Back ground:-Pertusis is a very contagious disease characterized by severe coughing and caused by bacteria Bordutella pertusis On September 20 /2018 a rumour of an outbreak was received from Mekdella district health office and a team was deployed to verify the presence of the outbreak and identify factors associated with the outbreak. Method: - unmatched case control study was conducted from October 24 to November 10/2018 in Mekdella district. Data were collected using a structured interviewer questionnaire; review of line list, discussion with health workers. cases definition used to identify cases and 80 cases and160 control collected by simple random sampling by computer generation from 227 line list cases and neighbouring control selected, the data entered Epi data 3.1 with check command, export SPSS 23 and cleaned chi square, bi-variables and multivariable binary logistic regression conducted for identified candidate (P value ≤0.25) and significant (p value<0.05) variable for pertussis Result: Total 992 pertussis cases were identified among this 13 confirmed Bordutella pertusis, 51.5% of cases were male and a person under 14 years old more affected with 83% the most affected kebele were Medone with attack rate of 208 per 1000 population. The cold chin management of vaccine status was in one year morning and afternoon monitoring at Geha health centres indicated 72% of the recorded among this 66% with normal temperature and 6% with alarm temperature. Low vaccination [AOR=3.1:95%CI= (1.12-8.99], lived with suspected individual [AOR=6.2: 9%CI=4.1-13.8] were statistically significant with pertussis cases in the study area Conclusion:- According to this study strengthen vaccination service for all unvaccinated children and increases health education to community for pertusis prevention and control to address high burden of pertusis diseases Key words: pertussis, outbreak, Mekedela district INTRODUCTION