Characteristics of study participants and distribution of malaria test positivity at Primary Hospital of Wonji Sugar estate
A total of 36,753 malaria-suspected cases were registered and diagnosed by microscopy in the primary Hospital of Wonji sugar estate from which 34,388 cases were legible for analysis, and 2,367 were excluded because of data incompleteness. Of the 34,388 suspected patients for malaria, 45.7% (15,708) were females. Among those diagnosed with malaria in the past nine years, 19.25% (6,619) were <5 years old children, and more than half (52.1%, n= 17920) were individuals above >15 years old. The overall malaria test positivity among total malaria suspected cases was 11.74% (95%CI:11.4-12.08). The proportion of Plasmodium vivax, Plasmodium falciparum and mixed infections (P. vivax and P. falciparum) was 8.2% (95%CI:7.91-8.49), 3.48% (95%CI=3.53-3.95), and 0.06 (95%CI:0.04-0.09), respectively. Malaria test positivity in older individuals above 15 years old was 16.34%.
Table 1. Characteristics of study participants tested for malaria at Wonji sugar estate primary Hospital from 2013 to 2021.
Attributes
|
Malaria positivity rate %(n/N)
[95%CI]
|
P-value
|
Gender
|
9.71 (1,525/15,708)
[9.25-10.18]
|
<0.001
|
Female
|
Male
|
13.44 (2,511/18,680)
[12.96-13.94]
|
Age
|
|
<0.001
|
<5yrs
|
4.14 (274/6,619)
[3.7-4.6]
|
5-15yrs
|
8.47 (834/9,847)
[7.9-9.03]
|
>15yrs
|
16.34 (2,928/17,920)
[15.8-16.9]
|
P. falciparum
|
3.48 (1,195/34,388)
[3.53-3.95]
|
|
P. vivax
|
8.20 (2,820/34,388)
[7.91-8.49]
|
Mixed (P. vivax and P. falciparum)
|
0.06(21/34,388)
[0.04-0.09]
|
Overall malaria positivity prevalence
|
11.74 (3834/30410)
[11.40-12.08]
|
-
|
Season
|
|
|
Wet
|
11.4 (2097/16,250)
[10.97- 11.89]
|
0.059
|
Dry
|
12.1(1,939/14,102)
[11.59-12.60]
|
Note: CI= 95% confidence interval, P-value= Pearson’s chi square p-value
The odds of being positive for malaria were related to the age of patients as it was highest in older individuals >15 years old (AOR=4.55, 95%CI=4.01-5.17, P<0.001) followed by school-age children (5–15 years old) (AOR=2.16; 95%CI: 1.88–2.49, P<0.001) compared to preschool-age children of <5years old (Table 2). Moreover, the frequency of malaria test positivity was higher among males (14.56%) than females (10.3%) (AOR = 1.46; 95%CI: 1.36-1.52; P< 0.001) (Table 1 &2).
Table 2. Associations between malaria test positivity and characteristics (age and gender) of individuals tested from 2013 to 2021
Attributes
|
COR [95%CI]
|
P-value
|
AOR [95%CI]
|
P-value
|
Gender
|
1
|
<0.001
|
|
<0.001
|
Female
|
1
|
Male
|
1.44 [1.35-1.54]
|
1.46 [1.36-1.52]
|
Age categories
|
1
|
<0.001
|
1
|
<0.001
|
<5yrs
|
5-15yrs
|
2.14 [1.86-2.46]
|
2.16 [1.88-2.49]
|
>15yrs
|
4.52 [3.98-5.13]
|
4.55 [4.01-5.17]
|
Note: COR= Crude odds ratios, AOR=Adjusted odds ratios
Association of malaria case positivity rate and meteorological variables over the study years (2013-2021)
Over the past nine years (January 2013 to December 2021), the median maximum temperature of the area was 28.9℃ (IQR: 27.3-30.20℃) while the median rainfall was 28.7mm (IQR: 0-108.3mm. The median relative humidity was 40.8% (IQR: 34.03-50.93%). During the past nine years, the proportion of monthly malaria-positive cases was higher in the years from 2013 to 2017 with significant epidemic-like reports in February 2016; it then declined onwards in the consecutive years of 2018-2021 (Figure 3).
In this study, during the last nine years, clinical malaria case occurrence was observed with moderate fluctuation (figure 4), where only 4 months were registered with malaria case free out of 108 studied months.
There was only marginal seasonal variation in the proportion of malaria-positive cases during the dry season months (12.08%, 1,939/14,102) compared to the wet season months of the year (April, May, June, July, and August) (11.4%, 2097/16,250) (ᵪ2=3.57, P=0.059) (Table 1). In both adjusted and unadjusted analyses, malaria test positivity rates were significantly associated with average monthly rainfall (AdjIRR=1.00, 95%CI=1.00-1.001, P<0.001) while negatively associated with average monthly minim temperature (adjIRR=0.94;95%CI=0.94–0.95; P<0.001) and average monthly relative humidity (adjIRR=0.99, 95%CI=0.99-1.00, P=0.023). On the other hand, the average monthly maximum temperature was not associated with the malaria test positivity rate during the study period (Table3).
Table 3. Associations between malaria test positivity rates with temperature, rainfall, and humidity in Wonji sugar factory primary Hospital (from 2013-2021).
Attributes
|
Crude analysis
IRR [95%CI]
|
P-value
|
Adjusted analysis IRR [95%CI]
|
P-value
|
Average monthly minimum temperature (℃)
|
0.94 [0.94- 0.95]
|
<0.001
|
0.94(0.93-0.94)
|
<0.001
|
Average monthly maximum temperature (℃)
|
0.99 [0.97-1.01]
|
0.447
|
1.00[0.98-1.02]
|
0.902
|
Monthly rainfall
|
1.00 [1.00- 1.01]
|
<0.001
|
1.00[1.00-1.01]
|
<0.001
|
Monthly RH
|
0.99 [0.99- 1.00]
|
<0.001
|
0.99[0.99-1.00]
|
0.529
|
Note: crudeIRR=Crude Incidence Rate Ratio, adjIRR= adjusted Incidence Rate Ratio, RH= Relative humidity.