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BioMed Central
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Malaria Journal
Open Access
Research
Malaria – a major health problem within an oil palm plantation
around Popondetta, Papua New Guinea
Bianca Pluess*1, Ivo Mueller2, Damien Levi3, Graham King3,
Thomas A Smith1 and Christian Lengeler1
Address: 1Swiss Tropical Institute, PO Box, 4002 Basel, Switzerland, 2Institute of Medical Research, PO Box 60, Goroka, Papua New Guinea and
3CTP (PNG) Ltd., Higaturu Oil Palms, PO Box 28, Popondetta, Papua New Guinea
Email: Bianca Pluess* - bianca.pluess@unibas.ch; Ivo Mueller - ivo@pngimr.org.pg; Damien Levi - dlevi@ctpholdings.com;
Graham King - gking@hargy.com.pg; Thomas A Smith - Thomas-A.Smith@unibas.ch; Christian Lengeler - Christian.lengeler@unibas.ch
* Corresponding author
Abstract
Background: For companies operating in malaria endemic countries, malaria represents a
substantial risk to workers and their dependants, and can lead to significantly reduced worker
productivity. This study provides an overview of the malaria epidemiology within an oil palm
plantation in Popondetta, south-eastern Papua New Guinea, its implication for the company with
its employees and their families and the potential for control.
Methods: In 2006, we carried out a cross-sectional study within six company villages, which
included the determination of parasite rates by conventional microscopy, interviews and
haemoglobin measurements. Passive surveillance data were collected from the 13 company aid
posts for the years 2005 and 2006.
Results: Malaria prevalence was found to be high: all-age prevalence was 33.5% (95% CI 30.1–37.0)
in 723 individuals. Plasmodium falciparum was the dominant species, followed by Plasmodium vivax
and Plasmodium malariae. Children between five and nine years of age were most affected (40.3%,
95% CI 0.32–0.49). Haemoglobin levels were found to be low; 11.0 g/dl (95% CI 10.8–11.1) for men
and 10.4 g/dl (95% CI 10.3–10.5) for women, respectively. Plasmodium falciparum infections were
significantly associated with anaemia (Hb < 10 g/dl). At the aid posts, all malaria cases in 2005 and
January-March 2006 were diagnosed by symptoms only, while from April 2006 onwards most cases
were tested by rapid diagnostic tests. Between 2005 and 2006, 22,023 malaria cases were
diagnosed at the aid posts and malaria accounted for 30–40% of all clinical cases. Of the malaria
cases, 13–20% were HOP employees. On average, an employee sick with malaria was absent for
1.8 days, resulting in a total of 9,313 workdays lost between 2005 and 2006. Sleeping outside of the
house did not increase the risk of a malaria infection, neither did getting up before 7 am.
Conclusion: Malaria was found to be a major health burden in the Higaturu Oil Palm plantation,
posing a high risk for company staff and their relatives, including expatriates and other non-immune
workers. Reducing the malaria risk is a highly recommended investment for the company.
Published: 8 April 2009
Malaria Journal 2009, 8:56 doi:10.1186/1475-2875-8-56
Received: 3 December 2008
Accepted: 8 April 2009
This article is available from: http://www.malariajournal.com/content/8/1/56
© 2009 Pluess et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Background
Papua New Guinea (PNG) is characterized by its variabil-
ity and complexity in culture, ecology and geography. This
complexity is also reflected in the malaria situation [1].
Malaria ranks first amongst the diseases causing illness
and death in Papua New Guinea [2], although there is a
great variation in the relative importance of malaria for
people in different areas. The epidemiology of malaria in
PNG ranges from complete absence of malaria, through
unstable low levels of transmission with recurring epi-
demics, to permanently high levels of transmission [3,4],
even reaching the highest transmission levels known out-
side of Africa. About 46% of all Papua New Guineans live
in an altitude zone of 0 – 600 m above sea level [1], where
malaria is highly endemic.
Malaria represents not only a health, but also an eco-
nomic burden. In Africa alone, the estimated direct and
indirect costs of malaria exceed US$ 12 billion annually
[5]. Malaria negatively influences economic growth,
reducing it for example by 1.3% annually in endemic
countries between 1965 and 1990. In 1995, the average
gross domestic product in non-malarious countries was
five times higher than in countries affected with malaria
[6]. The most immediate effect of malaria on a company
is its impact on the workforce and the resulting cost of car-
ing for sick employees. Employees sick with malaria are
not working efficiently and are likely to take time off to
recover. In a worst case, employees die and replacements
need to be recruited and trained [7].
