Background
About 75% of Ethiopia’s landmass is potentially malarias and two thirds of the population is at risk. Boloso Bombe district had reported unusual increase in malaria cases and almost all villages were endemic and affected malaria transmission despite lack of evidence to the problem. Thus, the aim of this study was to investigate malaria outbreak in the district.

Methods
A case control study was conducted in Boloso Bombe district from April, 16 to 23/ 2021. Cases were defined as febrile cases confirmed by microscopy or RDT for plasmodium parasites; whereas, controls were having with no fever in same period. For every cases identified at health facilities two neighbor controls were selected. Structured questionnaire was used to collect outbreak related data. Epi Info version 3.5.1 was used for data entry and exported to SPSS version 21 for analysis. Bi-variable and multivariable analysis and odds ratio with its corresponding 95% confidence interval was calculated to determine the significance of the risk factors with the outbreak.

Results
A total of 536 cases were identified and alert threshold of the district crossed during the Epi-week 16 to 23 of 2021. The positivity rate was 41.75%. Forty cases and 80 controls were recruited in the investigation. Sixty eight of cases were (OR: 0.68, 95% CI: 0.18-0.249) contracted the illness because of poor utilization of LLITNS. Moreover, water holding container in the vicinity (OR: 4.6, 95% CI: 1.233-17.782) and sleeping outdoor (OR: 4.6, 95% CI: 0.233-17.78) were found to be significantly associated with malaria infection.

Conclusion
Investigation implicated that lack of proper LLITN utilization, water holding container around vicinity and sleeping outdoor were the risk factors for malaria. We recommended strict environmental management, regular vector surveillance and replacing of worn out mosquito nets.