodes of infection, the likely
routes of introduction and transmission
were monitored.
Study Objective
The general objective of the LISS was
to identify possible adverse effects on
human health from slow rate (sprinkler)
land application of wastewater which con-
tained potentially pathogenic micro-
organisms. More precisely, the objective
was to determine the association, if any,
between the occurrence of infectious
diseases in residents and workers and their
exposure to the wastewater and aerosols
produced by wastewater spray irrigation.
This objective was accomplished by
disease surveillance of the study popula-
tion, by description of the distribution of
infections, and principally by evaluation of
the incidence of infections for association
with exposure.
Study Design
The LISS was designed to monitor in-
fections and illnesses occurring in the
study population and concurrent environ-
mental levels of the infectious agents.
Disease surveillance was maintained to
protect the population from any obvious
untoward effects. However, the study
focused on infections and the infecting
agents rather than illness in order to ob-
tain greater objectivity, sensitivity,
specificity, and etiologic evidence.
All participants were asked to provide
blood samples semiannually, usually in
June and December. Sera were assayed
for antibody titers to specific enteroviruses
and other microorganisms known or sus-
pected to be present in the sprayed
wastewater. A seroconversion, defined as
the four-fold or greater increase in agent-
specific antibody titer in simultaneously
tested successive sera from one individual,
was considered serologic evidence that
the individual had been infected by the
agent during the time interval between the
blood collections. Since mycobacteria
were present in the wastewater, tuberculin
skin tests were administered annually to
give suggestive evidence of a non-
tuberculosis mycobacterial infection.
An adult from each household and any
children under 13 years of age were
designated as fecal donors. Each donor,
whether well or ill, was asked to submit
routine stool specimens for microbio-
logical testing during scheduled weeks
which spanned each major irrigation
period in 1982 and 1983. A series of three
1-week fecal collection sessions were
scheduled before, during, and near the end
of each irrigation period to detect infec-
tion events occurring in the interim.
Clinical bacteriological analyses were per-
formed to isolate overt and opportunistic
pathogens. A semiquantitative measure-
ment of growth (as heavy, moderate, light,
or very light) was obtained by streaking
primary plates by a four-quadrant method.
Three categories of bacterial infection
events were identified by comparing
results from consecutive monthly speci-
mens from an individual. Clinical viro-
logical analyses were performed to isolate
enteric viruses in the fecal specimens by
tissue culture techniques. Electron micro-
scopic examination was performed on
about 1/4 of the routine fecal specimens
to detect a variety of virus-like particles,
many of which are not recoverable by
tissue culture techniques. Detection of a
specific virus by laboratory cultivation or
by electron microscopic examination was
considered evidence of a viral infection.
Each non-adenovirus viral infection was
regarded to be new, unless the same agent
had been recovered from the individual in
the prior 6 weeks.
Each household was contacted weekly
by telephone for a report of any illnesses
during the prior week. When a sufficient-
ly recent respiratory or gastrointestinal ill-
ness was reported, the ill participant was
requested to submit a throat swab or stool
specimen to identify the causative agent.
Weekly self-reports of illness and appro-
priate illness specimens were obtained
over the entire period of irrigation from
January 1982 until October 1983 and over
baseline periods corresponding to seasons
of heavy irrigation.
The types and densities of potentially
pathogenic bacteria and viruses were
monitored in the wastewater, wastewater
aerosol, and other environmental routes of
introduction and transmission. An effort
was made to determine the fluctuations
in levels of every measurable infectious
agent utilized in the health watch.
However, the low densities of many agents
in environmental samples necessitated
reliance on indicator organisms to
establish environmental patterns.