In PNG, oil palm is a major agro-industry. In 2001, over
100,000 hectares of oil palms were planted. Since 2000,
palm oil has been the most important agricultural export
industry in PNG, with nearly 400,000 tons exported in
2002, amounting to approximately 136 million USD
[8,9]. Commercial plantations such as oil palm planta-
tions offer suitable environmental conditions for Anophe-
les mosquitoes breeding and people living and working in
such plantations are thus likely to be at high risk for
malaria [10]. However, such plantations also provide rel-
atively good housing and infrastructure for their workers,
making it relatively easy to deploy screening or indoor
residual spraying, and improvement in case management.
Higaturu Oil Palms plantations (HOP) is one of the major
employers in Oro Province (south-east PNG). It provides
housing for its employees and their dependants within
the plantation. HOP is located in the area around Popon-
detta, the capital of Oro province, on a coastal plain at the
foot of the Owen-Stanley range. So far, and to the best of
our knowledge, no data have ever been collected on the
epidemiology of malaria for this part of the country.
Therefore, this study aims to provide (1) an overview of
the malaria epidemiology in Oro province, and (2) to
quantify the problem of malaria within a commercial oil
palm plantation, its implications for the company and the
potential for control. Few such studies have been carried
out and this economic risk (in addition to the health risk)
urgently requires to be better quantified.
Methods
Study site
The study was conducted within the oil palm plantations
of CTP (PNG) Ltd. (trading as Higaturu Oil Palms –
HOP), close to Popondetta, the capital of Oro Province in
Papua New Guinea. HOP processes palm fruits from an
area of about 22,997 hectares. The company owns 8,997
hectares which are divided into five estates (namely
Javuni, Sumbiripa, Ambogo, Mamba and Embi). Small-
holders own another 14,000 hectares. While the small-
holders are responsible for maintaining and harvesting
the palms, Higaturu buys their fruits and processes them
into palm oil and palm kernel oil.
People living in the 14 villages within the plantation con-
sist of HOP employees and their dependants, for whom
housing is provided by the company. Every village is
equipped with a small health centre, staffed with one
Community Health Worker or nursing officer. A bigger
health centre with a laboratory is situated in Siroga village,
which is easily accessible by car or foot.
The cross-sectional study took place in six villages
(namely Epa, Irigi, Sumbiripa, Irihambo, Javuni and
Moale), located within three of the five estates. Two of the
estates (Mamba and Embi) were excluded as they were dif-
ficult to reach due to their geographical distance. Mamba
estate is located in the mountains and hence is not ecolog-
ically comparable to the other estates. For the passive sur-
veillance system, all aid posts were included.
Ecologically the study villages are very similar to each
other, all being surrounded by oil palms. Within the study
area, rainfall usually shows some seasonality with a wet
season from November to April and a drier season from
May/June to October. During our study period the average
rainfall was 189 mm, with 243 mm in April and 135 mm
in May (Figure 1).
A company village consists of 100 houses of which 87–
98% are so-called "labour houses", wooden two-bedroom
houses with a cooking place outside on the veranda and
its own ablution block and toilet next to the house (Figure
2).
Cross-sectional parasitology surveys
The cross-sectional surveys were conducted between April
and May 2006. Every village was visited once. Households
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to be included were selected by random sampling from
the existing list of houses provided by the company.
Inclusion/exclusion criteria
Every person living within the selected villages and house-
holds was eligible for the study. Consent procedures are
described below. Persons ill at the time of the survey, as
well as visitors to the household who had lived less than
four weeks in the village, were excluded from the study.
Measurements
From each participant we measured the axillary tempera-
ture with an electronic thermometer. At the same time, a
questionnaire was administered on the use of bed nets,
the history of malaria sickness in the previous two weeks,
the use of anti-malarial drugs and health facility attend-
ance, travel behaviour, evening leisure activities and sleep-
ing habits (outside or inside their house). The interview
was performed in English or Melanesian pidgin by bilin-
gual interviewers. At the same time as the interview, a
blood slide including a thick and a thin film was prepared.
Thin blood films were fixed with methanol. All smears
were stained with 2.5% buffered Giemsa (pH 7.2) for 35
minutes and examined afterwards microscopically for 100
fields under oil immersion (× 1000 magnification) before
Average monthly rainfall within the study area from 2004 to 2006Figure 1
Average monthly rainfall within the study area from 2004 to 2006.
