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| Journal of the New Zealand Medical Association,
14-March-2003, Vol 116 No 1170
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|
Symptom complaints following aerial spraying with biological
insecticide Foray 48B
Keith Petrie, Mark Thomas and Elizabeth Broadbent
Following the discovery of the painted apple moth in West
Auckland in 1999, an eradication programme was instituted by the Ministry of
Agriculture and Forestry (MAF). This programme initially involved ground
spraying in the area of the outbreak, and subsequently included aerial spraying
in a targeted area of West Auckland starting in January 2002. The spray area
included the suburbs of Te Atatu South, Glendene, Kelston, Glen Eden and the
Avondale Peninsula, and contained a population of approximately 13 500
residents. The spray programme was expanded later in the year to include other
Auckland suburbs, after moths were found outside the initial aerial spray
zone.
The spray (Foray 48B) contains spores of
Bacillus thuringiensis kurstaki (Btk)
in a solution derived from the bacterial culture medium. This spray has been
used in a number of similar eradication programmes, including the white-spotted
tussock moth programme (Operation Evergreen) in the eastern suburbs of Auckland
in 1996. Previous health assessments of the effects of this aerial spray have
been based on the monitoring of a variety of health services after the spraying.
In the case of Operation Evergreen, this included surveillance of consultation
patterns at sentinel general practices and birth outcomes at catchment hospitals
two years following spraying. No increased risk of adverse events was detected
in the exposed population.1
Aerial spray programmes generate a great deal of anxiety in
the communities exposed to the spray and there is currently a lack of data on
the effect of Foray 48B on symptom complaints and perceptions of health as
opposed to its effect on the rates of medically diagnosed illness. In this
study, we investigated self-reported symptoms before and after exposure to Foray
48B.
MethodsParticipants
and procedure The participants were
residents within the most intensively sprayed area of the initial MAF aerial
spray zone. Participants were recruited by a door-to-door survey of the homes
identified by MAF as being within a 100 metre zone along the riparian margins of
the Whau River, Wairau Creek and Waikumete Cemetery spray zones. With informed
consent and ethics committee approval, residents aged over 18 were invited to
participate in a survey of health and symptoms related to the aerial spray
programme. Of the 315 residents approached to participate in the study, 292
agreed to participate (refusal rate = 7%). Baseline data were gathered at the
end of October 2001, 10 weeks prior to the first spraying by MAF aircraft. At
the end of March 2002, after the area had been sprayed on three occasions, study
participants were asked to complete a postal questionnaire. Non-respondents were
sent two reminder letters.
Questionnaires
The baseline questionnaire was completed
by participants at their homes in the presence of the research assistant. In
this questionnaire, participants provided demographic information and also
indicated whether or not they had previously been diagnosed with asthma, hay
fever or other allergies. Participants were asked to indicate which, if any, of
25 symptoms they had experienced in the preceding four weeks. This symptom list
was derived from the Subjective Health Complaint
Scale.2 This scale has been used previously in
a New Zealand population and found to be a highly reliable means of assessing
symptom complaints.3 Participants were also
asked to rate their overall health using a seven-point scale from
“terrible” to “excellent”, and to state the number of
visits they had made to a general practitioner (GP) or alternative healthcare
provider during the past three months. The participants’ names and
addresses were also collected by the research assistant in order that they could
be sent a follow-up questionnaire.
In the follow-up
questionnaire, participants were asked to repeat the symptom checklist and the
self-rated health item, and to estimate the number of visits they had made to a
GP or alternative healthcare provider during the previous three-month period.
Participants also indicated whether or not they had changed their medication or
taken any new medicines in response to the spraying and if they had discussed
concerns related to the spraying with their GP or other doctor. Participants
were asked to rate “How much was your health affected by the spray
programme in your area?” and, if they had children at home, “How
much was your children’s health affected by the spray programme in your
area?” Both questions were rated on a five-point scale from “not at
all” to “extremely”.
Statistical analysis was
carried out using SPSS for Windows statistical software. Differences between the
frequency of symptoms and self-rated health reported at baseline and follow up
were analysed by comparing subjects who answered both baseline and follow-up
questionnaires using paired sample t-tests. Differences in frequency of symptoms
reported by participants who gave a history of asthma, hay fever or other
allergies and by participants without these conditions were conducted using
analysis of variance (ANOVA). Changes in the frequency of visits to GPs and
alternative healthcare providers were analysed with non-parametric tests due to
the skewed nature of these distributions.