Wastewater samples of the effluent from
the pipeline and reservoirs to be utilized for
spray irrigaion, and of the Wilson effluent,
were obtained and analyzed for indicator
bacteria and enteroviruses biweekly to
span the major irrigation periods; cor-
responding baseline samples had been
obtained with the same frequency in 1981
and at lesser frequency in 1980 to char-
acterize the effluents. Microbiological
screens of indigenous enteric bacteria
were conducted on one sample each from
the pipeline and the reservoir per irrigation
season. The purpose of the routine
wastewater samples was to document the
presence, prevalence, longitudinal pattern,
and passage through the study communi-
ty of viral and bacterial pathogens possibly
introduced by the wastewater. Extensive
aerosol sampling was conducted to char-
acterize the aerosol density of indicatoi
microorganisms produced by the spray ir-
rigation of both pipeline and reservoii
wastewater. Virus runs were also con-
ducted to measure the density and diver-
sity of enteroviruses in aerosols emanatinc
from the sprinkler rigs. Drinking water
houseflies, and dust storms also were
evaluated as other means of introducing
microorganisms into the study population
An aerosol exposure index (AEI) was
devised to measure the degree of a par
ticipant's cumulative exposure to micro
organisms in the wastewater aerosol
relative to all other study participants dur
ing a given irrigation period. When i
number of similar infection events wert
observed either serologically oi
microbiologically in the study populatior
within a time interval corresponding to ar
irrigation period, this infection episode
was statistically analyzed for associatior
with wastewater aerosol exposure usin<
AEI. Infection incidence rates were com
pared among exposure subgroups aru
with baseline rates to determine th<
relative risk of infection.
Conclusions
1. The LISS employed an epidemiologit
analytic prospective cohort stud^
design which was quite appropriate tc
measure the strength of associatior
between exposure to the wastewate
used for irrigation and the develop
ment of new infections. The result!
from the isolation and serology pro
cedures used to detect infections ap
pear to be adequate. These detectioi
methods were sufficiently sensitivi
and specific to observe man'
episodes of infection in the stud'
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population in which the etiologic
agent was identified. The size of the
population was sufficient to analyze
the distribution of observed infections
for possible association with exposure
to wastewater irrigation and to con-
trol for extraneous variables via
logistic regression analysis. However,
the small population size led to in-
stability of the association. The
significance of the study findings
have not been limited to a great ex-
tent by such major confounding fac-
tors as age, gender, antibody level,
head of household education, and
time spent in Lubbock.
2. The quality of the wastewater to
which the study population was ex-
posed was highly variable during the
study. During the initial spring 1982
irrigation period, the quality of the ir-
rigation wastewater approximated
that of a low quality primary effluent,
as determined by physical and
chemical analyses. While the quality
of the irrigation wastewater was
greatly improved in 1983, its fecal
coliform concentration still exceeded
the EPA guideline for controlled
agricultural irrigation as practiced at
the study site.
3. Spray irrigation of wastewater ob-
tained via pipeline directly from the
Lubbock SeWRP was a more substan-
tial source of aerosolized micro-
organisms than spray irrigation of
wastewater stored in reservoirs.
Enteroviruses were consistently
recovered in the aerosol at 44 to 60
m downwind of irrigation with pipe-
line wastewater.
4. Microorganism levels in air downwind
of spray rigs using pipeline
wastewater were significantly higher
than upwind levels: fecal streptococci
levels to at least 300 m downwind,
and levels of fecal conforms,
mycobacteria and coliphage to at
least 200 m downwind. Levels down-
wind were also significantly higher
than background levels in ambient air
outside of participants' homes: fecal
coliform levels to beyond 400 m
downwind, mycobacteria and coli-
phage levels to at least 300 m and
fecal streptococci levels to at least
200 m.
5. The exposure which most of the
study population received to most
microorganisms via the wastewater
aerosol was greater in 1982 than in
1983. The cumulative enterovirus
dose received from aerosol exposure
at a given distance downwind in sum-
mer 1982 was estimated to be at
least an order of magnitude greater
than in any other irrigation period.
6. Individuals in the high (AEJ>3) and
low (AEK3) exposure groups were
generally well balanced with regard
to infection risk factors, including
age, gender and previous antibody
titer. The high exposure fecal donors
ate food prepared by a local restau-
rant very significantly more often,
made greater use of evaporative
coolers for air conditioning, and had
more farmers as head of household.