0
100
200
300
400
500
600
700
800
JFMAMJJASONDJFMAMJJASONDJFMAMJJASOND
2004 2005 2006
Data not available
Rainfall (mm)
A typical worker's houseFigure 2
A typical worker's house.
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being declared negative. In positive films, parasite species
were identified and densities recorded as the number of
parasites/200 white blood cells (WBC). Densities were
converted to the number of parasites/μl of blood assum-
ing 8,000 WBC/μl.
Haemoglobin levels were measured from the same finger
prick as from the blood slide, using a HaemoCue machine
(HemoCue B-Hemoglobin, Angholm, Sweden). From
each individual the spleen size was determined according
to Hackett's grading by a local nurse.
Routine data assessment
Malaria incidence data routinely collected by the health
staff of the HOP aid posts were available from January
2005 to December 2006. Until April 2006, all patients
presenting with fever were considered as malaria cases. In
April 2006 Rapid Diagnostic Tests (RDTs, ICT Malaria
Combo Cassette, R&R Marketing, South Africa) were
introduced in all aid posts within the Higaturu Oil Palm
estates. Before the introduction of the RDTS, a three-day
training course on the theory and usage of the RDTs was
provided to every member of the health staff of HOP.
After the introduction of RDTs, patients were classified as
having malaria only if the RDT result was positive. Com-
pared to microscopy the RDT sensitivity was 89%, which
is excellent.
For every patient visiting a HOP aid post, the date of the
visit, data of joining the company (employee, dependant
or outsider) and the diagnosis were collected.
In 2006, for an ad hoc sample of employees, the numbers
of days missing from work due to malaria were recorded.
Data entry and analysis
The data from the questionnaires were entered in an
Access 2002 database (Microsoft Corp., Redmond, US).
To check for data entry mistakes, the entered data were
checked and corrected by one person, while a second per-
son was reading out the entries of the original question-
naires. The blood slides were read twice by two different
microscopists and the results entered into two different
Excel databases (Microsoft Corp., Redmond, US). A
Kappa test for checking for consistency between the two
datasets showed an expected agreement of 78.4% (k =
0.43). In case one microscopist only found few parasites
(< 3 parasites/200WBC) and the other none, the slides
were considered to be positive. Slide results were excluded
from the analysis if one microscopist found a high para-
sites density (>12 parasites/200 WBC) and the second one
found none. Differences in categorical variables were
tested using the Pearson chi-square test. Differences were
regarded as significant if the p-value of the test statistic
was ≤5%.
Changes of haemoglobin values were calculated using lin-
ear regression, adjusting for age, gender and mosquito net
use. Difference between males and females in haemo-
globin levels were tested with Wilcoxon test, as the Bar-
tlett's test for the differences in the variance was
significant. Participants were classified as having anaemia
if haemoglobin levels were under 10 g/dl. For obtaining
odds ratios, relevant variables (age, sex, village, sleep out-
side on the veranda, sleep outside in a shelter, sleeping
under a bed net, work and getting up before 7 am) were
added one-by-one in the model and a likelihood ratio
tests was performed to test for significance.
Work days lost for the company were calculated by taking
the arithmetic mean of the days not worked per employee
due to malaria.
Unfortunately, it was not possible to get the results of RDT
testing from all the clinics because these statistics were not
available to us. In order to have at least an estimate of test-
ing positivity rate, a sample of 90 successive patients in
one clinic (Siroga) who were clinically diagnosed with
malaria were also tested with a RDT in order to calculate
the RDT positivity rate.
All statistical analyses were performed in Intercooled Stata
9 (StataCorp, Texas, US).
Informed consent
The community was informed about the aims and the
methods of the study before the start of the data recording
and sample collection by the company health care work-
ers. Consent was then sought individually from all study
participants or their guardians. This was done by explain-
ing again the aim and procedure of the study at the begin-
ning of the interview. A signature of each participant on
their understanding and willingness to participate was
then collected. All enrolled individuals retained their right
to withdraw from the study at any stage.
The survey methodology was approved by the PNG Med-
ical Research Advisory Committee (approval number
MRAC No. 06.07).
