Malaria outbreak investigation in a rural area south of Zimbabwe: a case–control study

Nearly half the global population is exposed to malaria [1] and in 2018, an estimated 228 million malaria cases occurred globally (95% Confidence interval (CI) 206–258 million) [2], up from 212 million in 2015 [3]. 405,000 malaria deaths were recorded in 2018 with the sub-Saharan region and India carrying 85% of the global malaria burden [2]. Malaria disease burden in Africa is very high and 90% of the global annual malaria mortality cases come from the African region [3]. In sub-Saharan Africa, 80–90% of malaria transmissions primarily occurs indoors during the night [4].

In Zimbabwe, malaria is a major public health problem affecting all age-groups and according to the World Health Organization (WHO) malaria report of 2016, 79% of the population are at risk of contracting the disease. Malaria incidence in the country was 139 per 1000 population at risk in 2013 [5]. The Ministry of Health and Child Care reported a surge in the malaria case fatality rate from 6.1% in 2012 to 13.8% in 2014 [6] and the malaria mortality cases were being reported throughout the year although transmission of the disease usually happens in seasonal epidemics largely occurring during the summer months of November to April [7].

The Zimbabwe National Malaria Control Programme and Roll Back Malaria Programme have achieved major successes in combating the diseases over the last 13 years, and this led to the reorientation of focus from malaria control to elimination [8]. These two programmes whose leadership is centrally stationed in the capital city, Harare, are informed by provincial and disease control officers who gets information from the district health teams which oversees malaria case management, surveillance and outbreak response at a local level [9]. The progress in malaria elimination was tenaciously challenged by vector and parasite resistance to insecticides and anti-malarial medicines, outdoor malaria transmission, dynamic vector behaviour and invasion of new areas by vectors. Climate change, erratic funding, local economic and political disturbances as well as increased cross border population movements have also contributed to the regression of malaria control programmes [8]. These factors have contributed to sporadic malaria outbreaks throughout Zimbabwe.

In 2017, the Beitbridge District was experiencing a second malaria outbreak in a space of less than 12 months. The first malaria outbreak in the district started in late 2016 and was declared over in week 22 of 2017. This earlier malaria outbreak recorded over 800 cases resulted in five fatalities, three children and two adults [10]. The recent malaria outbreak in Beitbridge District had resulted in one death in Beitbridge town during week 42 of 2017 [11]. Situated in Ward 6 of Beitbridge District, the Mtetengwe Clinic started to record a rapid increase in malaria cases during week 36, 2017 and subsequent weeks. Malaria threshold and alert levels for the clinic could not be calculated because the health facility was established in 2016, however malaria threshold levels for Makakabule Clinic which is in Ward 7 were used. Makakabule Clinic used to serve most of the population in Ward 6 before Mtetengwe Clinic was constructed.

This study aimed to investigate the malaria outbreak and determine the factors associated with contracting malaria in Ward 6 of Beitbridge. Understanding the risk factors associated with the occurrence of a malaria outbreak enables early and effective initiation of prevention interventions and control measures towards elimination of the disease in the affected area. The study also sought to investigate the malaria outbreak preparedness and response in the district. District health teams are responsible for detecting and responding to outbreaks at a local level. The assessment of the measures taken by the district health team to respond to a rise in malaria cases disease was imperative since the district was experiencing a second malaria outbreak; thus, this assessment could identify gaps in the malaria response system processes and make recommendations directed towards efficient and effective local disease outbreak response.

An unmatched 1:1 case–control study was conducted in October 2017. This study employed the stages used in the investigation of an outbreak guidelines recommended by the Centre for Disease Control and Prevention (CDC) [12]. This is a guide to real time stepwise investigation of acute public health events at a local, national, or multinational level. The systematic approach was used in preparing for field work after establishing the existence of an outbreak, verifying a diagnosis to finding and recording cases before epidemiologically evaluating the study hypotheses. The results from the investigation were communicated to the authorities were they were used to implement control and preventive measures.

This study sought to investigate a malaria outbreak, determine the factors associated with contracting malaria and to investigate the malaria epidemic preparedness and response in Ward 6 of Beitbridge District. The majority of the malaria cases were between the ages of 20–30 years which is contrary to the findings of the study by Drakeley et al. in which the disease was more prevalent in the age group 5–19 years [16]. This may be attributed to the young population in the study area as evidenced by the proportion of cases decreasing with age. Many people come to Ward 6 for economic opportunities particularly seeking employment in the farming estates and selling goods from South Africa. Most of the farmworkers and traders are between the ages of 20 to 30 years.