7. The lack of a strong, stable associa-
tion of clinical illness episodes with
the level of exposure to irrigation
wastewater indicates that waste-
water spray irrigation did not produce
obvious disease during the study
period. However, the participants in
the high exposure level (AEI>5)
reported a slight excess crude in-
cidence density of total acute illness
shortly after the onset of wastewater
irrigation, both in spring 1982 and in
summer 1982, the seasons of initial
and heaviest microbial exposure, re-
spectively. The extent to which this
reflects actual illness versus possible
reporting bias by high exposure par-
ticipants cannot be ascertained.
8. The occurrence of enteric Gram-
negative bacteria (EGNB) at moderate
and heavy levels in the throats of both
healthy and ill study participants was
frequent and widespread between
July 19 and October 12, 1982. The
household environment was strong-
ly associated with the continuing
EGNB throat infections of one house-
hold. Among the ill throat swab
donors, use of an evaporative cooler
for home air conditioning was
associated with the EGNB throat
infections.
9. Some excess risk of viral infection
(risk ratio of 1.5 to 1.8) was asso-
ciated with wastewater aerosol ex-
posure, based on comparison of
crude seroconversion incidence den-
sities by aerosol exposure level and
by irrigation vs. baseline period.
10. A symmetric risk ratio score approach
provided evidence of a stable and
dose-related association between in-
fection events and wastewater
aerosol exposure in the infection
episodes observed by the LISS.
11. Some infection episodes appear to
have been related to wastewater
aerosol exposure, because more
statistically significant associations
than expected were found in the con-
firmatory analysis of independent in-
fection episodes using a one-sided
Fisher's exact test. Some imbalances
in the two populations may provide
alternate explanations for the excess
associations. On the other hand, the
number of detected increases in in-
cidence rates associated with the
wastewater irrigation may be
underestimated, considering the
relatively modest power of the tests
to detect small differences.
12. An exploratory logistic regression
analysis found significant (p<0.05)
associations between presence of
infection and degree of aerosol ex-
posure while controlling for the ef-
fects of extraneous variables in four
infection episodes. More supporting
evidence was found for the waste-
water aerosol route of exposure than
for direct contact with wastewater or
spending time in the irrigation en-
vironment on the Hancock farm.
13. Eight specific infection episodes
displayed good or marginally consis-
tent evidence of association with
wastewater aerosol exposure.
a. Two of these episodes were
probably unrelated to wastewater
exposure because a more plaus-
ible alternative explanation was
identified:
• Episode of Klebsiella infections
in summer 1983
— alternative: eating at a local
restaurant
• Spurious control episode of
echovirus 9 seroconversions in
the baseline period
— alternative: within house-
hold spread
b. The evidence is inconclusive in
five episodes because both
aerosol exposure and the iden-
tified alternative explanation(s) are
plausible risk factors:
• Episode of clinical viral isolates
excluding adenoviruses and
immunization-associated
polioviruses in summer 1982
— alternative: eating at a local
restaurant
• Episode of echovirus 11 sero-
conversions in 1982
— alternatives:
• contaminated drinking water
• Caucasian, large household
• Episode of seroconversions to
viruses isolated from waste-
water in summer 1982
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— alternatives:
• contaminated drinking water
• low income, Caucasian
• Episode of seroconversfons to
viruses isolated from waste-
water in 1982
— alternative: farmer, history of
pneumonia
• Episode of seroconversions in
summer 1982 to all serum
neutralization-tested viruses
— alternative: contaminated
drinking water
All five of these infection epi-
sodes relate to echo or coxsackie
B viral infections observed primari-
ly in summer 1982 and primarily
to agents recovered from the
wastewater at that time.
c. Some of the infections in one
episode were probably caused by
wastewater aerosol exposure
because a strong association ex-
isted and no alternative explana-
tion could be identified:
• Episode of poliovirus 1 serocon-
versions in spring 1982
Three distinct risk factors
(poliovirus immunization in spring
1982, low polio 1 antibody titer in
January 1982, and a high degree
of aerosol exposure) were in-
dependently associated with the
poliovirus 1 seroconversions in
spring 1982 and each appears to
have been responsible for some of
the poliovirus 1 infections.