Results
Cross-sectional survey: general description
A total of 843 individuals were included in the survey
(Table 1). The study participants consisted of 423
(50.2%) females and 419 (49.8%) males and were
grouped into the following five age categories: 0–4, 5–9,
10–19, 20–39 and >40 years. There was a big excess of
individuals aged 20–39 years (40.9% of the participants),
which were made up largely of workers, as expected in this
population. Over half of the participants (57.1%) came
from Oro province, and overall 81.7% of the people had
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Table 1: Description of cross-sectional survey participants
Variable N (%) Male Female
Sex Male 423 (50.2)
Female 419 (49.8)
Total 842
Age 0–4 169 (20.1) 89 (21.1) 79 (18.9)
5–9 148(17.6) 76 (18.0) 72 (17.2)
10–19 117 (13.9) 47 (11.1) 70 (16.7)
20–39 344 (40.9) 167 (39.6) 177 (42.2)
>40 64 (7.6) 43 (10.2) 21 (5.0)
Total 842 422 419
Origin Oro 480 (57.1) 218 (51.8) 261 (62.4)
Morobe 160 (19.1) 97 (23.0) 63 (15.1)
Oro/Morobe 46 (5.5) 24 (5.7) 22 (5.3)
Other provinces 157(18.3) 82(19.5) 72(17.2)
Total 840 421 418
Work Permanent 238 (28.2) 205 (86.1) 33 (13.9)
Casual 57 (6.8) 7 (12.3) 50 (87.7)
Not working 548 (65.0) 211 (38.6) 336 (61.4)
Total 843 423 419
Work department Field 211 (89.4) 178 (87.7) 33 (100.0)
Security 12 (5.1) 12 (5.9) 0 (0.0)
Transport 7 (3.0) 7 (3.5) 0 (0.0)
Mill 4 (1.7) 4 (2.0) 0 (0.0)
Growers 1 (0.4) 1 (0.5) 0 (0.0)
HR 1 (0.4) 1 (0.5) 0 (0.0)
Finance 0 (0.0) 0 (0.0) 0 (0.0)
Total 236 203 33
Work casual Collect mama lusfrut 22 (38.6) 0 22 (44.0)
Weeding 13 (22.8) 1 (14.3) 12 (24.0)
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an Oro, a Morobe or a mixed Oro/Morobe origin. 28.2%
(238/843) of the interviewee were permanently employed
by the company and of those, 89.4% (211/236) were
working within the field department. Employees within
the field department work in the plantations, mainly har-
vesting ripe palm fruits. Only 6.8% (57/843), of the par-
ticipants were hired as casuals, of whom 87.7% (50/57)
were women.
Population movement was low with only 7.9% (66/839)
individuals reporting to have been travelling within the
last four weeks. 70.9% of 839 participants slept under a
mosquito net the previous night. However, many people
reported, that the treatment status of their nets was poor,
with many of the nets not having been retreated within
one year of usage.
Parasitological results
A total of 723 blood slides were collected, of which 242
were positive for malaria (33.5%, 95% confidence inter-
val [CI]: 30.1–37.0). This result documents the high level
of endemicity in this area. Between the three estates, the
malaria prevalence differed significantly (χ2 = 24.85, 2 df,
p < 0.001), ranging from 20.3% (95% [CI] 0.14–0.26) in
Ambogo to 43.1% (0.37–0.49) in Sumbiripa (Table 2). At
village level, the malaria prevalence ranged from 17.7%
(95% CI 0.09–0.27) in Epa to 44.6% (95% CI 0.36–0.53)
in Sumbiripa village (χ2 = 25.80, 5 df, p < 0.001) (Table
2). There was no significant difference between prevalence
among males and females (χ2 = 0.10, 1 df, p = 0.319).
Overall, prevalence was highest in the age group 5–9 years
(40.3%, 95% CI 0.32–0.49) (Figure 3). The same pattern
was seen with P. falciparum infections, with 27.9% (95%
CI 0.20–0.36) of the 5 to 9 years old children infected
(Figure 4). For P. vivax, no difference between the age-
groups was found (Figure 4).
With 59.5% (144/242) of all positives, P. falciparum was
the dominant species, followed by P. vivax (91/242,
37.6%) and P. malariae (16/242, 6.6%). No Plasmodium
ovale was found. A high number of the positive slides (26/
242, 10.7%) were mixed infections. The parasite densities
of the infections were low, with 91.1% (194/213) of the
slides having <500 parasites/μl. No difference in parasite
densities between age groups was found (χ2 = 20.18, 12
df, p = 0.064). When investigating differences by species,
11.1% (14/144) of P. falciparum infections were >500 par-
asites/μl, compared to 4.4% (4/91) of the P. vivax infec-
tions (significant difference χ2 = 10.48, 2 df, p = 0.005).
