Pertussis outbreak investigation in Janamora district, Amhara Regional State, Ethiopia: a case-control study

INTRODUCTION: On April 17/2017 Janamora district, Amhara regional state health officials reported an increasing number of people with a cough. The objectives of this study was to investigate the outbreak, describe risk factors and implement control measures. METHODS: We conducted a community based unmatched 1:1 case-control study April 22-May 10, 2017. We used a probable case definition (≥2 weeks cough with vomiting, apnea, or inspiratory whoop) to identify suspected pertussis cases. Neighbors of cases were considered as controls. We conducted a door-to-door active case search and reviewed medical records, assessed vaccination status by parental interview or vaccination card. We implemented multivariable logistic regression to identify independent factors associated with the outbreak. RESULTS: We investigated 60 cases and 60 controls. Most (68.3%) of the cases were under the age of 15. The majority (86.6%) of pertussis suspected cases, and 83.4% controls had not received any pertussis vaccine. The overall attack rate was 0.13% and the case fatality rate was 3.3%. The age-specific attack rate for under-five children was 0.33%. Females were more likely to have pertussis (AOR: 2.91; 95% CI: 1.17-7.22), contact with pertussis suspected person (AOR: 6.29; 95% CI: 2.53-15.62) and living in a relatively poorly ventilated house (AOR: 3.01; 95% CI: 1.17-7.70) were also significant risk factors of pertussis. CONCLUSION: Weak supplementary immunization activities might have contributed to the outbreak. Treating household contacts and integration of diagnostic laboratory test of pertussis into the local health system is of paramount importance to detect outbreaks early on.