14. Despite the efforts to obtain a random
sample, the study participants during
the irrigation periods were essential-
ly volunteers who were not represen-
tative of the entire population of the
study area. Furthermore, the frequen-
cy of patronizing local restaurants and
the use of evaporative coolers were
factors that were largely confounded
with wastewater aerosol exposure.
For these reasons, the LISS findings
cannot easily be generalized to other
sites.
15. In summary, a general association ex-
isted between exposure to irrigation
wastewater and new infections. A
viral dose-response relationship was
observed over the four irrigation
seasons, since the aerosol exposure-
associated episodes of viral infection
occurred primarily in 1982 during the
irrigation seasons of greater
enterovirus aerosol exposure. Some
poliovirus 1 seroconversions during
the spring of 1982 were probably
related to wastewater aerosol ex-
posure. However, even during 1982,
the strength of association remained
weak and frequently was not stable.
Wastewater of poor quality com-
prised much of the irrigation water in
1982. Of the many infection episodes
observed in the study population, few
appear to have been associated with
wastewater aerosol exposure, and
none resulted in serious illness.
Recommendations
1. To minimize exposure, it would be
prudent to use wastewater from the
reservoirs at the Hancock farm for ir-
rigation (or to apply equivalent treat-
ment measures), rather than irrigating
directly from the pipeline.
2. Poliovirus serology should be per-
formed on archived sera from June
1982 through October 1983 to identify
poliovirus seroconversions in the study
population spanning the summer 1982
and the 1983 irrigation periods. Any
observed poliovirus infection episodes
should be fully analyzed by the inferen-
tial methods employed in the LISS.
Since summer 1982 and possibly sum-
mer 1983 appear to have been seasons
of higher poliovirus aerosol exposure
than spring 1982 was, these data
would confirm or dispute the probable
relationship of poliovirus 1 seroconver-
sions to wastewater aerosol exposure
which was observed in spring 1982.
3. Serological testing of archived sera is
recommended for selected enterovi-
ruses and rotavirus to observe and
analyze additional infection episodes in
order to clarify the apparent dose-
response relationship with wastewater
aerosol exposure detected in the LISS.
a. Perform serum neutralization re-
testing to improve existing infection
episode data. There are 56 echo-
virus and adenovirus infections
reported for the years 1982 or 1983
that need additional serologic
testing to identify the exact
6-month interval in which the sero-
conversion occurred. Also, there
were 28 serologic series in which in-
fection status was indeterminate
due to inconsistent or contradictory
titer results and 33 unconfirmed
four-fold or greater titer rises in un-
paired sera; these cases were not
used in the LISS data analysis.
b. Conduct rotavirus and coxsackie B
virus serology having a high prob-
ability of yielding additional infec-
tion episodes to agents found in
sprayed wastewater. Rotavirus
serology should be performed on
the entire serum donor population.
since a very high incidence density
of seroconversions to rotavirus was
observed throughout the study
period in both the 45 children and
the 11 adults tested in the LISS. Ad-
ditional serology testing for cox-
sackieviruses B2, B3, and B4 is
recommended based on their
recovery from the wastewater in
1982 and 1983.
c. Serologic testing of echoviruses 12,
25, 27, and 31 is recommended
because they were each recovered
from wastewater in several of the ir-
rigation periods.
4. An exposure assessment should be
performed to estimate the range o)
cumulative organism exposure
dosages that applied to the LISS infec-
tion episodes and other situations ir
which reasonable evidence of associa-
tion with wastewater irrigation was ob
tained, A dosage to the infectious
agent should be estimated for each in-
fected individual and the dosage range
of the high exposure level of par
ticipants should be approximated
Determination of the dosage range ir
which observed infection effects were
found would provide a crucial missinc
link in the relationship between viable
aerosol concentration and infection
This would facilitate transferring thf
dose-response findings of the LISS tc
other sites of wastewater aeroso
exposure.