Reported malaria episodes and spleen rates
25 participants presented with fever at the survey and a
quarter (26.1%) of the 842 participants reported having
had malaria during the past two weeks. No correlation
between measured or reported fever and malaria parasi-
taemia was found: eight of the 20 (40.0%) people present-
ing with fever and having a blood slide taken, had a
positive blood slide (χ2 = 0.41, 1 df, p = 0.521). Of the
participants with reported fever during the last two weeks
and having a malaria slide taken, only 37.6% (70/186)
had a positive slide (χ2 = 1.86, 1 df, p = 0.173).
Empty Fruit Bunch (EFB) distribution 8 (14.0) 1 (14.3) 7 (14.0)
Fertilizer application 6 (10.5) 0 (0.0) 6 (12.0)
Harvest helper 3 (5.3) 2 (28.6) 1 (2.0)
Other 5 (8.8) 3 (42.9) 2 (4.0)
Total 57750
Table 1: Description of cross-sectional survey participants (Continued)
Malaria prevalence (all species) by age group, with 95% confi-dence intervalsFigure 3
Malaria prevalence (all species) by age group, with
95% confidence intervals.
0−4 5−9 10−1920−39 >40
0
5
10
15
20
25
30
35
40
45
50
Age [years]
Prevalence [%]
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Almost everybody who reported having had malaria
within the last two weeks visited a health centre (99.5%)
and took anti-malarials (96.2%).
Overall, 59.7% of the participants had an enlarged spleen
with an average size of 3.2 on the Hackett scale, but no
association with a current malaria infection was seen, nei-
ther at individual (χ2 = 0.78, 1 df, p = 0.377) nor at village
level. Looking at age groups, the average Hackett score was
lowest for the youngest age group (0–4 years) with 2.4,
and it rose with age to 3.8 for the oldest age group (>40
years). Despite the fact that this was reported differently
by Genton et al. within the Wosera [3], a high rate of
enlarged spleens in adults is a particular feature of malaria
in PNG. Often, enlarged spleens in adults are linked to
hyperreactive malarial splenomegaly [1]. Though usually
present within mid altitude zones [1], this syndrome
might also occur within this study area.
Haemoglobin levels were low with a significantly higher
level for men (11.0 g/dl, 95% CI 10.8–11.1) than for
women (10.4 g/dl, 95% CI 10.3–10.5) (χ2 = 24.73, 1 df, p
< 0.001). In children aged 5–9 years, the haemoglobin
Malaria prevalence by species and age group, with 95% confi-dence intervalsFigure 4
Malaria prevalence by species and age group, with
95% confidence intervals.
0−4 5−9 10−1920−39 >40
0
5
10
15
20
25
30
35
40
45
Age [years]
Prevalence [%]
pfalc
pvivax
Table 2: Malaria prevalence and bed net usage, by estates and by villages (cross-sectional survey).
Estate Number examined Prevalence all species n
infected; % (95% CI)
Prevalence P. falci-
parum n infected; %
(95% CI)
Prevalence P. vivax n
infected; % (95% CI)
Bed net usage (%)
Ambogo 177 36; 20.3
(0.14–0.26)
28; 15.8
(0.10–0.21)
6; 3.4
(0.01–0.06)
84.3
Sangara 279 91; 32.6
(0.27–0.38)
56; 20.0
(0.15–0.25)
35; 12.5
(0.09–0.16)
69.7
Sumbiripa 267 115; 43.1
(0.37–0.49)
60; 22.5
(0.17–0.27)
50; 18.7
(0.14–0.23)
63.3
Village
Epa 68 12; 17.7
(0.09–0.27)
9; 13.2
(0.05–0.21)
2; 2.9
(-0.01–0.07)
97.5
Irigi 109 24; 22.0
(0.14–0.30)
19; 17.4
(0.10–0.25)
4; 3.7
(0.00–0.07)
75.8
Moale 154 48; 31.2
(0.24–0.38)
28; 18.1
(0.12–0.24)
23; 14.8
(0.09–0.20)
65.6
Javuni 125 43; 34.4
(0.26–0.43)
28; 22.4
(0.15–0.30)
12; 9.6
(0.04–0.15)
75.0
Irihambo 137 57; 41.6
(0.33–0.50)
33; 24.1
(0.17–0.31)
21; 15.3
(0.09–0.21)
57.6
Sumbiripa 130 58; 44.6
(0.36–0.53)
27; 20.8
(0.14–0.28)
29; 22.3
(0.15–0.29)
68.9
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levels were significantly decreased with a malaria infec-
tion: by 1.0 g/dl (95% CI -1.43 – -0.47, p < 0.001) for any
species and 1.2 g/dl (95% CI -1.66 – -0.63, p < 0.001) for
P. falciparum infections. A significant association between
P. falciparum and anaemia was found (χ2 = 4.41, 1 df, p =
0.036).