ResultsThe sample comprised 131 males and
161 females. Participants’ ages ranged from 18–79 years, with a mean
age of 42.1 years (SD = 15.2). Europeans made up 60.3% of the sample, Maori
7.5%, Pacific Islanders 13.5%, and other ethnic groupings 12%. These demographic
characteristics are approximately the same as those identified for the total
population of the spray area.4 In total, 181
(62%) of the initial participants responded to the postal questionnaire.
Non-respondents to the follow-up questionnaire were significantly younger (t
(87) = 5.20, p = 0.001), and more likely to be non-European
(Π2 = 19.46, p = 001), but did not differ
by gender (Π2 = 0.85, p = 0.36), number of
baseline symptoms (t (285) = 0.69, p = 0.49), previous diagnosis of asthma
(Π2 = .71, p = 0.39), hay fever
(Π2 = 0.46, p = 0.49), or rates of other
allergies (Π2 = 0.34, p = 0.56).
Table 1. Percentage of population reporting each
symptom at baseline and following spraying
The data were first analysed to examine differences between
reported symptoms at baseline and following the commencement of the spraying
programme. Overall, the total number of reported symptoms increased
significantly from baseline (mean = 3.90, SD = 3.56) to follow up (mean = 4.78,
SD = 4.48), t (156) = -2.99, p = 0.003. As can be seen from Table 1,
participants reported increases in a number of symptoms following the spraying.
Significant increases were noted for the following symptom reports: sleep
problems, difficulty concentrating, dizziness, irritated throat, itchy nose,
diarrhoea, stomach discomfort, gas discomfort, and extra heartbeats.
At the baseline survey, 14.7% of participants reported they
had previously been diagnosed with asthma, 24.6% with hay fever, and 19.2% with
other allergies. To examine whether participants suffering from these conditions
were affected by the spray programme, an analysis of variance was conducted for
each of these groups compared to those without the diagnoses, controlling for
their symptom scores at baseline. These analyses showed a significant increase
in symptoms for participants with a history of hay fever (F (1147) = 5.30, p =
0.02) compared with those participants not previously diagnosed with hay fever,
but no significant increase for participants with a history of asthma (F (1151)
= 2.19, p = 0.14) or other allergies (F (1139) = 1.53, p = 0.22) when compared
with participants without these diagnoses.
 Figure 1. Percentage of participants reporting that
their own health or their children’s health was affected by the MAF spray
programme
Participants’ self-rated health declined significantly
from baseline (mean = 5.40, SD = 1.12) to follow up (mean = 5.08, SD = 1.21) t
(175) = 3.69, p = 0.0001. However, there were no significant increases in the
number of visits to the GP (Wilcoxon Z = -0.94, p = 0.35) or to alternative
healthcare providers (Wilcoxon Z = -0.39, p = 0.69) following the spraying .
Overall, 9.2% of participants reported discussing the effects of the spray with
their GP, and 6.5% reported changing their medication because of the spray. Most
participants reported that their own and their children’s health was not
affected by the spray programme, with children’s health more likely to be
seen as being affected than the participants’ own health (see Figure
1).
Discussion
This study found significant changes in the pattern of
symptom reports among residents exposed to aerial spraying with Foray 48B. The
most notable change was a doubling in the rate of irritated throat following the
spraying. Gastrointestinal symptoms also increased significantly following
spraying, with increases in stomach and gas discomfort as well as in diarrhoea.
Increases in sleep problems, dizziness and concentration difficulties were also
noted. Hay fever sufferers were more likely to have increased symptoms following
spraying, but no significant increases in symptoms were noted for asthmatics or
participants with other allergies. Relatively few subjects considered that the
spray programme had produced more than a moderate effect on their health, and
there was no increase noted in the rate of consultations with either medical
practitioners or alternative healthcare providers.
It was noteworthy that those symptoms that significantly
increased in frequency following the aerial spraying, fell into three loose
clusters. Sleep problems, difficulty concentrating and dizziness might be
considered indicators of a neuropsychiatric response to the spray programme,
while irritated throat and itchy nose may reflect local effects on the upper
airway, and stomach discomfort, gas discomfort and diarrhoea suggest that there
may be effects of the spray on the gastrointestinal system. The factors
responsible for these symptom clusters may be different. The neuropsychiatric
symptoms may result from sleep disturbance caused by the early morning spraying
by low-flying aircraft, as well as increased anxiety in some residents because
of the perceived risks of the programme. The upper airway symptoms may result
from the local irritant effects of inhaled spray. The gastrointestinal effects
may result from preformed endotoxin in the spray or from enterotoxin produced by
B. thuringiensis replicating in the gut
of exposed persons, or may be due to some other mechanism.