5. An improved model of microbiologica
dispersion should be developed basec
on the LISS aerosol sampling data. The
LISS data provide a much better basi:
for model development than the dat.
bases previously employed. The mode
would permit the determination of th<
estimated range of microorganism ex
posure dosages at considerabli
distances downwind (i.e., 400-800 m
from any spray irrigation source o
wastewater aerosols.
6. If recommendation 1 is not im
plemented, a limited program o
wastewater and aerosol samplirn
should be conducted at the Hancocl
farm to determine densities o
enteroviruses and indicator bacteria ii
wastewater and downwind air and t
reevaluate aerosolization efficiency fc
the current treatment process an
mode of operation. "Pulsed break
point chlorination" of pipelin
wastewater and installation of prope
spray nozzles to reduce aerosol forme
tion and drift are two major change
in irrigation practices at the Hancoc
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farm since 1983. The sampling pro-
gram would permit determination of
where the current irrigation practices
fit into the seasonal dose-effect gra-
dient found in the LISS.
7. It is recommended that analyses of ex-
isting LISS data be performed as pilot
studies to investigate whether clinical-
ly and serologically detected infections
and self-reported illness were associ-
ated with several apparent environ-
mental sources of infection identified
in the LISS.
a. Evaluate bacterial contamination
of wells that served as sources of
household drinking water.
b. Evaluate patronage of local
restaurants in this rural community
to help to address the extent to
which food prepared for public con-
sumption may be a source of inap-
parent infections and minor acute
illness.
c. Evaluate the use of evaporative
coolers for air conditioning as a
source of bacterial infections and ill-
ness, especially when bacterial con-
tamination of water supplies is quite
widespread.
8. Certain additional data analyses are
recommended to facilitate proper inter-
pretation of the LISS results:
a. Calculate incidence density ratios
and their confidence intervals for
clinical agents, as was done for
serologic agents and self-reported
illness, in order to balance the pro-
cedure for selection of infection
episodes with good and marginal
evidence of association with
aerosol exposure.
b. Investigate the need to control by
logistic regression analysis for the
effects on infection status of three
additional factors which were par-
tially confounded with wastewater
aerosol exposure: evaporative
cooler use prior to 1983, rural ver-
sus Wilson location, and children in
the household.
c. Conduct a stratified analysis of
serologic and illness incidence den-
sities to control for major potential
risk factors, such as age, gender,
previous antibody titer, occupation
and education of head of house-
hold, restaurant patronage, and
dwelling location. These analyses
would clarify interpretation of ap-
parent associations with aerosol
exposure of seroconversions and
self-reported illness which were
based on test-based confidence in-
tervals of crude incidence density
ratios.
d. Determine if there is evidence of
association of infections with
residential aerosol exposure when
the individuals with occupational
exposure to wastewater irrigation
are excluded from the study
population.
The LISS was conducted by Southwest
Research Institute (SwRI), the University
of Illinois (Ul), the University of Texas at
San Antonio (UTSA) and the University of
Texas at Austin (UTA). The full report was
submitted in fulfillment of CR 807501 and
S806204 by SwRI under primary sponsor-
ship of the U.S. Environmental Protection
Agency. The full report covers field ac-
tivities performed from May 1, 1980, to
October 31, 1983; work was completed as
of June 30, 1985.
D. £. Camann, H. J. Harding, K. T. Kimball, and R. L Mason are with Southwest
Research Institute, San Antonio, TX 78284; P. J. Graham, R. L. Northrop, N. L
Alt man, andC. B. Popescu are with University of Illinois, Chicago, IL 60680; M.
N. Guentzelis with University of Texas, San Antonio, TX 78285; B. E. Moore and
C. A. Sorber are with University of Texas, Austin, TX 78712; and R. B. Harrist
and A. H. Holguin are with University of Texas School of Public Health, Houston.
TX 77025.
Walter Jakubowski is the EPA Project Officer (see below).
The complete report, entitled "The LubbockLand Treatment System Research and
Demonstration Project: Volume IV. Lubbock Infection Surveillance Study
(LISS)," (Order No. PB 86-173 622/AS; Cost: $46.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
. S. GOVERNMENT PRINTING OFFICE: 1986/646-116/20838
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
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