Behavioural aspects
There was no difference between employees and depend-
ants in the risk of getting infected with malaria (Table 3).
Neither were sleeping outside during the night (on the
veranda or on a shelter) nor getting up before 7 am asso-
ciated with a higher risk of a malaria infection. On an
individual level, sleeping under a bed net showed no pro-
tection against malaria (OR 1.2, 95% CI 0.8–1.7). How-
ever, there was a clear trend towards less malaria with
higher bed net coverage between villages (Table 2). For
every percentage increase in net coverage, the odds of
malaria cases decreased by 3% (OR 0.97, 95% CI 0.96–
0.99).
Incidence of routinely diagnosed malaria infections
Malaria was the most common disease diagnosed by HOP
health staff in 2005 and 2006. In 2005 all malaria patients
seen at the aid posts were diagnosed by clinical symptoms
only. Of all patients seen at the 13 HOP aid posts in 2005,
Table 3: Risk factors for getting a malaria infection (cross-sectional survey).
Variable Total (n) Infected (%) Odds ratio CI 95% p-value (LRT)
Village
Moale 154 48 (31.2) 1 0.00
Epa 68 12 (17.7) 0.5 0.2–1.0 0.00
Irigi 109 24 (22.0) 0.6 0.3–1.1
Javuni 125 43 (34.4) 1.1 0.7–1.9
Irihambo 137 57 (41.6) 1.5 0.8–2.6
Sumbiripa 130 58 (44.6) 1.2 1.1–3.2
Sex 0.9 0.6–1.3 0.51
Age
0–4 130 37 (28.5) 1 0.14
5–9 129 52 (40.3) 1.9 1.1–3.2
10–19 101 32 (31.7) 1.1 0.6–2.0
20–39 306 103 (33.7) 1.2 0.6–2.3
>40 56 18 (32.1) 1.0 0.4–2.4
Work permanent (vs not working (= dependants)) 215 74 (34.4) 1.0 0.5–1.8 1.00
Work casual (vs not working (= dependants)) 50 18 (36.0) 1.0 0.5–2.1
Sleep under a bed net (yes vs no) 507 160 (31.6) 1.2 0.8–1.7 0.39
Sleep on veranda (yes vs no) 136 44 (32.4) 1.1 0.4–1.3 0.56
Sleep in a shelter (yes vs no) 63 25 (39.7) 0.7 0.4–1.3 0.25
Get up before 7 am (vs getting up after 7 am) 538 181 (33.6) 0.9 0.8–1.1 0.51
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39% (12,083/30,864) were diagnosed with malaria. Of
the 12,083 malaria patients, 26% (3159/12083) were
employees. On average, 1007 patients were diagnosed
with malaria every month at the 13 aid posts. Malaria
cases were found to be evenly distributed throughout the
year 2005 (Figure 5), hence showing no seasonality.
In 2006, fewer patients were diagnosed with malaria than
in 2005, especially after the introduction of RDTs in April.
The RDT positivity rate, calculated for a sample of 90
patients, was found to be 48%. Overall, 9,940 patients
were sick with malaria, still representing 29% (9,940/
34,216) of all diagnosis made at the aid posts. 20%
(2,015/9,940) of the malaria patients were employees.
The malaria burden was highest in the beginning of the
year, and then, after the introduction of RDTs in April a
sharp decline until August was seen. During the three
months in 2006 before the introduction of RDTs, 1,220
malaria cases were clinically diagnosed every month, of
which 17% (211/1,220) were employees. After the intro-
duction of RDTs in April and until the end of 2006, the
monthly average of overall malaria cases decreased to
698. 153 (22%) of these malaria cases were employees.
Malaria cases showed a seasonal peak in October, which
did not reach the level of 2005, before RDT introduction
(Figure 5).
