First Confirmed Pertussis Outbreak in Ethiopia - Daramallo District, GamoGofa Zone, Southern Ethiopia, 2018

  • Vaccine preventable diseases
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Background:
Pertussis is a highly contagious vaccine-preventable respiratory illness caused by Bordetella pertussis bacteria. Globally, 24.1 million cases and 160,700 deaths from pertussis were reported in 2014. Pertussis outbreaks were rarely reported in Ethiopia.
On August 29, 2018, a funeral attendee reported from a remote village in Southern Ethiopia to Zonal health depart- ment, three respiratory illness-related deaths in one family, suspicious for pertussis. We investigated the outbreak to confirm the etiology, describe risk factors, and implement control measures.
Methods:
An unmatched case-control study was conducted between October 11- December 30, 2018 in Daramallo District, GamoGofa zone. A modified WHO suspected case definition was used to identify cases. About 100 cases and 100 asymptomatic household/neighbor controls were selected based on geographical accessibility and interviewed with a semi-structured questionnaire. 25 nasopharyngeal swabs were collected and tested with Real Time-Polymerase Chain Reaction (RT-PCR). We assessed district’s immunization coverage and cold chain system. Simple and multiple binary logistic regression was performed.
Results:
A total of 1,847 cases and six deaths were identified during the outbreak period, attack rate =26.5/1,000 population and case fatality rate =0.32%. Majority 67.2% (n=1,241) of cases were under five children. About 12.7% (235) cases were unvaccinated. Of 25 specimens tested with RT-PCR, 13 were positive for Bordetella pertussisbacteria. Half (12/24) of district health posts had non-functional cold chain. History of contact with a case (aOR=4.17; 95%CI: 1.89-9.18), time since last vaccination >4years (aOR=8.70; 95%CI: 2.34-32.4) and sex being female (aOR=3.43; 95%CI: 1.6-7.34) were the main identified risk factors while full immunization (aOR=0.31; 95%CI: 0.13-0.70) was protective.
Conclusion
This is laboratory confirmed pertussis outbreak, occurred primarily due to low DTP3 vaccination coverage. Contact with a case and time since last vaccination greater than four years (due to waning immunity) were associated with developing pertussis infection. To control this epidemic; case treatment, prophylaxis (family members and high risk contacts) with macrolide antibiotics and vaccination campaigns were conducted. To prevent future outbreaks cold chain and routine DTP3 coverage of the district should be improved.

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