Previous work by others suggests that it is not unreasonable
to expect that exposure to spray containing B.
thuringiensis might cause health effects. Commercial sprays such as Foray
48B contain spores of B. thuringiensis
kurstaki, spore-associated crystals of
B. thuringiensis kurstaki-derived
endotoxin, various volatile chemicals, and residual components of the medium in
which the organism was cultivated. Health effects might be due to germination of
spores to produce replicating bacilli, direct effects of the pre-formed
endotoxin, or irritant or allergic effects of the nutrient or other components
of the culture medium. Exposure to sprays containing
B. thuringiensis commonly leads to
human infection with the organism and an associated immune
response.5,6 In one study of farm workers who
picked sprayed vegetables, positive skin test responses and IgG and IgE antibody
responses to B. thuringiensis were
common and were correlated with the intensity of exposure to the
spray.6 B.
thuringiensis is almost indistinguishable from
B. cereus, a relatively common cause of
food poisoning, and produces an enterotoxin which is identical to that produced
by B. cereus, although at a much lower
level.7 B.
thuringiensis may have been responsible, at least in part, for an
outbreak of gastroenteritis in a Canadian chronic care institution, where it was
isolated from spice and from the faeces of four affected patients, two of whom
also had Norwalk virus in their faeces.8 Thus,
there appear to be a number of potential means by which the spray might cause
human illness.
Previous research on the health effects of similar spray
programmes has not found conclusive evidence of adverse health effects as a
result of the spray. These studies have been largely based on monitoring the use
of healthcare services,1,9,10 isolation
of B. thuringiensis from clinical
specimens submitted for culture,9,10 or
specific studies of possible high-risk groups, such as children with
asthma.11 The current study differs from
previous approaches by examining changes in symptom complaints in the population
before and after being exposed to the spray and is therefore likely to be
sensitive to changes in symptoms that are not presented to health services. In
fact, individuals only present a very small proportion of physical symptoms to
doctors, and the vast majority are managed through restricting activity and self
medication.12 The decision to seek medical care
for symptoms is influenced by a wide number of factors, such as the perceived
efficacy of medical treatment for the complaint, the presence of pain, level of
disability, and economic
considerations.13
There are a number of limitations of the study, which mean
our findings should be interpreted with caution. Although the response rate to
the follow-up questionnaire was relatively high for a study of this type, it is
likely that people who perceived themselves as being affected by the spray would
have been more inclined to respond. Furthermore, we cannot be certain that the
changes in self-reported symptoms were a direct result of the spray programme,
nor can we exclude the possibility that severe health effects occurred in a very
small proportion of the people exposed to the spray. It is also possible that
changes in exposure to pollen or other seasonal environmental factors may have
contributed to the differences in symptom rates between the two surveys. The
main pollen season in Auckland is from October to February, and this may have
influenced upper airway symptom reports. However, we would not expect the
changes in neuropsychiatric and gastrointestinal symptoms to be related to
pollen exposure. Furthermore, the pattern of symptoms (no significant increase
in eye irritation, wheezing, coughing) does not support an explanation based on
changes in exposure to pollen. The use of a control group without spray exposure
in future studies would help to resolve this issue.
While no significant differences in the frequency of visits
to GPs or other healthcare providers were evident, it should be noted that the
follow-up period may have been too short to pick up such changes in healthcare
attendance. It should also be noted that the time period referred to in the
initial symptom checklist was made longer in the follow-up questionnaire, in
order to ensure all respondents had been exposed to the spray. This may be
partly responsible for the overall increase in the number of symptoms found at
follow up. However, it does not explain the unequal pattern of symptom changes
found following spraying. Bearing in mind these limitations, the results of this
study do suggest that aerial spraying with Foray 48B is associated with some
adverse health consequences. Further research should focus on the potential
effects of the spray on upper airway and gastrointestinal symptoms in
populations exposed to it and should investigate the relationship between such
symptoms and evidence of B.
thuringiensis infection.
Author information:
Keith J Petrie, Associate Professor, Department of Health Psychology; Mark
Thomas, Associate Professor, Department of Molecular Medicine and Pathology;
Elizabeth Broadbent, Research Fellow, Department of Health Psychology, Faculty
of Medical and Health Sciences, University of Auckland, Auckland
Correspondence: Dr
Keith J Petrie, Department of Health Psychology, Faculty of Medical and Health
Sciences, University of Auckland, Private Bag 92019, Auckland. Fax: (09) 373
7013; email: kj.petrie@auckland.ac.nz
References:
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