Days lost for the company
According to HOP administration, an employee sick with
malaria was absent from work for an average of 1.8 days.
Since 3,159 employees were sick with malaria in 2005 and
2,015 employees in 2006, this resulted in 5,686 lost days
in 2005 and 3,627 lost days in 2006.
Discussion
To our knowledge, this work presents one of the few pub-
lications on the impact of malaria within an agro-indus-
trial operation in endemic countries and the first one in
PNG. Furthermore, it provides for the first time malario-
logical information for the region around Popondetta,
south-east PNG.
Clearly, malaria was found to be a major health problem
within the CTP Plantation. The overall prevalence rate of
33.5% found among workers and their families is high.
Furthermore, children and adults are both affected and
this suggests there is little acquired immunity. This level of
endemicity is similar to that found in other surveys done
in the lowlands of PNG outside agro-industrial opera-
tions. Genton et al [3] and Cattani et al [11] found preva-
lence rates of 60% in the Wosera (East Sepik) and 35.0%
to 42.7% surrounding Madang, respectively. The preva-
lence data of Genton et al and Cattani et al have been col-
lected between 10 and 20 years ago and it is likely that the
overall rate of transmission has decreased since. Further-
more, an oil palm plantation represents an artificial envi-
ronment with its own ecosystem, which is likely to have a
different transmission rate than a natural habitat. Com-
parisons with other oil palm plantations within PNG on
the same altitudes would have been interesting, but such
data are not available. Given the particular malaria epide-
miology of PNG, which is by far the highest in the region,
Monthly routine malaria incidence data from 2005 to 2006Figure 5
Monthly routine malaria incidence data from 2005 to 2006.
0
200
400
600
800
1000
1200
1400
Jan Feb Mar Ap r M ay June July Aug Sept Oct Nov Dec Jan Feb Mar Ap r M ay June July Aug Sept Oct No v Dec
Num ber o f malaria cases
Introduction of RDTs
2005 2006
Malaria Journal 2009, 8:56 http://www.malariajournal.com/content/8/1/56
Page 10 of 11
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comparison with other Asian and Pacific countries is
meaningless.
HOP offers housing to their employees within the geo-
graphical boundaries of the plantation. This special set-
ting, with only employees and their dependants being
allowed to live within the plantation, resulted in 40% of
the participants being aged between 20 and 39. This is
clearly not representative for the general population of the
country and hence caution needs to be exerted when gen-
eralizing our results to the rest of the population.
Ripe palm fruits are collected by company trucks, creating
deep wheel tracks on the ground. With enough rainfall
such tracks present perfect breeding sites for Anopheles
punctulatus [12], which were found by human landing
catches within the study area (Cooper R.D. personal com-
munication). Though we conducted only one cross-sec-
tional survey, the age peak for malaria infections (5–9
years old) was found to be characteristic for a highly
endemic area [1,3]. Such an intense malaria transmission
can pose a high risk for all residents, especially for expatri-
ates and other non-immune workers (for example coming
from the cooler highlands). In one of the few documented
examples, a large joint venture in Mozambique lost 13
expatriate employees due to malaria within two years
[13]. Undoubtedly, malaria endemicity weighs down the
attractiveness of industrial or agro-industrial sites.
Almost everybody who was feeling sick with presumptive
malaria within the last two weeks had visited a health cen-
tre and received anti-malarials. This finding was not sur-
prising, as employees and their dependants have free and
ready health services provided by the company. This good
access to treatment explains that we have not come across
of any reported deaths from malaria.
In 2005, with the exception of one clinic, all malaria cases
were diagnosed purely on a symptomatic basis. Unfortu-
nately, symptoms of malaria are non-specific and many
other diseases can present with the same clinical picture,
including harmful diseases such as dengue, HIV or hepa-
titis B. But also many harmless viral infections present
similar to a malaria infection. Thus, a purely symptomatic
diagnosis of malaria can lead to a vast over-diagnosis of
malaria cases [14-16]. This was illustrated by the fact that
after the introduction of RDTs in April 2006 the number
of reported malaria cases decreased steadily. But even with
systematic testing with RDTs, still about 10,000 patients
were diagnosed with malaria in 2006. This high level of
morbidity represents a considerable cost of treatment
(estimated cost per treatment: USD 0.18) and a substan-
tial loss of productivity. These episodes resulted in 5686
lost days for the company in 2005, amounting to lost
wages of over USD 60,000 (King G., personal communi-
cation). In 2006, the company lost 3627 working days
due to malaria. The costs associated with malaria illness
will increase significantly as PNG moves towards intro-
ducing the significantly more expensive Coartem® (arte-
mether-lumefantrine) as the national first-line treatment.
