Malaria Outbreak in Kisooro District, January, 2018

Authors: Joyce Nguna1, Denis Okethwangu1, Daniel Kadobera1 Affiliation: 1 Uganda Public Health Fellowship Program

Summary

Malaria is a febrile illness liable for high morbidity and mortality worldwide. Analysis of DHIS2 data revealed an upsurge in malaria cases in Kisoro District in December 2017 and January 2018. We investigated this outbreak to determine its extent, identify risk factors, and recommend control and prevention measures. We reviewed health records from June, 2017 to January, 2018 in all health facilities in the 2 most affected sub-counties. In a case control study we compared potential exposures between 145 case-persons and 145 asymptomatic controls matched by age and village. We carried out an entomological and environmental assessment in affected sub counties. Persons older than 5 years of age were the most affected. 22% (32/145) of case-persons and 15% (21/145) of control-persons reported not sleeping under a mosquito net (ORM-H=4; 95%CI=1.2-1.3) in Chibumba village; 89% (129/145) of case-persons and 73% (106/145) of control-persons were bitten by mosquitoes before bed time ORM-H=2.9; 95%CI=1.6-5.7). Anopheles gambiae sensu lato was the dominant identified species. We recommend increased sensitization and further entomological investigations to ascertain vector bionomics.

Introduction

Despite significant progress in scaling up malaria control interventions, malaria remains one of the most important global health challenges accounting for high morbidity and mortality. Malaria is highly endemic in about 95% of Uganda and is the leading cause of attendance at health facilities [8]. Transmission is unstable and epidemic-prone in extreme south-western areas around Rwenzori mountains, Mt. Elgon in the east and areas extending above 1,800 meters in altitude. Kisoro is one of the highland areas in Uganda with a low malaria prevalence of 12% [8]. A detailed investigation and understanding of the factors impacting increase in Malaria cases in Kisoro was crucial to improve well targeted malaria control strategies.

Methods

We defined a confirmed case as any positive malaria test result from mRDT or microscopy from 1st June, 2017 to 27 January, 2018 in a resident or visitor of Kisoro District. We systematically searched for malaria cases by reviewing health records in all health facilities in the 2 most affected sub-counties of Kanaba and Murora. In a case-control study we compared potential exposures between 145 case-persons and 145 asymptomatic controls matched by age and village. We carried out an entomological and environmental assessment of the affected sub counties.

Results

We line listed 2,720 malaria case-patients with a median age of 19 years (IQR 10-30).

Person characteristics

Age Group Frequency Population AR/1000
<5 317 7,692 41
5-18 1023 15,383 67
>18 1380 19,657 70
Total 2720 42,732 100

Table 1: Distribution of cases by age group

Persons older than 18 years old were most affected, closely followed by those between 5 and 18 years old.

Sub county Parishes Cases Population Attack Rate/1000
Kanaba Kagezi 832 8,619 97
Muhindura 159 10,148 16
Murora Chahafi 485 13,149 37
Chibumba 1211 10,816 112

Table 2: Distribution by Parish

Place characteristics

Chibumba Parish had the highest attack rate per 1000 population (112), followed by Kagezi (97), Chahafi (37) and Muhindura (16) parishes (Table 2). In Kagezi, Butoke had the highest attack rate (329/1000 population) followed by Mukaka and Kooga villages with 156 and 146 respectively. In Chibumba Parish, two villages; Chibumba (337/1000) and Mpundu (314/1000) were the most affected.

Figure 1: Location of affected villages around Sereri and Mpundu Swamps

Mpundu, Chibumba, Butoke, Mukaka and Kooga villages around Sereri swamp contributed 60% of all the con- firmed cases in the 2 most affected sub-counties.

Time characteristics

There was a marked increase in the number of malaria cases in December and January (Figure 3). There has been continuous transmission since September 2017 and is bound to continue if transmission is not broken. The epicurve is indicative of a continuous common source pattern with waves of transmissions that have kept in creasing since November 2017.

Figure 2: Distribution of cases by month

Figure 3: Epidemic curve showing cases in the most affected months of November, December 2017 and January 2018.

Environmental and entomological assessment: The villages in these sub-counties with high malaria trans- mission; Mpundu, Chibumba, Kooga, Butoke, Mukaka are located on hills around the Chibumba-Sereri wet- land. This swamp an extensive lowland into which run off water from the hilly villages affected by the outbreak drains. Communities have encroached on the wetland to carry out farming and brick activities thus creating suitable breeding sites of malaria (Appendix 1). Stagnant water in brick pits and garden trenches in the swamp were the major breeding sites of Anopheles. Temporary breeding sites which depended on continuous rains were road- side pools and tyre-tracks on feeder roads. Anopheles gambiae sensu lato was the only vector identified from the Pyrethrum Spray Catches (PSC). Low adult catches were observed by the assessment.

Case control results: Not sleeping under a mosquito net and mosquito bites before bed time were significantly associated to malaria infection. The odds for malaria infection were 3 times higher if the person was bitten by mosquitoes before bed time (ORM-H: 2.9, CI: 1.6 – 5.7) and 4 times higher if one was not sleeping under a mosquito net (ORM-H: 4, CI: 1.2 – 1.3) in Chibumba village.

Exposure Cases (n=145) Control (n=145) Cases Controls ORM-H
Not using mosquito net 32 21 22 15 1.7 (0.94 –3.06 )
Chibumba village 14 05 39 14 3.9 (1.2-13)
Mosquito nets before bed time 129 106 89 73 2.9 (1.6 –5.7)
History of sick in 86 73 59 50 1.4 (0.91 –2.3)
household Entering bed after 9:00pm  109  113  76  78  0.91 (0.52–1.6)
Travel history 8 6 5.5 4.1 1.4 (0.45 –4.3)
Wearing long clothes 38 39 26 27 0.96 (0.57– 1.6)
Outdoor activities 56 69 39 48 0.69 (0.43– 1.2)

Discussion

This investigation revealed that there is continuous transmission of malaria in Kisoro District which peaked in late 2017 and early 2018. High malaria transmission is evident among villages of Mpundu, Chibumba, Kooga, Butoke, Mukaka located at the slopes of hills around the Chibumba-Sereri wetland. It’s propagated by favorable vector breeding sites located within the affected sub-counties due to human activity in the swamp specifically brick making and agriculture. These pro- vide favorable breeding sites for the anopheles mosquito whose population has steadily increased in the affected areas over time. Homes in the affected sub-counties receive returnees for the Christmas holidays from early November till end of December, many of which are from high malaria endemic areas in Uganda. These easily provide the source for malaria parasites for the anopheles mosquito to transmit. In other areas of Uganda where Anopheles gambiae is largely endophilic, the low adult catches by PSC suggests few mosquitoes rest indoors perhaps due to hot conditions facilitated by iron sheet roofs for the houses. This points to the possibility of changes in vectors behaviors, mutation or , changes in the known vector dynamics of biting humans.

Conclusion and Recommendations

To ascertain the true vector feeding and resting behavior de- tailed bionomic studies have to be conducted using different adult collection methods. Conducting molecular characterization of the An. gambiae s.l is key. Community mass action to fill such small pools could be used by environmental health officers through initiating and promoting participation of area residents. Larviciding can be effective in the garden trench pools.

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