This study revealed that sleeping in a poorly constructed house were significantly associated with contracting malaria while closing eaves was protective. A similar study in Gambia reported that closing eaves halved the prevalence of malaria caused malaria in children [17]. A systematic study of five case–control studies and two cohort studies showed that both living in houses made of brick walls and closing eaves reduced the odds of contracting malaria infection by a quarter [18]. Well-constructed houses protect inhabitants from malaria by preventing entry of the malaria vectors. Modern brick walls and roofs also limit resting places for mosquitoes and reduce the attractiveness of the internal environment to the vectors when compared to the traditional mud/pole and thatch houses [18]. Although the use of LLINs and IRS are equally important, housing improvements have significantly contributed to a decline in malaria cases and elimination of the disease in many countries [19, 20]. Two studies on malaria outbreak in Zimbabwe also cited that the presence of open eaves increased the likelihood of contracting malaria [13, 21]. The majority of the remote Ward 6 residents lived in poorly constructed houses and similar settings of poverty and remoteness were found to be risky with regards to contracting malaria in Amazon Villages [22].

Spending time outdoors after sunset was significantly associated with contracting malaria and this finding was similar to another study in which overnight hunting and spending night time outdoors were significant malaria transmission risk factors in French Guiana [23]. Zimbabwean studies in Chipinge and Mberengwa also cited that routine outdoor activities such as bathing and night fishing were significantly associated with contracting malaria [13, 24]. Mothers and children in Ward 6 were known to spend evening time outdoors sitting around a fire, cooking and exposing themselves to mosquito bites thus increasing their chances of contracting malaria. Adult males particularly those who were employed at the farms were also exposed to mosquito bites since they dismissed well after sunset.

The community had fairly good knowledge of malaria disease since the majority of participants managed to identify infected mosquitoes as the vector for the disease although a few still believed that eating infected fruits cause malaria. Most of the cases and controls could identify the signs and symptoms of malaria and all cases reported to have completed the treatment course. A similar study done also recorded high knowledge of the signs and symptoms as well as prevention of the disease [13]. This finding was also consistent with the malaria survey which also cited reasonably good knowledge about malaria causes, signs and symptoms and prevention among the rural community of Zimbabwe [25].

Participants reported that malaria disease was curable and they would visit a healthcare centre upon suspecting that they had the disease. Health-seeking behaviour in Ward 6 was good, a finding that was contrary to what Onwjekwe and colleagues, found out in Nigeria were populations consulted herbalists, used spiritual/ritual water or just pray ignoring the malaria symptoms [26]. This difference in results can be attributed to increased sensitization on the disease in Beitbridge District since this was a second malaria outbreak within the same year.

Having an LLIN does not directly translates to its consistent use in malaria prevention; this was noted in 56% of LLIN owners being malaria cases. A study by Msellemu et al. in Tanzania also made the same conclusion after finding out that LLINs were often reserved for children and visitors exposing other family members to the vector [27]. The study participants who had LLINs in Ward 6 reported that the LLINs were donated in 2015 and on observation some nets had developed holes. Such damages to the preventive barrier can still expose individuals to mosquito even though they used the nets. Some LLIN owners mentioned that the nets were suffocating or caused itchiness as barriers to LLIN use. This resulted in inconsistencies in the use of nets as malaria preventive measures. The fact that some of the controls who had LLINs did not use them reveals the idea that mosquito-proof housing provides some form of protection that does not depend on human compliance.

The use of EPR team to mount a response against the outbreak was an effective way of combating the malaria outbreak. Unlike in 2015 when the Beitbridge Emergency Response team did not consistently conduct EPR meetings [21], the team was sitting every Wednesday for the past 6 months and there were meeting minutes to support this. All the nurses at Mtetengwe Clinic were trained in integrated disease surveillance and response, a finding that was contrary to a similar study done in Shamva, Zimbabwe [9]. Repeated malaria outbreak attacks had prepared the Beitbridge District team to be on high alert for a possible increase in cases of the disease. This encouraged prompt outbreak notification and response to prevent further proliferation of the disease in Ward 6. Overall, both the healthcare centre and district were well prepared to respond to this malaria outbreak because most essential stocks were available and there were no stock outs during the course of the outbreak.

Zimbabwe faces a critical shortage of human resource for health and the shortage of nurses, EHTs and microscopists can have a negative impact on the control of malaria in Zimbabwe [9]. The EHT deployed during the current outbreak was from another clinic while Mtetengwe Clinic had a vacant EHT post due to the recruitment freeze on health posts [28]. The cadre was evidently overwhelmed with responsibility and rarely had time to cover Mtetengwe Clinic. This may have resulted in the insidious increase of cases in the study area.

Health promotion messages should emphasize the importance of closing eaves and other entry points of the malaria vector, and constructing better houses in the future. Resident should also be educated on the importance of consistent use of LLINs. The district had to improve on preventive measures like distribution of LLINs and lobby for more human resources to assist with malaria surveillance thus, curbing the recurrence of malaria outbreaks in the future. To counter the possibility of another malaria outbreak, these measures had to be instituted promptly.