More than half of the infections were caused by P. falci-
parum (57.4%), followed by P. vivax with 36.2%. Plasmo-
dium falciparum infections are well known for their impact
on morbidity and mortality, but also P. vivax infections
are considered to be responsible for a substantial health
burden [15,17-19]. For an oil palm plantation, where
approximately 60–75% of the employees do a physically
strenuous work, a healthy workforce is crucial for a high
productivity. The negative impact of malaria is also dem-
onstrated by the low average haemoglobin level, which is
a further drain on the energy of workers.
Virtually all inhabitants within the study area live within
so-called "labour houses" (Figure 2), wooden two-bed-
room houses, in which room temperatures can get very
high, including at night. As a result, people sometimes
sleep outside on their veranda or in a self-built shelter,
where they are fully exposed to biting mosquitoes. Sur-
prisingly, sleeping on a veranda or sleeping on a shelter
was not found to be a risk-factor for a malaria infection.
The most likely explanation for this finding is that the
mosquitoes prevalent within the plantation, Anopheles
punctulatus (RD Cooper, personal communication) are
exo- but also endophagic [20] and can easily enter and
bite occupants inside the non mosquito-proofed houses.
The two main tools to prevent malaria infections are
insecticide-treated mosquito nets (ITNs) and indoor
residual spraying (IRS). Within HOP, nets are sold for half
their commercial price, which explains the high usage rate
of 70%. On an individual level no significant protection
against malaria could be detected but this is expected in a
situation with a homogeneously high level of net use. The
village comparison showed a trend of decreasing number
of malaria infections with increasing bed net level, con-
firming that the nets actually do have an impact. Unfortu-
nately, the insecticide re-treatment level of the nets was
poor since most nets were not retreated after 2004. There-
fore, the introduction of LLINS, which are designed to
maintain their efficacy against mosquitoes for at least
three years without any re-treatment necessary, would be
highly recommended [21]. The high level of net protec-
tion also suggests that endemicity would be even higher if
there was no protection.
Indoor residual spraying requires 1) an adequate knowl-
edge of vector behaviour and occurrence, and (2) a highly
structured programme including well-trained personnel,
properly used insecticides, good logistics and scheduling
Malaria Journal 2009, 8:56 http://www.malariajournal.com/content/8/1/56
Page 11 of 11
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and a high level of sustained financing [22]. These terms
would clearly be doable by a commercial oil palm planta-
tion and thus, IRS would also be a feasible option for
malaria control in the HOP setting. With housing pro-
vided by the plantation, upgrading the housing condi-
tions including house screening would be a more long-
term solution of malaria control. This approach has
already shown great success within military barracks in
Pakistan and India, reducing the malaria incidence up to
72% [23].
Conclusion
Malaria was found to be a major health burden to the Hig-
aturu Oil Palms, posing a high risk for all inhabitants,
indigenous workers as well as non-immune workers. Det-
rimental effect included direct cost of treatment, days
away from work and reduced physical ability. These losses
are substantial enough to warrant the implementation of
energetic and long-lasting malaria control measures.
Competing interests
GK was the General Manager of the Higaturu Oil Palms
plantations (HOP) from March 2005 to October 2007. DL
is employed as Health Extension officer at HOP. BP, IM,
TS and CL declare that they have no competing interests.
Authors' contributions
BP participated in the design of the study, conducted the
field work, analysed and interpreted the data and drafted
the manuscript. IM and CL were involved in designing
and implementing the study and writing of the manu-
script. TS assisted in the data analysis and writing of the
manuscript. DL and GK were facilitating the overall coor-
dination of the fieldwork and helped with the acquisition
of the data. All authors read and approved the final man-
uscript.
Acknowledgements
We would like to thank all the inhabitants of the study area for their excel-
lent cooperation. A special thanks to the health staff of HOP for their help
in collecting data and to Daniel Sirere for his help in staining the slides. We
are furthermore grateful to the microscopists reading the blood slides.
Finally, thanks to Laura Gosoniu, Don deSavigny, Allan Schapira and Blaise
Genton for valuable scientific inputs.
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