An unmatched 1:1 case-control study was conducted in October 2017. This study employed the stages used in the investigation of outbreak guidelines recommended by the Centre for Disease Control and Prevention (CDC) [10].
Study Setting
Beitbridge District is located 583 kilometers south of the Zimbabwean capital, Harare bordering Zimbabwe and South Africa. Mtetengwe Clinic is a rural health center under the administration of Beitbridge Rural District Council, Matabeleland South Province, Zimbabwe. The clinic was opened in 2016 and it provides health services to Ward 6 population estimated at 3 548. Mtetengwe Clinic covers villages like Mtetengwe, Mzingwane, Mapani, Tshinabazwimi, Malala and Bishopstone, BK Cawood, Beitbridge Juicing farming estates among others. Villagers and farmworkers in this area live in houses made of mud and wood or bricks roofed using thatch, asbestos or corrugated sheets.
The Ward 6 of Beitbridge District is primarily rural and it is located in natural region V which is semi-arid with erratic rains and very hot climate. Due to poor annual rainfalls, the population depends on the buying and selling of commodities purchased from South Africa. Furthermore, the district is also known for its thriving goat, cattle, and game ranching activities. Beitbridge District offices are in Beitbridge town 22 km east of Ward 6. According to the Matabeleland South Generic Report of June 2017, the district had an estimated population of 128 454.
Study Population
The study population consisted of all adults and children residing in Ward 6 of Beitbridge District between week 36 and week 44 of 2017. A case was a patient who resided within Ward 6, of Beitbridge District who presented with signs and symptoms of malaria and tested positive on the random diagnostic test (RDT) for malaria from week 36 to week 44 of 2017. Symptoms of malaria referred to one or a combination of fever, vomiting, headache, general body malaise and rigors/chills. Controls who saved as the comparison group were individuals who resided with or near a case and did not contract malaria during the period under study.
Sampling
Using Stat-Cal and assuming that engaging in outdoor activities during the evening was a significant risk factor for contracting malaria with an odds ratio (OR) of 8.5 and 81.6% of controls having been exposed. A power of 80% and a 95% confidence interval (CI) gave the minimum required sample size of 63 cases and 63 controls [11]. With an expected 20% attrition rate, the sample size was approximately equal to 79 thus, the final sample size was 79 cases and 79 controls.
The Mtetengwe Clinic line list which was used as the sampling frame for this study had 109 malaria cases and Ward 6 was purposively selected as the study site in this investigation. A simple random sampling of cases was done by allocating numbers to all the 109 cases on the Mtetengwe Clinic line list and putting the numbered cards in a hat. After mixing, 79 card numbers were blindly picked by a nurse from the clinic without replacement until the calculated sample size was reached. Controls were purposively selected from individuals residing with or within the neighbourhood of cases. A case who was not found at home or a case who refused to participate was replaced by the next case as selected from the line list.
Data Collection And Analysis
Data collection was conducted over a period of two weeks using structured and pretested interviewer-administered questionnaires. These were translated from English to the local language Shona and back-translated to English to ensure comprehension of the questions. Treatment records, clinic registers as well as healthcare workers were part of the study population. The participant questionnaire aimed to determine the demographic characteristics, the knowledge levels on the transmission of malaria and practices used for protection against the disease. Checklists were also used to assess environmental health risk factors and the availability of resources essential to mount an outbreak response. Healthcare workers were also interviewed to assess the district’s preparedness to respond to a malaria outbreak. Data collection tools were pretested using ten participants from a village in Gwanda District.
The researcher and his assistant camped at Mtetengwe Clinic from the beginning of week 44 to the end of week 46 of 2017. Local VHWs were used to assist in locating selected cases using the clinic line list during community visits which were conducted during weekdays from 8 am to 4 pm. The researchers were fluent in both Shona and English visited interviewees at their home and used the structured questionnaire to collect data on demographic characteristics, risk factors associated with contracting malaria, knowledge, and practices of malaria prevention. Appointments for interviewing key informants were made in advance to minimize inconveniences. Interviewed key informants included the two nurses working at the clinic, the Medical Officer, Environmental Health Officer, District Laboratory Scientist, District Pharmacist, and local VHWs.
Data were entered into Microsoft Excel before it was exported into Epi Info version 7 (CDC, USA) for data cleaning, coding, and analysis. The statistical software was used to calculate frequencies, means, proportions, odds ratios, and p-values at 95% CI. Backward stepwise multivariate logistic regression analysis was done to control for any confounding variables.
Permission to conduct the study was sought from Provincial Medical Director of the Matabeleland South Province, and District Medical Officer Beitbridge District. Ethical review and approval were granted by the Africa University Research Ethics Committee and the approval number was 266/17. Written informed consent was obtained from the study participants before data was collected. Participation in this study was voluntary.
Operational Definitions
Well-constructed house: a modern house with closed eaves, brick walls, asbestos or corrugated roof, conventional windows, and doors that can be closed without leaving gaps for mosquito entry [12].
Poorly constructed house: a house with no conventional windows or unscreened windows, multiple openings, open eaves or doors that leave gaps when closed.
Eaves: gaps between the top of the wall and the overhanging roof [12].